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  • 1.
    Amani, Mozhdeh
    et al.
    Chalmers University of Technology, Sweden.
    Al-Emrani, Mohammad
    Chalmers University of Technology, Sweden.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Shear Behavior of Stainless Steel Girders with Corrugated Webs2022In: Proc. of Stainless Steel in Structures – Sixth International Experts Seminar, 2022Conference paper (Refereed)
    Abstract [en]

    This paper reports experimental and finite element investigations conducted to assess the shear strength of corrugated web girders in stainless steel. The steel under consideration is LDX 2101. Four trapezoidal corrugated web girders were tested under shear. All tested girders reached the shear yield strength followed by strain hardening. An imperfection sensitivity study was done with the aid of finite element modelling. It was observed that an initial geometric imperfection based on the first eigen buckling mode with a maximum amplitude of the minimum dimension of the critical corrugation sub panel divided by 200, 𝑎max200⁄, leads to an ultimate shear strength greater than the shear yield strength and close to the test findings. It is concluded that EN 1993-1-5 shear design model for corrugated webs is conservative for stainless steel girders tested in the current study.

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  • 2.
    Amani, Mozhdeh
    et al.
    Chalmers University of Technology, Sweden.
    Al-Emrani, Mohammad
    Chalmers University of Technology, Sweden.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Shear behavior of stainless steel girders with corrugated webs2023In: Journal of constructional steel research, ISSN 0143-974X, E-ISSN 1873-5983, Vol. 210, article id 108086Article in journal (Refereed)
    Abstract [en]

    In this paper, the shear strength of corrugated web girders made of EN 1.4162/LDX 2101 stainless steel is investigated. Four full-scale trapezoidal corrugated web girders were tested under shear. Before conducting the tests, DIC was used to measure the real geometric imperfections in the web panels. Complementary finite element analysis studies were conducted to assess the sensitivity of the shear strength to initial imperfections. The experimental results indicated that all the tested girders with a local slenderness ratio of λ = 0.7 attained the shear yield strength, which was then followed by strain hardening in the material at a level that was 8–18% higher than the yield strength. This implies that the Eurocode's limit of λ = 0.25 to attain the plastic shear strength in corrugated webs can be quite conservative for stainless steel. According to the findings of the imperfection sensitivity studies, an initial geometric imperfection based on the first eigen buckling mode and with a maximum amplitude of amax/200, where amax is the maximum corrugation fold length, yielded ultimate strength within 3% of the test results. When the amplitude was increased to hw/200, where hw is the web height, the ultimate strength was estimated to be 25% lower on average than in the experiments. In three of the studied girders, initial imperfections with other forms than the first buckling mode were found to be more critical. Further, it was found that regardless of mode number, mode shapes that are more extended over the web panel result in a higher degradation of the ultimate shear strength. © 2023 The Authors

  • 3.
    Arellanoa, Santiago
    et al.
    Chalmers University of Technology, Sweden.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Kasani, Björn
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Steffen, Holger
    Lantmäteriet, Sweden.
    EPOS Sweden: A national contribution to the European Plate Observing System-European Research Infrastructure Consortium2022In: Abstract book, 2022Conference paper (Other academic)
    Abstract [en]

    The pan-European “European Plate Observing System (EPOS)” is focussed on Europe and adjacent regions and includes geophysical monitoring networks, local observations (including permanent in-situ and volcano observatories), topographic/surface dynamics information, surface and subsurface geological information, experimental and laboratory data and functions, and satellite data. In 2021 the Swedish Research Council (VR) approved an application for Sweden to join EPOS-ERIC, formally establishing existing collaborations between EPOS and Swedish research infrastructures.

  • 4.
    Arrhenius, Karine
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Bacquart, Thomas
    NPL National Physical Laboratory, UK.
    Schröter, Karin
    EMPA Swiss Federal Laboratories for Materials Science and Technology, Switzerland.
    Carré, Martine
    Air Liquide, France.
    Gozlan, Bruno
    Air Liquide, France.
    Beurey, Claire
    Air Liquide, France.
    Blondeel, Claire
    Air Liquide, France.
    Detection of contaminants in hydrogen fuel for fuel cell electrical vehicles with sensors—available technology, testing protocols and implementation challenges2022In: Processes, ISSN 2227-9717, Vol. 10, no 1, article id 20Article in journal (Refereed)
    Abstract [en]

    Europe’s low-carbon energy policy favors a greater use of fuel cells and technologies based on hydrogen used as a fuel. Hydrogen delivered at the hydrogen refueling station must be compliant with requirements stated in different standards. Currently, the quality control process is performed by offline analysis of the hydrogen fuel. It is, however, beneficial to continuously monitor at least some of the contaminants onsite using chemical sensors. For hydrogen quality control with regard to contaminants, high sensitivity, integration parameters, and low cost are the most important requirements. In this study, we have reviewed the existing sensor technologies to detect contaminants in hydrogen, then discussed the implementation of sensors at a hydrogen refueling stations, described the state-of-art in protocols to perform assessment of these sensor technologies, and, finally, identified the gaps and needs in these areas. It was clear that sensors are not yet commercially available for all gaseous contaminants mentioned in ISO14687:2019. The development of standardized testing protocols is required to go hand in hand with the development of chemical sensors for this application following a similar approach to the one undertaken for air sensors. © 2021 by the authors. 

  • 5.
    Arrhenius, Karine
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Culleton, Lucy
    NPL National Physical Laboratory, UK.
    Nwaboh, Javis
    PTB Physikalisch-Technische Bundesanstalt, Germany.
    Li, Jianrong
    VSL Van Swinden Laboratorium B.V., Netherlands.
    Need for a protocol for performance evaluation of the gas analyzers used in biomethane conformity assessment2023In: Accreditation and Quality Assurance, ISSN 0949-1775, E-ISSN 1432-0517Article in journal (Refereed)
    Abstract [en]

    Biomethane may contain trace components that can have adverse effects on gas vehicles performances and on the pipelines when injected in the gas grid. Biomethane quality assurance against specifications is therefore crucial for the integrity of the end-users’ appliances. Analytical methods used to assess biomethane conformity assessment must be validated properly and possibly, new methods specifically for biomethane should be developed. This paper provides an overview of the biomethane quality assurance infrastructure and the challenges faced with focus on sampling, analysis methods, reference gas mixtures, and performance evaluation. Currently, requirements for analytical method validation and fit-for-purpose assessments do not exist for biomethane. The industry is in urgent need of a protocol to evaluate the fit-for-purpose of methods in a harmonized manner. Reference gas mixtures to check the accuracy of the instrument and to determine the traceability of the measurement are also urgently required. 

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  • 6.
    Arrhenius, Karine
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Francini, Lorena
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Büker, Oliver
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Sampling methods for renewable gases and related gases: challenges and current limitations2022In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 414, p. 6285-6294Article in journal (Refereed)
    Abstract [en]

    Renewable gases, hydrogen and biomethane can be used for the same applications as natural gas: to heat homes, power vehicles and generate electricity. They have the potential to contribute to the decarbonisation of the gas grid. Hydrogen blending with existing natural gas pipelines is also proposed as a means to increase the performance of renewable energy systems. Carbon capture and storage (CCS) and carbon capture and utilisation (CCU) technologies can be an answer to the global challenge of significantly reducing greenhouse gas emissions. Due to production methods, these gases typically contain species in trace amounts that can negatively impact the equipment they come into contact with or pipelines when injected into the gas grid. It is therefore necessary to ensure proper (and stable) gas quality that meets the requirements set out in the relevant standards. The gas quality standards require the collection and transport of a representative gas sample from the point of use to the analytical laboratory; i.e., no compounds may be added to or removed from the gas during sampling and transport. To obtain a representative sample, many challenges must be overcome. The biggest challenge is material compatibility and managing adsorption risks in the sampling systems (sampling line and sampling vessels). However, other challenges arise from the need for flow measurement with non-pure gases or from the nature of the matrix. Currently, there are no conclusive results of short-term stability measurements carried out under gas purity conditions (suitable pressure, matrix, appropriate concentrations, simultaneous presence of several species). © 2022, The Author(s).

  • 7.
    Arrhenius, Karine
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Francini, Lorena
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Fischer, Andreas
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Büker, Oliver
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Arques, Laurent
    AP2E, France.
    Comparison of optical feedback cavity enhanced absorption spectroscopy and gas chromatography for the measurement of the main components and impurities in biogas, landfill gas, biomethane and carbon dioxide streams2023In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 34, no 9, article id 095011Article in journal (Refereed)
    Abstract [en]

    In this study, we evaluated the performances of a custom-built optical feedback cavity enhanced absorption spectroscopy (OFCEAS) instrument for the determination of the composition of energy gases, focusing on methane and carbon dioxide as main components, and carbon monoxide as impurities, in comparison with the well-established, validated, and traceable gas chromatographic method. A total of 115 real sample gases collected in biogas plants or landfills were analyzed using with both techniques over a period of 12 months. The comparison of the techniques showed that the virtual model which allows the measurement, needs to be optimized using real samples of varied compositions. The OFCEAS measurement technique was found to be capable of measuring both the main components and a trace component in different matrices; to within a 2% measurement uncertainty (higher than the gas chromatograph/thermal conductivity detector (GC/TCD) method). The OFCEAS method exhibits a very fast response, does not require daily calibration, and can be implemented online. The agreements between the OFCEAS technique and the GC/TCD method show that the drift of the OFCEAS instruments remains acceptable in the long term as long as no change is made to the virtual model. Matrix effects were observed, and those need to be taken into consideration when analyzing different types of samples. © 2023 The Author(s). Published by IOP Publishing Ltd.

  • 8.
    Arvidsson, Hans
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. SLU Swedish University of Agricultural Sciences, Sweden.
    Larsson, Gunnar
    SLU Swedish University of Agricultural Sciences, Sweden.
    Larsolle, Anders
    SLU Swedish University of Agricultural Sciences, Sweden.
    Neely, Gregory
    Umeå University, Sweden.
    Hansson, Per-Anders
    SLU Swedish University of Agricultural Sciences, Sweden.
    Easily applicable methods for measuring the mental load on tractor operators2020In: Journal of Agricultural Safety and Health, ISSN 1074-7583, Vol. 26, no 1, p. 5-14Article in journal (Refereed)
    Abstract [en]

    Agriculture technology is moving toward automation, placing operators in a supervisory role. This change in operator workload may lead to increased stress and higher mental load, resulting in reduced attention and hence greater risk of illness or injury to humans and damage to equipment. This study investigated the use of easily applicable equipment to measure mental load. Three methods were used to measure the mental load on machine operators: heart rate monitoring, two types of electroencephalograph (EEG) evaluation, and an assessment protocol. Three driving exercises (general driving, slalom driving, and loading) and a counting exercise were used in a driving simulator to create different levels of mental load. Due to the number of exercises, a singlescale assessment protocol was used to save time. We found that only the assessment protocol gave clear results and would work well as an evaluation tool. The heart rate and EEG measurements did not provide clear data for mental load assessment. 

  • 9.
    Bacquart, Thomas
    et al.
    NPL National Physical Laboratory, UK.
    de Huu, Marc
    METAS, Switzerland.
    Arrhenius, Karine
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Aarhaug, Thor Anders
    SINTEF, Norway.
    Viitakangas, Jaana
    VTT, Finland.
    Murugan, Arul
    NPL National Physical Laboratory, UK.
    METROLOGY FOR HYDROGEN VEHICLE 2: ACHIEVEMENTS AND PROGRESSES2022In: Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2, International Association for Hydrogen Energy, IAHE , 2022, p. 1223-1225Conference paper (Refereed)
    Abstract [en]

    Hydrogen fuel cells are an alternative power supply for electric drive trains and could represent 32 % of fuel demand by 2050. To deploy fuel cell electrical vehicles, there is current regulatory barriers (ISO 14687, OIML recommendations) that requires accurate measurements. The European funded project MetroHyVe has provided solutions and improvements in the four measurements challenges (flow metering, quality control, quality assurance and sampling). New challenges arised due to increase of hydrogen economy, therefore a new European project MetroHyVe 2 started in 2020 and its objectives will provide perspectives for the hydrogen economy to solve all regulatory barriers (ISO 14687, ISO 19880-8, ISO 19880-1, ISO 21087, OIML R139-1) and new measurement challenges (flow metering, quality control, sampling and fuel cell stack testing). The presentation will provide a comprehensive overview of the project achievements. The achievements around primary standard for flow metering (light and heavy duty), worldwide inter-laboratory comparison for hydrogen fuel quality, hydrogen sampling intercomparison and fuel cell stack testing recommendations will be highlighted.

  • 10.
    Bouckaert, Igor
    et al.
    UCLouvain, Belgium.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Almeida, Joao
    UCLouvain, Belgium.
    Large-displacement response of unreinforced masonry structures: comparison between analytical solutions and DEM models including open-source software2021Conference paper (Refereed)
  • 11.
    Bouckaert, Igor
    et al.
    UCLouvain, Belgium.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Pacheco de Almeida, Joao
    UCLouvain, Belgium.
    A strategy for generating pushover curves of block assemblies including post-peak branch using the discrete element method2022In: Proceedings of 3rd EUROPEAN CONFERENCE ON EARTHQUAKE ENGINEERING & SEISMOLOGY., 2022, p. 839-Conference paper (Refereed)
    Abstract [en]

    Pushover analyses are often used to evaluate the seismic performance of a structure. They give an estimate of the ultimate displacement a structure can undergo, as well as of the residual resisting forces in the post-peak response. When modelling masonry structures composed of multiple blocks, obtaining the post-peak branch of the pushover curve can be difficult with a classic displacement-control strategy. This paper describes a strategy designed to compute this branch for multi-block systems subjected to a given pattern of forces, without the need to apply a displacement-control algorithm. The strategy is general, therefore straightforwardly implementable in different software tools and applicable to complex block assemblies. In the present work, it is implemented in two different DEM software, namely LMCG90 and UDEC, and tested on a benchmark problem for evaluating the in-plane response of masonry walls.

  • 12.
    Bouckaert, Igor
    et al.
    UCLouvain, Belgium.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Pacheco de Almeida, Joao
    UCLouvain, Belgium.
    MODELING OF FRAMES WITH HYBRIDFEM, A PSEUDO-DISCRETE-FINITE MODEL INCLUDING NONLINEAR GEOMETRIC EFFECTS AND NONLINEAR MATERIALS2023Conference paper (Refereed)
    Abstract [en]

    In this paper, a novel numerical method for strucural analysis, called the Hybrid Discrete-Finite Element Method (HybriDFEM), is presented. In this method, a structure is modeled as an assembly of rigid blocks in contact. All the deformation is concentrated at the interfaces, which are modeled as series of distributed nonlinear multidirectional springs. The method shares similarities with the Discrete Element Methods (DEM) in its ability to account for contact interfaces and/or block deformability, and with the Applied Element Method (AEM) in the representation of interfaces as a series of normal and shear springs. However, it is close to the FEM in the way it is formulated, which offers the possibility to readily link both methods for potential hybrid applications. This paper focuses on the modeling of continuous and discontinuous frames with the HybriDFEM. It is shown how the model can do so with a nonlinear material model, and considering (or not) nonlinear geometric effects through large nodal displacements. Different nonlinear solution procedures implemented in HybriDFEM are demonstrated, such as load-control and various displacement-controlled methods. This model is able to simulate contacts between rigid or deformable units, an important feature when it comes to the modeling of, e.g., unreinforced masonry structures, with a reasonable computational cost and a formulation that is cast within the framework of the classical FEM.

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  • 13.
    Cid Gomes, L.
    et al.
    Uppsala University, Sweden.
    Rana, A.
    Uppsala University, Sweden.
    Berglund, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Wiklund, P.
    Biobase Sweden AB, Sweden.
    Ottosson, H.
    Uppsala University, Sweden.
    Light-driven (cross-)dimerization of terpenes as a route to renewable C15-C30 crudes for fuel and lubricant oil applications2023In: Sustainable Energy & Fuels, E-ISSN 2398-4902, Vol. 7, no 3, p. 868-882Article in journal (Refereed)
    Abstract [en]

    Non-fossil hydrocarbons are desirable for transport fuels and lubricant oils to reach a fossil carbon neutral economy. Herein, we show the production of such end-products from crude raw materials via the photosensitized dimerization of terpenes. Terpenes are hydrocarbons originating from renewable sources, such as forestry, industrial bio-waste and photosynthetically active microorganisms. Under irradiation at 365 nm, we observed high conversions of terpenes with conjugated diene segments into their dimers (e.g. 96.1 wt%, 12 h for α-phellandrene), and remarkable results were obtained using simulated and natural sunlight (90.8 wt% and 46.6 wt%, respectively, for α-phellandrene). We show that the lower reactivities of some isomeric monoterpenes could be overcome by a cross-photodimerization with α-phellandrene. We also utilized the cross-photodimerization approach to obtain C15 and C30 products, combining mixtures of isoprene, monoterpenes and sesquiterpenes. Hydrogenation of the terpene dimers gave materials with physical properties suitable as high energy density fuels and lubricant oils. Finally, our preliminary analysis based on recent literature points to the commercial viability of this route to produce fuels and lubricant oils, as well as to a potential for reduction of the environmental impact compared to fossil-based routes. 

  • 14.
    Culleton, Lucy
    et al.
    NPL National Physical Laboratory, UK.
    Di Meane, Elena
    NPL National Physical Laboratory, UK.
    Ward, Michael
    NPL National Physical Laboratory, UK.
    Ferracci, Valerio
    NPL National Physical Laboratory, UK.
    Persijn, Stefan
    VSL, Netherlands.
    Holmqvist, Albin
    RISE Research Institutes of Sweden, Safety and Transport, Control and Calibration.
    Arrhenius, Karine
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Murugan, Arul
    NPL National Physical Laboratory, UK.
    Brewer, Paul
    NPL National Physical Laboratory, UK.
    Characterization of Fourier Transform Infrared, Cavity Ring-Down Spectroscopy, and Optical Feedback Cavity-Enhanced Absorption Spectroscopy Instruments for the Analysis of Ammonia in Biogas and Biomethane2022In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 94, no 44, p. 15207-15214Article in journal (Refereed)
    Abstract [en]

    Novel traceable analytical methods and reference gas standards were developed for the detection of trace-level ammonia in biogas and biomethane. This work focused on an ammonia amount fraction at an upper limit level of 10 mg m-3(corresponding to approximately 14 μmol mol-1) specified in EN 16723-1:2016. The application of spectroscopic analytical methods, such as Fourier transform infrared spectroscopy, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy, was investigated. These techniques all exhibited the necessary ammonia sensitivity at the required 14 μmol mol-1amount fraction. A 29-month stability study of reference gas mixtures of 10 μmol mol-1ammonia in methane and synthetic biogas is also reported. 

  • 15.
    Engström, Jens
    et al.
    Uppsala University, Sweden.
    Shahroozi, Zahra
    Uppsala University, Sweden.
    Katsidoniotaki, E
    Uppsala University, Sweden; Centre of Natural Hazards and Disaster Science, Sweden.
    Stavropoulou, C.
    Uppsala University, Sweden.
    Johannesson, Pär
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Göteman, M.
    Uppsala University, Sweden; Centre of Natural Hazards and Disaster Science, Sweden.
    Offshore Measurements and Numerical Validation of the Mooring Forces on a 1:5 Scale Buoy2023In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 11, no 1, article id 231Article in journal (Refereed)
    Abstract [en]

    Wave energy conversion is a renewable energy technology with a promising potential. Although it has been developed for more than 200 years, the technology is still far from mature. The survivability in extreme weather conditions is a key parameter halting its development. We present here results from two weeks of measurement with a force measurement buoy deployed at Uppsala University’s test site for wave energy research at the west coast of Sweden. The collected data have been used to investigate the reliability for two typical numerical wave energy converter models: one low fidelity model based on linear wave theory and one high fidelity Reynolds-Averaged Navier–Stokes model. The line force data is also analysed by extreme value theory using the peak-over-threshold method to study the statistical distribution of extreme forces and to predict the return period. The high fidelity model shows rather good agreement for the smaller waves, but overestimates the forces for larger waves, which can be attributed to uncertainties related to field measurements and numerical modelling uncertainties. The peak-over-threshold method gives a rather satisfying result for this data set. A significant deviation is observed in the measured force for sea states with the same significant wave height. This indicates that it will be difficult to calculate the force based on the significant wave height only, which points out the importance of more offshore experiments. © 2023 by the authors.

  • 16.
    Eskilsson, Claes
    et al.
    Aalborg University, Denmark.
    Palm, Johannes
    Sigma Energy & Marine AB, Sweden.
    Johannesson, Pär
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Moura Paredes, Guilherme
    Universidade Lusófona do Porto, Portugal.
    Sensitivity analysis of extreme loads acting on a point-absorbing wave energy converter2022In: International Marine Energy Journal, ISSN 2631-5548, Vol. 5, no 1, p. 91-101Article in journal (Refereed)
    Abstract [en]

    There are many uncertainties associated with the estimation of extreme loads acting on a wave energy converter (WEC). In this study we perform a sensitivity analysis of extreme loads acting on the Uppsala University (UU) WEC concept. The UU WEC consists of a bottom-mounted linear generator that is connected to a surface buoy with a taut mooring line. The maximum stroke length of the linear generator is enforced by end-stop springs. Initially, a Variation Mode and Effect Analysis (VMEA) was carried out in order to identify the largest input uncertainties. The system was then modelled in the time-domain solver WEC-SIM coupled to the dynamic mooring solver Moody. A sensitivity analysis was made by generating a surrogate model based on polynomial chaos expansions, which rapidly evaluates the maximum loads on the mooring line and the end-stops. The sensitivities are ranked using the Sobol index method. We investigated two sea states using equivalent regular waves (ERW) and irregular wave (IRW) trains. We found that the ERW approach significantly underestimate the maximum loads. Interestingly, the ERW predicted wave height and period as the most important parameters for the maximum mooring tension, whereas the tension in IRW was most sensitive to the drag coefficient of the surface buoy. The end-stop loads were most sensitive to the PTO damping coefficient.

  • 17.
    Eskilsson, Claes
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Safety Research. Aalborg University, Denmark.
    Palm, Johannes
    Sigma Energy & Marine AB, Sweden.
    Johannesson, Pär
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Moura Paredes, Guilherme
    Universidade Lus´ofona do Porto, Portugal.
    Sensitivity Analysis of Extreme Loads Actingon a Point-Absorbing Wave Energy Converter2021In: Proceedings of the 14th European Wave and Tidal Energy Conference 5-9th Sept 2021, Plymouth, UK, 2021, p. 1992-1-1992-10Conference paper (Refereed)
    Abstract [en]

    There are many uncertainties associated with the estimation of extreme loads acting on a wave energy converter (WEC). In this study we perform a sensitivity analysis of extreme loads acting on the Uppsala University (UU) WEC concept. The UU WEC consists of a bottommounted linear generator which is connected to a surface buoy with a taut mooring line. The maximum stroke length of the linear generator is enforced by end-stops. Initially, a Variation Mode and Effect Analysis (VMEA) was carried out in order to identify the largest input uncertainties. The system was then modelled in the time-domain solver WECSIM coupled to the dynamic mooring solver Moody. A sensitivity analysis was made by generating a surrogate model based on polynomial chaos expansions, which rapidly evaluates the maximum loads on the mooring line and the endstops. The sensitivities are ranked using the Sobol index method. We investigated two sea states using equivalent regular waves (ERW) and irregular wave (IR) trains. We found that the ERW approach significantly underestimate the maximum loads. Interestingly, the ERW predicted wave height and period as the most important parameters for the maximum mooring tension, while the tension in IR waves was most sensitive to the drag coefficient of the surface buoy. The end-stop loads were most sensitive to the PTO damping coefficient.

  • 18.
    Fellinger, Joris
    et al.
    Max Planck Institute for Plasma Physics, Germany.
    Richou, M.
    CEA Institute for Magnetic Fusion Research, France.
    Ehrke, G.
    Max Planck Institute for Plasma Physics, Germany.
    Endler, M.
    Max Planck Institute for Plasma Physics, Germany.
    Kunkel, F.
    Max Planck Institute for Plasma Physics, Germany.
    Naujoks, D.
    Max Planck Institute for Plasma Physics, Germany.
    Kremeyer, Th.
    Max Planck Institute for Plasma Physics, Germany.
    Menzel-Barbara, A.
    Max Planck Institute for Plasma Physics, Germany.
    Sieber, Th.
    Max Planck Institute for Plasma Physics, Germany.
    Lobsien, J-F
    Max Planck Institute for Plasma Physics, Germany.
    Neu, R.
    Max Planck Institute for Plasma Physics, Germany.
    Tretter, J.
    Max Planck Institute for Plasma Physics, Germany.
    Wang, Z.
    Max Planck Institute for Plasma Physics, Germany.
    You, J-H
    Max Planck Institute for Plasma Physics, Germany.
    Greuner, H.
    Max Planck Institute for Plasma Physics, Germany.
    Hunger, K.
    Max Planck Institute for Plasma Physics, Germany.
    Junghanns, P.
    Max Planck Institute for Plasma Physics, Germany.
    Schneider, O.
    Max Planck Institute for Plasma Physics, Germany.
    Wirtz, M.
    Forschungszentrum Jülich GmbH, Germany.
    Loewenhoff, Th.
    Forschungszentrum Jülich GmbH, Germany.
    Houben, A.
    Forschungszentrum Jülich GmbH, Germany.
    Litnovsky, A.
    Forschungszentrum Jülich GmbH, Germany.
    Fraysinnes, P-E
    CEA LITEN DTCH LCA, France.
    Emonot, P.
    CEA LITEN DTCH LCA, France.
    Roccella, S.
    ENEA Frascati Research Centre, Itay.
    Widlund, Ola
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Koncar, B.
    Jožef Stefan Institute, Slovenia.
    Tekavčič, M.
    Jožef Stefan Institute, Slovenia.
    Tungsten based divertor development for Wendelstein 7-X2023In: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 37, article id 101506Article in journal (Refereed)
    Abstract [en]

    Wendelstein 7-X, the world’s largest superconducting stellarator in Greifswald (Germany), started plasma experiments with a water-cooled plasma-facing wall in 2022, allowing for long pulse operation. In parallel, a project was launched in 2021 to develop a W based divertor, replacing the current CFC divertor, to demonstrate plasma performance of a stellarator with a reactor relevant plasma facing materials with low tritium retention. The project consists of two tasks: Based on experience from the previous experimental campaigns and improved physics modelling, the geometry of the plasma-facing surface of the divertor and baffles is optimized to prevent overloads and to improve exhaust. In parallel, the manufacturing technology for a W based target module is qualified. This paper gives a status update of project. It focusses on the conceptual design of a W based target module, the manufacturing technology and its qualification, which is conducted in the framework of the EUROfusion funded WPDIV program. A flat tile design in which a target module is made of a single target element is pursued. The technology must allow for moderate curvatures of the plasma-facing surface to follow the magnetic field lines. The target element is designed for steady state heat loads of 10 MW/m2 (as for the CFC divertor). Target modules of a similar size and weight as for the CFC divertor are assumed (approx. < 0.25 m2 and < 60 kg) using the existing water cooling infrastructure providing 5 l/s and roughly maximum 15 bar pressure drop per module. The main technology under qualification is based on a CuCrZr heat sink made either by additive manufacturing using laser powder bed fusion (LPBF) or by uniaxial diffusion welding of pre-machined forged CuCrZr plates. After heat treatment, the plasma-facing side of the heat sink is covered by W or if feasible by the more ductile WNiFe, preferably by coating or alternatively by hot isostatic pressing W based tiles with a soft OFE-Cu interlayer. Last step is a final machining of the plasma-exposed surface and the interfaces to the water supply lines and supports to correct manufacturing deformations.

  • 19.
    Fjellgaard Mikalsen, Ragni
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Fire Technology.
    Durgun, Özum
    RISE Research Institutes of Sweden, Built Environment, System Transition and Service Innovation.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Orosz, Katalin
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Honfi, Daniel
    RISE Research Institutes of Sweden, Built Environment, Building and Real Estate.
    Reitan, Nina Kristine
    RISE Research Institutes of Sweden, Safety and Transport, Fire Technology.
    Efficient emergency responses to vehicle collision, earthquake, snowfall, and flooding on highways and bridges: A review2020In: Journal of Emergency Management, ISSN 1543-5865, Vol. 18, no 1, p. 51-72Article in journal (Refereed)
    Abstract [en]

    This review article analyzes factors affecting emergency response to hazardous events on highways and their bridges, with focus on man-made and natural scenarios: heavy vehicle collision with a bridge, earthquake, heavy snowfall, and flooding. For each disaster scenario, selected historical events were compiled to determine influential factors and success criteria for efficient emergency response, both related to organizational and technical measures. This study constituted a part of a resilience management process, recently developed and demonstrated within the European Union (EU)-funded H2020 project IMPROVER and can be a useful approach in aiding operators of transportation infrastructure to improve their resilience to emergency incidents.

  • 20.
    Gagliardo, Raffaele
    et al.
    University of Naples Federico II, Italy.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Cascini, Lucrezia
    University of Naples Federico II, Italy.
    Portioli, Francesco
    University of Naples Federico II, Italy.
    Landolfo, Raffaele
    University of Naples Federico II, Italy.
    Vulnerability assessment of monumental artworks using contact time-history analysis2021Conference paper (Refereed)
  • 21.
    Gagliardo, Raffaele
    et al.
    University of Naples “Federico II”, Italy.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Portioli, Francesco
    University of Naples “Federico II”, Italy.
    Landolfo, Raffaele
    University of Naples “Federico II”, Italy.
    Rigid block modelling approach for the prediction of seismic performance of adjacent interacting masonry structures2022In: Proceedings of 3rd EUROPEAN CONFERENCE ON EARTHQUAKE ENGINEERING & SEISMOLOGY., 2022, p. 3245-Conference paper (Refereed)
    Abstract [en]

    The current paper discusses the contents of the work completed for the project “SERA AIMS – BLIND PREDICTION COMPETITION”. The competition was focused on the prediction of the response of a masonry building composed of two adjacent interacting structural units under earthquake excitation. This research investigates the response of the experimental mock-up by using a numerical model based on the rigid block limit analysis and mathematical programming. The results of the analysis, namely, the failure modes and the corresponding collapse load multipliers, are related to base shear and peak ground accelerations observed for the damage and ultimate limit states using code provisions for the assessment of failure mechanisms in existing masonry structures. Finally, a preliminary comparison of numerical and experiemental results is presented.

  • 22.
    Gagliardo, Raffaele
    et al.
    University of Naples Federico II, Italy.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Portioli, Francesco P. A.
    University of Naples Federico II, Italy.
    Landolfo, Raffaele
    University of Naples Federico II, Italy.
    Seismic analysis of failure mechanisms in adjacent interacting stone masonry buildings via rigid block modeling2023In: Bulletin of Earthquake Engineering, ISSN 1570-761X, E-ISSN 1573-1456Article in journal (Refereed)
    Abstract [en]

    Groups of contiguous unreinforced stone masonry buildings are a common type of housing seen in old European downtowns. However, assessing their response to earthquakes poses several challenges to the analysts, especially when the housing units are laid out in compact configurations. In fact, in those circumstances a modeling technique that allows for the dynamic interaction of the units is required. The numerical study carried out in this paper makes use of a rigid block modeling approach implemented into in-house software tools to simulate the static behavior and dynamic response of an aggregate stone masonry building. Said approach is used to reproduce the results of bi-axial shake-table tests that were performed on a building prototype as part of the activities organized within the Adjacent Interacting Masonry Structures project, sponsored by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe. The experimental mock-up consisted of two adjacent interacting units with matching layout but different height. Two rigid block models are used to investigate the seismic response of the mock-up: a 3D model allowing for the limit analysis of the building on one hand, and a 2D model allowing for the non-linear static pushover and time-history analysis on the other. The 3D model was built for the blind prediction of the test results, as part of a competition organized to test different modeling approaches that are nowadays available to the analysts. The 2D model was implemented once the experimental data were made available, to deepen the investigation by non-linear static pushover and time-history analysis. In both models, the stonework is idealized into an assemblage of rigid blocks interacting via no-tension frictional interfaces, and mathematical programming is utilized to solve the optimization problems associated to the different types of analysis. Differences between numerical and experimental failure mechanisms, base shears, peak ground accelerations, and displacement histories are discussed. Potentialities and limitations of the adopted rigid block models for limit, pushover and time-history analyses are pointed out on the basis of their comparisons with the experimental results.

  • 23.
    Godio, Michele
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Safety and Transport, Fire and Safety.
    Low-velocity out-of-plane impact tests on double-wythe unreinforced brick masonry walls instrumented with optical measurements2023In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509Article in journal (Refereed)
    Abstract [en]

    Unreinforced brick masonry makes up today a significant piece of the European built environment, including not only residential buildings but also strategically important structures that are not designed to withstand blasts and impacts. Yet, it is difficult to accurately estimate the response of these structures and the extent of damage they sustain during such extreme loading conditions. This paper presents the implementation and discusses the results of laboratory impact tests conducted on natural-scale double-wythe unreinforced brick masonry walls, a typology that is frequently found in Northern Europe. The walls were spanning vertically between two reinforced concrete slabs and were subjected to low-velocity drop-weight pendulum tests in which they were repeatedly hit until the opening of a breach in the center of the wall. The tests were instrumented with both hard-wired and optical measurements, the latter consisting of high-speed cameras and digital image correlation techniques, to face the difficulty of observing cracks and determining the deflections of the walls with adequate accuracy at the time of the impact. Investigated in these tests were the out-of-plane response of the walls and their capacity to resist the impacts. The axial load applied on the top of the walls was varied for two wall configurations and monitored throughout the tests to study the effect of arching on the failure mechanism produced and number of repeated hits needed to open the breach. Of interest was also the evidence of cracking, more specifically the way it initiated on the undamaged walls and next propagated upon consecutive hits. The data generated from these tests are made available to support further investigations on unreinforced masonry structures subjected to extreme actions.

  • 24.
    Godio, Michele
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Safety and Transport, Fire and Safety.
    Low-velocity out-of-plane impact tests on double-wythe unreinforced brick masonry walls instrumented with optical measurements2023In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 178, article id 104597Article in journal (Refereed)
    Abstract [en]

    Unreinforced brick masonry makes up today a significant piece of the European built environment, including not only residential buildings but also strategically important structures that are not designed to withstand blasts and impacts. Yet, it is difficult to accurately estimate the response of these structures and the extent of damage they sustain during such extreme loading conditions. This paper presents the implementation and discusses the results of laboratory impact tests conducted on natural-scale double-wythe unreinforced brick masonry walls, a typology that is frequently found in Northern Europe. The walls were spanning vertically between two reinforced concrete slabs and were subjected to low-velocity drop-weight pendulum tests in which they were repeatedly hit until the opening of a breach in the centre of the wall. The tests were instrumented with both hard-wired and optical measurements, the latter consisting of high-speed cameras and digital image correlation techniques, to face the difficulty of observing cracks and determining the deflections of the walls with adequate accuracy at the time of the impact. Investigated in these tests were the out-of-plane response of the walls and their capacity to resist the impacts. The axial load applied on the top of the walls was varied for two wall configurations and monitored throughout the tests to study the effect of arching on the failure mechanism produced and number of repeated hits needed to open the breach. Of interest was also the evidence of cracking, more specifically the way it initiated on the undamaged walls and next propagated upon consecutive hits. The data generated from these tests are made available to support further investigations on masonry structures subjected to extreme actions.

  • 25.
    Godio, Michele
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Safety and Transport, Fire and Safety.
    Single- and double-wythe brick masonry walls subjected to four-point bending tests under different support conditions: Simply supported, rigid, non-rigid2023In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 404, article id 132544Article in journal (Refereed)
    Abstract [en]

    Out-of-plane actions cause confined unreinforced masonry walls (URM) to develop what is known as an arching action. The role of arching is central in the resisting mechanisms of a wall; it contributes significantly to its loadbearing capacity as long as the wall’s deflections are minor, but gradually loses effect with increasing deflections, until collapse occurs. To date, limited experimental data is available on how arching develops in relation to the out-of-plane behaviour of the wall. This study brings new experimental evidence to this aspect. Quasi-static monotonic four-point bending tests were conducted on eleven brick wall strips, with reinforced concrete (RC) slabs affixed below and over the walls to simulate contact conditions of a typical construction system. The walls were tested vis-à-vis three different support conditions: simply supported, rigid, and non-rigid. The influence of these support conditions on the out-of-plane behaviour of the walls was studied on specimens with varying thickness – single and double wythe – and subjected to different levels of axial compression (or overload). While the former support condition was designed not to yield any arching inside the wall (unconfined masonry), the intermediate and latter solutions generated an arching action that was proportional respectively to the elongation of the wall (partially confined masonry), and its deflection (confined masonry). The walls were tested inside a bi-axial test setup that allowed not only the out-of-plane force but also the arching action to be measured, corroborating its central role in the development of the out-of-plane capacity of the walls. To support the observations, deformation characteristics and crack distributions were determined using two optical measurement systems placed in front and to the side of the walls, making use of the Digital Image Correlation (DIC) technique. The results of the tests are discussed in terms of failure mechanism as well as force and displacement capacity of the walls in relation to the investigated parameters. The test data is collected and made available to help with future research on the out-of-plane capacity of URM walls.

  • 26.
    Godio, Michele
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Experimental study on the hydromechanical behaviour of a natural unperturbed fracture under normal loading: Derivation of the equivalent hydraulic aperture and its digital reconstruction2024Report (Other academic)
    Abstract [en]

    This report describes the laboratory work undertaken to characterize the hydromechanical behaviour of a natural rock fracture under varying normal loading. The hydraulic transmissivity of a granite specimen with a sealed (unopened) quasi-planar natural fracture of length 200 mm and width 200 mm was measured. The transmissivity measurements were conducted in the two perpendicular directions of the fracture, repeating them at five different normal compression stress levels, namely, ~0, 1, 2, 4, and 8 MPa, and flow gradients. The fracture was mechanically opened, and the measurements were repeated to investigate the effect of opening the fracture on its hydraulic transmissivity and hydromechanical behaviour. For one direction, the change in transmissivity was explored for high normal compression stress levels, up to ~40 MPa. Laminar flow conditions were ensured at every stage of the experimental campaign by working at very low Reynolds numbers (<1). The equivalent hydraulic aperture of the fracture was derived by resorting to the parallel-plate model theory. The hydraulic aperture was compared to the mechanical aperture, which was obtained by measuring the deformation of the specimen. In addition to the transmissivity tests, the geometry of the lateral walls and surfaces of the fracture was documented and measured by a series of tools, namely, digital scans, high-resolution pictures, optical readings by a stand microscope, and contact pressure-sheet measurements. The results achieved in this campaign shed light on the hydraulic transmissivity of sealed (unopened) and consequently opened natural fractures, and its dependency to the applied normal compression stress at low to very-low flow rates.

    The full text will be freely available from 2024-05-01 08:00
  • 27.
    Godio, Michele
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Laboratory low-transmissivity tests on natural rock fracture under varying normal load2022In: Programme of Geological Society of Sweden 150 year Anniversary meeting., 2022Conference paper (Other academic)
    Abstract [en]

    There is limited available data on natural rock fractures with low hydraulic transmissivity. In this study, we measured the transmissivity of a granite specimen with a 200×200 mm naturally-induced closed fracture under varying normal load. We repeated the measurements after opening the fracture to investigate how this affects its transmissivity. At each stage, we ensured laminar flows by setting Reynolds numbers << 1. Finally, we resorted to the parallel-plate theory to obtain the equivalent hydraulic aperture, that we compared to the mechanical aperture derived from the observed deformation.

  • 28.
    Godio, Michele
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Magnusson, Johan
    Swedish Fortifications Agency, Sweden.
    Byggnevi, Magnus
    Swedish Fortifications Agency, Sweden.
    Experimental and numerical approaches to investigate the out-of-plane response of unreinforced masonry walls subjected to free far-field blasts2021In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 239, article id 112328Article, review/survey (Refereed)
    Abstract [en]

    Masonry walls are bulky and heavy and have therefore the potential to act naturally as a protective system to blasts. Yet, they are known to have a limited flexural and torsional capacity, particularly when unreinforced. When exposed to shockwaves, they experience out-of-plane failure mechanisms which may affect the overall stability of the building and engender flying debris inside the building. The out-of-plane response of unreinforced masonry walls to blasts depends on many factors characterizing both the wall and blast action, making any sort of prediction difficult. In this context, experimental tests and numerical models become key tools that can be used to study the wall’s response on a case-by-case basis. This review covers the major experimental and numerical approaches to assess the out-of-plane response of unreinforced masonry walls subjected to blasts. A methodological appraisal is used for the test methods, focusing on the preparation of the test items and test setup, the boundary conditions and failure mechanisms investigated, as well as the commonly employed measurement techniques. The survey on the modelling approaches includes key topics such as level of detail and cost, and reports strategies to model the wall and blast scenario. The review provides a thematic analysis of the available literature, aimed to assist the analyst in selecting a suitable tool for the investigation of masonry in the field of blast engineering. Furthermore, the findings presented herein can support amendments of existing codes and guidelines pertaining to the design of protective masonry structures.

  • 29.
    Grigull, Susanne
    et al.
    SGI Sveriges geologiska undersökning, Sweden.
    Evins, Paul
    WSP, Sweden.
    Berglund, Johan
    SGI Statens geotekniska institut, Sweden.
    Bäckström, Ann
    Nitro Consult.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Loorents, Karl-Johan
    Trafikverket, Sweden.
    Samuelsson, Eva
    Geosigma.
    Svensson, Mats
    Tyréns.
    Swindell, Robert
    Sweco.
    Johan, Thörn
    Bergab / Chalmers.
    Winell, Sofia
    Geosigma.
    Enkätstudie – Insamling och lagring av bergtekniska och hydrogeologiska data2020Report (Other academic)
    Abstract [en]

    Geotechnical and hydrogeological data are collected during all phases of construction projects. Currently, the collection of such data is not standardized and there is no central, national system for storing the collected data. It is also difficult to evaluate or re-use such data from previous projects which results in collecting the same field data from scratch for new infrastructure projects. Previous studies and this feasibility study have shown the need for clearer, improved methodologies for data collection along with a national portal for access to geotechnical and hydrogeological archives and data from previous projects.

    Through two surveys answered by key parties in the rock construction industry, we have identified geotechnical and hydrogeological parameters that need improved methodology and method descriptions and possibly standardization. Existing database solutions, as well as suggestions for the functionality of a future national database have also been analyzed from the survey responses.

    Survey results also show that data collection standardization is necessary to ensure data reliability and traceability, and that standardized methodologies should be adapted to project complexity and try to conform to current internationally accepted methodologies. However, the study also shows that industry views are divided on certain issues. How new methodologies and data portals / databases will be developed, funded, managed andimplemented also remains to be clarified.

    This feasibility study recommends a national database divided into a searchable document archive and a parameter database. One or more government organizations should be responsible for administration.

    The present report serves as a decision basis for initiating and financing projects in the area concerned. It is strongly recommended that any organization(s) that build a document archive and a national parameter database take into account the functional requirements mentioned in this report.

    Note that this report is also available in PDF format on Stiftelsen Bergteknisk Forskning- BeFo's website. The links in the report can be easily opened directly from the PDF file and images can be enlarged.

  • 30.
    Hanquist, Caroline
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Davidsson, Sandra
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Laboratory tests in borehole KFM01A, KFM08A, KFM11A, KFR102A and KFR104: Uniaxial compression and indirect tensile strength tests of intact rock2023Report (Other academic)
    Abstract [en]

    The density and mechanical properties were determined on water saturated specimens from boreholesKFM01A, KFM08A, KFM11A, KFR102A and KFR104 in the Forsmark site investigation area. Therock types in the selected sections were amphibolite (102017) and metavolcanic rock (103076). Somespecimens had a more or less foliated rock structure. The cores were sampled from a depth rangingbetween 196–901 m.The specimens were water saturated using tap water and all subsequent measurements wereconducted at this moisture condition. The density was determined on 30 specimens. The testingended with 20 indirect tensile tests yielding the indirect tensile strength and 10 uniaxial compressiontests including the post-peak response yielded the Young’s modulus, Poisson’s ratio and the uniaxialcompressive strength.Some variation of rock material along the short cores could be seen, which is reflected in themeasured data. The density at a water saturated condition was 2892–3067 kg/m3 for amphibolite, and2697–2763 kg/m3 for metavolcanic rock.The indirect tensile tests were conducted such that every specimen with visible foliation was testedwith the diametrical compression across the foliation planes, with higher values for the indirecttensile strength on the specimens. The strength variation in the amphibolite was large. The indirecttensile strength was 10.8–21.4 MPa for amphibolite and 16.9–20.7 MPa for metavolcanic rock. Twoof the amphibolite specimens had a deviating lower strength, indirect tensile strength 5.7 MParespectively 5.8 MPa, with a ductile failure. Those specimens had a high content of mica.The Young’s modulus obtained from the uniaxial compression tests was 88.6–114.5 GPa foramphibolite and 68.2–89.1 GPa for metavolcanic rock and the Poisson’s ratio was 0.339–0.386 foramphibolite and 0.236–0.313 for metavolcanic rock. The peak values of the axial compressive stresswere in the range 213.1–333.7 MPa for amphibolite and 104.1–283.1 MPa for metavolcanic rock.One of the amphibolite specimens had a deviating lower strength and a ductile failure with Young’smodulus 41.2 GPa, Poisson’s ratio 0.500 and peak axial compressive stress of 44.5 MPa. Thatspecimen had a high content of mica. 

  • 31.
    Jacobsson, Lars
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Larsson, Jörgen
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Direct shear tests on large natural and artificially induced rock fractures in a new laboratory equipment2023In: Proceedings of the ISRM 15th International Congress on Rock Mechanics and Rock Engineering & 72nd Geomechanics Colloquium: Challenges in Rock Mechanics and Rock Engineering / [ed] Schubert, W. & Kluckner, A., Salzburg: Austrian Society for Geomechanics , 2023, p. 2709-2714, article id 1827Conference paper (Refereed)
    Abstract [en]

    A direct shear equipment for testing rock fractures up to 400×600 mm size, and up to 5 MN force in both normal and shear loading directions, was developed. Normal loading and direct shear tests under constant normal stiffness (CNS) and constant normal load (CNL) conditions were conducted on 300×500 mm specimens, one planar steel joint and two natural and two tensile induced rock fractures. Design targets, e.g. system to maintain undisturbed fractures up to testing and high system stiffnesses to achieve well-controlled shear tests, were verified by the experiments. A new optical system for local deformation measurements was used to accurately determine fracture displacements besides conventional non-local deformation measurements. The determined normal stiffnesses were similar previous results from the literature on smaller fractures, whereas the shear stiffness data are novel. The results provide a new insight into processes at the onset of fracture slip.

  • 32.
    Jacobsson, Lars
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Measuring the hydraulic transmissivity of a rock joint under varying normal load2022Conference paper (Refereed)
  • 33.
    Jacobsson, Lars
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Godio, Michele
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Measuring the hydraulic transmissivity of a rock joint under varying normal load2023In: IOP Conference Series: Earth and Environmental Science, Institute of Physics , 2023, no 1Conference paper (Refereed)
    Abstract [en]

    The water flow rate through a rectangular granite specimen with a tight unopened natural induced joint of dimensions 200×200 mm was measured in two perpendicular directions. The measurements were conducted at five different levels of stress corresponding to loading from 0 to 8 MPa and unloading back to 0 MPa. The flow was measured at different hydraulic gradients in the range of 10 to 25. The results showed a joint transmissivity between 0.002-0.03 mm2/s and a hydraulic aperture of 8-32 μm. It was shown that the measurements performed in the second orientation displayed smaller transmissivity and hydraulic aperture as compared to those in the first orientation, showing a residual compaction after the first load cycle. The Reynolds number was less than one in all the measurements yielding laminar flow conditions. Deviations from the linear regime relationship were observed for the lowest flow rates (Re &lt; 0.1). A transitory regime was observed when varying the hydraulic gradient. This regime was observed to be longer at the lowest flow rates. © 2023 Institute of Physics Publishing. All rights reserved.

  • 34.
    Jacobsson, Lars
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Ivars, D. M.
    SKB, Swedish Nuclear Fuel and Waste Management Company, Sweden; KTH Royal Institute of Technology, Sweden.
    Kasani, H. A.
    Nuclear Waste Management Organization, Canada.
    Johansson, F.
    KTH Royal Institute of Technology, Sweden.
    Lam, T.
    Nuclear Waste Management Organization, Canada.
    Experimental program on mechanical properties of large rock fractures2021In: IOP Conference Series: Earth and Environmental Science, IOP Publishing Ltd , 2021, Vol. 833, no 1, article id 012015Conference paper (Refereed)
    Abstract [en]

    Predictions of fracture displacements are required to support the safety assessments of a deep geological repository for nuclear spent fuel. Laboratory and in-situ experiments are used to estimate these properties. Despite significant contributions in the last decades, there is a knowledge gap in terms of the impact of high normal stresses on the mechanical properties of large-scale fractures under Constant Normal Stiffness (CNS) boundary conditions. Within the framework of the POST project, a cooperative effort was made by SKB (Sweden), NWMO (Canada), and Posiva from Finland (in phase 1) to study these questions. In the second phase of the POST project, a first of a kind direct shear testing machine was manufactured and calibrated that can accommodate samples up to 400 × 600 mm under normal stresses up to 10 MPa, for both CNS and Constant Normal Load (CNL) conditions, with the ability to shear the sample up to 50 mm. Several best practice procedures were developed for fracture characterization pre-, syn-, and post-shear test which utilize high resolution optical scanning, contact pressure measurements, Digital Image Correlation (DIC) measurements, and acoustic emission measurements during the shear test. Natural and tensile-induced fractures of a granitic rock as well as replicas of the hard rock fractures, at three different fracture sizes of 35×60 mm, 70×100 mm, and 300×500 mm, are now being tested. It is hoped that this program will provide a set of high-quality data which will help reduce the knowledge gap in the understanding of fracture behavior. 

  • 35.
    Jacobsson, Lars
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Mas Ivars, Diego
    SKB Swedish Nuclear Fuel and Waste Management Company, Sweden; KTH Royal Institute of Technology, Sweden.
    Kasani, Hossein A
    Nuclear Waste Management Organization, Canada.
    Johansson, Fredrik
    KTH Royal Institute of Technology, Sweden.
    Experimental program to study scale effects on mechanical properties of large rock fractures2022In: Abstract Volume, 2022, p. 102-103Conference paper (Other academic)
    Abstract [en]

    The scale effect of natural and artifically induced rock fractures and replicas up to a 500 mm length are experimentally studied by direct shear tests in a testing program including a newly manufactured large shear testing equipment. The fractures are chatacterised pre-, syn-, and post-shear test. Combinations of different measurements provide a high-quality dataset enabling deeper understanding of, and constitutive model development for rock fractures used for safety assessment of deep geological respoitories for nuclear waste disposal.

  • 36.
    Johannesson, Pär
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Lang, X.
    Chalmers University of Technology, Sweden.
    Yang, S. -H
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Ringsberg, J. W.
    Chalmers University of Technology, Sweden.
    Mechanical reliability of flexible power cables for marine energy2021In: Proceedings of the European Wave and Tidal Energy ConferencePages 2146-1 - 2146-102021, European Wave and Tidal Energy Conference Series , 2021, p. 2146-1-2146-10Conference paper (Refereed)
    Abstract [en]

    Marine power cables play a crucial role to utilize energy in marine areas, such as offshore wind, wave energy and tidal energy. Marine energy devices are typically grouped into arrays to increase the economic viability, and power cables transfer the energy from the devices to a central hub which is then transmitted ashore. Cables connected to moving devices may experience millions of load cycles per year, and thus they need to be flexible and designed for mechanical loads due to the movements of the cable. In this study, the focus is on the mechanical life of flexible cables connecting devices to hubs, and thus lowand medium voltage power cables is the focus. The reliability design method Variational Mode and Effect Analysis (VMEA) is applied that is based on identifying and quantifying different types of uncertainty sources, such as scatter, model uncertainties and statistical uncertainties. It implements a load-strength-approach that combines numerical simulations to assess the loads on the cable and experimental tests to assess the strength of the cable. The VMEA method is demonstrated for an evaluation of bending fatigue, and it has been found to be a useful tool to evaluate uncertainties in fatigue life for cables in WEC (Wave Energy Converter) systems during the design phase. The results give a firm foundation for evaluation of safety against fatigue and are also helpful for identifying weak spots in the reliability assessment that can motivate actions  in the improvement process. Uncertainties in terms of scatter, statistical uncertainty and model uncertainty have been evaluated with respect to the WaveEL 3.0, a WEC designed by the company Waves4Power, and deployed in Runde, Norway. A major contribution to the overall uncertainty is found to originate from the fatigue life model, both in terms of scatter and model uncertainty. 

  • 37.
    Johannesson, Pär
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Lang, Xiao
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. Chalmers University of Technology, Sweden.
    Ringsberg, Jonas W
    Chalmers University of Technology, Sweden.
    Mechanical Reliability Analysis of Flexible Power Cables for Marine Energy2022In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 10, no 6, article id 716Article in journal (Refereed)
    Abstract [en]

    Marine power cables connected to moving devices at sea may experience millions of load cycles per year, and thus they need to be flexible due to the movements of the cable and designed for mechanical loads. In this study, the focus is on the mechanical life of flexible low-and medium voltage power cables connecting devices to hubs. The reliability design method Variational Mode and Effect Analysis (VMEA) is applied, based on identifying and quantifying different types of uncertainty sources, including scatter, model and statistical uncertainties. It implements a load–strength approach that combines numerical simulations to assess the loads on the cable and experimental tests to assess the strength of the cable. The VMEA method is demonstrated for an evaluation of bending fatigue, and is found to be a useful tool to evaluate uncertainties in fatigue life for WEC (Wave Energy Converter) system cables during the design phase. The results give a firm foundation for the evaluation of safety against fatigue and are also helpful for identifying weak spots in the reliability assessment, thereby motivating actions in the improvement process. Uncertainties in terms of scatter, statistical uncertainty and model uncertainty are evaluated with respect to the WaveEL 3.0, a WEC designed by the company Waves4Power, and deployed in Runde, Norway. A major contribution to the overall uncertainty is found to originate from the fatigue life model, both in terms of scatter and model uncertainty. © 2022 by the authors. 

  • 38.
    Johansson, Ann-Christine
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Biorefinery and Energy.
    Sott, Richard
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Mattsson, Cecilia
    RISE Research Institutes of Sweden, Materials and Production, Polymeric Materials and Composites.
    Comparative study of thermochemical recycling with solvolysis and pyrolysis of End-of-Life wind turbine blades: Rekovind2 - WP32023Report (Other academic)
    Abstract [en]

    There is an urgent need for the development of viable recycling solutions for the increasing waste streams of glass fiber composites (GFRPs) from all sectors i.e. leisure boats, windmills and building constructions. Two potential recycling methods that can separate and recover both the polymers and the high-quality fibers from these kinds of materials are pyrolysis and solvolysis. In this project recycling of an epoxy-based Endof-Life wind turbine blade was evaluated in lab scale using the two methods. In previous literature the main focus has been on the quality of the fibers but in this project the main focus was to compare the chemical composition of the oil products. The produced oils from solvolysis and pyrolysis have been compared with a multianalysis approach by using elemental analysis, GC-MS, pyro-GC-MS/FID, 2D NMR (HSQC) for gaining more information about the chemical structure of the produced monomers (phenols), oligomers and polymers. Almost all the volatile matter in the End-of-Life wind turbine blade was recovered as pyrolysis oil, 36 wt.% yield. The solvolysis oil yield was lower, 17 wt.%, mainly due to a major part of the solvolysis oil ended up in the aqueous solvent. The composition of the oils from both technologies was analyzed based on both their volatile i.e. monomeric and polymeric content. The result point to that both methods produced oils with similar polymeric parts according to NMR and pyro-GC-MS/FID, based on an oxygenated aliphatic network connected with aromatic phenolic structures. Increased information of chemical oil composition will be useful for further processing as raw material in refineries/chemical industries. The monomeric part of the oil produced from pyrolysis was found in relatively large amounts, ~57 wt.%, and can be a future high-value product from recycling of wind turbine blades. The total recovery of phenolics from the pyrolysis was 18 wt.% of the wind turbine blade weight.

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  • 39.
    Kiuru, R.
    et al.
    Aalto University School of Engineering, Finland.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Király, D.
    SOM System Kft, Hungary.
    Suikkanen, J.
    Posiva Oy, Finland.
    Effects of Excavation Damage on the Physical Properties of Rock Matrix2021In: IOP Conference Series: Earth and Environmental Science, IOP Publishing Ltd , 2021, Vol. 833, no 1, article id 012020Conference paper (Refereed)
    Abstract [en]

    Posiva Oy has conducted investigations into excavation damage, including comprehensive laboratory testing of physical properties of rock specimens from excavation damaged rock mass. Laboratory testing was conducted on drill core specimens extracted from the excavated surface of a tunnel located at approximately 345 m depth in Olkiluoto, Finland. A total of 141 drill core specimens of three main rock types, a structurally isotropic coarse-grained pegmatoid (PGR) and structurally anisotropic veined gneiss (VGN) and diatexitic gneiss (DGN), were subjected to petrophysical testing, rock mechanics testing and petrographic analyses. Results from the various tests were subjected to rigorous statistical analysis in order to reveal the effects excavation damage has on the physical properties of the rock mass. Results of the study revealed changes that are credited to excavation damage in resistivity, S-wave velocity and various elastic properties of the rock specimens. Effects of excavation damage and the depth of the excavation damaged zone seem to be different to gneiss compared to pegmatoid. On microscopic level, the extent of excavation damaged zone appears to be 0.2 - 0.4 m depending on the measured property. This means that the deeper excavation damaged layer observed by geophysical surveys may be caused by larger scale fractures. 

  • 40.
    Kiuru, Risto
    et al.
    Aalto University, Finland.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Király, Dorka
    Budapest University of Technology and Economics, Hungary.
    Suikkanen, Johannes
    Posiva Oy, Finland.
    Geofysiikka louhintavauriotutkimuksissa2022In: XXX Geofysiikan päivät: Helsingissä 18.‐19.5.2022, Helsingfors: Geofysiikan Seura , 2022, p. 34-35Conference paper (Other academic)
  • 41.
    Kiuru, Risto
    et al.
    Aalto University, Finland.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Király, Dorottya
    Suikkanen, Johannes
    Louhintavaurion vaikutus kalliomassan fysikaalisiin ominaisuuksiin2021In: Conference proceedings of the XXIII Sovelletun geofysiikan neuvottelupäivät in Espoo, Finland, 23.‐24.11.2021., 2021Conference paper (Other academic)
  • 42.
    Kiuru, Risto
    et al.
    Aalto University, Finland.
    Király, Dorka
    Budapest University, Hungary.
    Dabi, Gergely
    University of Szeged, Hungary.
    Jacobsson, Lars
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Comparison of dfn modelled microfracture systems with petrophysical data in excavation damaged zone2021In: Applied Sciences, E-ISSN 2076-3417, Vol. 11, no 7, article id 2899Article in journal (Refereed)
    Abstract [en]

    Physical and petrographic properties of drill core specimens were determined as a part of investigations into excavation damage in the dedicated study area in the ONKALO® research facility in Olkiluoto, Western Finland. Microfractures in 16 specimens from two drillholes were analysed and used as a basis for fractal geometry-based discrete fracture network (DFN) modelling. It was concluded that the difference in resistivity between pegmatoid granite (PGR) and veined gneiss (VGN) specimens of similar porosity was likely due to differences in the types of microfractures. This hypothesis was confirmed from microfracture analysis and simulation: fractures in gneiss were short and mostly in one preferred orientation, whereas the fractures in granite were longer and had two preferred orientations. This may be due to microstructure differences of the rock types or could suggests that gneiss and granite may suffer different types of excavation damage. No dependencies on depth from the excavated surface were observed in the geometric parameters of the microfractures. This suggests that the excavation damaged zone cannot be identified based on the changes in the parameters of the microfracture networks, and that the disturbed layer observed by geophysical methods may be caused by macro-scale fractures. © 2021 by the authors.

  • 43.
    Kjellin, Per
    et al.
    Promimic AB, Sweden.
    Danielsson, Karin
    Promimic AB, Sweden.
    Håkansson, Joakim
    RISE Research Institutes of Sweden, Materials and Production, Product Realisation Methodology. University of Gothenburg, Sweden.
    Agrenius, Karin
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Andersson, Therese
    RISE Research Institutes of Sweden, Materials and Production, Product Realisation Methodology.
    Stenlund, Patrik
    RISE Research Institutes of Sweden, Materials and Production, Product Realisation Methodology.
    Biomechanical and histomorphometric evaluation of skin integration on titanium and PEEK implants with different surface treatments2022In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 33, no 10, article id 68Article in journal (Refereed)
    Abstract [en]

    Percutaneous implants are frequently affected by bacterial growth at the skin-implant interface. Integration between implant and surrounding skin is important to prevent bacteria from spreading to the underlying tissue. The standard method to evaluate skin-implant integration is by histomorphometry on samples which have been placed in tissue grown in vivo or ex vivo. In this study, a biomechanical method was developed and evaluated. The integration of implants into porcine skin was studied in an ex vivo model, where pig skin samples were cultivated in a nutrient solution. Cylindrical shaped implants, consisting of polyether ether ketone (PEEK) and titanium (Ti) with different surface treatments, were implanted in the skin tissue and the skin was grown in nutrient solution for 2 weeks. The implants were then extracted from the implantation site and the mechanical force during extraction was measured as a quantitative assessment of skin-implant integration. Implants from each group were also processed for histomorphometry and the degree of epidermal downgrowth (ED) and tissue to implant contact (TIC) was measured. A higher mean pullout force was observed for the PEEK implants compared to the Ti implants. Applying nanosized hydroxyapatite (HA) on Ti and PEEK increased the pullout force compared to uncoated controls, 24% for machined and 70% for blasted Ti, and 51% for machined PEEK. Treatment of Ti and PEEK with nanosized zirconium phosphate (ZrP) did not increase the pullout force. The histomorphometry analysis showed correlation between ED and pullout force, where the pullout force was inversely proportional to ED. For TIC, no significant differences were observed between the groups of same material (i.e. Ti, Ti+HA, Ti+ZrP, and PEEK, PEEK + HA, PEEK + ZrP), but it was significantly higher for PEEK compared to Ti. Scanning electron microscopy analysis was done on samples before and after the pullout tests, showing that the ZrP coating was unaffected by the 2 week ex vivo implantation and pullout procedure, no dissolution or detachment of the coating was observed. For the HA coating, a loss of coating was seen on approximately 5% of the total surface area of the implant. [Figure not available: see fulltext.] © 2022, The Author(s).

  • 44.
    Kuznecovs, Artjoms
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. Chalmers University of Technology, Sweden.
    Yamada, Yasuhira
    National Institute of Maritime, Japan.
    Ultimate limit state analysis of a double-hull tanker subjected to biaxial bending in intact and collision-damaged conditions2020In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 209, article id 107519Article in journal (Refereed)
    Abstract [en]

    This study presents a comparison between nonlinear finite element analysis (FEA) and the Smith method of Fujikubo et al. (2012). The objective was to compare the accuracy and computation effort of the two methods for a double-hull tanker under biaxial bending and various ship conditions: intact hull structure, collision-damaged hull structure, newly built condition, and ship hull aged due to corrosion. The results for the non-corroded and intact ship hull structures showed good agreement between FEA, the Smith method and IACS CSR-H for vertical bending loading conditions. For all other bending load combinations, FEA always gave lower ultimate bending moments than the Smith method. The differences between the two methods were larger for the corroded and damaged ship hull structure than for other conditions. Results from ultimate strength analyses of the collision-damaged hull structures showed that both methods captured the expected asymmetric ultimate strength response due to asymmetric damage. A residual strength index calculation showed that the reduction was larger for the FEA than for the Smith method. A procedure is proposed that combines results of a few FEAs with the advantages of the Smith method to generate accurate biaxial bending load interaction curves for different ship conditions. © 2020 Elsevier Ltd

  • 45.
    Kuznecovs, Artjoms
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas
    Chalmers University of Technology, Sweden.
    Mallaya Ullal, Anirudh
    Chalmers University of Technology, Sweden.
    Janardhana Bangera, Pavan
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. Chalmers University of Technology, Sweden.
    Consequence analyses of collision-damaged ships — damage stability, structural adequacy and oil spills2023In: Ships and Offshore Structures, ISSN 1744-5302, E-ISSN 1754-212X, Vol. 18, no 4, p. 567-Article in journal (Refereed)
    Abstract [en]

    A ship collision accident may pose a threat to human lives, the environment and material assets. A damaged ship can suffer from the loss of ship stability, reduced global structural strength, and the loss of the integrity of internal tanks carrying polluting liquids. This study presents a methodology as a framework that can be used to analyze the related consequences of ship-ship collision events using simulations and evaluations. The methodology includes nonlinear finite element analyses of the collision event, a METOCEAN data analysis module, damage stability simulations, analyses of the damaged ship’s ultimate strength and structural integrity, oil spill drift simulations, and finally, an evaluation of the three abovementioned consequences. A case study with a chemical tanker subjected to collision demonstrates the methodology. The collision event was assumed to occur in the Kattegat area (between Sweden and Denmark) at a ship route intersection with high ship traffic density. © 2022 The Author(s).

  • 46.
    Larsson, Jörgen
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. KTH Royal Institute of Technology, Sweden.
    Experimental investigation of the system normal stiffness of a 5 MN direct shear test setup and the compensation of it in CNS direct shear tests2021In: IOP Conference Series: Earth and Environment, ISSN 1755-1307, E-ISSN 1755-1315, Vol. 833, article id 012011Article in journal (Refereed)
    Abstract [en]

    Experiments at constant normal stiffness (CNS) are normally carried out to understand underground shear processes of rock joints. However, in many test setups the available space around the joint is limited implying it is not possible to measure the dilatancy directly over the joint. Therefore, the displacement transducers must be in locations where the risk is that additional displacements originating from deficiencies in the test system will be measured causing too low normal loads to be applied. Herein, this issue is investigated in a new 5 MN direct shear test setup. The system normal stiffness was found to be about 11 300 kN/mm derived from normal loading up to 4.5 MN using a steel specimen. The direct shear testing performance under the CNS configuration was evaluated using the steel specimen, which had a joint with a known angle of inclination. The normal load error at 3.9 MN (28 MPa) was 11%, but by application of the effective normal stiffness approach using the system normal stiffness as input the error basically could be eliminated. The results demonstrate the robustness of the setup designed for joint areas up to 400 × 600 mm with normal and shear loads up to 5 MN.

  • 47.
    Larsson, Jörgen
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. KTH Royal Institute of Technology, Sweden.
    Quality aspects in direct shear testing of rock joints2021Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The stability of rock masses is influenced by the occurrence of rock joints. Therefore, the shear strength of rock joints must be considered in dimensioning of underground constructions. One way to predict the shear strength is through usage of failure criteria, which are validated from results of direct shear tests under controlled laboratory conditions. Consequently, the quality of the results from the tests are crucial to the accuracy with which the criteria will be able to predict the shear strength. Since rock joints are unique by nature usage of replicas (man-made copies of rock joints) is of importance in parameter studies. The overall objective of this work is to facilitate the development of improved criteria for predictions of the shear strength of rock joints. To support this objective, two sources of uncertainty have been investigated, namely the geometry of replicas and the influence of the normal stiffness of test systems. Two quality assurance parameters for evaluation of geometrical differences between replicas and rock joints based on scanning data have been derived. The first parameter describes the morphological deviations. The second parameter describes the deviations in orientation with respect to the shear plane. The effective normal stiffness approach, which compensates for the influence of the normal stiffness of the test system in direct shear testing, has been developed, validated, and applied. With help of the quality assurance parameters it is demonstrated that it is possible to reproduce replicas within narrow tolerances. Application of the effective normal stiffness approach basically eliminates the normal load error. In all, the results support generation of improved quality of test data and consequently, the development of shear strength criteria with improved accuracy will also be facilitated.

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  • 48.
    Larsson, Jörgen
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics. KTH Royal Institute of Technology, Sweden.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    An Approach to Compensate for the Influence of the System Normal Stiffness in CNS Direct Shear Tests2020In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 53, p. 2185-2199Article in journal (Refereed)
    Abstract [en]

    Applying accurate normal load to a specimen in direct shear tests under constant normal stiffness (CNS) is of importance for the quality of the resulting data, which in turn influences the conclusions. However, deficiencies in the test system give rise to a normal stiffness, here designated as system normal stiffness, which results in deviations between the intended and actual applied normal loads. Aiming to reduce these deviations, this paper presents the effective normal stiffness approach applicable to closed-loop control systems. Validation through direct shear tests indicates a clear influence of the system normal stiffness on the applied normal load (13% for the test system used in this work). The ability of the approach to compensate for this influence is confirmed herein. Moreover, it is demonstrated that the differences between the measured and the nominal normal displacements are established by the normal load increment divided by the system normal stiffness. This further demonstrates the existence of the system normal stiffness. To employ the effective normal stiffness approach, the intended normal stiffness (user defined) and the system normal stiffness must be known. The latter is determined from a calibration curve based on normal loading tests using a stiff test dummy. Finally, a procedure is presented to estimate errors originating from the application of an approximate representation of the system normal stiffness. The approach is shown to effectively reduce the deviations between intended normal loads and the actual applied normal loads.

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  • 49.
    Larsson, Jörgen
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Johnson, Erland
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Johansson, F
    KTH Royal Institute of Technology, Sweden.
    Mas Ivars, D
    KTH Royal Institute of Technology, Sweden; SKB Swedish Nuclear Fuel and Waste Management Co, Sweden.
    Geometrical Quality Assurance of Rock Joint Replicas in Shear Tests – Introductory Analysis2020Conference paper (Other academic)
    Abstract [en]

    The presence of joints in rock masses influences the structural integrity of geotechnical structures. A critical failure mode is shearing, thus making the shearing process of importance to understand. Historically, studies have been mainly executed on the basis of laboratory experiments, since full-scale in situ tests are seldom performed due to technical and economic considerations. Since each rock joint is unique by nature, the utilization of replicas is applied to carry out controlled experimental parameter studies. However, the manufacturing process of replicas introduces many sources of uncertainty. Therefore, in this work the influence of geometrical variations in replicas on the shear strength characteristics is evaluated, mutually as well as in relation to the mother rock specimen of the replicas. The joint surfaces were 3D scanned and the contact area of the joint was measured using pressure sensitive film before direct shear tests. Deviations in morphology were evaluated by surface comparisons between the joint surfaces of the mother rock and replicas. The initial matching of the joints was evaluated by calibrating the scanning data with respect to the contact area measurements. It could be visualized that geometrical deviations were caused by rock fragments coming off during mould production, positioning of the moulds and pores resulting from replica casting. These factors were found to influence the shear strength characteristics of the replicas. The influence of the deviations originating from morphology on the joint matching is demonstrated. In summary, it is shown that replicas with similar shear strength characteristics as rock can be manufactured, but even small deviations affect the characteristics, in particular the peak strength. Therefore, parameters relevant for geometrical quality assurance should be identified along with required value ranges. Selected introductory results on quantified parameters for geometrical quality assurance are presented, serving as a basis for continued work.

  • 50.
    Larsson, Jörgen
    et al.
    KTH Royal Institute of Technology, Sweden.
    Johansson, F
    KTH Royal Institute of Technology, Sweden.
    Ivars, D. Mas
    KTH Royal Institute of Technology, Sweden; SKB Swedish Nuclear Fuel and Waste Management Co, Sweden.
    Johnson, Erland
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Flansbjer, Mathias
    RISE Research Institutes of Sweden, Materials and Production, Applied Mechanics.
    Williams Portal, Natalie
    RISE Research Institutes of Sweden, Materials and Production, Corrosion.
    A novel method for geometric quality assurance of rock joint replicas in direct shear testing : Part 2: Validation and mechanical replicability2023In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755Article in journal (Refereed)
    Abstract [en]

    Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies. However, a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking. In this study, a novel method is presented for geometric quality assurance of replicas. The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results. In Part 1 of this study, two quality assurance parameters, σmf and VHp100, are derived and their usefulness for evaluation of geometric deviations, i.e. geometric reproducibility, is shown. In Part 2, the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior, which qualifies the parameters for usage in the quality assurance method. Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σmf < 0.06 mm and < 0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength. The wear in these replicas, which have similar morphology as the rock joint, is in the same areas as in the rock joint. The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties, possibly from differences in toughness. It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics, which makes them useful in parameter studies.

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