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  • 1.
    Jacobsson, Lars
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Safety.
    Sandström, Johan
    RISE - Research Institutes of Sweden (2017-2019), Safety and Transport, Safety.
    Brander, Linus
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, CBI Swedish Cement and Concrete Research Institute.
    Wedge splitting tests on granite and gneiss specimens2018Conference paper (Refereed)
    Abstract [en]

    The conditions for initial tensile cracking around a rounded blunt and a sharp notch and subsequent propagation were investigated by means of wedge splitting tests on structurally isotropic granite. In addition, the crack initiation and propagation on anisotropic gneiss specimens with a blunt notch were investigated in two different material directions. The wedge splitting test specimens which has a straight notch is normally used to determine mode I fracture properties for concrete but not for rock materials. The use of a straight notch in the specimens instead of a chevron type of notch, which is commonly used for fracture mechanics tests, was found to be well suited for the actual type of investigation. 

    The development of fractures from the notch into the specimens was monitored by measuring the deformation field on the specimen surface by digital image correlation (DIC) and by the crack mouth opening displacement. The fracture patterns were different in the granite and the gneiss. The DIC illustratively showed how cracks branched along the main crack path in the granite whereas no branching occurred in the gneiss material. This could also be verified by studying thin sections taken along the fracture path. It was seen that the granite behaved more ductile than the gneiss. 

    A finite element model of the wedge splitting test was made where the crack propagation was modelled using a cohesive-zone model and calibrated using the results from the experiments. The fracture energies were computed and it was found that the energies were about 50-100 percent higher in the granite than in the gneiss. The tensile stress cracking initiation in granite for the blunt and the sharp notch was slightly different. The gneiss specimens were all with a blunt notch and a comparison of the two notch types could not be made in this case.

  • 2.
    Jacobsson, Lars
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Sandström, Johan
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Flansbjer, Mathias
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Sjögren, Torsten
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Brander, Linus
    RISE, SP – Sveriges Tekniska Forskningsinstitut, CBI Betonginstitutet AB.
    ONKALO POSE Experiment - Laboratory Determination of Density, Porosity and Mechanical Anisotropy of Gneiss and Granite2016Report (Other academic)
  • 3.
    Molander, Marcus
    et al.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Jansson, Anna
    RISE - Research Institutes of Sweden, Bioscience and Materials, Chemistry and Materials.
    Sandström, Johan
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Development of condition monitoring methods for polymeric com-ponents including low dose rate radiation exposure2018Conference paper (Refereed)
    Abstract [en]

    Different plastics, rubber and other polymer based materials are widely used in various applications in nuclear power plants and inside containments, e.g. cable jacketing/insulators, sealants, paint coatings, lubricants and greases. As any other material or component, polymers are susceptible to ageing. Ele-vated temperature, ionizing radiation and moisture are considered to be the most important ageing stressors and they tend to interact with the polymer structure in different ways. In addition to these ageing stressors, properties of polymer composition, e.g. crystallinity degree, amount of fillers and antioxidants, has an effect to the ageing behavior. Thus, the degradation mechanism can be quite complex.

    Proper ageing management procedures are based on knowledge on the ageing behavior and how to set correct requirements for the polymer components in use that they will endure their designed life-time. The ageing behavior needs to be known when polymer components are qualified. Accelerated ageing is used as part of the artificial ageing of the qualified polymer and the ageing mechanism should be the same as in the real service environment in order to yield in identical ageing conditions. Thus, the effects of dose rate and temperature to the ageing mechanism must be known as well as the synergistic effects rising from the simultaneous and/or sequential exposure to ionizing radiation and excess heat.

    In a previous feasibility study [2015:157]1 the acceptance criteria for functional properties for different polymers in system components was studied. The components were selected based on interviews with the five Nordic nuclear power plants. A need to study the polymer degradation, using low dose rates (20-50 Gy/h to total dose of 14 kGy) was identified since previous work described in literature often focused on using a high dose rate to achieve the life time dose during a short period of time to achieve a life time dose2. This may cause different degradation, compared to that obtained with a long exposure at a low dose rate, which is the case for many O-rings inside a Nuclear Power plant (NPP). Like the previous feasibility study this research project is performed in collaboration with the Nordic nuclear industry for in a longer perspective implementing the results.

    Rubber materials were tested for different properties such as compression set, stress relaxation, elon-gation at break, Oxidation Induction Temperature (T

    ox) and hardness after heat ageing and gamma irradiation. These properties were then correlated to the function of the O-ring i.e. tightness verified by a leakage test in a specially designed test rig. To be able to better compare the degradation effect caused by the irradiation, a parallel test on samples aged in heat only was performed. By testing the correlation between material data and tightness of an O-ring an understanding of the function (tight-ness) based on a material property (compression set) can be made. The aim was to be able to use this to set acceptance criteria for an O-ring using compression set as a property. A model using Finite Elements (FE) based on the relaxation data and compression set data from the experiment was also done but is only described briefly in this paper.

  • 4.
    Olsson, Kim
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Fire Research, Brandmotstånd.
    Sandström, Johan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Bygg och Mekanik, Tillförlitlighet och Livslängd.
    Albrektsson, Joakim
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Fire Research, Brandmotstånd.
    Anderson, Johan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Fire Research, Brandmotstånd.
    Simulation of Delamination and Collapse of a Fire Exposed FRP Composite Bulkhead2015Conference paper (Other academic)
  • 5.
    Sandström, Johan
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Simulation and calibration of rubber materials for seals2018Report (Other academic)
    Abstract [en]

    Finite element (FE) simulations of how rubber materials for seals behave over time isperformed. The application is seals for nuclear power plants where seals are exposed toelevated levels of ionizing radiation and temperature.A major challenge for the simulations is to find an appropriate material model for the rubbermaterials and how to calibrate it to experiments. Here is a material model proposed that caninclude effects like creep, permanent set, and temperature dependence. Calibration of materialmodels for relaxation tests on EPDM rubber is performed and presented with good results.Further modelling to include more effects in the material and to simulate leak and tightness ofseals are proposed.

    Download full text (pdf)
    fulltext
  • 6.
    Sandström, Johan
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Simulation of rubber materials for seals in use in nuclear power plants2019Report (Other academic)
    Abstract [en]

    Finite element (FE) simulations of how rubber materials for seals behave over time is performed. The application is seals for nuclear power plants where seals are exposed to elevated levels of ionizing radiation and temperature.

    A major challenge for the simulations is to find an appropriate material model for the rubber materials and how to calibrate it to experiments. Here is a material model proposed that can include effects like creep, permanent set, and temperature dependence. Calibration of material models for relaxation tests on EPDM rubber is performed and presented with good results. Simulations of leak and tightness of seals are evaluated and some initial observations on the effects temperature and ageing on the tightness are made.

    Download full text (pdf)
    fulltext
  • 7.
    Sandström, Johan
    et al.
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Albrektsson, Joakim
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Composite materials for railways2019In: EUROMAT: European Congress And Exhibition On Advanced Materials And Processes, Boutersem, Belgium, 2019Conference paper (Other academic)
    Abstract [en]

    Introduction/Purpose

    Europe’s railway industries require a step change in technologies and design for the next generation of railway vehicles in order to remain competitive globally. One way is use of composite materials that can reduce the weight of railway vehicles. Safety regulations for fire, smoke & toxicity requirements in the railway sector limits which materials that can be used for the composites and require special flame-retardant additives. The mechanical properties need to be asserted to reach the demands given by railway standards such as EN 12663. These standards are written for metallic materials requiring adaptation when designing and testing with composite materials.

    To address this, the EU funded project Mat4Rail – “Designing the railway of the future: Fire resistant composite materials and smart modular design” have been formed. It is part of the Shift2Rail program.

    Methods

    To find composites that meet the demands for fire safety and high mechanical strength, different combinations of resins and fibers are tested. The resins that are investigated are epoxies, benzoxazines and hybrid chemistry together with additives for enhanced fire performance. The fibers that are investigated are carbon, glass and basalt.

    The manufactured composite combinations are tested for reaction to fire EN 45545-2 and fire resistance EN 45545-3. The composites with the best fire-performance results are then further characterized for mechanical properties. A crucial property is the fatigue strength which is performed to harmonize with EN 12663-1 that is written with metals in mind. Several types of static tests are also performed.

    Another topic is adhesive joints for composites that also are investigated for fire performance and mechanical properties. Results Composites reaching higher hazard levels of EN 45545-2 are developed. For these are static strengths and SN-curves determined.

    Conclusions

    It is shown that composite material can be used for railway applications e.g. carbodyshell parts.

  • 8.
    Sandström, Johan
    et al.
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Johannesson, Pär
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Mikael, Sidenmark
    Ocean Harvesting Technologies AB, Sweden.
    Reliability analysis with VMEA of a rack and pinion mechanism in a wave energy gravity accumulator2018Report (Other academic)
    Abstract [en]

    The method Variation and Mode Effect Analysis (VMEA) is successfully implemented for the AGMA based gear design of the rack pinion mechanism. The rack and pinion is a feature in Ocean Harvesting Technologies (OHT) gravity accumulator device. The purpose of it is to make the electrical power output to the grid more uniform. This is a novel technology where previous experience in designing is absent. The VMEA method is there for useful for incorporating all known uncertainties to estimate the uncertainty and reliability of the technology. This allows for adequate safety factors to be set so the desired reliability can be achieved.

    The uncertainty and reliability analysis is performed for different OHT designs and methods where the reliability is calculated. This calculation can be used as basis for further analysis when more design details are determined and modifications are made, thus allowing for more optimized and reliable design to be made.

    Download full text (pdf)
    fulltext
  • 9.
    Sandström, Johan
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Bygg och Mekanik, Tillförlitlighet och Livslängd.
    Svensson, Thomas
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SP – Sveriges Tekniska Forskningsinstitut / Hållfasthet (BMh).
    Load/Strength analysis of wave energy components2014Report (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 10.
    Sällström, Jan Henrik
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Bygg och Mekanik, Rörcentrum.
    Larsson, Jörgen
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Bygg och Mekanik, Tillförlitlighet och Livslängd.
    Sandström, Johan
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Bygg och Mekanik, Tillförlitlighet och Livslängd.
    Stormwater boxes - aspects on verification, simulation and installa2014Report (Refereed)
    Download full text (pdf)
    FULLTEXT01
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