During the manufacturing process of composite structural parts, layer of fabrics or unidirectional prepreg may have to be cut in order to fulfil production requirements. From a general mechanical point of view, cutting fibres in a composite part has a large negative impact on the mechanical properties. However, such interventions are necessary in particular cases, for example due to draping of complex geometries. A rather extensive test program was launched to investigate the effects of defects that typically could arise during manufacturing. The overall purpose of the test program was to determine knock-down factors on strength for typical manufacturing defects that occasionally arise and sometimes are hard to avoid in production: cuts/gaps and fibre angle deviations. Four types of specimens were tested, reference, intersection of cuts in adjacent layers combined with a bolt hole, cut in a zero degree ply combined with a bolt hole and specimens with misaligned fibres. The specimens with misaligned fibres were tested with three different fibre angles. In addition to the experimental procedure, FE-analyses utilising cohesive elements were conducted, and after mechanical tests, Non Destructive Investigation (NDI) and fractographic investigations were performed. An excellent correlation between analyses and experiments were obtained.

The Rekovind2 project, financed by the Swedish Energy Agency, focuses on digitizing wind turbine blade streams for reuse and recycling. This is of the utmost importance to enable new, more circular technical solutions that can replace today’s non-sustainable recycling, i.e. landfill and incineration of wind turbine blades. In this report, the work carried out to map the wind turbine blades in service in Sweden is presented. The digital platform intended to make possible the re-use of blades reaching end-of-life is build around key features that will be required for re-use: blade database with all needed informations on the blade (age, damages, material, model, ...), map with blades geolocation, digital tool to help blade processing such as cutting, and information on what can be done with EoL blades.

The use of bolted or welded elements to upgrade metallic structures has been a common practice for many years. Moreover, the use of adhesively bonded carbon fiber reinforced polymer (CFRP) laminates, as an alternative method, has attracted a great deal of attention in recent years. One important aspect of the design of adhesive joints used to bond CFRP laminates to steel substrates is the determination of the properties of the CFRP/adhesive/steel interfaces, which have not yet been established in codes or standards. The purpose of this paper is experimentally to determine the fracture properties of the adhesive material and to evaluate the accuracy of numerical methods using this information, in order to predict the strength of adhesive joints in steel members bonded with CFRP laminates. The results from four series of experimental tests are compared with numerical results and discussed in terms of load-bearing capacity and failure modes. © 2011 Elsevier Ltd. All rights reserved.

The weak mechanical properties of wood in tension perpendicular to the grain are often the origin of catastrophic brittle failure. In order to enhance the tension strength perpendicular to the grain and achieve a more ductile failure, flax fiber and glass fiber-reinforced polymer (FRP) composites were used to strengthen glue-laminated (glulam) timber specimens. Three series of specimen of glulam timber (flax fiber reinforced, glass fiber reinforced, and unreinforced), with a grand total of 28 specimens, were tested in tension perpendicular to the grain. For an approximate amount of FRP reinforcement of 1.2% in volume (thickness of ∼0.7 mm), an increase of the tensile strength of up to 74% was shown, with a stiffness increase of up to 41%. For all reinforced specimens, semiductile failures were observed. A parametric study was carried out using both the Monte Carlo (MC) method and the first-order second moment (FOSM) method. It is shown that the mean values obtained during experiments are in agreement with those from the MC simulation. However, the standard deviations from the MC simulation are larger. From the FOSM analysis, it is demonstrated that the variation in glulam stiffness perpendicular to the grain is not the first parameter driving the variation for the reinforced system. The variation in mechanical properties of the flax fibers appeared to be the driving parameter for the strength of the system. © 2010 ASCE.

In response to global challenges in resource supply, many industries are adopting the principles of the Circular Economy (CE) to improve their resource acquisition strategies. This paper introduces an innovative approach to address the environmental impact of waste Glass Fiber Reinforced-Polymer (GFRP) pipes and panels by repurposing them to manufacture structural components for new bicycle and pedestrian bridges. The study covers the entire process, including conceptualization, analysis, design, and testing of a deck system, with a focus on the manufacturing process for a 7-m-long prototype bridge. The study shows promising results in the concept of a sandwich structure utilizing discarded GFRP pipes and panels, which has the flexibility to account for variabilities in dimensions of incoming products while still meeting mechanical requirements. The LCA analysis shows that the transportation of materials is the governing contributing factor. It was concluded that further development of this concept should be accompanied by a business model that considers the importance of the contributions from the whole value chain. 

In order to achieve a more resource-efficient society and a future with reduced carbon dioxide emissions, new technological challenges must be dealt. One way to reach a more sustainable world is to start re-using end-of-life structures and waste and give them a “Second Life” with new functions in the society. As fiber reinforced polymer (FRP) composites are lightweight, strong, stiff and durable materials, there is great potential to re-use decommissioned FRP structures for new resource-efficient solutions in the building and infrastructure sectors. The present paper investigates innovative solutions in re-using wind turbine blades and glass fibre reinforced polymer (GFRP) pipes as structural elements in new bicycle and pedestrian bridges. Specifically, a concept design for decking system made of GFRP pipes is developed and discussed. The main design requirements for pedestrian bridges are considered and assumptions regarding end-of-life GFRP quality and their mechanical properties have been addressed. The aim of this paper is to contribute to a sustainable use of GFRP waste and at the same time provide a more cost-effective solution for short span pedestrian bridges. In a larger perspective, the authors would like to highlight the economically profitable potential of recovering and reusing/re-manufacturing end-of-life GFRP composites. © 2022, The Author(s)

When it comes to strengthening, structural timber engineering has seen polymer composite materials becoming key materials over the last decades. A great number of studies have already shown that the majority of the results were promising. Several strengthening systems applied to structural timber or glued-laminated timber beams revealed that the ultimate failure mode remains in tension regardless of the reinforced system. However, the collapse can be controlled and postponed by optimising the strengthening system. It has been shown that strengthening timber on the tension and compression side simultaneously increases the stiffness and moment capacity more than if the reinforcement was only positioned on the tension side. This is mainly due to the ductility of wood in compression which is fully utilised when strengthening is located on both sides. The main objective behind this study is to develop an experimental method to determine the compressive behaviour of small clear timber specimens reinforced with CFRP.

Understanding the failure mechanism of wood loaded in compression parallel to the grain has been shown to be an important parameter in the design of timber beams strengthened with fibre-reinforced plastics (FRP). In this paper, a constitutive relationship for wood under uniaxial compression load parallel to the grain was determined experimentally. Several parameters, such as silviculture, moisture content and radial position in the log in relation to the pith from where the specimen was sawn, were considered. Small clear-wood specimens were used. The strain localisation in the failure region (kinkband) was monitored using the digital image correlation method. The results show that silviculture and moisture content are two very important parameters which influence the compression failure mechanism. Furthermore, there is a significant difference in behaviour between specimens from the juvenile region of the log and specimens from mature wood. Based on experimental results, two numerical models were built, considering either a global or a local constitutive relationship. It was demonstrated that both numerical models yield accurate results and that, depending on the experimental equipment available, a constitutive relationship could be extracted and used as input in these numerical models.

The optimal use of Carbon Fibre Reinforced Polymer (CFRP) when strengthening timber beams loaded in bending involves considering placing the reinforcement on both the tension and the compression side, in order to utilise the ductile compression failure of the wood to the full. In this respect, a knowledge and understanding of the compression failure mechanism of the timber/CFRP system becomes a point of paramount importance. However, no testing method specific to the compression loading of small wood specimens reinforced with CFRP is currently available. This investigation focuses on the experimental developments of the geometry and test set-up necessary in order to determine the compression failure mechanism of small wood block specimens reinforced with CFRP loaded in compression parallel to the grain. The method is based on an existing testing method for unreinforced wood specimens. The Digital Image Correlation (DIC) method is used to monitor deformation during experiments. The experimental results of reinforced specimens are compared with those of paired unreinforced specimens tested in a previous study. The experimental method presented in this study shows that specific geometry and test considerations must be implemented when compared with the existing method for unreinforced specimens.

To achieve a more resource-efficient society with a future with reduced carbon dioxide emissions, new technological challenges must be dealt. One way to reach a more sustainable world is to start re-using end-of-life structures and waste and give them a Second Life"with a new function in the society. As composite structures are lightweight, strong, stiff and durable materials, there is great potential to re-use decommissioned composite for new resource-efficient solutions in the building and infrastructure sector. The present paper investigates innovative solutions in re-using wind turbine blades as elements in new bicycle and pedestrian bridge designs. Several conceptual bridge designs where wind blades utilized as load bearing elements were developed and studied. The main design requirements for pedestrian bridges were considered and assumptions regarding wind blades quality and their mechanical properties addressed based on interviews with industries working with wind turbine blades repair and recycling. The aim of this paper is to contribute to a sustainable use of fibre reinforced polymer (FRP) waste and at the same time provide a more cost-effective FRP bridges. In a larger perspective, the authors would like to highlight the economically profitable potential of recovering and reusing / re-manufacturing end-of-life glass FRP composites.

I regleringsbrevet för 2023 fick Energimyndigheten i uppdrag av regeringen att utreda hur solcellspaneler och vindturbinblad till vindkraftverk i högre utsträckning ska kunna tas om hand på ett giftfritt och cirkulärt sätt i enlighet med avfallshierarkin. Redovisningen av detta regeringsuppdrag, rapporten Från avfall till resurs – Förslag för en mer cirkulär hantering av solcellspaneler och vindturbinblad, ER 2024:11, baseras på denna underlagsrapport som har tagits fram av forskningsinstitutet RISE på uppdrag av Energimyndigheten. Analyser, slutsatser och förslag/rekommendationer som framförs i rapporten är författarnas egna.En fortsatt utbyggnad av fossilfri elproduktion är av stor vikt för att vi ska kunna nå Sveriges energi- och klimatmål. För att utbyggnaden i sig ska vara hållbar är det viktigt att vi redan nu planerar för hur avfallet från dessa elproduktionsanläggningar ska förebyggas, minimeras och sedan hanteras.Det finns redan i dagsläget aktörer som har utvecklat och håller på att utveckla ett flertal olika lösningar för ökad cirkularitet. Dessa möjligheter kan tas tillvara och främjas genom regelbunden kartläggning och genom att arbeta gemensamt inom EU. Genom ett sådant arbete finns det också större möjligheter att etablera industriella värdekedjor i Sverige för hanteringen av avfallet från solcellspaneler och vindturbinblad.En cirkulär hantering av avfall ger ett betydligt mindre avtryck på miljön än det som en linjär hantering ger upphov till. Det är viktigt att de aktörer som tillhandahåller fossilfri elproduktion tar ansvar under hela livscykeln och att det finns goda förutsättningar för aktörerna att göra det.

The delamination process in notched composite plates under flexural loading has been investigated using finite element analysis. Cohesive elements implemented in the commercial finite element package ABAQUS have been used in the region around the drilled-hole, and positioned between layers where delamination was observed during experiments presented in an accompanying paper. The delamination initiation and subsequent propagation was studied between the layers at the tension side separately and simultaneously. For all FE models, the load displacement curve was in good agreement with the one from experiments. However, the amount of damage reported from the fractography study was more extensive than that predicted by the models. Finally, it was shown that the models with only one cohesive layer show significantly different results to that of the model with four cohesive layers in terms of size of the degradation area.

In this study different concepts to attain a material that can reduce its stiffness upon external stimulation were evaluated regarding their suitability for traffic safety applications. All concepts rely on resistive heating of a carbon fibre reinforcement upon application of electric current through the fibres. The stiffness reduction is achieved by a phase transformation due to heating of the material. The phase transformation takes place either in a thermoplastic interphase, in a thermoplastic matrix or in a thermoset matrix, depending on the concept. The different concepts were studied regarding their thermomechanical and processing properties and their ability to reduce their stiffness upon application of an electric current was tested. Moreover, the materials were evaluated regarding their potential for fast activation, which is crucial for applications in traffic safety. Stiffness-reduction was achieved upon application of an electric current, where the activation temperature was between 60 and 120°C and the extent of stiffness-reduction varied between 50 and 90%, depending on the material. The response time was found to depend to a large extent on the amount of material, which leads to the conclusion that smart design solutions are required for larger parts. It is concluded that the concepts vary in their thermal, mechanical and processing properties as well as in their extent of stiffness-reduction upon activation. The results presented in this work prove the feasibility of the studied materials for traffic safety applications and the concepts allow further optimization of the materials for specific applications

The variety of failure modes that are likely to occur in fibre-reinforced polymer (FRP)/steel joints used in the construction industry adds to the complexity associated with the design of these joints. This variation in possible failure modes is mainly attributed to the lack of a controlled application environment and to rather insufficient quality assurance protocols and procedures. The use of energy-based methods such as, cohesive zone modelling (CZM), can be a solution to circumvent such complexities. This paper investigates a number of issues related to CZM analyses of FRP/steel adhesive joints using various test configurations and a comprehensive numerical study. Parameters such as the effect of shape and type of cohesive law, crack path location, length of damage process zone, variations of adhesive and FRP properties, and different failure modes including cohesive, interfacial debonding and FRP failure on the strength of joints are investigated. The results show that the behaviour of the tested joints is accurately predicted provided that the variation of failure modes are taken into account. Moreover, it is shown that the damage process zone in adhesive layer is directly proportional to the shape of cohesive laws. This feature can be employed in the design phase to ensure sufficient overlap length and to account for important in-service parameters such as temperature and moisture.

The focus of this contribution is to highlight the challenges of chemical recycling of End-of-Life glass fiber composite (GFRP) waste from wind turbine blades utilizing solvolysis/HTL (hydrothermal liquefaction) methods based on subcritical water as solvent. A multitude of investigations have been published during the years regarding solvolysis of newly produced composite laminates and known thermoset composition (epoxy, polyester, and vinyl ester). However, a real wind turbine blade is more complex and constitutes of thermosets, thermoplastics, and other materials such as balsa wood. It is a very challenging task to separate these materials from each other within the wind turbine blade structure, so the premise for recycling is a mixed waste stream where little is known about the chemical composition. In the present study, the solvolysis process for GFRPs based on sub/supercritical water at 250-370 C and 100-170 bar process conditions with catalyst (acid and base) and additives (alcohols and glycols) was studied and optimized. The samples used are representative for End-of-Life wind turbine blades. The aim is therefore to investigate if it is possible to develop a general process that can accept all material constituents in a real wind turbine blade, resulting in recycled glass fibers and a hydrocarbon fraction that can be used as a refinery feedstock.

Simulation of damage in composite laminates using currently available three-dimensional finite element tools is computationally demanding often to the point that analysis is not practical. This paper presents an enriched shell element that can provide a computationally efficient means to simulate low-velocity impact damage in a composite. The enriched element uses the Floating Node Method and a damage algorithm based on the Virtual Crack Closure Technique that is capable of simulating progressive damage growth consisting of delamination and delamination-migrations from ply to ply during a dynamic impact load. This paper presents results from the shell model in a test-analysis correlation for impact testing of 7-ply and 56-ply laminates. Analysis results from a separate high-fidelity three-dimensional finite element analysis are included also for comparison in the case of the 7-ply laminate, but not in the case the 56-ply laminate due to excessive computational demand. This paper serves as the first application of both models in low-velocity impact simulation. The shell model is considerably more computationally efficient than the high-fidelity model by at least an order of magnitude and is shown to produce results, while not as accurate as the high-fidelity model, potentially sufficiently accurate for a wide range of engineering applications including structural design and rapid prototype assessments.

This paper presents an experimental and numerical study of impact response, damage and tension after impact of thin ply HTS45/RTM6 carbon/epoxy laminates, manufactured via resin transfer moulding. A plain weave from carbon fibre spread-tow bands was used in a quasi-isotropic layup. Finite element simulations were performed using layered shell elements accounting for in-plane damage mechanics, with cohesive surfaces between a few layers of shell elements to account for delamination. The damage was found to include a combination of fibre damage and delaminations, in contrast to a previous study on similar cross-ply laminates, where fibre damage dominated. The rate of decrease in tensile strength after impact was similar to prepreg laminates with conventional ply thickness, but the impacted strength was slightly higher due to a higher undamaged strength for thin ply laminates.

Thin-ply composites offer reduced or suppressed matrix cracking and higher strains to first ply failure. Initial tests indicate a significantly different impact damage than for conventional composites, with less delamination and more fibre fracture. The current paper presents models focused on the observed fibre damage, including an analytical model for the response and damage initiation during impact on thin ply composites as well as a finite element FE model for prediction of damage growth. The limitations and challenges of the analytical model and FE model are discussed and illustrated by comparisons with response histories and fractography for drop weight impact on a thin-ply composite laminate.

Recently, novel material concepts for high-performance carbon fiber–reinforced composites with active stiffness control were presented in the literature. Although this new class of intelligent, smart, and responsive materials has wide application potential, actual design concepts using active stiffness control are still rare. The integration of smart materials into conventional products often requires radically new design concepts. This communication presents an innovative automotive hood design concept, which integrates active stiffness control composites in order to achieve improved design performance trade-offs in terms of structural weight reduction and vulnerable road user safety. The integration of active stiffness control composites in the hood structure aims to enable active stiffness reduction of the hood or bonnet structure in order to reduce head impact injuries in case of a collision, while satisfying the structural stiffness requirements and lightweight objectives under normal operating conditions. The design concept is investigated using simulation-based evaluation of static, dynamic, and lightweight design criteria. The results are promising, and the presented concept design is a step toward the realization of lightweight smart hood structures for head impact mitigation. Several design features could also be of interest for the integration of active stiffness control composites, in other applications. © The Author(s) 2019.