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  • 1.
    Alfredsson, K. Svante
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Salimi, Saeed
    Högskolan i Skövde.
    Shear testing of thick adhesive layers using the ENF-specimen2015Ingår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 62, s. 130-138Artikel i tidskrift (Refereegranskat)
  • 2.
    Biel, Anders
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Alfredsson, K. Svante
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Carlberger, Thomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Adhesive Tapes; Cohesive Laws for a Soft Layer2014Ingår i: Procedia Materials Science, ISSN 2211-8128, Vol. 3, s. 1389-1393Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For adhesive tapes, the strain before fracture often exceeds 500%. Although the maximum stresses are quite modest the high strains to fracture result in impressive fracture energy. Due to hydrostatic stress the fracture process often starts by nucleation of microscopic cracks inside the layer. The final crack path is usually close to one of the adherends.

    Repeated experiments are performed both with DCB-specimens and butt-joints. The used adhesive tape is an acrylic foam tape with a thickness of 1.1 mm and a width of 19 mm. The geometry of the specimen is adapted to the properties of the soft layer. For the DCB-specimen this implies that the length of the specimen is about 1 m. The evaluated cohesive laws from the DCB- specimens give a fracture energy of 2 kN/m and a maximum stress about 0.5 MPa. For the butt-joints, the evaluated cohesive law corresponds well to the results from the DCB-experiments. However, the strain to fracture is slightly smaller. The stress in these specimens is distributed over a larger area and a nucleated crack rapidly crosses the load bearing area and fails the joint prematurely. For both kinds of experiments the evaluated cohesive laws show a small linear part. After this part there is an almost linear strain-hardening phase until fracture.

  • 3.
    Biel, Anders
    et al.
    Department of Wind Energy, Technical University of Denmark, Roskilde, Denmark.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Cohesive zone modelling of nucleation, growth and coalesce of cavities2017Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 204, nr 2, s. 159-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stress-deformation relation i.e. cohesive law representing the fracture process in an almost incompressible adhesive tape is measured using the double cantilever beam specimen. As in many ductile materials, the fracture process of the tape involves nucleation, growth and coalesce of cavities. This process is studied carefully by exploiting the transparency of the used materials and the inherent stability of the specimen configuration. Utilising the path independence of the J -integral, the cohesive law is measured. The law is compared to the results of butt-joint tests. The law contains two stress peaks—the first is associated with nucleation of cavities at a stress level conforming to predictions of void nucleation in rubber elasticity. The second stress peak is associated with fracture of stretched walls between fully-grown cavities. After this second peak, a macroscopic crack is formed. The tape suffers at this stage an engineering strain of about 800%. A numerical analysis with the determined cohesive law recreates the global specimen behaviour.

  • 4.
    Biel, Anders
    et al.
    Karlstad University.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Comparison of J-integral methods to experimentally determine cohesive laws in shear for adhesives2019Ingår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 94, s. 64-75Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-quality simulation methods demand accurate material models. In simulations an adhesive can be represented by a cohesive layer. A cohesive layer model utilizes a cohesive law to represent the homogenized mechanical behaviour of a layer with a thickness. In the current paper we use three experimental methods to measure the cohesive law in shear using the ENF-specimen; one of the methods is novel and is also useful for evaluation of experiments with the ELS-specimen. Two sets of experiments are performed, one with elastic substrates and one with plastically deforming substrates. Each experiment is evaluated using all three methods. The evaluation shows that all methods provide reasonable data; the results are similar if the substrates are elastic. With smaller specimens, the substrates deform plastically and one of the methods is identified as the most accurate.

  • 5.
    Biel, Anders
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Strength and toughness in shear of constrained layers2018Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 138, s. 50-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Confined layers may fracture in shear. This occurs, for example in adhesive joints and composite materials. A common mechanism for shear fracture is the formation of shear hackles associated with an expansion of the layer. This makes shear toughness and strength depend on the constraint of the expansion. By constraining the expansion using external loading in experiments, the expansion is reduced but not totally inhibited. The experiments are evaluated using the path independent properties of the J-integral. It is shown that the shear toughness increases for the more constrained case. Thus, from a strength analysis perspective, ignoring the expansion leads to a conservative estimate of the fracture properties. Extrapolation of the evaluated properties to totally inhibited expansions gives the traction separation relation and the fracture toughness for a layer in simple shear.

  • 6.
    Dabbagh, Armanj
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Garza, Carlos
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Finite Element Analysis of the Vasa’s Bottom Structure2012Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The royal warship Vasa sank on its maiden voyage outside Stockholm and was salvaged more than 300 years later in 1961. Nowadays the vessel lies in its eponymous museum in Stockholm on a dry dock. However, it was determined that the ship cannot handle its own weight in a satisfactory manner with the current support system. Measurements during the past ten years have ascertained that the upper structure components of the hull are slowly deforming, mostly due to creep behavior.

     

    A new support system for the ship needs to be designed in the near future and therefore, the mechanical behavior of its structural members and the stresses they are subjected to have to be determined. Factors that complicate a stress analysis include both inhomogeneity of the oak’s mechanical properties and limited opportunities for experimental testing. Furthermore, contamination, microbial degradation and preservation agents have significantly changed the integrity of the oak.

     

    In this project a section of the Vasa’s bottom structure is studied through Finite Element Analysis in order to determine the stresses and deformations originated by the support system and to have a better understanding of these effects on the ship’s structure. Due to the considerable deterioration of the oak, especially on the external structural members, several assumptions are considered in order to perform analytical calculations to determine appropriate material properties for the FE-Models. 

     

    After performing the computational simulations, the obtained results indicate that the bottom structure exhibits sufficient mechanical integrity to endure the stresses generated by the support system. Even by assuming the possibility of several damaged structural connections, only a minor difference of the effects of the reaction forces on the structure members was determined.

     

    The thesis work ends with further conclusions from the performed analysis and suggested future work.

  • 7.
    Eklind, Alexander
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Walander, Tomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Carlberger, Thomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    High cycle fatigue crack growth in Mode I of adhesive layers: modelling, simulation and experiments2014Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 190, nr 1-2, s. 125-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The capability to predict high cycle fatigue properties of adhesive joints is important for cost-efficient and rapid product development in the modern automotive industry. Here, the adaptability of adhesives facilitates green technology through the widening of options of choosing and joining optimal materials. In the present paper a continuum damage mechanics model is developed based on the adhesive layer theory. In this theory, through-thickness averaged variables for the adhesive layer are used to characterise the deformation, damage and local loading on the adhesive layer. In FE-simulations, cohesive elements can thereby be used to model the adhesive layer. This simplifies simulations of large scale complex built-up structures. The model is adapted to experimental results for two very different adhesive systems; one relatively stiff rubber based adhesive and one soft polyurethane based adhesive. The model is able to reproduce the experimental results with good accuracy except for the early stage of crack propagation when the loads are relatively large. The model also predicts a threshold value for fatigue crack growth below which no crack growth occurs. The properties of the model are also compared with the properties of Paris’ law. The relations between the parameters of the continuum damage mechanics law and the parameters of Paris’ law are used to adapt the new law. It also shows that the properties of a joined structure influence the Paris’ law properties of the adhesive layer. Thus, the Paris’ law properties of an adhesive layer are not expected to be transferable to joints with adherends having different mechanical properties.

  • 8.
    Linero Jiménez, Adriano
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    DEVELOPMENT OF A MODEL OF THE DEGRADATION OF THE MECHANICAL PROPERTIES OF POLYOXYMETHYLENE (POM) IN THE PRESENCE OF BIODIESEL2014Självständigt arbete på avancerad nivå (magisterexamen), 40 poäng / 60 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This project analyses the impact in the mechanical properties of Polyoxymethylene (POM) of three different blends of biodiesels: B0 with 0% of Rapeseed Methyl-ester (RME), B20 with 20% of RME and B100 with 100% of RME. Polyoxymethylene specimens have been subjected to an accelerated aging during 1600 hours at 85ºC. This is the equivalent to 20 years of life time. In addition, a thermal oxidation in air at the same temperature has been performed to check the impact of the temperature in the final degradation.Three different methods have been performed to calculate the diffusion rate, however and one of them has been selected for its reliable results. The second Fick´s law have been chosen to model the diffusion. The diffusion rate has been calculated for the B20 and B100 blend due to the B0 blend has a non-constant diffusion rate. B20 shows also some divergence while B100 fits the Fickian behaviour.A Finite Different approximation method has been used to predict the concentration profiles of the diffusion process of B20 blend. They have been compared with the results of the IR Microscope, with a clear misalignment between the expected and the actual values.Tensile tests have been done in different stages of the test to check the stress-strain behaviour of the specimens for each aging type. The most relevant parameter of degradation is the Elongation At Break (EAB), which decrease considerably a cause of the embrittlement. A study of the real stress-strain has been also done to assure the real behaviour of the material.A fracture surface study through Scanning Electron Microscope (SEM) and Light Microscope has been done to assure the brittle behaviour with the aging and the changes in the structure of the material.The swelling behaviour has been also modelled, and the bases for a future FEM analysis have been exposed.

  • 9.
    Marruecos Sola, Eugenio José
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Valenzuela Romero, Juan Diego
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Drop testing applied to adhesive research in automotive structures2007Självständigt arbete på grundnivå (kandidatexamen), 15 poäng / 22,5 hpStudentuppsats
    Abstract [en]

    The design and analysis of drop test to investigate the behaviour of adhesive joints in automotive structures is performed. The drop test is simulated by FE software. The specimen geometry is based on Volvo Car Corp. drop test standard.

    In the drop test machine, a general beam structure is supporting all the parts. The machine includes a lifting system. The test is applied to a pre designed specimen, which will provide the information about adhesive joint strength.

  • 10.
    Marzi, Stephan
    et al.
    Fraunhofer IFAM, Bremen, Germany.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Hesebeck, Olaf
    Fraunhofer IFAM, Bremen, Germany.
    3D optical displacement measurements on dynamically loaded adhesively bonded T-peel specimens2015Ingår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 56, s. 41-45Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adhesively bonded T-Peel specimens are loaded in a rotary impact device to investigate the behaviour of adhesive joints under high-strain rates. To gain a better understanding of that kind of tests and their results, the deformation of the samples as well as the movement of specimen support during the test is analyzed. A three-dimensional optical measurement system is used in combination with two synchronized high-speed cameras to obtain the deformations. The paper explains the experimental challenges and discusses the results of the analyses with respect to a planned usage of the experimental results in a finite element crash simulation. As main results of the investigations it can be summarized that the compliant clamping leads to an inadvertent out-of-plane-movement of the load introduction point. Based on finite element calculations it can be concluded that the measured out-of-plane-movement possesses a negligible influence on the obtained force signal, which is of primary interest in a T-Peel test.

  • 11.
    Marzi, Stephan
    et al.
    Fraunhofer IFAM, Bremen, Germany.
    Hesebeck, Olaf
    Fraunhofer IFAM, Bremen, Germany.
    Brede, Markus
    Fraunhofer IFAM, Bremen, Germany.
    Nagel, Christof
    Fraunhofer IFAM, Bremen, Germany.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Walander, Tomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Effects of the bond line thickness on the fracture mechanical behaviour of structural adhesive joints2014Ingår i: Proceedings of the Annual Meeting of the Adhesion Society 2014, Adhesion Society , 2014, s. 189-192Konferensbidrag (Refereegranskat)
  • 12.
    Muñoz García, Marina
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Hurtado Sierra, Juan Carlos
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Structural analysis of the 17th century warship Vasa: Influence of the dowels on the stiffness of the hull2014Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    After 333 years under depths of the Baltic Sea, the warship Vasa was salvaged and nowadayslies in a dry dock inside the Vasa Museum in Stockholm. Its current support system, which consists on eighteen cradle-stanchions pairs of steel, is not able to handle the present loads in a satisfactory manner. Experimental tests showed that the Vasa's hull is gradually deforming mainly due to creep behavior.

    Thus, in order to preserve the Vasa for future generations, a new support system has to be implemented in a foreseeable future. There are several factors to take into consideration for its construction, which are: the degradation of the oak, its current mechanical properties and its inhomogeneity in addition to the climatic conditions of the Museum and the impossibility of taking unlimited specimens for its analysis. Hence, it is crucial to investigate the areas where the stresses and deformations are critical in the ship and how affected is the stiffness of the hull, its most important component.

    In this dissertation work two Finite Element Analyses are accomplished. The first study consists on the creation of a superelement of a section of Vasa's hull with the intention of investigating the influence of the dowels on the stiffness of the hull. In the second analysis a simplied model of the entire warship Vasa is created in order to analyze it and locate possible critical areas on the hull due to its own weight and the stresses originated by the support system. The software selected for these simulations are Abaqus and CreoSimulate 2.0.

    From the first study it is concluded that that the dowels do not have a signicant influence in the stiffness coeffcients of the hull. The second analysis determines that the maximum stresses are located on the bottom part of the hull. This dissertation work concludes with a suggested future work.

  • 13.
    Perez Romero, Roberto
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Lazuen Ramirez, Alvaro
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Analysis of rubber adhesive: FE simulation of damage propagation over rubber adhesive under fatigue in mixed-mode loading2014Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This thesis refers to a simulation of an adhesive joint used to bond two metal sheets of a component of the side skirt bracket implemented in trucks. The adhesive joint must support fatigue and mixed-mode loading. The principal goal is the implementation of a novel material model, which governs the damage produced by a mixed-mode fatigue loading in a rubber adhesive layer.

    Two approaches to define the material model are implemented: the filament model and the principal strain model. The models are fitted against experiments, which have been performed parallel to the development of this thesis by the Mechanics of Materials (MoM) research group of the University of Skövde. The models incorporate fitting parameters with the aim of adjusting the models against experimental results. Simulations are performed using the Finite Element (FE) software, ABAQUS, and the material models are implemented using UMAT subroutines.

    The filament model is inaccurate and it is considered unable to model the mixed-mode behaviour of the adhesive joint. The principal strain model is considered a well-established method to define the damage and to predict the fatigue life of the adhesive under fatigue in mixed-mode loading.

  • 14.
    Popov Popov, Nikita
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Design and preliminary finite element analysis of structural frame of a double base for an infant child restraint system.2015Självständigt arbete på grundnivå (kandidatexamen), 15 poäng / 22,5 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Child restraint systems (CRS) are used for protection of the child in case of car accident. These systems have been found to have a difficult installation process that in many cases can cause greater loads on the child and as a consequence can lead to an increased risk of injury and a reduction in safety. The problems are even more significant in cases of families with two or more children and in small cars with lack of available space. Misuse and its causes are identified from literature as well as from surveys and market research. The design guidelines are gathered from existing CRS designs. Currently available automotive and CRS fastening systems are studied. A specific methodological approach is used for project development. A new concept for a child restraint system is introduced. The main aims are the design proposal of a double ISOFIX base for two children, reduction in the misuse of the CRS, improving the user experience and achieving technological, societal and environmental contributions. The second aspect is to verify the structure of the double base by means of preliminary finite-element analysis using the case of a frontal collision in accordance to current approval testing procedures. Al 2024 is chosen for design by the material selection performed in order to optimize the structure in relation to strength and weight. The finite-element preliminary static analysis is performed employing shell elements. The results are analysed with respect to the mesh convergence. In addition a linearized buckling check is carried out. Finally, the achieved results are discussed in comparison with initial assumptions and goals and future work is suggested.

  • 15.
    Quesada Díaz, Raquel
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Horseshoe Bending Machine: Bending Mechanism2014Självständigt arbete på grundnivå (kandidatexamen), 15 poäng / 22,5 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Horseshoes are manufactured metal plates developed in an extensive assortment of materials and shapes and their main function is to protect the horse’s hooves and legs against abrasion and rupture. After a certain period of time the horseshoes are lost, worn out, or the hoof needs to be treated. Horseshoeing is a repetitive time consuming process for the farrier who has to heat the horseshoe inside a forge until it reaches the required temperature and shape it with a hammer until it fits perfectly to the horses’ hoof. The main goal of this project is to develop a horseshoe bending machine able to shape the horseshoe so its shape fits perfectly the horse’s hoof. The calculation of the bending force needed to be applied to the horseshoe in order to provoke a plastic deformation will be done with Euler-Bernoulli beam theory. The bending force is then used to design and dimension each element of the bending mechanism so that it may be able to resist the stresses and prevent the parts from collapsing during its working life span. A study of the springback effect will be done followed by the analysis of the hertzian contact stresses between the rollers and the horseshoe. In addition, a clamping system is selected to constrain the movements of the horseshoe during the bending process. This machine will reduce the final user’s horse maintenance costs at the same time that makes the fitting process easier and less demanding, which will improve the farrier’s working life span and quality.

  • 16.
    Rodríguez Moronta, Francisco Manuel
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Segurola Lucas, Judith
    Högskolan i Skövde, Institutionen för informationsteknologi.
    Comparison of ASTM and BSI Standards for the calculation of fracture energy of adhesives: Design of a fixture and testing of DCB specimens2015Självständigt arbete på grundnivå (kandidatexamen), 15 poäng / 22,5 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Modern synthetic structural adhesives are finding a place in the drive to improve the fuel efficiencyof automobiles through weight reduction of the structure. One of the most important properties ofthe adhesives used in this type of joining is the fracture energy.A literature study is carried out to gain a broader understanding of the methods used for thedetermination of the fracture energy of adhesives. One of the most common experimental methodsrelies on the use of the Double Cantilever Beam (DCB) test specimen. International standards for theDCB test are studied. Prediction of the fracture energy using Linear Elastic Fracture Mechanics andthe J-integral approach, a closed form solution and finite element methods are also seen. Differencesin these methods are attributed in part to the nonlinear behaviour of the adhesive being studied. It isdecided to use the results of a non-standard DCB test and the 40% error calculated by a theoreticalstandard method as a point of reference.A comprehensive comparison of the American Society for Testing Materials (ASTM) and BritishStandard Institution (BSI) standards for the determination of the fracture energy of adhesives isundertaken. Limitations and overlaps in the standards are identified. A DCB specimen isrecommended and an experimental procedure that satisfies elements one or both standards issuggested along with several small additions such as using a wire to assist in the application of theadhesive and the use of cameras to track the crack growth. In addition, a new fixture to allow testingof the recommended DCB specimen according to the standards is designed and manufactured.Materials for the preparation of tests specimens are ordered and, based on available laboratorytime, a single DCB test specimen is made for the purposes of testing a rubber-based automotivestructural adhesive. The specimen is tested using the recommended experimental procedure usingthe new fixture. The data produced during the test are collected and interpreted using themethodology proposed in the BSI standard for the calculation of the fracture energy of the selectedrubber-based adhesive. Several challenges found during this process are identified. The fractureenergy determined from the standard-based experiment ranges from 140 J/m2 to 1380 J/m2depending on the methodology used.The values of the fracture energy determined from the standard-based DCB experiment are thencompared to the fracture energy seen with the nonstandard-based experiment and to the standardbasednumerical test seen in the literature. It is shown that when simple beam theory method isused the difference in the results found in the standard-based experiment and nonstandard-basedexperiment can be confirmed to lie within the 40% error observed in the literature.Finally, the contributions of the project are summarized and recommendations for future work aremade. In particular, the lack of information given in the BSI standard when calculating the fractureenergy and the need for multiple test specimens are required by the standard, must be addressed inorder to support the obtained results and conclusions.

  • 17.
    Saha, Ujjal kumar
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Avdic, Adis
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Simulating a tensile test of a carbon fiber composite test specimen in ABAQUS2011Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This work aims at providing a numerical tool for the efficient design of the multidirectional carbon fiber reinforced composite material by means of finite element simulations. Abaqus/ CAE v 6.9-1 software has been used to establish a 3D model for simulation of the tensile test on the composite specimen. The aim of this analysis of multidirectional carbon fiber reinforced composite is to predict the strain and stress distribution in different plies through thickness. Tensile test experiment was carried out and the result was analyzed by ARAMIS to calculate the young’s modulus, stress, loads and strain of the composite specimen. The numerical model was compared against the result obtained from tensile test experiment to arrive at meaningful results for validation. This is done in order to understand the mechanical strength and strain at failure of the composite material. In this work three types of CFRP composite specimens are used, all have same 15 no. of ply but stacked in different orientation. It is found out that mechanical strength, failure load and strain differ slightly depending on this different ply orientation. A series of different modeling technique has also been done to verify the best modeling technique.

    The micromechanics of composite material is complex and the experimental predictions are time consuming and expensive. Though using FEM frequently solves the problem.

  • 18.
    Salomonsson, Kent
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    On the apparent influence of the adherends on the fracture toughness of adhesive layers2007Ingår i: Interface design of polymer matrix composites: mechanics, chemestry, modelling and manufacturing, 2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    A detailed model of experiments with the double cantilever beam specimen is set up. Analysis of the model shows that an experimentally deduced apparent increase of fracture energy with severely deforming adherends is due to contributions of in-plane straining of the adhesive layer to the fracture energy. An analysis with the J-integral confirms the result.

  • 19.
    Shingu, Patrick
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Garcia Cabrera, Miguel
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Analysis of fan blade attachment2014Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This thesis work is based on the analysis of a fan blade attachment whereby a complete 3D model is presented by a partner company. The acceptability of a new design regarding the mechanical loads consisting of dividing the hub into two parts instead of using a solid hub is studied. From the model some critical parameters for the attachment of the blade with respect to the stresses are chosen such as the rotational speed, fillet size of the blade and the neck size of the blade. Parametric studies of these parameters are carried out in order to suggest the new design. Bearing in mind that a safety factor of 2 is the prerequisite, based on the analysis performed on ANSYS Workbench, it is suggested from the preliminary design that the axial fan can operate in two specific scenarios consisting of a rotational speed of 1771 rpm and a rotational speed of 1594 rpm. Using this set of parameters, a suggestion is drawn up on the blade fillet which will give lower stress. Blade fillet size of 30 to 35mm is recommended while a size of 45mm is recommended on the neck of the blade. A modal analysis is performed in order to find at what frequency will the model be vibrating and a lowest and critical frequency of 16.8 Hz is obtained. Finally, a fatigue analysis of some interesting areas is performed in order to determine the numbers of cycles before fatigue failure occur. It is recommended to use the rotational speed since these speeds have offered a High Cycle Fatigue results.

  • 20.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Applications of equilibrium of configurational forces for the measurement of cohesive laws2016Ingår i: Proceedings ECCM17: 17th European Conference on Composite Materials Munich, Germany, 26-30th June 2016, 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    A methodology to develop experimental methods to measure cohesive laws is introduced. This methodology is based on the property of all configurational forces equilibrium acting on a specimen to be in equilibrium. Two applications are given. The first shows a method to measure the cohesive law for shear representing the mechanical behaviour of an adhesive layer. The second application is a method to measure the cohesive law for the formation of a kink-band in a unidirectional composite. It is concluded that the methodology is critically dependent on the ability to associate a pseudopotential to the inelastic properties of the deforming material where the fracture process takes place. The importance to clearly identify the material that is modelled with the cohesive zone is also stressed.

  • 21.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Continuum Damage Mechanics and the Life-Fraction rule2006Ingår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 73, nr 4, s. 702-704Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper gives a short review of two different methods for life prediction at high temperature; namely continuum damage mechanics (CDM) and the linear life-fraction rule (LFR). It is well known that the class of CDM theories with a separable evolution law gives a life prediction in accordance with the LFR. However, it appears to be an open question if this is a necessary condition. It is here shown that in order for a CDM theory to comply with the LFR it must have a separable evolution law. That is, if we can assume that a material follows the LFR, it is necessary to chose a separable evolution law for this material. The reverse is also true, to get a life-fraction different from unity, we must chose a nonseparable evolution law.

  • 22.
    Stigh, Ulf
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Effects of strain rate on the cohesive properties and fracture process of a pressure sensitive adhesive2018Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 203, s. 266-275Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pressure sensitive adhesives provide high toughness at low stress and stiffness. These properties are beneficial for bimaterial bonding. In the present study the tape is modelled with a cohesive layer characterized by a cohesive law. This is suitable for FE-analysis of bonded structures. The cohesive law is measured using a method based on the path independent property of the J-integral. Complementing an earlier study, we here focus on influences of loading rate on the properties of the pressure sensitive adhesive. Transparent PMMA substrates are used with the transparent tape in Double Cantilever Beam specimens. The transparency of both the tape and the substrates provides the possibility of in-situ studies of the fracture process. The results indicate that the fracture energy levels off at about 1 kN/m for small loading rates. Moreover, the cohesive law also appears to level off below an engineering strain rate of about 2 s-1. The cohesive law contains two peak stresses. The first is associated with the nucleation of cavities in the tape. This occurs at a stress level comparable to the critical stress associated with an unbonded growth rate of a spherical cavity in rubber. The second peak stress is associated to the breaking down of walls formed between the fully developed cavities. This process precedes the final fracture of the tape. It also appears as nucleation of cavities is influenced by the strain rate where slower rates give more time for cavities to nucleate. This results in larger cavity density at smaller loading rates. The results also indicate a similarity of the effects of loading rate and ageing of the macroscopic properties of the present pressure sensitive adhesive.

  • 23.
    Stigh, Ulf
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Shear properties of an adhesive layer exposed to a compressive load2014Ingår i: Procedia Materials Science, ISSN 2211-8128, Vol. 3, s. 1626-1631Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adhesive joints are designed to transfer load in shear since both the fracture energy and the fracture stress are larger in shear than in peel. Shear deformation is isochoric, however, the fracture process involves nucleation and growth of a multitude of slanted microcracks. In order to grow, these microcracks open up. Thus, adhesive layers show a tendency to deform in peel during shear fracture. This opening is localized to the fracture process zone and the adherends have to separate locally over the process zone to allow for the adhesive to swell. Depending on the stiffness of the adherends, the opening mode is more or less prohibited. With stiffer adherends, the opening is obstructed more efficiently than with softer adherends. Micromechanical studies indicate that the constraints of the peel deformation during shear loading have a profound influence on the strength of the joint. In the present study, we compress the process zone during experiments. Repeated experiments with ENF-specimens are performed. A compressive force is applied on the first part of the adhesive layer by use of a pneumatic cylinder. The experiments are evaluated using the path independent J-integral. Together with measurements of the shear and peel deformation of the adhesive layer at the start of the layer, the complete shear stress vs shear deformation relations are evaluated. It is shown that the inhibited peel deformation gives a substantial increase of the fracture energy

  • 24.
    Stigh, Ulf
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Studies of fracture in shear of a constrained layer2017Ingår i: Advanced Problems in Mechanics: Proceedings of the XLV Summer School Conference / [ed] Dmitri A. Indeitsev & Anton M. Krivtsov, St Petersburg: Institute for Problems in Mechanical Engineering RAS , 2017, s. 420-428Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cracks normally propagate in the opening mode associated with a state of local symmetry at a crack tip. However, the micro- or macrostructure of a material or structure sometimes forces cracks to propagate in a shearing mode. Irrespective of the actual material studied, fracture in shear is frequently asso- ciated with the formation of a large number smaller sigmoidal-shaped cracks in the propagation direction of the major crack. Propagation of the major shear crack is accomplished by coalescing the sigmoidal-shaped cracks. Ex- periments show that the formation of sigmoidal cracks due to shear loading leads to a normal separation of the joined substrates. Theoretical studies show that constraining the local opening of the sigmoidal cracks increases the frac- ture resistance for the propagation of the major crack. In the present study, experiments with a ductile adhesive loaded in shear and where the normal sep- aration is constrained are presented. The experiments are evaluated using the path independent J-integral. The associated cohesive law shows that consid- erable normal compressive stress develops in the adhesive during macroscopic shear loading. It is also concluded that by ignoring the normal separation in the evaluation of the experiments, the strength of the adhesive is underesti- mated. Thus, the procedure developed in earlier studies is conservative from a strength analysis perspective. The present technique might be possible to extend to other materials to reveal their properties in shear fracture.

  • 25.
    Stigh, Ulf
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Department of Wind Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark.
    Svensson, Daniel
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Cohesive zone modelling and the fracture process of structural tape2016Ingår i: Proceedia Structural Integrity, ISSN 2452-3216, Vol. 2, s. 235-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Structural tapes provide comparable toughness as structural adhesives at orders of magnitude lower stresses. This is potentially useful to minimize the effects of differences in thermal expansion in the joining of mixed materials. The strength properties are modelled using the cohesive zone model. Thus, a cohesive zone represents the tape, i.e. stresses in the tape are transmitted to the substrates through tractions determined by the separations of the surfaces of substrates. This simplification allows for structural analysis of large complex structures. The relation between the traction and the separation is measured experimentally using methods based on the path independence of the J-integral. Repeated experiments are performed at quasi-static loading. A mixed mode cohesive law is adapted to the experimental data. The law is implemented as a UMAT in Abaqus. Simulations show minor thermal distortions due to thermal loading and substantial structural strength in mechanical loading of a mixed material structure.

  • 26.
    Stigh, Ulf
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Walander, Tomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Shear strength of adhesive layers – models and experiments2014Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 129, s. 67-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mode II properties of adhesives joints are of special interest since these joints are strongest if loaded in shear. Today no standardized method is available to measure shear properties. After a brief discussion of different models used to analyse adhesive joints, we identify some of the reasons for problems that arise in some of the more frequently used experimental methods. It is shown that transversally loaded specimens with elastically deforming adherends can lead to unstable crack growth provided the un-cracked specimen is flexible. With tough adhesives, a substantial process zone develops at the crack tip. That is, most specimens are in a state of large scale yielding. If not properly taken into account, the evaluated properties will be in error. Moreover, the process zone may grow in under the loading point which hinders its evolution and yield errors in the evaluated properties. Modest variations in loading conditions using the same specimen can yield considerable variation in the evaluated properties. However, properly designed and used, both the thick-adherend lap-shear joint and the end-notched flexure specimen provide useful results.

  • 27.
    Stigh, Ulf
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Svensson, Daniel
    Högskolan i Skövde, Institutionen för teknik och samhälle. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    On cohesive laws for delamination of composites2010Ingår i: 14th European conference on Composite materials, Budapest: University of Technology and Economics , 2010, s. 1-10, artikel-id 159-ECCM14Konferensbidrag (Refereegranskat)
    Abstract [en]

    Analysis of delamination of carbon fibre reinforced composite using cohesive models is studied. A method to measure the cohesive law associated with delamination is presented. The method allows for identification of a cohesive law fit to model the fracture process at the crack tip, i.e. not considering fibre bridging. Due to the small size of the cohesive zone, an elaborated method involving simulations of the fracture process is developed. The results show larger scatter in the parameters of the cohesive law than in the fracture energy.

  • 28.
    Sukia Garmendia, Alex
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Echaniz Granado, Iñigo
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Design, Verification and Manufacturing of a New Binding System for Crampons2013Självständigt arbete på grundnivå (kandidatexamen), 15 poäng / 22,5 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Crampons are a device composed of a framework containing prongs, a front-part binding and a rear-part binding system that are attached to the boots in order to climb through steep walls covered by ice, snow or rocks. Currently, the process to attach the binding system is complicated and time consuming. A new design of the rear-part binding system of the step-in crampon adapted to the current boot is therefore desired to create. The Five-Step Method is implemented to obtain the concept design. The refinement of the concept is then performed and the mechanism is designed based on the action of a spring. This improvement provides a simpler and faster attachment process to the boot and it does not require removing the gloves. The steps for the new fastening and unfastening process are lowered compared to the step-in crampon. The Value Engineering Method is used when establishing the materials and manufacturing process of the components. Chromoly steel AISI 4130 is determined for the most critical components suffering highest stresses. High Density Polyethylene polymer is used for the parts with the lowest demands concerning the stresses they have to bear. These materials stand extremely low temperatures and provide low density and high tensile strength. Commercial elements are used when possible to reduce the costs and simplify the design and assembly process. A CNC milling machine is used to manufacture the steel pieces with simple shape. The moulding process for steels is established for the steel components with more complicated shapes. Injection moulding is determined to produce the polymer parts. A simple and effective process is established for the assembly of the elements, which does not required high ability or specific tools. The design of the assembly provides the opportunity to recycle the materials. The functionality of the attachment mechanism is proved. It is verified that the critical components withstand the stresses created at them according to a security factor of 4. This is concluded accomplishing an analytical analysis and also using the Finite Element Method. The cost of the new product is estimated to be more expensive than the reference step-in crampon. The designed product weights almost the same than the current step-in crampon and it has reduced dimensions for storing it. It includes a security system that avoids the binding system being released even if a high force is applied to the system. It is important to regulate the binding system to the height of the rear-part groove of the boot and to fasten the security system tightly to avoid any clearances between the boot and the crampon. 

  • 29.
    Svensson, Daniel
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system. Chalmers Tekniska Högskola.
    On Cohesive Modelling ofCarbon/Epoxy Composites: Delamination and Fibre Compressive Failure2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Carbon Fibre Reinforced Polymers are widely used in engineering applications where weight saving and high mechanical performance are a key factors. However, an inheren tweakness of laminated CFRP:s is there relatively low resistance to delamination. Therst part of this thesis is devoted to extract cohesive laws associated with delamination.The method is based on fracture mechanical tests and measurement of the displacementeld close to the crack tip. The second part of the thesis is concerned with mixed modecohesive modelling under small scale yielding conditions. Under such loading conditions,a robust cohesive model should conform to Linear Elastic Fracture Mechanics (LEFM). Itis shown that two design rules for mixed mode cohesive laws are sucient to achieve thisproperty. The third part focuses a failure mode entirely dierent from delamination. Theobjective is to determine cohesive laws associated with longitudinal compressive failure.Equilibrium of congurational forces is used for this purpose. Identied congurationalforces are continuously measured by monitoring the displacements eld on the specimen'slateral surface. This allows for identication of the cohesive law.

  • 30.
    Svensson, Daniel
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Alfredsson, K. Svante
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Biel, Anders
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Measurement of cohesive laws for interlaminar failure of CFRP2014Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 100, s. 53-62Artikel i tidskrift (Refereegranskat)
  • 31.
    Svensson, Daniel
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Alfredsson, K. Svante
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    On the ability of coupled mixed mode cohesive laws to conform to LEFM for cracks in homogeneous orthotropic solids2016Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 163, s. 426-448Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ability of coupled cohesive laws to conform to the predictions of linear elastic fracturemechanics (LEFM) in the case of small-scale-yielding (SSY) is explored. The study is concerned with cracks in homogeneous orthotropic solids and the results apply also for the case of isotropy. Both potential based and non-potential based cohesive laws are considered. It is shown that the initial stiffnesses of the cohesive law must be matched to the elastic moduli of the orthotropic solid in order to achieve a constant ratio of the cohesive stress components ahead of the crack tip. A simple condition for this is provided. For non potential based laws an additional apparently sufficient condition on the non-linear part of the cohesive law is identified: The traction vector must not change direction if the directionof the separation vector is constant. Fulfillment of this condition provides a uniform local mode mix in the cohesive zone with a value equal to the global mode mix. It is demonstrated that potential based cohesive laws display a varying local mode mix at the crack tip for cases with a mode dependent work of separation. This is identified as acomplicating feature in terms of calibrating the parameters of a cohesive law to experimental data.

  • 32.
    Svensson, Daniel
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Alfredsson, K. Svante
    Högskolan i Skövde, Institutionen för teknik och samhälle. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för teknik och samhälle. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Jansson, N. E.
    GKN Aerospace Engine Systems Sweden, Trollhättan, Sweden.
    An experimental method to determine the critical energy release rate associated with longitudinal compressive failure in CFRP2013Ingår i: Proceeding of the 19th international conference on composite materials (ICCM 19), 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    A test specimen for measurement of the critical energy release rate associated with longitudinal compressive failure is proposed. High strains are localized by decreasing the out-of-plane thickness towards the anticipated damage region which consists of a unidirectional (UD) laminate. Thus, the compressive fibre failure mode is isolated. Microscopic studies show that the UD-material fails in a kinking mode. A method based on a generalized form of the J-integral and full-field measurements of the strain field is developed to extract the fracture energy. The fracture energy in four experiments is measured to be 20-40 kN/m. Finite element simulations  are  performed  to  validate  the experimental results. The essential features of the response are captured by modelling the damage region with cohesive elements.

  • 33.
    Svensson, Daniel
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Alfredsson, K. Svante
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Jansson, Nicklas E.
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Measurement of cohesive law for kink-band formation in unidirectional composite2016Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 151, s. 1-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Kink-band formation is an important mechanism limiting the compressive strength of high strength composites. A cohesive zone model is used to model the material in a unidirectional carbon fibre composite that forms the kink-band. Equilibrium of configurational forces is used to design and evaluate the experiments. Microscopic studies show that a kink-band is formed with the height of about 200 μm. The corresponding cohesive law has a peak stress of about 1.5 GPa, a compression at failure of about 50 μm and a fracture energy of about 25 kJ/m2.

  • 34.
    Walander, Tomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system. Chalmers University of Technology.
    Influences of temperature, fatigue and mixed mode loading on the cohesive properties of adhesive layers2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis concerns some aspects that have influence on the strength of adhesive layers. The strength is determined by the stress deformation-relation of the layer. This relation is also referred to as cohesive law. The aspects having influence on the cohesive laws that are studied in this work are temperature, fatigue, multi-axial fatigue and mixed mode loading.

    For each aspect, a model is developed that can be used to describe the influence of the aspects on the cohesive laws numerically, e.g. by using the finite element method. These models are shown to give good agreement with the experimental results when performing simulations that aims at reproducing the experiments. For the aspect of temperature, a FE-model is suggested that can be used to simulate the mechanical behaviour in pure mode loadings at any temperature within the evaluated temperature span. Also, a damage law for modelling high cycle fatigue in a bonded structure in multi-axial loading is presented. Lastly, a new experimental set-up is presented for evaluating strength of adhesives during mixed mode loading. The set-up enables loading with a constant mode-mix ratio and by the experimental results, a potential model for describing the mechanical behaviour of the evaluated adhesive is presented.

  • 35.
    Walander, Tomas
    et al.
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Eklind, Alexander
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Carlberger, Thomas
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Fatigue damage of adhesive layers: experiments and models2014Ingår i: Procedia Materials Science, ISSN 2211-8128, Vol. 3, s. 829-834Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mode I fatigue crack growth at load levels close to the threshold is studied with the aim of improving the understanding of the fatigue properties. We also aim at identifying a suitable damage evolution law for large-scale simulation of built-up structures. A fatigue test rig is designed where up to six specimens are tested simultaneously. Each specimen is evaluated separately indicating the specimen-to-specimen variation in fatigue properties. A rubber-based and a PUR-based adhesive are tested. The two adhesives represent adhesives with very different material properties; the rubber adhesive is a stiff structural adhesive and the PUR adhesive is a soft modular adhesive. The experiments are first evaluated using a traditional Paris’ law approach. Inspired by an existing damage evolution law, a modified damage evolution law is developed based on only three parameters. The law is implemented as a user material in Abaqus and the parameters are identified. The results from simulations show a very good ability to reproduce the experimental data. With this model of fatigue damage, a zone of damage evolves at the crack tip. The extension of this zone depends on the stiffness of the adherends; stiffer adherends leads to a larger damage zone. This means that the rate of crack growth depends on the stiffness of the adherends. Thus, not only the state at the crack tip governs the rate of crack growth. This is in contrast to the results of a model based on Paris’ law where only the state at the crack tip, through the energy release rate, governs the rate of crack growth. This indicates that the threshold value of the energy release rate may depend on the stiffness of the adherends.

  • 36.
    Werner, Elin
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Materialanalys & optimering av hydrauliska högtryckskopplingar med hjälp av simuleringar2018Självständigt arbete på grundnivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Optimering av prestanda görs på FEM ½” koppling på Parker Hannifin AB med hjälp av finita element analyser (FEA). De kritiska komponenterna som är styrningen, kulhållaren och nippelhuset är i fokus. En noggrannare materialanalys genomförs för att få mer verklighetbaserande materialdata på kopplingen. 

    Hela nippelhuset antas härdas efter varit i kontakt med företaget som utför härdningen på komponenten. För att få mer information om materialdata utförs statiska trycktester på en koppling. De uppmätta töjningarna från testerna jämförs med töjningarna i simuleringarna. Sträckgränsen och hårdnadskoefficienten på styrningen och kulhållaren kan justeras något från testerna men resultatet har flera osäkerheter. 

    Antalet kulor i kopplingen mellan 15 och 12 kulor undersöks efter önskemål från företaget. Analyser om hur en härdning påverkar styrningen görs samt hur nippelhuset påverkas av en ythärdning i form av sätthärdning.

    Vid härdning av styrningen uppkom de minsta deformationerna och spänningarna. Kulhållaren visade tydligt på mindre deformationer och spänningar om antalet kulor minskas från 15 till 12 kulor i kopplingen. För att minska kulintrycket på nippelhuset rekommenderas att ythärda komponenten med en 27 % hårdare yta än den nuvarande. På grund av uppskattade värden på materialdata på ythärdningen behöver mer information införskaffas. Detta för att kunna avgöra vilken tjocklek på ytans härdning som krävs för 12 kulor i kopplingen.

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