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Papers by Thomas Carlberger
Choice of the engine and design of the structural support. Abstract Electric cars have appeared a... more Choice of the engine and design of the structural support. Abstract Electric cars have appeared as an alternative to the big pollution caused by internal combustion engine cars. However, electric cars as the Renault Fluence Z.E. are not very sold in the market because of their small range of autonomy. To make this car an attractive option, it is necessary to add a range extender that extends its autonomy. This range extender is based in the addition of a small internal combustion engine to be attached only when the electric autonomy cannot fulfill the trip. A range extender is chosen by means of a comparison between different electric engines sold in the market. By means of a classification tree, the different places of the car where to mount it are compared and the most appropriate is chosen. By using Solidworks, a structure to support the engine and attach it to the car is designed. The result is a Range Extender device to mount in the hitch hook of the Renault Fluence Z.E. that p...
Experiments are performed to evaluate the temperature dependence of the stress-elongation relatio... more Experiments are performed to evaluate the temperature dependence of the stress-elongation relation for an engineering epoxy adhesive. Seven temperatures from -40oC to 80oC are considered. At each temperature, about seven experiments are performed with a double cantilever beam specimen. The experiments are evaluated using an inverse solution. The results show that the peak stress decreases monotonically with temperature, from about 55 MPa at -40oC to about 11 MPa at 80oC. Thus, the shape of the stress-elongation relation varies with the temperature. At higher temperatures, the fracture energy decreases slightly.
Today, crash simulations replace crash testing in the product development phase in the automotive... more Today, crash simulations replace crash testing in the product development phase in the automotive industry. High quality simulations enable shorter product development time and higher competitiveness. However, increasing requirements regarding emissions and crashworthiness are demanding optimised material choice in the parts constituting the car body structure. Lightweight materials are becoming frequently used. Joining dissimilar materials is difficult using common joining techniques like spot welding. To this end, adhesive joining is currently gaining popularity not only due to the ability to join dissimilar materials, joint integrity and structural stiffness both increase by the use of adhesive joining. Moreover, the number of spot welds may be reduced in hybrid joints. In this thesis, adhesive joints are studied with respect to crashworthiness of automotive structures. The main task for the adhesive is not to dissipate the impact energy, but to keep the joint integrity so that t...
The development of competitive and crashworthy automotive car bodies has reached so far that the ... more The development of competitive and crashworthy automotive car bodies has reached so far that the manufacturers no longer rely on mono-material steel structures. Improved strength/weight performance ...
International Journal of Adhesion and Adhesives, 2016
A cohesive zone model is presented for analyzing the fatigue life of an adhesive joint in the ran... more A cohesive zone model is presented for analyzing the fatigue life of an adhesive joint in the range of 104–106 load cycles. The parameters of the model are derived from Mode I double cantilever beam experiments. Fatigue experiments with adhesively joined components from the automotive industry are performed, and the results from the experiments are compared to the results of simulations. The error in the predicted fatigue strength is of the same order as the statistical deviation of the fatigue experiments, indicating that the simulation method produces acceptable predictions of the fatigue strength for applications in e.g. early product development.
Att berakna limfogars hallfasthet ar inte helt enkelt, vilket beror pa spanningskoncentrationens ... more Att berakna limfogars hallfasthet ar inte helt enkelt, vilket beror pa spanningskoncentrationens inflytande vid limfogens kanter.Materialmekanik vid Hogskolan i Skovde har specialiserat sig pa hall ...
International Journal of Fracture, Feb 18, 2010
An overview of recent development of cohesive modelling is given. Cohesive models are discussed i... more An overview of recent development of cohesive modelling is given. Cohesive models are discussed in general and specifically for the modelling of adhesive layers. It is argued that most cohesive models model a material volume and not a surface. Detailed microscopic and mesomechanical studies of the fracture process of an engineering epoxy are discussed. These studies show how plasticity on the mesomechanical length scale contributes to the fracture energy in shear dominated load cases. Methods to measure cohesive laws are presented in a general setting. Conclusions and conjectures based on experimental and mesomechanical studies are presented. The influence of temperature and strain rate on the peak stress and fracture energy of cohesive laws indicates fundamentally different mechanisms responsible for these properties. Experiments and mesomechanical studies show that in-plane straining of an adhesive layer can give large contributions to the registered fracture energy. Finite element formulations including a method to incorporate this influence are discussed.
International Journal of Fracture, Feb 1, 2009
Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive... more Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive are studied experimentally. Two parameters of the cohesive laws are given special attention: the fracture energy and the peak stress. Temperature experiments are performed in peel mode using the double cantilever beam specimen. The temperature varies from-40°C to +80ºC. The temperature experiments show monotonically decreasing peak stress with increasing temperature from about 50 MPa at-40ºC to about 10 MPa at +80ºC. The fracture energy is shown to be relatively insensitive to the variation in temperature. Strain rate experiments are performed in peel mode using the double cantilever beam specimen and in shear mode, using the end notch flexure specimen. The strain rates vary; for peel loading from about 10-4 s-1 to 10 s-1 and for shear loading from 10-3 s-1 to 1 s-1. In the peel mode, the fracture energy increases slightly with increasing strain rate; in shear mode, the fracture energy decreases. The peak stresses in the peel and shear mode both increase with increasing strain rate. In peel mode, only minor effects of plasticity are expected while in shear mode, the adhesive experiences large dissipation through plasticity. Rate dependent plasticity, may explain the differences in influence of strain rate on fracture energy between the peel mode and the shear mode.
International Journal of Fracture, 2014
Procedia Materials Science, 2014
ABSTRACT Mode I fatigue crack growth at load levels close to the threshold is studied with the ai... more ABSTRACT 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.
Procedia Materials Science, 2014
ABSTRACT For adhesive tapes, the strain before fracture often exceeds 500%. Although the maximum ... more ABSTRACT 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.
Experiments are performed to evaluate the temperature dependence of the stress-elongation relatio... more Experiments are performed to evaluate the temperature dependence of the stress-elongation relation for an engineering epoxy adhesive. Seven temperatures from -40ºC to 80ºC are considered. At each temperature, about seven experiments are performed with a double cantilever beam specimen. The experiments are evaluated using an inverse solution. The results show that the peak stress decreases monotonically with temperature, from about 55 MPa at -40ºC to about 11 MPa at 80ºC. Thus, the shape of the stress-elongation relation varies with the temperature. At higher temperatures, the fracture energy decreases slightly.
Thin-Walled Structures, 2010
ABSTRACT A specimen is developed for real-like low velocity impact testing of bi-material joint c... more ABSTRACT A specimen is developed for real-like low velocity impact testing of bi-material joint configurations. Six different joint configurations are analysed. Two engineering adhesives are evaluated with and without discrete mechanical fasteners, i.e. adhesive and hybrid joints. Experiments and simulations are performed. The simulations are performed using adhesive cohesive finite elements. Simulations show good agreement with experiments in impact energy and overall deformation mode. The histories of applied load vs. load-point deflection show reasonably good correlation. The results show that the impact energy consumption depends on the joint integrity. A threshold value for the fracture energy of the adhesive seems to exist. Beneath this value, adhesive and discrete fastener work together increasing the impact energy capacity. Above this value the discrete fastener has a negative effect, and may be regarded as a stress concentration.
The Journal of Adhesion, 2010
ABSTRACT Cohesive laws are determined for different layer thicknesses of an engineering adhesive.... more ABSTRACT Cohesive laws are determined for different layer thicknesses of an engineering adhesive. The shape of the cohesive law depends on the adhesive layer thickness. Of the two parameters of the cohesive law—the fracture energy and the strength—the fracture energy is more sensitive to thickness variation than the strength. The fracture energy in peel mode (Mode I) increases monotonically as the thickness is increased from 0.1 to about 1.0 mm. At an adhesive thickness of 1.5 mm, the fracture energy is slightly lower than for a 1.0 mm adhesive thickness, indicating a maximum between 1.0 and 1.5 mm. In shear mode (Mode II), the thickness dependence is not as strong, but an increasing trend in fracture energy with increasing adhesive thickness is evident. A slight decrease in strength with increasing adhesive thickness is found in both loading modes.
Choice of the engine and design of the structural support. Abstract Electric cars have appeared a... more Choice of the engine and design of the structural support. Abstract Electric cars have appeared as an alternative to the big pollution caused by internal combustion engine cars. However, electric cars as the Renault Fluence Z.E. are not very sold in the market because of their small range of autonomy. To make this car an attractive option, it is necessary to add a range extender that extends its autonomy. This range extender is based in the addition of a small internal combustion engine to be attached only when the electric autonomy cannot fulfill the trip. A range extender is chosen by means of a comparison between different electric engines sold in the market. By means of a classification tree, the different places of the car where to mount it are compared and the most appropriate is chosen. By using Solidworks, a structure to support the engine and attach it to the car is designed. The result is a Range Extender device to mount in the hitch hook of the Renault Fluence Z.E. that p...
Experiments are performed to evaluate the temperature dependence of the stress-elongation relatio... more Experiments are performed to evaluate the temperature dependence of the stress-elongation relation for an engineering epoxy adhesive. Seven temperatures from -40oC to 80oC are considered. At each temperature, about seven experiments are performed with a double cantilever beam specimen. The experiments are evaluated using an inverse solution. The results show that the peak stress decreases monotonically with temperature, from about 55 MPa at -40oC to about 11 MPa at 80oC. Thus, the shape of the stress-elongation relation varies with the temperature. At higher temperatures, the fracture energy decreases slightly.
Today, crash simulations replace crash testing in the product development phase in the automotive... more Today, crash simulations replace crash testing in the product development phase in the automotive industry. High quality simulations enable shorter product development time and higher competitiveness. However, increasing requirements regarding emissions and crashworthiness are demanding optimised material choice in the parts constituting the car body structure. Lightweight materials are becoming frequently used. Joining dissimilar materials is difficult using common joining techniques like spot welding. To this end, adhesive joining is currently gaining popularity not only due to the ability to join dissimilar materials, joint integrity and structural stiffness both increase by the use of adhesive joining. Moreover, the number of spot welds may be reduced in hybrid joints. In this thesis, adhesive joints are studied with respect to crashworthiness of automotive structures. The main task for the adhesive is not to dissipate the impact energy, but to keep the joint integrity so that t...
The development of competitive and crashworthy automotive car bodies has reached so far that the ... more The development of competitive and crashworthy automotive car bodies has reached so far that the manufacturers no longer rely on mono-material steel structures. Improved strength/weight performance ...
International Journal of Adhesion and Adhesives, 2016
A cohesive zone model is presented for analyzing the fatigue life of an adhesive joint in the ran... more A cohesive zone model is presented for analyzing the fatigue life of an adhesive joint in the range of 104–106 load cycles. The parameters of the model are derived from Mode I double cantilever beam experiments. Fatigue experiments with adhesively joined components from the automotive industry are performed, and the results from the experiments are compared to the results of simulations. The error in the predicted fatigue strength is of the same order as the statistical deviation of the fatigue experiments, indicating that the simulation method produces acceptable predictions of the fatigue strength for applications in e.g. early product development.
Att berakna limfogars hallfasthet ar inte helt enkelt, vilket beror pa spanningskoncentrationens ... more Att berakna limfogars hallfasthet ar inte helt enkelt, vilket beror pa spanningskoncentrationens inflytande vid limfogens kanter.Materialmekanik vid Hogskolan i Skovde har specialiserat sig pa hall ...
International Journal of Fracture, Feb 18, 2010
An overview of recent development of cohesive modelling is given. Cohesive models are discussed i... more An overview of recent development of cohesive modelling is given. Cohesive models are discussed in general and specifically for the modelling of adhesive layers. It is argued that most cohesive models model a material volume and not a surface. Detailed microscopic and mesomechanical studies of the fracture process of an engineering epoxy are discussed. These studies show how plasticity on the mesomechanical length scale contributes to the fracture energy in shear dominated load cases. Methods to measure cohesive laws are presented in a general setting. Conclusions and conjectures based on experimental and mesomechanical studies are presented. The influence of temperature and strain rate on the peak stress and fracture energy of cohesive laws indicates fundamentally different mechanisms responsible for these properties. Experiments and mesomechanical studies show that in-plane straining of an adhesive layer can give large contributions to the registered fracture energy. Finite element formulations including a method to incorporate this influence are discussed.
International Journal of Fracture, Feb 1, 2009
Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive... more Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive are studied experimentally. Two parameters of the cohesive laws are given special attention: the fracture energy and the peak stress. Temperature experiments are performed in peel mode using the double cantilever beam specimen. The temperature varies from-40°C to +80ºC. The temperature experiments show monotonically decreasing peak stress with increasing temperature from about 50 MPa at-40ºC to about 10 MPa at +80ºC. The fracture energy is shown to be relatively insensitive to the variation in temperature. Strain rate experiments are performed in peel mode using the double cantilever beam specimen and in shear mode, using the end notch flexure specimen. The strain rates vary; for peel loading from about 10-4 s-1 to 10 s-1 and for shear loading from 10-3 s-1 to 1 s-1. In the peel mode, the fracture energy increases slightly with increasing strain rate; in shear mode, the fracture energy decreases. The peak stresses in the peel and shear mode both increase with increasing strain rate. In peel mode, only minor effects of plasticity are expected while in shear mode, the adhesive experiences large dissipation through plasticity. Rate dependent plasticity, may explain the differences in influence of strain rate on fracture energy between the peel mode and the shear mode.
International Journal of Fracture, 2014
Procedia Materials Science, 2014
ABSTRACT Mode I fatigue crack growth at load levels close to the threshold is studied with the ai... more ABSTRACT 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.
Procedia Materials Science, 2014
ABSTRACT For adhesive tapes, the strain before fracture often exceeds 500%. Although the maximum ... more ABSTRACT 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.
Experiments are performed to evaluate the temperature dependence of the stress-elongation relatio... more Experiments are performed to evaluate the temperature dependence of the stress-elongation relation for an engineering epoxy adhesive. Seven temperatures from -40ºC to 80ºC are considered. At each temperature, about seven experiments are performed with a double cantilever beam specimen. The experiments are evaluated using an inverse solution. The results show that the peak stress decreases monotonically with temperature, from about 55 MPa at -40ºC to about 11 MPa at 80ºC. Thus, the shape of the stress-elongation relation varies with the temperature. At higher temperatures, the fracture energy decreases slightly.
Thin-Walled Structures, 2010
ABSTRACT A specimen is developed for real-like low velocity impact testing of bi-material joint c... more ABSTRACT A specimen is developed for real-like low velocity impact testing of bi-material joint configurations. Six different joint configurations are analysed. Two engineering adhesives are evaluated with and without discrete mechanical fasteners, i.e. adhesive and hybrid joints. Experiments and simulations are performed. The simulations are performed using adhesive cohesive finite elements. Simulations show good agreement with experiments in impact energy and overall deformation mode. The histories of applied load vs. load-point deflection show reasonably good correlation. The results show that the impact energy consumption depends on the joint integrity. A threshold value for the fracture energy of the adhesive seems to exist. Beneath this value, adhesive and discrete fastener work together increasing the impact energy capacity. Above this value the discrete fastener has a negative effect, and may be regarded as a stress concentration.
The Journal of Adhesion, 2010
ABSTRACT Cohesive laws are determined for different layer thicknesses of an engineering adhesive.... more ABSTRACT Cohesive laws are determined for different layer thicknesses of an engineering adhesive. The shape of the cohesive law depends on the adhesive layer thickness. Of the two parameters of the cohesive law—the fracture energy and the strength—the fracture energy is more sensitive to thickness variation than the strength. The fracture energy in peel mode (Mode I) increases monotonically as the thickness is increased from 0.1 to about 1.0 mm. At an adhesive thickness of 1.5 mm, the fracture energy is slightly lower than for a 1.0 mm adhesive thickness, indicating a maximum between 1.0 and 1.5 mm. In shear mode (Mode II), the thickness dependence is not as strong, but an increasing trend in fracture energy with increasing adhesive thickness is evident. A slight decrease in strength with increasing adhesive thickness is found in both loading modes.