In the present work, we investigate the effects of strain rate (ė = 0.01 s −1 , 0.1 s −1 , and 1.... more In the present work, we investigate the effects of strain rate (ė = 0.01 s −1 , 0.1 s −1 , and 1.0 s −1) and low temperature (T = −30 • C, −15 • C, 0 • C, and 25 • C) on the mechanical behaviour in tension and compression of two materials: a rubber-modified polypropylene copolymer (PP) and a cross-linked low-density polyethylene (XLPE). Local stress-strain data for large deformations are obtained using digital image correlation (DIC) in the uniaxial tension tests and point tracking in the compression tests. Since both materials exhibit slight transverse anisotropy, two digital cameras are used to capture the strains on two perpendicular surfaces. Self-heating resulting from the elevated strain rates is monitored using an infrared (IR) camera. To enable the application of multiple digital cameras and an IR camera, a purpose-built transparent polycarbonate temperature chamber is used to create a cold environment for the tests. The mechanical behaviour of both materials, including the true stress-strain response and the volume change, is shown to be dependent on the temperature and strain rate. The dependence of the yield stress on the temperature and strain rate follows the Ree-Eyring flow theory for both materials, whereas Young's modulus increases with decreasing temperature for PP and XLPE and with increasing strain rate for XLPE. Furthermore, a scanning electron microscope (SEM) study was performed on both materials to get a qualitative understanding of the volumetric strains.
Simulation of ductile polymers subjected to impact loading has become an important topic [1, 2], ... more Simulation of ductile polymers subjected to impact loading has become an important topic [1, 2], especially for automotive components related to passenger and pedestrian safety. The aim of our work is to establish and validate numerical models for impact response, and this presentation will focus on a study of impact on injection molded polypropylene plates. SAMP-1 (Semi-Analytical Model for Polymers) [3] was selected as constitutive model in LS-DYNA. This model takes tabulated data from experiments as input, and includes strain rate effects, pressure sensitive plasticity, plastic volume dilatation and damage. As the material behavior is complex, and data for large strains are needed, a major task is to obtain reliable data from material tests.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
This paper presents an experimental/numerical study of low temperature pipe reeling, full-scale t... more This paper presents an experimental/numerical study of low temperature pipe reeling, full-scale tests and small scale tests simulating the deformations and loads seen during reeling. The emphasis is on the polymer thermal insulation coating and the interfaces between the coating and steel pipe and between different polymer layers and field joint material. A newly developed constitutive model for polymers is used. This material model takes into account strain rate and hydrostatic stress on plastic yielding, large strain hardening and ductile damage growth.
This paper presents numerical simulations of quasi-static perforation of circular AA5083-H116 alu... more This paper presents numerical simulations of quasi-static perforation of circular AA5083-H116 aluminium plates. The perforation process was analysed with 2D-axisymmetric elements, brick elements and shell elements. Slightly modified versions of the Johnson-Cook constitutive relation and fracture criterion were used in the finite element simulations to model the material behaviour. A factorial design was used to investigate the influence of varying plate thickness, boundary conditions, punch diameter and nose shape. Comparisons between LS-DYNA simulations and experiments were made and good qualitative agreement was in general found. However, some quantitative differences were observed.
Stand alone compiled executable version of the DACOMAT Micromechanical fibre bridging model descr... more Stand alone compiled executable version of the DACOMAT Micromechanical fibre bridging model described in the conference paper. <em>Micromechanical model of cross-over fiber bridging: (DOI:10.5281/zenodo.3784691)</em> and the DACOMAT project deliverable <em>D1.1 Micromechanical model for fibre peel-off and pull-out (Can be downloaded from www.dacomat.eu) </em> All plots and data presented in these papers/reports can generated with the software. Plots based on any other valid user input can also be generated. Input data is to be provided in an Excel sheet. An input example file is extracted to the installation folder upon installation.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
The mechanical properties of the glass-epoxy composite material known as "G-10," which is primari... more The mechanical properties of the glass-epoxy composite material known as "G-10," which is primarily used for electrical insulation purposes in electromechanical systems, have long been a topic of uncertainty and controversy. In the present paper, we demonstrate the application of an experimental methodology that exploits the Direct Strain Imaging (DSI) full field method to fully assess the elastic anisotropic mechanical properties of G-10. Tension and compression experiments were conducted for three distinct inclinations of the specimen orthotropic axes relative to the loading directions, while strain and displacement were monitored at relevant locations on the specimens via digital image capturing and subsequent application of DSI. Based on these experiments, we present the stress-strain experimental data, the associated data post processing, the engineering properties, the anisotropic compliance matrix and the ultimate strength properties of the G-10 composite material. Confidence bounds on the material properties based on the results from repeated tests on identical specimens are also reported.
This study addresses the nonlinear stress-strain response in glass fibre reinforced polymer compo... more This study addresses the nonlinear stress-strain response in glass fibre reinforced polymer composite laminates subjected to in-plane loading. A user defined material model is implemented in the finite element code LS-DYNA. The model is calibrated and evaluated using results from a large material testing survey. Failure theory as well as the damage evolution is based on the Puck failure criterion. The constitutive model treats the mix of fibre and matrix as homogeneous and anisotropic, whereas failure is either associated with the fibres or the polymer matrix. The progressive damage is initiated by matrix failure, and treated as a smeared degradation of the lamina properties. The laminates are modelled using both shell and solid elements. The benefits of using solid elements are shown to be small compared to the severe increase in computational cost.
A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscop... more A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscopic mixed mode bridging laws (traction-separation laws). The bridging ligament/fiber is treated as a beam, using moderately large deflection beam theory. The model includes debonding between fiber and matrix as well as buckling of fibers in compression. The predictions made by the proposed semi-analytical micromechanical model are shown to be in excellent agreement with those made by detailed finite element models. The computational efficiency of the novel model enables parameter studies that would otherwise be unfeasible. Further, the proposed model can be implemented as a physics based cohesive law for use in meso and macroscale finite element models.
The present study investigated how learners' knowledge of a second language (L2) can influence th... more The present study investigated how learners' knowledge of a second language (L2) can influence the processing of their first language (L1). The study recorded the eye movements of 47 L1 Chinese participants with different L2 English proficiency levels as they read and judged the grammaticality of 240 Chinese sentences (60 anglicized ungrammatical relative clauses, 90 non-anglicized ungrammatical sentences, and 90 grammatical sentences). Participants were also given a language-background questionnaire (LEAP-Q) to assess their English proficiency. An analysis using mixed-effects modeling showed that acceptance of anglicized ungrammatical Chinese sentences was correlated with age of acquisition, L2 cultural identification, and L2 reading skill and exposure. These results suggest that the L1 is a more flexible system than previously thought, one that can be changed to some degree by the mastery of an L2.
A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscop... more A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscopic mixed-mode bridging laws (traction-separation laws). The model is based on non-linear beam theory and takes into account debonding between fiber and matrix as well as buckling of fibers in compression. Further, it is shown how failure of the bridging fibers can be taken into account through a Weibull distributed failure strain. Predictions made by the proposed model are compared with predictions made by detailed 3D finite element models, and a very good agreement was observed. It is shown that models based on linear beam theory are only valid for small transverse deflections of the bridging ligament and greatly underestimate the force transferred by ligaments subjected to moderately large deflections. The novel model, on the other hand, is applicable in the entire range where the bridging problem transitions from a beam bending problem to a bar-like problem. Finally, an example of how...
HNBR was analyzed following low temperature storage (between 0°C and-50°C) in order to measure th... more HNBR was analyzed following low temperature storage (between 0°C and-50°C) in order to measure the effects of cold crystallization during exposure close to, and below, the glass transition temperature (Tg). Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and hardness testing were performed to measure the changes in melting enthalpy, shear stiffness and hardness as a result of low temperature exposure. An increase in crystallinity was measured even when the HNBR was held well below the Tg of the HNBR. Although the degree of crystallinity due to low temperature exposure is estimated to be quite small, a significant increase in hardness was seen after 24 hours exposure. The changes in properties due to the presence of "microcrystalline" regions are especially relevant for permanently low temperature applications, since the material properties over longer timescales at low temperatures may deviate significantly from the material properties measured immediately after cooling.
Journal of the Mechanics and Physics of Solids, 2018
In this study, a thermo-elasto-viscoplastic model is developed for a low density cross-linked pol... more In this study, a thermo-elasto-viscoplastic model is developed for a low density cross-linked polyethylene (XLPE) in an attempt to describe the combined effects of temperature and strain rate on the stress-strain response and the self-heating of the material at elevated strain rates. The proposed model consists of two parts. On the one side, Part A models the thermo-elastic and thermo-viscoplastic response, and incorporates an elastic Hencky spring in series with two Ree-Eyring dashpots. The two Ree-Eyring dashpots represent the effects of the main α relaxation and the secondary β relaxation processes on the plastic flow. Part B, on the other side, consists of an eight chain spring capturing the entropic strain hardening due to alignment of the polymer chains during deformation. The constitutive model was implemented in a nonlinear finite element (FE) code using a semi-implicit stress update algorithm combined with sub-stepping and a numerical scheme to calculate the consistent tangent operator. After calibration to available experimental data, FE simulations with the constitutive model are shown to successfully describe the stress-strain curves, the volumetric strain, the local strain rate and the self-heating observed in the tensile tests. In addition, the FE simulations adequately predict the global response of the tensile tests, such as the force-displacement curves and the deformed shape of the tensile specimen.
In the present work, we investigate the effects of strain rate (ė = 0.01 s −1 , 0.1 s −1 , and 1.... more In the present work, we investigate the effects of strain rate (ė = 0.01 s −1 , 0.1 s −1 , and 1.0 s −1) and low temperature (T = −30 • C, −15 • C, 0 • C, and 25 • C) on the mechanical behaviour in tension and compression of two materials: a rubber-modified polypropylene copolymer (PP) and a cross-linked low-density polyethylene (XLPE). Local stress-strain data for large deformations are obtained using digital image correlation (DIC) in the uniaxial tension tests and point tracking in the compression tests. Since both materials exhibit slight transverse anisotropy, two digital cameras are used to capture the strains on two perpendicular surfaces. Self-heating resulting from the elevated strain rates is monitored using an infrared (IR) camera. To enable the application of multiple digital cameras and an IR camera, a purpose-built transparent polycarbonate temperature chamber is used to create a cold environment for the tests. The mechanical behaviour of both materials, including the true stress-strain response and the volume change, is shown to be dependent on the temperature and strain rate. The dependence of the yield stress on the temperature and strain rate follows the Ree-Eyring flow theory for both materials, whereas Young's modulus increases with decreasing temperature for PP and XLPE and with increasing strain rate for XLPE. Furthermore, a scanning electron microscope (SEM) study was performed on both materials to get a qualitative understanding of the volumetric strains.
Simulation of ductile polymers subjected to impact loading has become an important topic [1, 2], ... more Simulation of ductile polymers subjected to impact loading has become an important topic [1, 2], especially for automotive components related to passenger and pedestrian safety. The aim of our work is to establish and validate numerical models for impact response, and this presentation will focus on a study of impact on injection molded polypropylene plates. SAMP-1 (Semi-Analytical Model for Polymers) [3] was selected as constitutive model in LS-DYNA. This model takes tabulated data from experiments as input, and includes strain rate effects, pressure sensitive plasticity, plastic volume dilatation and damage. As the material behavior is complex, and data for large strains are needed, a major task is to obtain reliable data from material tests.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
This paper presents an experimental/numerical study of low temperature pipe reeling, full-scale t... more This paper presents an experimental/numerical study of low temperature pipe reeling, full-scale tests and small scale tests simulating the deformations and loads seen during reeling. The emphasis is on the polymer thermal insulation coating and the interfaces between the coating and steel pipe and between different polymer layers and field joint material. A newly developed constitutive model for polymers is used. This material model takes into account strain rate and hydrostatic stress on plastic yielding, large strain hardening and ductile damage growth.
This paper presents numerical simulations of quasi-static perforation of circular AA5083-H116 alu... more This paper presents numerical simulations of quasi-static perforation of circular AA5083-H116 aluminium plates. The perforation process was analysed with 2D-axisymmetric elements, brick elements and shell elements. Slightly modified versions of the Johnson-Cook constitutive relation and fracture criterion were used in the finite element simulations to model the material behaviour. A factorial design was used to investigate the influence of varying plate thickness, boundary conditions, punch diameter and nose shape. Comparisons between LS-DYNA simulations and experiments were made and good qualitative agreement was in general found. However, some quantitative differences were observed.
Stand alone compiled executable version of the DACOMAT Micromechanical fibre bridging model descr... more Stand alone compiled executable version of the DACOMAT Micromechanical fibre bridging model described in the conference paper. <em>Micromechanical model of cross-over fiber bridging: (DOI:10.5281/zenodo.3784691)</em> and the DACOMAT project deliverable <em>D1.1 Micromechanical model for fibre peel-off and pull-out (Can be downloaded from www.dacomat.eu) </em> All plots and data presented in these papers/reports can generated with the software. Plots based on any other valid user input can also be generated. Input data is to be provided in an Excel sheet. An input example file is extracted to the installation folder upon installation.
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
The mechanical properties of the glass-epoxy composite material known as "G-10," which is primari... more The mechanical properties of the glass-epoxy composite material known as "G-10," which is primarily used for electrical insulation purposes in electromechanical systems, have long been a topic of uncertainty and controversy. In the present paper, we demonstrate the application of an experimental methodology that exploits the Direct Strain Imaging (DSI) full field method to fully assess the elastic anisotropic mechanical properties of G-10. Tension and compression experiments were conducted for three distinct inclinations of the specimen orthotropic axes relative to the loading directions, while strain and displacement were monitored at relevant locations on the specimens via digital image capturing and subsequent application of DSI. Based on these experiments, we present the stress-strain experimental data, the associated data post processing, the engineering properties, the anisotropic compliance matrix and the ultimate strength properties of the G-10 composite material. Confidence bounds on the material properties based on the results from repeated tests on identical specimens are also reported.
This study addresses the nonlinear stress-strain response in glass fibre reinforced polymer compo... more This study addresses the nonlinear stress-strain response in glass fibre reinforced polymer composite laminates subjected to in-plane loading. A user defined material model is implemented in the finite element code LS-DYNA. The model is calibrated and evaluated using results from a large material testing survey. Failure theory as well as the damage evolution is based on the Puck failure criterion. The constitutive model treats the mix of fibre and matrix as homogeneous and anisotropic, whereas failure is either associated with the fibres or the polymer matrix. The progressive damage is initiated by matrix failure, and treated as a smeared degradation of the lamina properties. The laminates are modelled using both shell and solid elements. The benefits of using solid elements are shown to be small compared to the severe increase in computational cost.
A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscop... more A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscopic mixed mode bridging laws (traction-separation laws). The bridging ligament/fiber is treated as a beam, using moderately large deflection beam theory. The model includes debonding between fiber and matrix as well as buckling of fibers in compression. The predictions made by the proposed semi-analytical micromechanical model are shown to be in excellent agreement with those made by detailed finite element models. The computational efficiency of the novel model enables parameter studies that would otherwise be unfeasible. Further, the proposed model can be implemented as a physics based cohesive law for use in meso and macroscale finite element models.
The present study investigated how learners' knowledge of a second language (L2) can influence th... more The present study investigated how learners' knowledge of a second language (L2) can influence the processing of their first language (L1). The study recorded the eye movements of 47 L1 Chinese participants with different L2 English proficiency levels as they read and judged the grammaticality of 240 Chinese sentences (60 anglicized ungrammatical relative clauses, 90 non-anglicized ungrammatical sentences, and 90 grammatical sentences). Participants were also given a language-background questionnaire (LEAP-Q) to assess their English proficiency. An analysis using mixed-effects modeling showed that acceptance of anglicized ungrammatical Chinese sentences was correlated with age of acquisition, L2 cultural identification, and L2 reading skill and exposure. These results suggest that the L1 is a more flexible system than previously thought, one that can be changed to some degree by the mastery of an L2.
A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscop... more A micromechanical model of cross-over fiber bridging is developed for the prediction of macroscopic mixed-mode bridging laws (traction-separation laws). The model is based on non-linear beam theory and takes into account debonding between fiber and matrix as well as buckling of fibers in compression. Further, it is shown how failure of the bridging fibers can be taken into account through a Weibull distributed failure strain. Predictions made by the proposed model are compared with predictions made by detailed 3D finite element models, and a very good agreement was observed. It is shown that models based on linear beam theory are only valid for small transverse deflections of the bridging ligament and greatly underestimate the force transferred by ligaments subjected to moderately large deflections. The novel model, on the other hand, is applicable in the entire range where the bridging problem transitions from a beam bending problem to a bar-like problem. Finally, an example of how...
HNBR was analyzed following low temperature storage (between 0°C and-50°C) in order to measure th... more HNBR was analyzed following low temperature storage (between 0°C and-50°C) in order to measure the effects of cold crystallization during exposure close to, and below, the glass transition temperature (Tg). Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and hardness testing were performed to measure the changes in melting enthalpy, shear stiffness and hardness as a result of low temperature exposure. An increase in crystallinity was measured even when the HNBR was held well below the Tg of the HNBR. Although the degree of crystallinity due to low temperature exposure is estimated to be quite small, a significant increase in hardness was seen after 24 hours exposure. The changes in properties due to the presence of "microcrystalline" regions are especially relevant for permanently low temperature applications, since the material properties over longer timescales at low temperatures may deviate significantly from the material properties measured immediately after cooling.
Journal of the Mechanics and Physics of Solids, 2018
In this study, a thermo-elasto-viscoplastic model is developed for a low density cross-linked pol... more In this study, a thermo-elasto-viscoplastic model is developed for a low density cross-linked polyethylene (XLPE) in an attempt to describe the combined effects of temperature and strain rate on the stress-strain response and the self-heating of the material at elevated strain rates. The proposed model consists of two parts. On the one side, Part A models the thermo-elastic and thermo-viscoplastic response, and incorporates an elastic Hencky spring in series with two Ree-Eyring dashpots. The two Ree-Eyring dashpots represent the effects of the main α relaxation and the secondary β relaxation processes on the plastic flow. Part B, on the other side, consists of an eight chain spring capturing the entropic strain hardening due to alignment of the polymer chains during deformation. The constitutive model was implemented in a nonlinear finite element (FE) code using a semi-implicit stress update algorithm combined with sub-stepping and a numerical scheme to calculate the consistent tangent operator. After calibration to available experimental data, FE simulations with the constitutive model are shown to successfully describe the stress-strain curves, the volumetric strain, the local strain rate and the self-heating observed in the tensile tests. In addition, the FE simulations adequately predict the global response of the tensile tests, such as the force-displacement curves and the deformed shape of the tensile specimen.
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Papers by Frode Grytten