The Experts below are selected from a list of 31407 Experts worldwide ranked by ideXlab platform
Odd Sture Hopperstad - One of the best experts on this subject based on the ideXlab platform.
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A through-thickness damage regularisation scheme for shell elements subjected to severe bending and Membrane deformations
Journal of the Mechanics and Physics of Solids, 2019Co-Authors: Miguel Costas, David Morin, Odd Sture Hopperstad, Tore Børvik, M LangsethAbstract:Abstract This research work proposes and validates a damage regularisation model for shell elements used in large-scale simulations. The model evaluates the ratio of bending to Membrane Loading in the elements based on the through-thickness gradient of the through-thickness plastic strain. The Cockcroft–Latham failure criterion is adopted, whose parameters are modified according to the length-to-thickness ratio of the shell elements in order to reduce the mesh dependency. This regularisation scheme is validated against experimental component tests on a double-chamber profile in an AA6005-T6 recrystallised aluminium alloy under quasi-static and impact Loading conditions. The results show that the model is able to accurately predict fracture initiation under all tested conditions.
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Ductile Fracture of Steel Sheets under Dynamic Membrane Loading
Procedia Engineering, 2017Co-Authors: Gaute Gruben, M Langseth, David Morin, Odd Sture HopperstadAbstract:Abstract Failure prediction assessment is conducted based on validated finite element simulations of impact tests performed on 1.8 mm dual-phase and 1.0 mm martensitic steel sheets. The sheets were clamped between two steel rings and subjected to lateral Loading by a punch with a hemispherical nose. Three different specimen geometries were applied. These were chosen to provide Membrane Loading in stress states near uniaxial tension, plane-strain tension and equi-biaxial tension. Thus, the most important stress states that may occur for thin sheets in an impact situation are covered. Finite element simulations of the impact tests are run with the nonlinear code LS-DYNA. The plastic behaviour of the materials is modelled using the Hershey yield function in combination with the associated flow rule and isotropic hardening. The specimens are discretized by shell elements, thus imposing a state of plane stress. Three different approaches for modelling ductile failure are evaluated by comparing the experimental and simulated force-displacement curves from the experiments on the two steel materials.
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low velocity impact on high strength steel sheets an experimental and numerical study
International Journal of Impact Engineering, 2016Co-Authors: Gaute Gruben, M Langseth, Egil Fagerholt, Odd Sture HopperstadAbstract:Abstract Low-velocity impact tests were performed on dual-phase and martensitic steel sheets and compared with corresponding quasi-static tests. The geometry and Loading condition of the specimens were similar to formability tests, and the average strain rates before failure were in the range 80–210 s − 1 for the low-velocity tests and 0.002-0.005 s − 1 for the quasi-static tests. For both Loading rates, the sheets failed under pre-dominant Membrane Loading, and by varying the specimen geometry, the stress states prior to failure ranged from uniaxial tension to equi-biaxial tension. Thus, the most important stress states occurring during an impact event in a thin-walled structure are covered. The experiments were complemented by nonlinear finite element simulations, where higher-order solid elements and a refined mesh were applied to capture the failure of the sheets. The materials were modelled using the Hershey high-exponent yield function combined with the associated flow rule and isotropic hardening. Quasi-static tensile and shear tests and tensile tests at elevated strain rates were performed to calibrate the constitutive relation. The results in terms of force-displacement curves and strain histories at critical positions in the specimens were similar for low-velocity and quasi-static Loading, independent of material and specimen geometry. This indicates that the quasi-static test gives a good description of the sheet behaviour under low-velocity impact Loading. The numerical simulations were found to be in good agreement with the experimental results, and strengthened the experimental finding that all the sheet-impact tests, except the martensitic steel sheet in a state close to equi-biaxial tension, displayed local necking before final fracture.
Wen Ying Shi - One of the best experts on this subject based on the ideXlab platform.
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A Novel SPES/PES Catalytic Membrane for Production Biodiesel: Optimization by Central Composite Design
Applied Mechanics and Materials, 2014Co-Authors: Wen Ying Shi, Hong Bin Li, Rong ZhouAbstract:A sulfonated polyethersulfone (SPES)/polyethersulfone (PES) blend catalytic Membrane was prepared and used as a heterogeneous catalyst in the esterification of oleic acid with methanol for producing biodiesel. Response surface methodology (RSM) based on central composite design (CCD) was used to optimize the three important reaction variables methanol/oleic acid mass ratio, catalytic Membrane Loading and reaction time for the esterification by SPES/PES blend catalytic Membrane. The optimum condition for the esterification was as follows: methanol/oleic acid mass ratio 1:1, catalytic Membrane Loading 1.66 meq/g, reaction time 6 h. The optimum predicted fatty acid methyl ester (FAME) yield was 97.44% and the actual value was 98.64%. The above results shows that the RSM study based on CCD is adaptable for FAME yield studied for the current esterification system.
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Esterification of acidified oil with methanol by SPES/PES catalytic Membrane.
Bioresource technology, 2010Co-Authors: Wen Ying ShiAbstract:A sulfonated polyethersulfone (SPES)/polyethersulfone (PES) blend catalytic Membrane was prepared and used as a heterogeneous catalyst in the esterification of the acidified oil (acid value 153 mg KOH/g) with methanol for producing biodiesel. The results showed that the free fatty acids conversion reached 97.6% using SPES/PES catalytic Membrane under the optimal esterification conditions. Meanwhile, the SPES/PES Membrane with 20.3% degree of sulfonation showed a good catalytic stability. A pseudo-homogeneous kinetic model was established. The results indicated that the reaction rate constant increased with increasing methanol/acidified oil molar ratio, the Loading of catalytic Membrane and reaction temperature. The reaction order was 2 and the activation energy decreased from 74.65 to 21.07 kJ/mol with increasing catalytic Membrane Loading from 0 to 0.135 meq/g(oil). It implies that the esterification is not diffusively controlled but kinetically controlled. The predicted results were in good agreement with the experimental data.
M Langseth - One of the best experts on this subject based on the ideXlab platform.
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A through-thickness damage regularisation scheme for shell elements subjected to severe bending and Membrane deformations
Journal of the Mechanics and Physics of Solids, 2019Co-Authors: Miguel Costas, David Morin, Odd Sture Hopperstad, Tore Børvik, M LangsethAbstract:Abstract This research work proposes and validates a damage regularisation model for shell elements used in large-scale simulations. The model evaluates the ratio of bending to Membrane Loading in the elements based on the through-thickness gradient of the through-thickness plastic strain. The Cockcroft–Latham failure criterion is adopted, whose parameters are modified according to the length-to-thickness ratio of the shell elements in order to reduce the mesh dependency. This regularisation scheme is validated against experimental component tests on a double-chamber profile in an AA6005-T6 recrystallised aluminium alloy under quasi-static and impact Loading conditions. The results show that the model is able to accurately predict fracture initiation under all tested conditions.
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Ductile Fracture of Steel Sheets under Dynamic Membrane Loading
Procedia Engineering, 2017Co-Authors: Gaute Gruben, M Langseth, David Morin, Odd Sture HopperstadAbstract:Abstract Failure prediction assessment is conducted based on validated finite element simulations of impact tests performed on 1.8 mm dual-phase and 1.0 mm martensitic steel sheets. The sheets were clamped between two steel rings and subjected to lateral Loading by a punch with a hemispherical nose. Three different specimen geometries were applied. These were chosen to provide Membrane Loading in stress states near uniaxial tension, plane-strain tension and equi-biaxial tension. Thus, the most important stress states that may occur for thin sheets in an impact situation are covered. Finite element simulations of the impact tests are run with the nonlinear code LS-DYNA. The plastic behaviour of the materials is modelled using the Hershey yield function in combination with the associated flow rule and isotropic hardening. The specimens are discretized by shell elements, thus imposing a state of plane stress. Three different approaches for modelling ductile failure are evaluated by comparing the experimental and simulated force-displacement curves from the experiments on the two steel materials.
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low velocity impact on high strength steel sheets an experimental and numerical study
International Journal of Impact Engineering, 2016Co-Authors: Gaute Gruben, M Langseth, Egil Fagerholt, Odd Sture HopperstadAbstract:Abstract Low-velocity impact tests were performed on dual-phase and martensitic steel sheets and compared with corresponding quasi-static tests. The geometry and Loading condition of the specimens were similar to formability tests, and the average strain rates before failure were in the range 80–210 s − 1 for the low-velocity tests and 0.002-0.005 s − 1 for the quasi-static tests. For both Loading rates, the sheets failed under pre-dominant Membrane Loading, and by varying the specimen geometry, the stress states prior to failure ranged from uniaxial tension to equi-biaxial tension. Thus, the most important stress states occurring during an impact event in a thin-walled structure are covered. The experiments were complemented by nonlinear finite element simulations, where higher-order solid elements and a refined mesh were applied to capture the failure of the sheets. The materials were modelled using the Hershey high-exponent yield function combined with the associated flow rule and isotropic hardening. Quasi-static tensile and shear tests and tensile tests at elevated strain rates were performed to calibrate the constitutive relation. The results in terms of force-displacement curves and strain histories at critical positions in the specimens were similar for low-velocity and quasi-static Loading, independent of material and specimen geometry. This indicates that the quasi-static test gives a good description of the sheet behaviour under low-velocity impact Loading. The numerical simulations were found to be in good agreement with the experimental results, and strengthened the experimental finding that all the sheet-impact tests, except the martensitic steel sheet in a state close to equi-biaxial tension, displayed local necking before final fracture.
Gaute Gruben - One of the best experts on this subject based on the ideXlab platform.
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Ductile Fracture of Steel Sheets under Dynamic Membrane Loading
Procedia Engineering, 2017Co-Authors: Gaute Gruben, M Langseth, David Morin, Odd Sture HopperstadAbstract:Abstract Failure prediction assessment is conducted based on validated finite element simulations of impact tests performed on 1.8 mm dual-phase and 1.0 mm martensitic steel sheets. The sheets were clamped between two steel rings and subjected to lateral Loading by a punch with a hemispherical nose. Three different specimen geometries were applied. These were chosen to provide Membrane Loading in stress states near uniaxial tension, plane-strain tension and equi-biaxial tension. Thus, the most important stress states that may occur for thin sheets in an impact situation are covered. Finite element simulations of the impact tests are run with the nonlinear code LS-DYNA. The plastic behaviour of the materials is modelled using the Hershey yield function in combination with the associated flow rule and isotropic hardening. The specimens are discretized by shell elements, thus imposing a state of plane stress. Three different approaches for modelling ductile failure are evaluated by comparing the experimental and simulated force-displacement curves from the experiments on the two steel materials.
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low velocity impact on high strength steel sheets an experimental and numerical study
International Journal of Impact Engineering, 2016Co-Authors: Gaute Gruben, M Langseth, Egil Fagerholt, Odd Sture HopperstadAbstract:Abstract Low-velocity impact tests were performed on dual-phase and martensitic steel sheets and compared with corresponding quasi-static tests. The geometry and Loading condition of the specimens were similar to formability tests, and the average strain rates before failure were in the range 80–210 s − 1 for the low-velocity tests and 0.002-0.005 s − 1 for the quasi-static tests. For both Loading rates, the sheets failed under pre-dominant Membrane Loading, and by varying the specimen geometry, the stress states prior to failure ranged from uniaxial tension to equi-biaxial tension. Thus, the most important stress states occurring during an impact event in a thin-walled structure are covered. The experiments were complemented by nonlinear finite element simulations, where higher-order solid elements and a refined mesh were applied to capture the failure of the sheets. The materials were modelled using the Hershey high-exponent yield function combined with the associated flow rule and isotropic hardening. Quasi-static tensile and shear tests and tensile tests at elevated strain rates were performed to calibrate the constitutive relation. The results in terms of force-displacement curves and strain histories at critical positions in the specimens were similar for low-velocity and quasi-static Loading, independent of material and specimen geometry. This indicates that the quasi-static test gives a good description of the sheet behaviour under low-velocity impact Loading. The numerical simulations were found to be in good agreement with the experimental results, and strengthened the experimental finding that all the sheet-impact tests, except the martensitic steel sheet in a state close to equi-biaxial tension, displayed local necking before final fracture.
David Morin - One of the best experts on this subject based on the ideXlab platform.
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A through-thickness damage regularisation scheme for shell elements subjected to severe bending and Membrane deformations
Journal of the Mechanics and Physics of Solids, 2019Co-Authors: Miguel Costas, David Morin, Odd Sture Hopperstad, Tore Børvik, M LangsethAbstract:Abstract This research work proposes and validates a damage regularisation model for shell elements used in large-scale simulations. The model evaluates the ratio of bending to Membrane Loading in the elements based on the through-thickness gradient of the through-thickness plastic strain. The Cockcroft–Latham failure criterion is adopted, whose parameters are modified according to the length-to-thickness ratio of the shell elements in order to reduce the mesh dependency. This regularisation scheme is validated against experimental component tests on a double-chamber profile in an AA6005-T6 recrystallised aluminium alloy under quasi-static and impact Loading conditions. The results show that the model is able to accurately predict fracture initiation under all tested conditions.
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Ductile Fracture of Steel Sheets under Dynamic Membrane Loading
Procedia Engineering, 2017Co-Authors: Gaute Gruben, M Langseth, David Morin, Odd Sture HopperstadAbstract:Abstract Failure prediction assessment is conducted based on validated finite element simulations of impact tests performed on 1.8 mm dual-phase and 1.0 mm martensitic steel sheets. The sheets were clamped between two steel rings and subjected to lateral Loading by a punch with a hemispherical nose. Three different specimen geometries were applied. These were chosen to provide Membrane Loading in stress states near uniaxial tension, plane-strain tension and equi-biaxial tension. Thus, the most important stress states that may occur for thin sheets in an impact situation are covered. Finite element simulations of the impact tests are run with the nonlinear code LS-DYNA. The plastic behaviour of the materials is modelled using the Hershey yield function in combination with the associated flow rule and isotropic hardening. The specimens are discretized by shell elements, thus imposing a state of plane stress. Three different approaches for modelling ductile failure are evaluated by comparing the experimental and simulated force-displacement curves from the experiments on the two steel materials.