Publications
2020
- AbstractURLBibTeXEndNoteDOIA massively parallel multiscale CAFE framework for the modelling of fracture in heterogeneous materials under dynamic loading. Hewitt, Sam; Margetts, Lee; Shterenlikht, Anton; Revell, Alistair (2020). 139 102737.This paper presents a novel computational framework for modelling multiscale fracture that can be used to solve engineering problems subject to dynamic loading. The framework simulates, mechanistically, at the mesoscale, the physical processes that lead to brittle fracture. A homogenisation step is used to translate the accumulation of damage from the mesoscale to the macroscale (as a reduced stiffness in the corresponding region of the structure). In order to achieve this, the multiscale framework couples together two open source Fortran packages; the macroscale ParaFEM with the mesoscale CASUP. ParaFEM is a highly parallel finite element analysis library used to model structures at the continuum scale. CASUP is a package that uses cellular automata to simulate brittle fracture in polycrystalline materials. A simple test problem involving a vibrating cantilever beam is used to demonstrate the simulation of dynamic cyclic loading, leading to brittle cracking. In the cellular automata software, there are a range of parameters that can be adjusted, such as the fracture energy and grain size. These are explored to demonstrate how they might affect the predicted structural integrity of the cantilever beam. Parallel performance is investigated using a Cray XC30 supercomputer, showing that the software can make efficient use of tens of thousands of cores. This paper highlights that modelling the physical mechanisms that lead to damage and plasticity could be an attractive alternative to phenomenological constitutive models. This work will be of interest to researchers and practitioners needing more precise predictions or a better understanding of damage propagation under cyclic or impact loading. With further development, this type of framework will enable the insilico design and evaluation of new material microstructures; leading to improved performance of components and devices subject to extreme operating conditions.
@article{Hewitt_2020,
abstract = {This paper presents a novel computational framework for modelling multiscale fracture that can be used to solve engineering problems subject to dynamic loading. The framework simulates, mechanistically, at the mesoscale, the physical processes that lead to brittle fracture. A homogenisation step is used to translate the accumulation of damage from the mesoscale to the macroscale (as a reduced stiffness in the corresponding region of the structure). In order to achieve this, the multiscale framework couples together two open source Fortran packages; the macroscale ParaFEM with the mesoscale CASUP. ParaFEM is a highly parallel finite element analysis library used to model structures at the continuum scale. CASUP is a package that uses cellular automata to simulate brittle fracture in polycrystalline materials. A simple test problem involving a vibrating cantilever beam is used to demonstrate the simulation of dynamic cyclic loading, leading to brittle cracking. In the cellular automata software, there are a range of parameters that can be adjusted, such as the fracture energy and grain size. These are explored to demonstrate how they might affect the predicted structural integrity of the cantilever beam. Parallel performance is investigated using a Cray XC30 supercomputer, showing that the software can make efficient use of tens of thousands of cores. This paper highlights that modelling the physical mechanisms that lead to damage and plasticity could be an attractive alternative to phenomenological constitutive models. This work will be of interest to researchers and practitioners needing more precise predictions or a better understanding of damage propagation under cyclic or impact loading. With further development, this type of framework will enable the insilico design and evaluation of new material microstructures; leading to improved performance of components and devices subject to extreme operating conditions.},
author = {Hewitt, Sam and Margetts, Lee and Shterenlikht, Anton and Revell, Alistair},
journal = {Advances in Engineering Software},
keywords = {myown},
month = {jan},
pages = 102737,
publisher = {Elsevier BV},
title = {A massively parallel multiscale CAFE framework for the modelling of fracture in heterogeneous materials under dynamic loading},
volume = 139,
year = 2020
}%0 Journal Article
%1 Hewitt_2020
%A Hewitt, Sam
%A Margetts, Lee
%A Shterenlikht, Anton
%A Revell, Alistair
%D 2020
%I Elsevier BV
%J Advances in Engineering Software
%P 102737
%R 10.1016/j.advengsoft.2019.102737
%T A massively parallel multiscale CAFE framework for the modelling of fracture in heterogeneous materials under dynamic loading
%U https://doi.org/10.1016%2Fj.advengsoft.2019.102737
%V 139
%X This paper presents a novel computational framework for modelling multiscale fracture that can be used to solve engineering problems subject to dynamic loading. The framework simulates, mechanistically, at the mesoscale, the physical processes that lead to brittle fracture. A homogenisation step is used to translate the accumulation of damage from the mesoscale to the macroscale (as a reduced stiffness in the corresponding region of the structure). In order to achieve this, the multiscale framework couples together two open source Fortran packages; the macroscale ParaFEM with the mesoscale CASUP. ParaFEM is a highly parallel finite element analysis library used to model structures at the continuum scale. CASUP is a package that uses cellular automata to simulate brittle fracture in polycrystalline materials. A simple test problem involving a vibrating cantilever beam is used to demonstrate the simulation of dynamic cyclic loading, leading to brittle cracking. In the cellular automata software, there are a range of parameters that can be adjusted, such as the fracture energy and grain size. These are explored to demonstrate how they might affect the predicted structural integrity of the cantilever beam. Parallel performance is investigated using a Cray XC30 supercomputer, showing that the software can make efficient use of tens of thousands of cores. This paper highlights that modelling the physical mechanisms that lead to damage and plasticity could be an attractive alternative to phenomenological constitutive models. This work will be of interest to researchers and practitioners needing more precise predictions or a better understanding of damage propagation under cyclic or impact loading. With further development, this type of framework will enable the insilico design and evaluation of new material microstructures; leading to improved performance of components and devices subject to extreme operating conditions.
2019
- URLBibTeXEndNoteDOIOpenFPCI: A parallel fluid structure interaction framework. Hewitt, Sam; Margetts, Lee; Revell, Alistair; Pankaj, Pankaj; Levrero-Florencio, Francesc (2019). 244 469--482.
@article{Hewitt_2019,
author = {Hewitt, Sam and Margetts, Lee and Revell, Alistair and Pankaj, Pankaj and Levrero-Florencio, Francesc},
journal = {Computer Physics Communications},
keywords = {myown},
month = {nov},
pages = {469--482},
publisher = {Elsevier BV},
title = {OpenFPCI: A parallel fluid structure interaction framework},
volume = 244,
year = 2019
}%0 Journal Article
%1 Hewitt_2019
%A Hewitt, Sam
%A Margetts, Lee
%A Revell, Alistair
%A Pankaj, Pankaj
%A Levrero-Florencio, Francesc
%D 2019
%I Elsevier BV
%J Computer Physics Communications
%P 469--482
%R 10.1016/j.cpc.2019.05.016
%T OpenFPCI: A parallel fluid structure interaction framework
%U https://doi.org/10.1016%2Fj.cpc.2019.05.016
%V 244
2018
- AbstractURLBibTeXEndNoteDOIModelling fracture in heterogeneous materials on HPC systems using a hybrid MPI/Fortran coarray multi-scale CAFE framework. Shterenlikht, A.; Margetts, L.; Cebamanos, L. (2018).A 3D multi-scale cellular automata finite element (CAFE) framework for modelling fracture in heterogeneous materials is described. The framework is implemented in a hybrid MPI/Fortran coarray code for efficient parallel execution on HPC platforms. Two open source BSD licensed libraries developed by the authors in modern Fortran were used: CGPACK, implementing cellular automata (CA) using Fortran coarrays, and ParaFEM, implementing finite elements (FE) using MPI. The framework implements a two-way concurrent hierarchical information exchange between the structural level (FE) and the microstructure (CA). MPI to coarrays interface and data structures are described. The CAFE framework is used to predict transgranular cleavage propagation in a polycrystalline iron round bar under tension. Novel results enabled by this CAFE framework include simulation of progressive cleavage propagation through individual grains and across grain boundaries, and emergence of a macro-crack from merging of cracks on preferentially oriented cleavage planes in individual crystals. Nearly ideal strong scaling up to at least tens of thousands of cores was demonstrated by CGPACK and by ParaFEM in isolation in prior work on Cray XE6. Cray XC30 and XC40 platforms and CrayPAT profiling were used in this work. Initially the strong scaling limit of hybrid CGPACK/ParaFEM CAFE model was 2000 cores. After replacing all-to-all communication patterns with the nearest neighbour algorithms the strong scaling limit on Cray XC30 was increased to 7000 cores. TAU profiling on non-Cray systems identified deficiencies in Intel Fortran 16 optimisation of remote coarray operations. Finally, coarray synchronisation challenges and opportunities for thread parallelisation in CA are discussed.
@article{SHTERENLIKHT2018,
abstract = {A 3D multi-scale cellular automata finite element (CAFE) framework for modelling fracture in heterogeneous materials is described. The framework is implemented in a hybrid MPI/Fortran coarray code for efficient parallel execution on HPC platforms. Two open source BSD licensed libraries developed by the authors in modern Fortran were used: CGPACK, implementing cellular automata (CA) using Fortran coarrays, and ParaFEM, implementing finite elements (FE) using MPI. The framework implements a two-way concurrent hierarchical information exchange between the structural level (FE) and the microstructure (CA). MPI to coarrays interface and data structures are described. The CAFE framework is used to predict transgranular cleavage propagation in a polycrystalline iron round bar under tension. Novel results enabled by this CAFE framework include simulation of progressive cleavage propagation through individual grains and across grain boundaries, and emergence of a macro-crack from merging of cracks on preferentially oriented cleavage planes in individual crystals. Nearly ideal strong scaling up to at least tens of thousands of cores was demonstrated by CGPACK and by ParaFEM in isolation in prior work on Cray XE6. Cray XC30 and XC40 platforms and CrayPAT profiling were used in this work. Initially the strong scaling limit of hybrid CGPACK/ParaFEM CAFE model was 2000 cores. After replacing all-to-all communication patterns with the nearest neighbour algorithms the strong scaling limit on Cray XC30 was increased to 7000 cores. TAU profiling on non-Cray systems identified deficiencies in Intel Fortran 16 optimisation of remote coarray operations. Finally, coarray synchronisation challenges and opportunities for thread parallelisation in CA are discussed.},
author = {Shterenlikht, A. and Margetts, L. and Cebamanos, L.},
journal = {Advances in Engineering Software},
keywords = {myown},
title = {Modelling fracture in heterogeneous materials on HPC systems using a hybrid MPI/Fortran coarray multi-scale CAFE framework},
year = 2018
}%0 Journal Article
%1 SHTERENLIKHT2018
%A Shterenlikht, A.
%A Margetts, L.
%A Cebamanos, L.
%D 2018
%J Advances in Engineering Software
%R https://doi.org/10.1016/j.advengsoft.2018.05.008
%T Modelling fracture in heterogeneous materials on HPC systems using a hybrid MPI/Fortran coarray multi-scale CAFE framework
%U http://sciencedirect.com/science/article/pii/S0965997817307494
%X A 3D multi-scale cellular automata finite element (CAFE) framework for modelling fracture in heterogeneous materials is described. The framework is implemented in a hybrid MPI/Fortran coarray code for efficient parallel execution on HPC platforms. Two open source BSD licensed libraries developed by the authors in modern Fortran were used: CGPACK, implementing cellular automata (CA) using Fortran coarrays, and ParaFEM, implementing finite elements (FE) using MPI. The framework implements a two-way concurrent hierarchical information exchange between the structural level (FE) and the microstructure (CA). MPI to coarrays interface and data structures are described. The CAFE framework is used to predict transgranular cleavage propagation in a polycrystalline iron round bar under tension. Novel results enabled by this CAFE framework include simulation of progressive cleavage propagation through individual grains and across grain boundaries, and emergence of a macro-crack from merging of cracks on preferentially oriented cleavage planes in individual crystals. Nearly ideal strong scaling up to at least tens of thousands of cores was demonstrated by CGPACK and by ParaFEM in isolation in prior work on Cray XE6. Cray XC30 and XC40 platforms and CrayPAT profiling were used in this work. Initially the strong scaling limit of hybrid CGPACK/ParaFEM CAFE model was 2000 cores. After replacing all-to-all communication patterns with the nearest neighbour algorithms the strong scaling limit on Cray XC30 was increased to 7000 cores. TAU profiling on non-Cray systems identified deficiencies in Intel Fortran 16 optimisation of remote coarray operations. Finally, coarray synchronisation challenges and opportunities for thread parallelisation in CA are discussed.
2017
- AbstractURLBibTeXEndNoteDOINonlinear homogenisation of trabecular bone: Effect of solid phase constitutive model. Levrero-Florencio, Francesc; Manda, Krishnagoud; Margetts, Lee; Pankaj, Pankaj (2017). 231(5) 405-414.Micro-finite element models have been extensively employed to evaluate the elastic properties of trabecular bone and, to a limited extent, its yield behaviour. The macroscopic stiffness tensor and yield surface are of special interest since they are essential in the prediction of bone strength and stability of implants at the whole bone level. While macroscopic elastic properties are now well understood, yield and post-yield properties are not. The aim of this study is to shed some light on what the effect of the solid phase yield criterion is on the macroscopic yield of trabecular bone for samples with different microstructure. Three samples with very different density were subjected to a large set of apparent load cases (which is important since physiological loading is complex and can have multiple components in stress or strain space) with two different solid phase yield criteria: Drucker–Prager and eccentric–ellipsoid. The study found that these two criteria led to small differences in the macroscopic yield strains for most load cases except for those that were compression-dominated; in these load cases, the yield strains for the Drucker–Prager criterion were significantly higher. Higher density samples resulted in higher differences between the two criteria. This work provides a comprehensive assessment of the effect of two different solid phase yield criteria on the macroscopic yield strains of trabecular bone, for a wide range of load cases, and for samples with different morphology.
@article{doi:10.1177/0954411916676220,
abstract = {Micro-finite element models have been extensively employed to evaluate the elastic properties of trabecular bone and, to a limited extent, its yield behaviour. The macroscopic stiffness tensor and yield surface are of special interest since they are essential in the prediction of bone strength and stability of implants at the whole bone level. While macroscopic elastic properties are now well understood, yield and post-yield properties are not. The aim of this study is to shed some light on what the effect of the solid phase yield criterion is on the macroscopic yield of trabecular bone for samples with different microstructure. Three samples with very different density were subjected to a large set of apparent load cases (which is important since physiological loading is complex and can have multiple components in stress or strain space) with two different solid phase yield criteria: Drucker–Prager and eccentric–ellipsoid. The study found that these two criteria led to small differences in the macroscopic yield strains for most load cases except for those that were compression-dominated; in these load cases, the yield strains for the Drucker–Prager criterion were significantly higher. Higher density samples resulted in higher differences between the two criteria. This work provides a comprehensive assessment of the effect of two different solid phase yield criteria on the macroscopic yield strains of trabecular bone, for a wide range of load cases, and for samples with different morphology.},
author = {Levrero-Florencio, Francesc and Manda, Krishnagoud and Margetts, Lee and Pankaj, Pankaj},
journal = {Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine},
keywords = {myown},
note = {PMID: 28427317},
number = 5,
pages = {405-414},
title = {Nonlinear homogenisation of trabecular bone: Effect of solid phase constitutive model},
volume = 231,
year = 2017
}%0 Journal Article
%1 doi:10.1177/0954411916676220
%A Levrero-Florencio, Francesc
%A Manda, Krishnagoud
%A Margetts, Lee
%A Pankaj, Pankaj
%D 2017
%J Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine
%N 5
%P 405-414
%R 10.1177/0954411916676220
%T Nonlinear homogenisation of trabecular bone: Effect of solid phase constitutive model
%U https://tinyurl.com/y7auu8e8
%V 231
%X Micro-finite element models have been extensively employed to evaluate the elastic properties of trabecular bone and, to a limited extent, its yield behaviour. The macroscopic stiffness tensor and yield surface are of special interest since they are essential in the prediction of bone strength and stability of implants at the whole bone level. While macroscopic elastic properties are now well understood, yield and post-yield properties are not. The aim of this study is to shed some light on what the effect of the solid phase yield criterion is on the macroscopic yield of trabecular bone for samples with different microstructure. Three samples with very different density were subjected to a large set of apparent load cases (which is important since physiological loading is complex and can have multiple components in stress or strain space) with two different solid phase yield criteria: Drucker–Prager and eccentric–ellipsoid. The study found that these two criteria led to small differences in the macroscopic yield strains for most load cases except for those that were compression-dominated; in these load cases, the yield strains for the Drucker–Prager criterion were significantly higher. Higher density samples resulted in higher differences between the two criteria. This work provides a comprehensive assessment of the effect of two different solid phase yield criteria on the macroscopic yield strains of trabecular bone, for a wide range of load cases, and for samples with different morphology. - AbstractURLBibTeXEndNoteDOIEffect of including damage at the tissue level in the nonlinear homogenisation of trabecular bone. Levrero-Florencio, Francesc; Manda, Krishnagoud; Margetts, Lee; Pankaj, Pankaj (2017). 16(5) 1681--1695.Being able to predict bone fracture or implant stability needs a proper constitutive model of trabecular bone at the macroscale in multiaxial, non-monotonic loading modes. Its macroscopic damage behaviour has been investigated experimentally in the past, mostly with the restriction of uniaxial cyclic loading experiments for different samples, which does not allow for the investigation of several load cases in the same sample as damage in one direction may affect the behaviour in other directions. Homogenised finite element models of whole bones have the potential to assess complicated scenarios and thus improve clinical predictions. The aim of this study is to use a homogenisation-based multiscale procedure to upscale the damage behaviour of bone from an assumed solid phase constitutive law and investigate its multiaxial behaviour for the first time. Twelve cubic specimens were each submitted to nine proportional strain histories by using a parallel code developed in-house. Evolution of post-elastic properties for trabecular bone was assessed for a small range of macroscopic plastic strains in these nine load cases. Damage evolution was found to be non-isotropic, and both damage and hardening were found to depend on the loading mode (tensile, compression or shear); both were characterised by linear laws with relatively high coefficients of determination. It is expected that the knowledge of the macroscopic behaviour of trabecular bone gained in this study will help in creating more precise continuum FE models of whole bones that improve clinical predictions.
@article{Levrero-Florencio2017,
abstract = {Being able to predict bone fracture or implant stability needs a proper constitutive model of trabecular bone at the macroscale in multiaxial, non-monotonic loading modes. Its macroscopic damage behaviour has been investigated experimentally in the past, mostly with the restriction of uniaxial cyclic loading experiments for different samples, which does not allow for the investigation of several load cases in the same sample as damage in one direction may affect the behaviour in other directions. Homogenised finite element models of whole bones have the potential to assess complicated scenarios and thus improve clinical predictions. The aim of this study is to use a homogenisation-based multiscale procedure to upscale the damage behaviour of bone from an assumed solid phase constitutive law and investigate its multiaxial behaviour for the first time. Twelve cubic specimens were each submitted to nine proportional strain histories by using a parallel code developed in-house. Evolution of post-elastic properties for trabecular bone was assessed for a small range of macroscopic plastic strains in these nine load cases. Damage evolution was found to be non-isotropic, and both damage and hardening were found to depend on the loading mode (tensile, compression or shear); both were characterised by linear laws with relatively high coefficients of determination. It is expected that the knowledge of the macroscopic behaviour of trabecular bone gained in this study will help in creating more precise continuum FE models of whole bones that improve clinical predictions.},
author = {Levrero-Florencio, Francesc and Manda, Krishnagoud and Margetts, Lee and Pankaj, Pankaj},
journal = {Biomechanics and Modeling in Mechanobiology},
keywords = {myown},
month = {oct},
number = 5,
pages = {1681--1695},
title = {Effect of including damage at the tissue level in the nonlinear homogenisation of trabecular bone},
volume = 16,
year = 2017
}%0 Journal Article
%1 Levrero-Florencio2017
%A Levrero-Florencio, Francesc
%A Manda, Krishnagoud
%A Margetts, Lee
%A Pankaj, Pankaj
%D 2017
%J Biomechanics and Modeling in Mechanobiology
%N 5
%P 1681--1695
%R 10.1007/s10237-017-0913-7
%T Effect of including damage at the tissue level in the nonlinear homogenisation of trabecular bone
%U https://tinyurl.com/y9z6shef
%V 16
%X Being able to predict bone fracture or implant stability needs a proper constitutive model of trabecular bone at the macroscale in multiaxial, non-monotonic loading modes. Its macroscopic damage behaviour has been investigated experimentally in the past, mostly with the restriction of uniaxial cyclic loading experiments for different samples, which does not allow for the investigation of several load cases in the same sample as damage in one direction may affect the behaviour in other directions. Homogenised finite element models of whole bones have the potential to assess complicated scenarios and thus improve clinical predictions. The aim of this study is to use a homogenisation-based multiscale procedure to upscale the damage behaviour of bone from an assumed solid phase constitutive law and investigate its multiaxial behaviour for the first time. Twelve cubic specimens were each submitted to nine proportional strain histories by using a parallel code developed in-house. Evolution of post-elastic properties for trabecular bone was assessed for a small range of macroscopic plastic strains in these nine load cases. Damage evolution was found to be non-isotropic, and both damage and hardening were found to depend on the loading mode (tensile, compression or shear); both were characterised by linear laws with relatively high coefficients of determination. It is expected that the knowledge of the macroscopic behaviour of trabecular bone gained in this study will help in creating more precise continuum FE models of whole bones that improve clinical predictions.
2016
- AbstractURLBibTeXEndNoteDOIUse of massively parallel computing to improve modelling accuracy within the nuclear sector. Evans, L; Arregui-Mena, J; Mummery, P; Akers, R; Surrey, E; Shterenlikht, A; Broggi, M; Margetts, L (2016). 10(2)The extreme environments found within the nuclear sector impose large safety factors on modelling analyses to ensure components operate in their desired manner. Improving analysis accuracy has clear value of increasing the design space that could lead to greater efficiency and reliability.Novel materials for new reactor designs often exhibit non-linear behaviour; additionally material properties evolve due to in-service damage a combination that is difficult to model accurately. To better describe these complex behaviours a range of modelling techniques previously under-pursued due to computational expense are being developed.This work presents recent advancements in three techniques: Uncertainty quantification (UQ); Cellular automata finite element (CAFE); Image based finite element methods (IBFEM). Case studies are presented demonstrating their suitability for use in nuclear engineering made possible by advancements in parallel computing hardware that is projected to be available for industry within the next decade costing of the order of $100k.
@article{IJM121,
abstract = {The extreme environments found within the nuclear sector impose large safety factors on modelling analyses to ensure components operate in their desired manner. Improving analysis accuracy has clear value of increasing the design space that could lead to greater efficiency and reliability.Novel materials for new reactor designs often exhibit non-linear behaviour; additionally material properties evolve due to in-service damage a combination that is difficult to model accurately. To better describe these complex behaviours a range of modelling techniques previously under-pursued due to computational expense are being developed.This work presents recent advancements in three techniques: Uncertainty quantification (UQ); Cellular automata finite element (CAFE); Image based finite element methods (IBFEM). Case studies are presented demonstrating their suitability for use in nuclear engineering made possible by advancements in parallel computing hardware that is projected to be available for industry within the next decade costing of the order of $100k.},
author = {Evans, L and Arregui-Mena, J and Mummery, P and Akers, R and Surrey, E and Shterenlikht, A and Broggi, M and Margetts, L},
journal = {The International Journal of Multiphysics},
keywords = {myown},
number = 2,
title = {Use of massively parallel computing to improve modelling accuracy within the nuclear sector},
volume = 10,
year = 2016
}%0 Journal Article
%1 IJM121
%A Evans, L
%A Arregui-Mena, J
%A Mummery, P
%A Akers, R
%A Surrey, E
%A Shterenlikht, A
%A Broggi, M
%A Margetts, L
%D 2016
%J The International Journal of Multiphysics
%N 2
%R 10.21152/1750-9548.10.2.215
%T Use of massively parallel computing to improve modelling accuracy within the nuclear sector
%U https://tinyurl.com/y9jwvet5
%V 10
%X The extreme environments found within the nuclear sector impose large safety factors on modelling analyses to ensure components operate in their desired manner. Improving analysis accuracy has clear value of increasing the design space that could lead to greater efficiency and reliability.Novel materials for new reactor designs often exhibit non-linear behaviour; additionally material properties evolve due to in-service damage a combination that is difficult to model accurately. To better describe these complex behaviours a range of modelling techniques previously under-pursued due to computational expense are being developed.This work presents recent advancements in three techniques: Uncertainty quantification (UQ); Cellular automata finite element (CAFE); Image based finite element methods (IBFEM). Case studies are presented demonstrating their suitability for use in nuclear engineering made possible by advancements in parallel computing hardware that is projected to be available for industry within the next decade costing of the order of $100k. - AbstractURLBibTeXEndNoteDOIEvaluating the macroscopic yield behaviour of trabecular bone using a nonlinear homogenisation approach. Levrero-Florencio, Francesc; Margetts, Lee; Sales, Erika; Xie, Shuqiao; Manda, Krishnagoud; Pankaj, Pankaj (2016). 61 384 - 396.Computational homogenisation approaches using high resolution images and finite element (FE) modelling have been extensively employed to evaluate the anisotropic elastic properties of trabecular bone. The aim of this study was to extend its application to characterise the macroscopic yield behaviour of trabecular bone. Twenty trabecular bone samples were scanned using a micro-computed tomography device, converted to voxelised FE meshes and subjected to 160 load cases each (to define a homogenised multiaxial yield surface which represents several possible strain combinations). Simulations were carried out using a parallel code developed in-house. The nonlinear algorithms included both geometrical and material nonlinearities. The study found that for tension-tension and compression-compression regimes in normal strain space, the yield strains have an isotropic behaviour. However, in the tension-compression quadrants, pure shear and combined normal-shear planes, the macroscopic strain norms at yield have a relatively large variation. Also, our treatment of clockwise and counter-clockwise shears as separate loading cases showed that the differences in these two directions cannot be ignored. A quadric yield surface, used to evaluate the goodness of fit, showed that an isotropic criterion adequately represents yield in strain space though errors with orthotropic and anisotropic criteria are slightly smaller. Consequently, although the isotropic yield surface presents itself as the most suitable assumption, it may not work well for all load cases. This work provides a comprehensive assessment of material symmetries of trabecular bone at the macroscale and describes in detail its macroscopic yield and its underlying microscopic mechanics.
@article{LEVREROFLORENCIO2016384,
abstract = {Computational homogenisation approaches using high resolution images and finite element (FE) modelling have been extensively employed to evaluate the anisotropic elastic properties of trabecular bone. The aim of this study was to extend its application to characterise the macroscopic yield behaviour of trabecular bone. Twenty trabecular bone samples were scanned using a micro-computed tomography device, converted to voxelised FE meshes and subjected to 160 load cases each (to define a homogenised multiaxial yield surface which represents several possible strain combinations). Simulations were carried out using a parallel code developed in-house. The nonlinear algorithms included both geometrical and material nonlinearities. The study found that for tension-tension and compression-compression regimes in normal strain space, the yield strains have an isotropic behaviour. However, in the tension-compression quadrants, pure shear and combined normal-shear planes, the macroscopic strain norms at yield have a relatively large variation. Also, our treatment of clockwise and counter-clockwise shears as separate loading cases showed that the differences in these two directions cannot be ignored. A quadric yield surface, used to evaluate the goodness of fit, showed that an isotropic criterion adequately represents yield in strain space though errors with orthotropic and anisotropic criteria are slightly smaller. Consequently, although the isotropic yield surface presents itself as the most suitable assumption, it may not work well for all load cases. This work provides a comprehensive assessment of material symmetries of trabecular bone at the macroscale and describes in detail its macroscopic yield and its underlying microscopic mechanics.},
author = {Levrero-Florencio, Francesc and Margetts, Lee and Sales, Erika and Xie, Shuqiao and Manda, Krishnagoud and Pankaj, Pankaj},
journal = {Journal of the Mechanical Behavior of Biomedical Materials},
keywords = {myown},
pages = {384 - 396},
title = {Evaluating the macroscopic yield behaviour of trabecular bone using a nonlinear homogenisation approach},
volume = 61,
year = 2016
}%0 Journal Article
%1 LEVREROFLORENCIO2016384
%A Levrero-Florencio, Francesc
%A Margetts, Lee
%A Sales, Erika
%A Xie, Shuqiao
%A Manda, Krishnagoud
%A Pankaj, Pankaj
%D 2016
%J Journal of the Mechanical Behavior of Biomedical Materials
%P 384 - 396
%R https://doi.org/10.1016/j.jmbbm.2016.04.008
%T Evaluating the macroscopic yield behaviour of trabecular bone using a nonlinear homogenisation approach
%U https://tinyurl.com/ycvlexbz
%V 61
%X Computational homogenisation approaches using high resolution images and finite element (FE) modelling have been extensively employed to evaluate the anisotropic elastic properties of trabecular bone. The aim of this study was to extend its application to characterise the macroscopic yield behaviour of trabecular bone. Twenty trabecular bone samples were scanned using a micro-computed tomography device, converted to voxelised FE meshes and subjected to 160 load cases each (to define a homogenised multiaxial yield surface which represents several possible strain combinations). Simulations were carried out using a parallel code developed in-house. The nonlinear algorithms included both geometrical and material nonlinearities. The study found that for tension-tension and compression-compression regimes in normal strain space, the yield strains have an isotropic behaviour. However, in the tension-compression quadrants, pure shear and combined normal-shear planes, the macroscopic strain norms at yield have a relatively large variation. Also, our treatment of clockwise and counter-clockwise shears as separate loading cases showed that the differences in these two directions cannot be ignored. A quadric yield surface, used to evaluate the goodness of fit, showed that an isotropic criterion adequately represents yield in strain space though errors with orthotropic and anisotropic criteria are slightly smaller. Consequently, although the isotropic yield surface presents itself as the most suitable assumption, it may not work well for all load cases. This work provides a comprehensive assessment of material symmetries of trabecular bone at the macroscale and describes in detail its macroscopic yield and its underlying microscopic mechanics.
2015
- AbstractURLBibTeXEndNoteDOISpatial variability in the coefficient of thermal expansion induces pre-service stresses in computer models of virgin Gilsocarbon bricks. Arregui Mena, Jose; Margetts, Lee; Griffiths, D V; Lever, Louise; Hall, Graham; Mummery, Paul (2015). 465 793--804.In this paper, the authors test the hypothesis that tiny spatial variations in material properties may lead to significant pre-service stresses in virgin graphite bricks. To do this, they have customized ParaFEM, an open source parallel finite element package, adding support for stochastic thermo-mechanical analysis using the Monte Carlo Simulation method. For an Advanced Gas-cooled Reactor brick, three heating cases have been examined: a uniform temperature change; a uniform temperature gradient applied through the thickness of the brick and a simulated temperature profile from an operating reactor. Results are compared for mean and stochastic properties. These show that, for the proof-of-concept analyses carried out, the pre-service von Mises stress is around twenty times higher when spatial variability of material properties is introduced. The paper demonstrates that thermal gradients coupled with material incompatibilities may be important in the generation of stress in nuclear graphite reactor bricks. Tiny spatial variations in coefficient of thermal expansion (CTE) and Young�s modulus can lead to the presence of thermal stresses in bricks that are free to expand
@article{0bf4b0928e15461c901a40a121e0b369,
abstract = {In this paper, the authors test the hypothesis that tiny spatial variations in material properties may lead to significant pre-service stresses in virgin graphite bricks. To do this, they have customized ParaFEM, an open source parallel finite element package, adding support for stochastic thermo-mechanical analysis using the Monte Carlo Simulation method. For an Advanced Gas-cooled Reactor brick, three heating cases have been examined: a uniform temperature change; a uniform temperature gradient applied through the thickness of the brick and a simulated temperature profile from an operating reactor. Results are compared for mean and stochastic properties. These show that, for the proof-of-concept analyses carried out, the pre-service von Mises stress is around twenty times higher when spatial variability of material properties is introduced. The paper demonstrates that thermal gradients coupled with material incompatibilities may be important in the generation of stress in nuclear graphite reactor bricks. Tiny spatial variations in coefficient of thermal expansion (CTE) and Young�s modulus can lead to the presence of thermal stresses in bricks that are free to expand},
author = {Arregui Mena, Jose and Margetts, Lee and Griffiths, D V and Lever, Louise and Hall, Graham and Mummery, Paul},
journal = {Journal of Nuclear Materials},
keywords = {myown},
pages = {793--804},
publisher = {Elsevier BV},
title = {Spatial variability in the coefficient of thermal expansion induces pre-service stresses in computer models of virgin Gilsocarbon bricks},
volume = 465,
year = 2015
}%0 Journal Article
%1 0bf4b0928e15461c901a40a121e0b369
%A Arregui Mena, Jose
%A Margetts, Lee
%A Griffiths, D V
%A Lever, Louise
%A Hall, Graham
%A Mummery, Paul
%D 2015
%I Elsevier BV
%J Journal of Nuclear Materials
%P 793--804
%R 10.1016/j.jnucmat.2015.05.058
%T Spatial variability in the coefficient of thermal expansion induces pre-service stresses in computer models of virgin Gilsocarbon bricks
%U https://tinyurl.com/j5srsyy
%V 465
%X In this paper, the authors test the hypothesis that tiny spatial variations in material properties may lead to significant pre-service stresses in virgin graphite bricks. To do this, they have customized ParaFEM, an open source parallel finite element package, adding support for stochastic thermo-mechanical analysis using the Monte Carlo Simulation method. For an Advanced Gas-cooled Reactor brick, three heating cases have been examined: a uniform temperature change; a uniform temperature gradient applied through the thickness of the brick and a simulated temperature profile from an operating reactor. Results are compared for mean and stochastic properties. These show that, for the proof-of-concept analyses carried out, the pre-service von Mises stress is around twenty times higher when spatial variability of material properties is introduced. The paper demonstrates that thermal gradients coupled with material incompatibilities may be important in the generation of stress in nuclear graphite reactor bricks. Tiny spatial variations in coefficient of thermal expansion (CTE) and Young�s modulus can lead to the presence of thermal stresses in bricks that are free to expand
2014
- AbstractBibTeXEndNoteDOIThermal characterisation of ceramic/metal joining techniques for fusion applications using X-ray tomography. Evans, Llion Marc; Margetts, Lee; Casalegno, Valentina; Leonard, Fabien; Lowe, Tristan; Lee, Peter D; Schmidt, M; Mummery, Paul M (2014). 89(6) 826--836.This work investigates the thermal performance of four novel CFC�Cu joining techniques. Two involve direct casting and brazing of Cu onto a chromium modified CFC surface, the other two pre-coat a brazing alloy with chromium using galvanisation and sputtering processes. The chromium carbide layer at the interface has been shown to improve adhesion. Thermal conductivity across the join interface was measured by laser flash analysis. X-ray tomography was performed to investigate micro-structures that might influence the thermal behaviour. It was found that thermal conductivity varied by up to 72%. Quantification of the X-ray tomography data showed that the dominant feature in reducing thermal conductivity was the lateral spread of voids at the interface. Correlations were made to estimate the extent of this effect.
@article{58388f4454924040b107927c64a39844,
abstract = {This work investigates the thermal performance of four novel CFC�Cu joining techniques. Two involve direct casting and brazing of Cu onto a chromium modified CFC surface, the other two pre-coat a brazing alloy with chromium using galvanisation and sputtering processes. The chromium carbide layer at the interface has been shown to improve adhesion. Thermal conductivity across the join interface was measured by laser flash analysis. X-ray tomography was performed to investigate micro-structures that might influence the thermal behaviour. It was found that thermal conductivity varied by up to 72%. Quantification of the X-ray tomography data showed that the dominant feature in reducing thermal conductivity was the lateral spread of voids at the interface. Correlations were made to estimate the extent of this effect.},
author = {Evans, Llion Marc and Margetts, Lee and Casalegno, Valentina and Leonard, Fabien and Lowe, Tristan and Lee, Peter D and Schmidt, M and Mummery, Paul M},
journal = {Fusion Engineering and Design},
keywords = {myown},
month = 6,
number = 6,
pages = {826--836},
publisher = {Elsevier BV},
title = {Thermal characterisation of ceramic/metal joining techniques for fusion applications using X-ray tomography},
volume = 89,
year = 2014
}%0 Journal Article
%1 58388f4454924040b107927c64a39844
%A Evans, Llion Marc
%A Margetts, Lee
%A Casalegno, Valentina
%A Leonard, Fabien
%A Lowe, Tristan
%A Lee, Peter D
%A Schmidt, M
%A Mummery, Paul M
%D 2014
%I Elsevier BV
%J Fusion Engineering and Design
%N 6
%P 826--836
%R 10.1016/j.fusengdes.2014.05.002
%T Thermal characterisation of ceramic/metal joining techniques for fusion applications using X-ray tomography
%V 89
%X This work investigates the thermal performance of four novel CFC�Cu joining techniques. Two involve direct casting and brazing of Cu onto a chromium modified CFC surface, the other two pre-coat a brazing alloy with chromium using galvanisation and sputtering processes. The chromium carbide layer at the interface has been shown to improve adhesion. Thermal conductivity across the join interface was measured by laser flash analysis. X-ray tomography was performed to investigate micro-structures that might influence the thermal behaviour. It was found that thermal conductivity varied by up to 72%. Quantification of the X-ray tomography data showed that the dominant feature in reducing thermal conductivity was the lateral spread of voids at the interface. Correlations were made to estimate the extent of this effect.
2011
- AbstractURLBibTeXEndNoteDOISimulating sauropod manus-only trackway formation using finite-element analysis. Falkingham, P. L.; Bates, K. T.; Margetts, L.; Manning, P. L. (2011). 7(1) 142--145.The occurrence of sauropod manus-only trackways in the fossil record is poorly understood, limiting their potential for understanding loco-motor mechanics and behaviour. To elucidate possible causative mechanisms for these traces, finite-element analyses were conducted to model the indentation of substrate by the feet of Diplodocus and Brachiosaurus. Loading was accomplished by applying mass, centre of mass and foot surface area predictions to a range of substrates to model track formation. Experimental results show that when pressure differs between manus and pes, as determined by the distribution of weight and size of respective autopodia, there is a range of substrate shear strengths for which only the manus (or pes) produce enough pressure to deform the substrate, generating a track. If existing reconstructions of sauropod feet and mass distributions are correct, then different taxa will produce either manus-or pes-only trackways in specific substrates. As a result of this work, it is predicted that the occurrence of manus-or pes-only trackways may show geo-temporal correlation with the occurrence of body fossils of specific taxa. This journal is circledC 2010 The Royal Society.
@article{b2128263f01146a7accbe6ae8cd0aaa7,
abstract = {The occurrence of sauropod manus-only trackways in the fossil record is poorly understood, limiting their potential for understanding loco-motor mechanics and behaviour. To elucidate possible causative mechanisms for these traces, finite-element analyses were conducted to model the indentation of substrate by the feet of Diplodocus and Brachiosaurus. Loading was accomplished by applying mass, centre of mass and foot surface area predictions to a range of substrates to model track formation. Experimental results show that when pressure differs between manus and pes, as determined by the distribution of weight and size of respective autopodia, there is a range of substrate shear strengths for which only the manus (or pes) produce enough pressure to deform the substrate, generating a track. If existing reconstructions of sauropod feet and mass distributions are correct, then different taxa will produce either manus-or pes-only trackways in specific substrates. As a result of this work, it is predicted that the occurrence of manus-or pes-only trackways may show geo-temporal correlation with the occurrence of body fossils of specific taxa. This journal is circledC 2010 The Royal Society.},
author = {Falkingham, P. L. and Bates, K. T. and Margetts, L. and Manning, P. L.},
journal = {Biology Letters},
keywords = {myown},
month = 2,
number = 1,
pages = {142--145},
publisher = {Royal Society of London},
title = {Simulating sauropod manus-only trackway formation using finite-element analysis},
volume = 7,
year = 2011
}%0 Journal Article
%1 b2128263f01146a7accbe6ae8cd0aaa7
%A Falkingham, P. L.
%A Bates, K. T.
%A Margetts, L.
%A Manning, P. L.
%D 2011
%I Royal Society of London
%J Biology Letters
%N 1
%P 142--145
%R 10.1098/rsbl.2010.0403
%T Simulating sauropod manus-only trackway formation using finite-element analysis
%U https://tinyurl.com/ycnzmaj3
%V 7
%X The occurrence of sauropod manus-only trackways in the fossil record is poorly understood, limiting their potential for understanding loco-motor mechanics and behaviour. To elucidate possible causative mechanisms for these traces, finite-element analyses were conducted to model the indentation of substrate by the feet of Diplodocus and Brachiosaurus. Loading was accomplished by applying mass, centre of mass and foot surface area predictions to a range of substrates to model track formation. Experimental results show that when pressure differs between manus and pes, as determined by the distribution of weight and size of respective autopodia, there is a range of substrate shear strengths for which only the manus (or pes) produce enough pressure to deform the substrate, generating a track. If existing reconstructions of sauropod feet and mass distributions are correct, then different taxa will produce either manus-or pes-only trackways in specific substrates. As a result of this work, it is predicted that the occurrence of manus-or pes-only trackways may show geo-temporal correlation with the occurrence of body fossils of specific taxa. This journal is circledC 2010 The Royal Society. - AbstractURLBibTeXEndNoteDOIThe 'Goldilocks' effect: Preservation bias in vertebrate track assemblages. Falkingham, P. L.; Bates, K. T.; Margetts, L.; Manning, P. L. (2011). 8(61) 1142--1154.Finite-element analysis was used to investigate the extent of bias in the ichnological fossil record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a range of substrate conditions. Outlines of autopodia were generated based upon osteology and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent to the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant. Ideal, semi-infinite elastic-plastic substrates displayed a 'Goldilocks' quality where only a narrow range of loads could produce tracks, given that small animals failed to indent the substrate, and larger animals would be unable to traverse the area without becoming mired. If a firm subsurface layer is assumed, a more complete assemblage is possible, though there is a strong bias towards larger, heavier animals. The depths of fossil tracks within an assemblage may indicate thicknesses of mechanically distinct substrate layers at the time of track formation, even when the lithified strata appear compositionally homogeneous. This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicators in terms of inferring substrate conditions at the time of track formation. Additionally, simulated undertracks are examined, and it is shown that complex deformation beneath the foot may not be indicative of limb kinematics as has been previously interpreted, but instead ridges and undulations at the base of a track may be a function of sediment displacement vectors and pedal morphology. circledC 2011 The Royal Society.
@article{3c67686a5eab4b88b9b47bf1d42d2f8e,
abstract = {Finite-element analysis was used to investigate the extent of bias in the ichnological fossil record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a range of substrate conditions. Outlines of autopodia were generated based upon osteology and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent to the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant. Ideal, semi-infinite elastic-plastic substrates displayed a 'Goldilocks' quality where only a narrow range of loads could produce tracks, given that small animals failed to indent the substrate, and larger animals would be unable to traverse the area without becoming mired. If a firm subsurface layer is assumed, a more complete assemblage is possible, though there is a strong bias towards larger, heavier animals. The depths of fossil tracks within an assemblage may indicate thicknesses of mechanically distinct substrate layers at the time of track formation, even when the lithified strata appear compositionally homogeneous. This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicators in terms of inferring substrate conditions at the time of track formation. Additionally, simulated undertracks are examined, and it is shown that complex deformation beneath the foot may not be indicative of limb kinematics as has been previously interpreted, but instead ridges and undulations at the base of a track may be a function of sediment displacement vectors and pedal morphology. circledC 2011 The Royal Society.},
author = {Falkingham, P. L. and Bates, K. T. and Margetts, L. and Manning, P. L.},
journal = {Journal of the Royal Society Interface},
keywords = {myown},
month = 8,
number = 61,
pages = {1142--1154},
publisher = {The Royal Society Publishing},
title = {The 'Goldilocks' effect: Preservation bias in vertebrate track assemblages},
volume = 8,
year = 2011
}%0 Journal Article
%1 3c67686a5eab4b88b9b47bf1d42d2f8e
%A Falkingham, P. L.
%A Bates, K. T.
%A Margetts, L.
%A Manning, P. L.
%D 2011
%I The Royal Society Publishing
%J Journal of the Royal Society Interface
%N 61
%P 1142--1154
%R 10.1098/rsif.2010.0634
%T The 'Goldilocks' effect: Preservation bias in vertebrate track assemblages
%U https://tinyurl.com/ycj8hulw
%V 8
%X Finite-element analysis was used to investigate the extent of bias in the ichnological fossil record attributable to body mass. Virtual tracks were simulated for four dinosaur taxa of different sizes (Struthiomimus, Tyrannosaurus, Brachiosaurus and Edmontosaurus), in a range of substrate conditions. Outlines of autopodia were generated based upon osteology and published soft-tissue reconstructions. Loads were applied vertically to the feet equivalent to the weight of the animal, and distributed accordingly to fore- and hindlimbs where relevant. Ideal, semi-infinite elastic-plastic substrates displayed a 'Goldilocks' quality where only a narrow range of loads could produce tracks, given that small animals failed to indent the substrate, and larger animals would be unable to traverse the area without becoming mired. If a firm subsurface layer is assumed, a more complete assemblage is possible, though there is a strong bias towards larger, heavier animals. The depths of fossil tracks within an assemblage may indicate thicknesses of mechanically distinct substrate layers at the time of track formation, even when the lithified strata appear compositionally homogeneous. This work increases the effectiveness of using vertebrate tracks as palaeoenvironmental indicators in terms of inferring substrate conditions at the time of track formation. Additionally, simulated undertracks are examined, and it is shown that complex deformation beneath the foot may not be indicative of limb kinematics as has been previously interpreted, but instead ridges and undulations at the base of a track may be a function of sediment displacement vectors and pedal morphology. circledC 2011 The Royal Society.
2010
- AbstractURLBibTeXEndNoteDOIFossil vertebrate tracks as paleopenetrometers: Confounding effects of foot morphology. Falkingham, P. L.; Margetts, L.; Manning, P. L. (2010). 25(6) 356--360.The depth to which a vertebrate track is indented can provide a wealth of information, being a direct result of the weight, duty factor, and limb kinematics of the animal as well as media ( substrate or sediment) consistency. In order to recreate the formation of the track and elucidate media consistency at the time of track formation, such factors as animal mass, duty factor, and foot morphology must be taken into consideration. This study uses Finite Element Analysis and physical modeling to demonstrate for the first time that the shape of the foot is an important factor that influences the depth to which the sediment is penetrated. In cohesive sediment, less compact morphology allows more sediment to move vertically upwards at the edges of the foot, dissipating force at the surface, and retarding transmission of load vertically down into the sediment. The reverse of this effect is seen in noncohesive sediment. Foot morphology, therefore, has a direct impact on preservation potential, both of surface tracks and undertracks, that is irrespective of the pressure exerted on the sediment surface by the foot and independent of mass and duty factor. Copyright circledC 2010, SEPM (Society for Sedimentary Geology).
@article{3066644fd8924e0abcc8335fe8205506,
abstract = {The depth to which a vertebrate track is indented can provide a wealth of information, being a direct result of the weight, duty factor, and limb kinematics of the animal as well as media ( substrate or sediment) consistency. In order to recreate the formation of the track and elucidate media consistency at the time of track formation, such factors as animal mass, duty factor, and foot morphology must be taken into consideration. This study uses Finite Element Analysis and physical modeling to demonstrate for the first time that the shape of the foot is an important factor that influences the depth to which the sediment is penetrated. In cohesive sediment, less compact morphology allows more sediment to move vertically upwards at the edges of the foot, dissipating force at the surface, and retarding transmission of load vertically down into the sediment. The reverse of this effect is seen in noncohesive sediment. Foot morphology, therefore, has a direct impact on preservation potential, both of surface tracks and undertracks, that is irrespective of the pressure exerted on the sediment surface by the foot and independent of mass and duty factor. Copyright circledC 2010, SEPM (Society for Sedimentary Geology).},
author = {Falkingham, P. L. and Margetts, L. and Manning, P. L.},
journal = {Palaios},
keywords = {myown},
month = 6,
note = {Natural Environment Research Council (NERC NER/S/A/2006/14033 Engineering and Physical Sciences Research Council (EPSRC EPF055595-1)},
number = 6,
pages = {356--360},
publisher = {SEPM Society for Sedimentary Geology},
title = {Fossil vertebrate tracks as paleopenetrometers: Confounding effects of foot morphology},
volume = 25,
year = 2010
}%0 Journal Article
%1 3066644fd8924e0abcc8335fe8205506
%A Falkingham, P. L.
%A Margetts, L.
%A Manning, P. L.
%D 2010
%I SEPM Society for Sedimentary Geology
%J Palaios
%N 6
%P 356--360
%R 10.2110/palo.2009.p09-164r
%T Fossil vertebrate tracks as paleopenetrometers: Confounding effects of foot morphology
%U https://tinyurl.com/y79m9jsd
%V 25
%X The depth to which a vertebrate track is indented can provide a wealth of information, being a direct result of the weight, duty factor, and limb kinematics of the animal as well as media ( substrate or sediment) consistency. In order to recreate the formation of the track and elucidate media consistency at the time of track formation, such factors as animal mass, duty factor, and foot morphology must be taken into consideration. This study uses Finite Element Analysis and physical modeling to demonstrate for the first time that the shape of the foot is an important factor that influences the depth to which the sediment is penetrated. In cohesive sediment, less compact morphology allows more sediment to move vertically upwards at the edges of the foot, dissipating force at the surface, and retarding transmission of load vertically down into the sediment. The reverse of this effect is seen in noncohesive sediment. Foot morphology, therefore, has a direct impact on preservation potential, both of surface tracks and undertracks, that is irrespective of the pressure exerted on the sediment surface by the foot and independent of mass and duty factor. Copyright circledC 2010, SEPM (Society for Sedimentary Geology).
2009
- AbstractURLBibTeXEndNoteDOIReinterpretation of palmate and semi-palmate (webbed) fossil tracks; insights from finite element modelling. Falkingham, Peter L.; Margetts, Lee; Smith, Ian M.; Manning, Phillip L. (2009). 271(1-2) 69--76.A track from the Late Cretaceous previously described as being generated by a semi-palmate bird was studied with the aid of high resolution laser scanning. Substrate conditions at the time of track formation were diagnosed (fine-grained, soft, waterlogged sediment) and used to constrain a finite element track simulator. The indentation of a non-webbed virtual tridactyl foot in such conditions created a resultant track with features analogous to 'webbing' between digits. This 'webbing' was a function of sediment deformation and subsequent failure in 3D, specific to rheology. Variation of substrate conditions and interdigital angle was incrementally stepped. Apparent webbing impressions were clearly developed only within a limited range of sediment conditions and pedal geometry. The implications of this work are that descriptions of 'webbed' tracks should account for the possibility that webbing was indirectly formed through sediment failure and not necessarily the direct impression of a webbed foot. Additionally, dating the earliest occurrence of webbed feet in the fossil record, and potentially extending phylogenetic ranges, should be treated with caution when based upon evidence from tracks. circledC 2008 Elsevier B.V. All rights reserved.
@article{36f8b0fb06484f52b079af2faac38805,
abstract = {A track from the Late Cretaceous previously described as being generated by a semi-palmate bird was studied with the aid of high resolution laser scanning. Substrate conditions at the time of track formation were diagnosed (fine-grained, soft, waterlogged sediment) and used to constrain a finite element track simulator. The indentation of a non-webbed virtual tridactyl foot in such conditions created a resultant track with features analogous to 'webbing' between digits. This 'webbing' was a function of sediment deformation and subsequent failure in 3D, specific to rheology. Variation of substrate conditions and interdigital angle was incrementally stepped. Apparent webbing impressions were clearly developed only within a limited range of sediment conditions and pedal geometry. The implications of this work are that descriptions of 'webbed' tracks should account for the possibility that webbing was indirectly formed through sediment failure and not necessarily the direct impression of a webbed foot. Additionally, dating the earliest occurrence of webbed feet in the fossil record, and potentially extending phylogenetic ranges, should be treated with caution when based upon evidence from tracks. circledC 2008 Elsevier B.V. All rights reserved.},
author = {Falkingham, Peter L. and Margetts, Lee and Smith, Ian M. and Manning, Phillip L.},
journal = {Palaeogeography, Palaeoclimatology, Palaeoecology},
keywords = {myown},
month = 1,
number = {1-2},
pages = {69--76},
publisher = {Elsevier BV},
title = {Reinterpretation of palmate and semi-palmate (webbed) fossil tracks; insights from finite element modelling},
volume = 271,
year = 2009
}%0 Journal Article
%1 36f8b0fb06484f52b079af2faac38805
%A Falkingham, Peter L.
%A Margetts, Lee
%A Smith, Ian M.
%A Manning, Phillip L.
%D 2009
%I Elsevier BV
%J Palaeogeography, Palaeoclimatology, Palaeoecology
%N 1-2
%P 69--76
%R 10.1016/j.palaeo.2008.09.011
%T Reinterpretation of palmate and semi-palmate (webbed) fossil tracks; insights from finite element modelling
%U https://tinyurl.com/yaemfw59
%V 271
%X A track from the Late Cretaceous previously described as being generated by a semi-palmate bird was studied with the aid of high resolution laser scanning. Substrate conditions at the time of track formation were diagnosed (fine-grained, soft, waterlogged sediment) and used to constrain a finite element track simulator. The indentation of a non-webbed virtual tridactyl foot in such conditions created a resultant track with features analogous to 'webbing' between digits. This 'webbing' was a function of sediment deformation and subsequent failure in 3D, specific to rheology. Variation of substrate conditions and interdigital angle was incrementally stepped. Apparent webbing impressions were clearly developed only within a limited range of sediment conditions and pedal geometry. The implications of this work are that descriptions of 'webbed' tracks should account for the possibility that webbing was indirectly formed through sediment failure and not necessarily the direct impression of a webbed foot. Additionally, dating the earliest occurrence of webbed feet in the fossil record, and potentially extending phylogenetic ranges, should be treated with caution when based upon evidence from tracks. circledC 2008 Elsevier B.V. All rights reserved.
2006
- AbstractURLBibTeXEndNoteDOIThe convergence variability of parallel iterative solvers. Smith, Ian M.; Margetts, Lee (2006). 23(2) 154--165.Purpose - To investigate the cause of a well-known phenomenon associated with a range of parallel iterative solvers - the variability in the number of iterations required to achieve convergence. Design/methodology/approach - The conclusions are based on extensive experiments undertaken using parallel computers. Recently published works are also used to provide additional examples of variability in iteration count. Findings - The variability of iteration counts experienced by parallelised, element-by-element iterative solvers is caused by numerical precision and roundoff. Research limitations/implications - A theoretical examination of the phenomenon may bring to light a methodology in which the iteration count could be limited to the lower end of the variable range - thus reducing solution times. Practical implications - The authors believe that the variability in iteration count described for element-by-element methods presents no real difficulty to the engineering analyst. Originality/value - The paper gives a detailed account of the phenomenon and is useful both to developers of parallel iterative solvers and to the analysts that use them in practice.
@article{adef1dc9b6434265abe469e992b6468e,
abstract = {Purpose - To investigate the cause of a well-known phenomenon associated with a range of parallel iterative solvers - the variability in the number of iterations required to achieve convergence. Design/methodology/approach - The conclusions are based on extensive experiments undertaken using parallel computers. Recently published works are also used to provide additional examples of variability in iteration count. Findings - The variability of iteration counts experienced by parallelised, element-by-element iterative solvers is caused by numerical precision and roundoff. Research limitations/implications - A theoretical examination of the phenomenon may bring to light a methodology in which the iteration count could be limited to the lower end of the variable range - thus reducing solution times. Practical implications - The authors believe that the variability in iteration count described for element-by-element methods presents no real difficulty to the engineering analyst. Originality/value - The paper gives a detailed account of the phenomenon and is useful both to developers of parallel iterative solvers and to the analysts that use them in practice.},
author = {Smith, Ian M. and Margetts, Lee},
journal = {Engineering Computations (Swansea, Wales)},
keywords = {myown},
number = 2,
pages = {154--165},
publisher = {Emerald Group Publishing Ltd.},
title = {The convergence variability of parallel iterative solvers},
volume = 23,
year = 2006
}%0 Journal Article
%1 adef1dc9b6434265abe469e992b6468e
%A Smith, Ian M.
%A Margetts, Lee
%D 2006
%I Emerald Group Publishing Ltd.
%J Engineering Computations (Swansea, Wales)
%N 2
%P 154--165
%R 10.1108/02644400610644522
%T The convergence variability of parallel iterative solvers
%U https://tinyurl.com/yd42ggj5
%V 23
%X Purpose - To investigate the cause of a well-known phenomenon associated with a range of parallel iterative solvers - the variability in the number of iterations required to achieve convergence. Design/methodology/approach - The conclusions are based on extensive experiments undertaken using parallel computers. Recently published works are also used to provide additional examples of variability in iteration count. Findings - The variability of iteration counts experienced by parallelised, element-by-element iterative solvers is caused by numerical precision and roundoff. Research limitations/implications - A theoretical examination of the phenomenon may bring to light a methodology in which the iteration count could be limited to the lower end of the variable range - thus reducing solution times. Practical implications - The authors believe that the variability in iteration count described for element-by-element methods presents no real difficulty to the engineering analyst. Originality/value - The paper gives a detailed account of the phenomenon and is useful both to developers of parallel iterative solvers and to the analysts that use them in practice.