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Stefanie Reese - One of the best experts on this subject based on the ideXlab platform.
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finite element modelling of rubber like polymers based on chain statistics
International Journal of Solids and Structures, 2006Co-Authors: Markus Bol, Stefanie ReeseAbstract:Abstract In this work finite element simulations are conducted based on the micro structure of polymers in order to transfer the information of the micro level to the macro level. The micro structure of polymers is characterized by chain-like macromolecules linked together at certain points. In this way an irregular three-dimensional network is formed. Many authors use the tool of statistical mechanics to describe the deformation Behaviour of the entire network. Most of these concepts can be reformulated as traditional continuum mechanical formulations. They are, however, restricted to affine deformation, regular chain arrangements and purely elastic Material Behaviour. For this reason, in the present contribution, we propose a new finite element-based simulation method for polymer networks which enables us to include non-affinity and arbitrary chain configurations. It can be easily extended to include chain breakage and reconnection. The polymer structure to be investigated, e.g. a rubber boot or a seal, is discretized by means of tetrahedral elements. To each edge of a tetrahedral element one truss element is attached which models the force–stretch Behaviour of a bundle of polymer chains. Each of these tetrahedral unit cells represents the micro mechanical Material Behaviour in a certain point of the network. The proposed method provides the possibility to observe how changes at the microscopic level influence the macroscopic Material Behaviour. Such information is especially valuable for the polymer industry.
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a micromechanically motivated Material model for the thermo viscoelastic Material Behaviour of rubber like polymers
International Journal of Plasticity, 2003Co-Authors: Stefanie ReeseAbstract:Abstract The Material Behaviour of rubber at the micro level is usually described by means of statistical mechanics. In particular, the Neo-Hooke model has been derived in this fashion. The micromechanical modelling can be extended to include also the breaking and reforming of chains. One possible approach at this level is the so-called transient network theory. Using certain assumptions for the chain distributions, one arrives at a continuum mechanical model of finite viscoelasticity which is based on the multiplicative decomposition of the deformation gradient. This means that the inelastic part of the deformation is regarded as an elastic isomorphism. Further, the considerations at the micro level give information about the temperature dependence of the mechanical Material parameters. For instance, it can be shown easily that the shear modulus depends approximately linearly on the temperature. This fact has important consequences for thermo-mechanical coupling which have not yet been discussed in detail in the literature.
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Theoretical and Numerical Aspects in the Thermo-Viscoelastic Material Behaviour of Rubber-Like Polymers
Mechanics of Time-Dependent Materials, 1997Co-Authors: Stefanie Reese, Sanjay GovindjeeAbstract:Most current models for finite deformation thermo-viscoelasticity are restricted to linear evolution laws for the viscous Behaviour and to thermorheologically simple Materials. In this paper, we extend a model for finite deformation viscoelasticity that utilizes a nonlinear evolution law to include thermal effects. In particular, we present a thermodynamically consistent framework for the model and give a detailed form for then on-equilibrium Helmholtz free energy of the Material in terms of the isothermal free energy function. The use of the model in a computational setting is addressed and it is shown that an efficient predictor-correct oralgorithm can be used to integrate the evolution equation of the proposed constitutive model. The integration algorithm makes crucial use of the exponential map as has been done previously in elastoplasticity. Numerical examples are presented to show some interesting features of the new model.
Dingena L Schott - One of the best experts on this subject based on the ideXlab platform.
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dem particle upscaling for large scale bulk handling equipment and Material interaction
Powder Technology, 2019Co-Authors: Stef Lommen, Mohammadjavad Mohajeri, Gabriel Lodewijks, Dingena L SchottAbstract:Abstract Purpose The development of bulk Material handling equipment can be accelerated and made less expensive when testing of virtual prototypes is adopted. However, the modelling of a grab unloader requires a large volume (77 m3) of iron ore pellets, making the computational costs prohibitive. This paper investigates the extent to which the original particles can be substituted by larger, coarser grains. It is crucial that this particle upscaling does not alter the realistic Behaviour of the simulated bulk Material, nor its interaction with the bulk handling equipment. Approach First, our coarse graining technique is explained and set out for the particle system at hand. The Material Behaviour is then characterized using three laboratory experiments (two angle of repose tests and a penetration test). Next, the results of simulations using two contact models with and without coarse graining with different scale factors are compared with the measured Material Behaviour and Material-equipment interaction. This includes a comparison of the macroBehaviour of the bulk Material and the tool interaction of coarser grains in a cutting and sliding process. After reaching a satisfactory verified solution on the laboratory scale, the Material Behaviour and interaction Behaviour of a large-scale experiment are modelled. A simulation model of a grab unloader was used for validation of the chosen coarse graining approach. Findings Using the scaling method presented, the macroscopic tests indicated consistent Material Behaviour, regardless of the chosen particle scale for two contactmodels. Scaling of the tool interaction process produced mixed results: the sliding process scaled consistently but the penetration process did not, most likely because it is significantly harder for coarser grains to move since they have to move further to the sides before the tool can pass, leading to higher normal forces and frictional forces on the tip. This inconsistency was compensated for by adjusting the wall friction coefficient in the tip of the penetration tool. Once this adapted coarse graining scheme was applied to the industrial-scale simulation of a grab unloader, it produced consistent particle-scale invariant results. Originality/value This research is the first to show how coarse graining schemes for DEM simulations can be applied to large-scale bulk handling equipment involving dominance of Material equipment interaction through penetration of the bulk Material.
Anna Tarakanova - One of the best experts on this subject based on the ideXlab platform.
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nonlinear Material Behaviour of spider silk yields robust webs
Nature, 2012Co-Authors: Steven W Cranford, Anna Tarakanova, Nicola PugnoAbstract:Natural Materials are renowned for exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre. Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence to the geometry of a web. This Material system, highly adapted to meet a spider's many needs, has superior mechanical properties. In spite of much research into the molecular design underpinning the outstanding performance of silk fibres, and into the mechanical characteristics of web-like structures, it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress--involving softening at a yield point and substantial stiffening at large strain until failure--as being crucial to localize load-induced deformation and resulting in mechanically robust spider webs. Control simulations confirmed that a nonlinear stress response results in superior resistance to structural defects in the web compared to linear elastic or elastic-plastic (softening) Material Behaviour. We also show that under distributed loads, such as those exerted by wind, the stiff Behaviour of silk under small deformation, before the yield point, is essential in maintaining the web's structural integrity. The superior performance of silk in webs is therefore not due merely to its exceptional ultimate strength and strain, but arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.
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nonlinear Material Behaviour of spider silk yields robust webs
Nature, 2012Co-Authors: Steven W Cranford, Anna Tarakanova, Nicola Pugno, Markus J. BuehlerAbstract:Spider web deformation simulations, theory and experiments reveal how the nonlinear response of spider silk to strain and the discrete geometry of a web contribute to its robustness, integrity and performance. Spider silk is one of nature's 'super-Materials'. Its remarkable mechanical properties include high extensibility and strength comparable to that of steel. But Markus Buehler and colleagues show that it is not just these virtues that make silk ideal for web construction. Silk's nonlinear stress response — linear at low strain, suddenly softening as strain increases then stiffening prior to failure — is also critical. This Behaviour allows webs to keep their shape when experiencing small, distributed loads such as those exerted by wind. But during strong local deformations, such as those caused by falling debris, the geometrical arrangement of the threads and the nonlinear stress response combine to limit damage to the area near the impact site, so that the web remains functional. Natural Materials are renowned for exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre1,2,3,4,5. Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence6 to the geometry of a web7. This Material system8, highly adapted to meet a spider’s many needs, has superior mechanical properties9,10,11,12,13,14,15. In spite of much research into the molecular design underpinning the outstanding performance of silk fibres1,6,10,13,16,17, and into the mechanical characteristics of web-like structures18,19,20,21, it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress—involving softening at a yield point and substantial stiffening at large strain until failure—as being crucial to localize load-induced deformation and resulting in mechanically robust spider webs. Control simulations confirmed that a nonlinear stress response results in superior resistance to structural defects in the web compared to linear elastic or elastic–plastic (softening) Material Behaviour. We also show that under distributed loads, such as those exerted by wind, the stiff Behaviour of silk under small deformation, before the yield point, is essential in maintaining the web’s structural integrity. The superior performance of silk in webs is therefore not due merely to its exceptional ultimate strength and strain, but arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.
J H Dautzenberg - One of the best experts on this subject based on the ideXlab platform.
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Material Behaviour in conditions similar to metal cutting flow stress in the primary shear zone
Journal of Materials Processing Technology, 2002Co-Authors: Spfc Serge Jaspers, J H DautzenbergAbstract:Abstract This paper is aimed at determining the flow stress in metal cutting. A major problem in finding the flow stress is the intense circumstances under which deformation takes place in the chip root. Large deformations are imposed on the workpiece Material at high speed in a very small area. This results in mechanical Material Behaviour far removed from that encountered in conventional Material tests. Therefore, to determine the flow stress in cutting, it is necessary to determine the conditions under which the Material is being deformed firstly. Hereafter, a Material test has been developed that can be used in conditions similar to those found in cutting. Based on the obtained information on the deformation conditions in cutting as found in previous work [J. Mater. Process. Technol, in press], a split Hopkinson pressure bar (SHPB) facility could be constructed for mechanical testing of Materials at high strain rates and elevated temperatures. From measurements with this SHPB facility, it appeared that both strain rate and temperature have a considerable influence on the flow stress of metals. Combining the information on the deformation conditions in the primary shear zone with the measured constitutive Behaviour, the flow stress of the metals in the primary shear zone is found.
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Material Behaviour in metal cutting strains strain rates and temperatures in chip formation
Journal of Materials Processing Technology, 2002Co-Authors: S P F C Jaspers, J H DautzenbergAbstract:Abstract A major problem in finding the flow stress in metal cutting is the intense circumstances under which deformation takes place in the chip root. Large deformations are imposed on the workpiece Material at high speed in a very small area. This results in mechanical Material Behaviour far removed from that encountered in conventional Material tests. Therefore, to determine the flow stress in cutting it is necessary to determine the conditions under which the Material is being deformed. This paper describes how the strains, strain rates and temperatures have been determined in orthogonal cutting tests of steel AISI 1045 and aluminium AA 6082-T6. It appears that in the region where the chip is separated from the workpiece (i.e. the primary shear zone) the workpiece Material is sheared considerably to equivalent strains in the order of 1–2. Also, the strain rate in the primary shear zone is found to be very large: in the order of 2.0×104 s−1. To find the temperatures in metal cutting an IR camera is used. It appears that the feed rate and cutting speed hardly influence the shear plane temperature. The measured shear plane temperature is approximately 290 °C in the case of the steel and approximately 190 °C in the case of the aluminium alloy.
Nicola Pugno - One of the best experts on this subject based on the ideXlab platform.
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nonlinear Material Behaviour of spider silk yields robust webs
Nature, 2012Co-Authors: Steven W Cranford, Anna Tarakanova, Nicola PugnoAbstract:Natural Materials are renowned for exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre. Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence to the geometry of a web. This Material system, highly adapted to meet a spider's many needs, has superior mechanical properties. In spite of much research into the molecular design underpinning the outstanding performance of silk fibres, and into the mechanical characteristics of web-like structures, it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress--involving softening at a yield point and substantial stiffening at large strain until failure--as being crucial to localize load-induced deformation and resulting in mechanically robust spider webs. Control simulations confirmed that a nonlinear stress response results in superior resistance to structural defects in the web compared to linear elastic or elastic-plastic (softening) Material Behaviour. We also show that under distributed loads, such as those exerted by wind, the stiff Behaviour of silk under small deformation, before the yield point, is essential in maintaining the web's structural integrity. The superior performance of silk in webs is therefore not due merely to its exceptional ultimate strength and strain, but arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.
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nonlinear Material Behaviour of spider silk yields robust webs
Nature, 2012Co-Authors: Steven W Cranford, Anna Tarakanova, Nicola Pugno, Markus J. BuehlerAbstract:Spider web deformation simulations, theory and experiments reveal how the nonlinear response of spider silk to strain and the discrete geometry of a web contribute to its robustness, integrity and performance. Spider silk is one of nature's 'super-Materials'. Its remarkable mechanical properties include high extensibility and strength comparable to that of steel. But Markus Buehler and colleagues show that it is not just these virtues that make silk ideal for web construction. Silk's nonlinear stress response — linear at low strain, suddenly softening as strain increases then stiffening prior to failure — is also critical. This Behaviour allows webs to keep their shape when experiencing small, distributed loads such as those exerted by wind. But during strong local deformations, such as those caused by falling debris, the geometrical arrangement of the threads and the nonlinear stress response combine to limit damage to the area near the impact site, so that the web remains functional. Natural Materials are renowned for exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre1,2,3,4,5. Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence6 to the geometry of a web7. This Material system8, highly adapted to meet a spider’s many needs, has superior mechanical properties9,10,11,12,13,14,15. In spite of much research into the molecular design underpinning the outstanding performance of silk fibres1,6,10,13,16,17, and into the mechanical characteristics of web-like structures18,19,20,21, it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress—involving softening at a yield point and substantial stiffening at large strain until failure—as being crucial to localize load-induced deformation and resulting in mechanically robust spider webs. Control simulations confirmed that a nonlinear stress response results in superior resistance to structural defects in the web compared to linear elastic or elastic–plastic (softening) Material Behaviour. We also show that under distributed loads, such as those exerted by wind, the stiff Behaviour of silk under small deformation, before the yield point, is essential in maintaining the web’s structural integrity. The superior performance of silk in webs is therefore not due merely to its exceptional ultimate strength and strain, but arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.