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USE OF ADVANCED MATERIAL MODELING TECHNIQUES IN LARGE-SCALE SIMULATIONS FOR HIGHLY DEFORMABLE STRUCTURES
| Title: | USE OF ADVANCED MATERIAL MODELING TECHNIQUES IN LARGE-SCALE SIMULATIONS FOR HIGHLY DEFORMABLE STRUCTURES |
| Author: | Vakada, Krishna Chaitanya |
| Description: | Recently advanced material models are becoming increasingly important for realistic engineering analyses. This is particularly true for flexible structures undergoing intense elastic and inelastic deformations; for example, combined large rotations and finite stretches, high strain gradients leading to localized failure modes due to damages, and in cases accounting for inherent (initial) and deformation-induced anisotropies such as large deformations of soft biological tissues. The part that has been mostly studied by researchers is the involved mathematical developments and physical relevancy of models in capturing a host of experimentally-observed phenomenon of the material response. In contrast, a rather limited amount of studies have been performed aiming at gaining insight and experiences in implementing and using these new generations of sophisticated models in Finite Element (FE) large scale commercial codes(such as ABAQUS, ANSYS, MARC, LSDYNA). Noting the lengthy time gap before such models are adapted in commercial codes the engineering users are left with an urgent need for actually implementing and independently using these routines. This task is certainly not trivial, particularly in view of several conflicting conclusions that were reached in the contemporary literature on the success or otherwise of these implementations. The main objective of the present study is to assess the performance of three different classes of advanced material models, in the context of large-scale FE computations; i.e., a model class for large-strain inelastic behavior of elastomers(Thermoplastic Vulcanizates); a highly anisotropic model for soft biological tissues and a material model capturing softening for damage/failure mode localization studies. To this end, and considering the complexity of large deformations the very marked differences in the response character of these material models there are three important considerations in the overall settings for the algorithmic developments, implementations and utilizations of the targeted FE commercial code: (a) an implicit scheme is needed for ability to handle both stiffening and softening structures, since for stiffening structures, a prior knowledge to estimate the size of a stable time is lacking (it varies with deformations); (b) a carefully designed user material routines are needed to bypass the many restrictions and assumptions implied in the provided kinematical quantities communicated by the main FE code (e.g.“small” neutralized rotation, elastic strain and shears) which are often parts of “native” FE codes material model library, and (c) for simulation of softening behavior models must include proper “internal length scales” to render the results that are objective with mesh refinements, without any radical changes necessitated by the non conventional approaches proposed in the recent literature such as gradient damage /plasticity, non local continua, Cosseratts’s continua etc. all of which are outside the scope of any of the presently available commercial FE codes. All results obtained in this study utilized standard ABAQUS FE program and it’s associated UMATS. They indicate very positive experiences in that all the different models considered can be employed successfully with large meshes and favorable convergence properties. This renders the realistic analysis even in the presence of extensive anisotropy, large finite inelastic stretches and very complex modes of failure in softening structures. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=akron1132331555
http://hdl.handle.net/2374.OX/3533 |
| Date: | 2005 |
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