Tip shape optimization for materials with elongated porous

Auxetic materials - Stress redution in crack-like geometries

Created on 2018.06.30 78 views
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Auxetic materials are materials that present a negative Poisson's ratio, meaning that when compressed in the axial direction they shrink also in the transversal directions. In general this is possible in nature, but very few materials present this behavior, however it is possible to achieve an effective negative Poisson ratio in almost any material by introducing specific kinds of perforations. Auxetic materials have been studied in the past, showing the opportunity of better performance in conditions as impact resistance, indentation and acoustics. However, this perforations in most scenarios lead to high stress concentration. As part of a master's tesis project I started, guided by my professor Dr. Michael Taylor, to analyze this particular case of mechanics. The tool selected to do it is ABAQUS, a powerful FEA simulation package that offered most of the tools that were required. Particularly I'm interested in reducing the stress at the tips of the perforations that introduced to the material in order to produce the auxetic response. A first approach to solving this problem is to compare several parametric geometries to be added at the tip of the voids (stop-holes). Expecting a considerable decrease of the stress while keeping most of the auxetic response achieve in the first place by introducing the elongated porous.  The comparison was made by simulating a representative volume subjected to periodic boundary condition of each of the parametric designs. To implement this boundary conditions Dr. Taylor provided an ABAQUS python script that he used in his FEA course capable of generating the geometry and applying the required constraints. However, the script I adapted the script to be able to generate several tip geometries in a parametric manner. Also to be able to perform the analysis at different parameter combinations an compare as many shapes as possible a MATLAB script was used, in communication with ABAQUS python interface, to sequentially ejecute simulations and analyze the data (displacement and stress) generated by them. In conclusion, ABAQUS proved to be a very capable tool for any kind of project, in particular given its capability of being operated by using python scripting. Allowing us to add more functionality to it and solve any kind of problem that was on hand during this investigation.  Note I: more information about the process followed is provided in the form of a diagram in the images. Note II: The results of this investigation are expected to be published in an engineering research article, due to that no more information can be disclosed.
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MB Max Barillas
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