Elastic and elasto-plastic finite element analysis of a tension test specimen with and without voids

Ravindranath Tagore, K. and Sidda Basha, D.

Finite Element Analysis (FEA) is an important engineering tool used to assist in approximating and verifying how a component will react under various external and internal loading conditions. The purpose of this master of engineering project is to investigate and analyze fully elastic and elastic-plastic deformation of a High Strength Steel (HSS) tensile test specimen in FEA ANSYS under various conditions. In general, material selection is a key component to engineering analysis. If the material selection is performed incorrectly and does not have the strength, ductility, or physical features to withstand the load then failure will become a realistic result. There are many conditions where the stress applied could extend beyond the yield point of the material but FEA does not necessarily provide visual indication that the part has yielded. The initial results showed that the fully elastic material property has a linear stress-strain relationship regardless of the load applied while the elastic-plastic has a linear relationship up to yield point and then becomes nonlinear beyond yield point. This FEA investigation will also include elastic-plastic analysis on reverse loading, cavity geometry, and random pores within the HSS tensile test specimen. This will be accomplished by using different modeling techniques to investigate how FEA ANSYS analyzes elastic-plastic material deformation under various loading conditions and material conditions. The reverse loading condition resulted in tensile and compressive stresses that were equal and opposite even in the plastic range. Work hardening should have increased the strength of the test specimen so the compressive stress should have been smaller than the tensile loading. The plastic data from the tensile test was not cyclic and only applied tensile force so FEA ANSYS did not know how to interpret the plastic range for compression.FEA ANSYS simply applied a negative force which resulted in an equal and opposite stress. The cavity model had higher stress than the tensile and reverse loading conditions with the elastic-plastic data. FEA showed significant visual deformation within the cavity of the specimen. The high stress and deformation were due to the reduction in cross sectional area because stress is a function of force over the area. The pores modeled within the test specimen had minimal effect on the overall stress, strain or deflection compared to the theoretical HSS test specimen that had no imperfections. The pore had high stress because the pores were a source of high stress concentrations but the stress and strains not within the pores did not change. The fully elastic and elastic-plastic material selections each play a vital role in FEA ANSYS while both can contain their sources of errors. In the fully elastic model, regardless of the amount of stress applied, the stress-strain curve acted linear for the fully elastic properties even beyond yield point. The elastic-plastic model applies actual stress strain test data beyond the yield point and applies it to the part being analyzed. The results showed nonlinear stress but when stresses outside the uploaded values were applied FEA ANSYS analysis resorted back to a linear stress-strain relationship.

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