Mechanical Behavior of Gas Metal Arc Welds and Lithium-Ion Battery Modules.

Abstract

The first part of the dissertation is related to a study of the failure mechanisms of gas metal arc welds. Cost savings can be gained by minimizing the weld length. However, improperly sized welds can result in the loss of structural integrity of the welded components. The necking/shear failure modes for the mid-sections of gas metal arc welds in lap-shear specimens of HSLA steel are investigated. Three-dimensional finite element models were developed with the geometric characteristics of the heat affected zones (HAZ) designed to match the micrographs of the cross sections for the welds. The distributions of the void volume fraction near the welds shown from the finite element analyses are consistent with the failure modes observed in the experiments. Further finite element analyses showed that the geometric characteristics of the HAZ are key factors for the resulting failure location. The mode I and mode II stress intensity factor (SIF) solutions for gas metal arc welds in lap-shear specimens are investigated by the analytical solutions and by finite element analyses. The computational results indicate that the SIF solutions for realistic welds are lower than the analytical solutions for idealized weld geometry. Further finite element analyses were carried out in order to obtain the computational SIF solutions for the realistic weld geometries with dissimilar sheet thicknesses. Finally, three-dimensional computational results indicate that the distributions of the SIF solutions for discontinuous welds are different from those for continuous welds. In the second part, a computational model is developed for simulations of representative volume element specimens of lithium-ion battery modules under in-plane constrained compression tests. The model allows for computational efficiency while simulating the overall mechanical response of battery modules and the deformation patterns of the heat dissipater. The model is based on the properties of the heat dissipater, the foam, and the macro behavior of the cell components. The computational results compare fairly well with the experimental results. Further finite element analyses showed the increase in the initial nominal buckling stress under dynamic loading conditions.