Simulations of similar and dissimilar weld joint failures and bearings for fatigue analyses

In the first part of this dissertation research, failure modes of similar laser and dissimilar ultrasonic welds in lap-shear specimens under quasi-static loading conditions were investigated. High strength low alloy (HSLA) steel sheets were used to make laser welded lap-shear specimens. Magnesium and HSLA steel sheets were used to make ultrasonic welded lap-shear specimens. Quasi-static tests were conducted on dog-bone shaped lap-shear specimens for both welds. In order to understand the failure mode of the welds, finite element analyses were conducted to identify the effects of the material properties and the weld geometry. The results of the finite element analyses for the laser weld based on multi-zone non-homogeneous material models show that the higher effective stress-plastic strain curves of the weld and heat affected zones and the geometry of the weld protrusion result in the necking/shear failure mode in the load carrying sheet. The results of the finite element analyses for the dissimilar ultrasonic weld based on multi-zone indentation models show that the weld indentation triggers different plastic flow patterns in the load carrying sheet.;In the second part of this dissertation research, closed-form analytical solutions to calculate the load distributions by the rolling elements on the raceway for zero-interference and interference conditions in roller bearings were investigated. A special case involving cam follower roller bearings was also investigated. The contact solutions by Hertz and Persson provided the analytical background for the proposed solutions. These solutions along with an assumption that the multiple contacts of rolling elements are similar to the contact of a lumped body corresponding to the rolling elements were used to derive the proposed solutions. The proposed closed-form solutions require minimal input parameters and therefore are expected to be widely used in the bearing industry. Finite element analyses were conducted to validate the proposed solutions for selected geometries and loads. Based on the proposed solutions, a complete yet simple procedure to estimate the fatigue lives of roller bearings were introduced for use in the bearing design and selection processes.