Automotive structures contain hundreds of welds. Most of the time, failure occurs at the weld ends (weld toe or weld root). Thus, welds affect the structural integrity of an entire structure. Thus, the modeling of welded joints is very important from a design point of view. In this research, the primary aim is to develop a weld model to assess the structural integrity of welded joints based on stress analysis by using a finite element method (FEM) and through experimental validation. The stress distribution in welded joints mainly depends on the geometry, loading type and material properties. Therefore, it is greatly challenging to develop a weld model that can predict the behavior of stress distribution and weld stiffness in joints. There are several approaches for modeling welded structures by using FEM. However, the effective notch stress approach has been used for weld joint modeling in this research which is gaining in popularity in the automotive industry. The effective notch stress approach calculates the local stress at a notch (weld toe or root) assuming that there is linear-elastic material behavior. Parameter tuning of the weld model has been done to obtain the lowest validation error with the experimental results. The effective notch radius is chosen as the only tuning parameter in this weld model. Through this investigation, the weld model based on the effective notch stress has been experimentally validated for the first time through parameter tuning. Two different types of welded joints are investigated. Both types of joints are analyzed with a fine meshed 3D finite element model by using the effective notch stress approach. The FEM model of these two joints is validated with the experimental results. The calculated FEM results show a good agreement with the experimental results (obtained by using strain gages) for the ASTM model. This modeling technique is also validated with real world data of a bus window pillar. The model of the bus window pillar shows a close approximation with the experimental results. / October 2016

This study addresses the fatigue life of the head–to–skirt welds of tall distillation columns. Fatigue tests were done on two types of weld geometries which approximate the head–toskirt configurations. From the fatigue tests it was determined that the fatigue life of the experimental samples can be substantially improved by applying weld build–up between the head and the skirt. The expected fatigue life of the test samples was determined by way of calculation employing the so called Nominal–Stress–Approach, the Effective–Notch–Stress–Approach and the Stress–Life–Approach. For both the Nominal–Stress–Approach and the Effective–Notch–Stress–Approach the predicted fatigue life was found to be overly conservative compared to the experimental results. The Stress–Life–Approach predicted the fatigue life to within a factor of 1.3 for both the geometries under investigation when displacements due to welding are taken into account. If displacements due to welding is omitted this factor is increased, for the geometry without weld build–up, to 2. For the geometry with weld build–up the factor remains 1.3. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2011.

This study addresses the fatigue life of the head–to–skirt welds of tall distillation columns. Fatigue tests were done on two types of weld geometries which approximate the head–toskirt configurations. From the fatigue tests it was determined that the fatigue life of the experimental samples can be substantially improved by applying weld build–up between the head and the skirt. The expected fatigue life of the test samples was determined by way of calculation employing the so called Nominal–Stress–Approach, the Effective–Notch–Stress–Approach and the Stress–Life–Approach. For both the Nominal–Stress–Approach and the Effective–Notch–Stress–Approach the predicted fatigue life was found to be overly conservative compared to the experimental results. The Stress–Life–Approach predicted the fatigue life to within a factor of 1.3 for both the geometries under investigation when displacements due to welding are taken into account. If displacements due to welding is omitted this factor is increased, for the geometry without weld build–up, to 2. For the geometry with weld build–up the factor remains 1.3. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2011.