Analysis of stress by the combination of thermoelastic stress analyzer and FEM

Since the strength of spot welding joints is characterized by the complex stress distribution, it is needed re analyze the stress of the spot welding in detail. However, as an actual construction such as a body of an automobile includes a lot of spot welding joints, it is difficult issue to analyze each of all spot welding joint in the construction. This technical paper describes how to evaluate the stress of spot welding joints both accurately and easily. The method to analyze the stress is based on thermoelastic stress analysis and numerical analysis. Firstly: a first invariable stress J1 inside Gamma, which is an arbitrary domain including the requested spot welding, is measured by the thermoelastic stress analyzer. Secondly, an optimum boundary traction along Gamma can be determined by the least square method so that the difference between the measured J1 and calculated J1 is minimum. Numerical analysis such as FEM may be used to calculate the stress under the acquired boundary condition. Applied examples using this method that is applicable to analyze the stress distribution of spot welding joints are investigated. One is the specimen s results of spot welding joints under the loading modes of shearing and peeling. The other is the result of an actual automotive construction that have a lot of spot welding joints. As a result, the method is possible to widely apply to the actual automobile construction under the complex stress condition. It is made clear that the appropriate stress distribution can be easily obtained on both the specimen and the actual construction by using this practical method, which has a possibility to reduce both rime and cost to ensure the strength of the spot welding such as the body of automobile.