Evaluating spot weld separation is one of the most challenging tasks in a quasi-static simulation. There are several factors that exist in modeling welds analytically that can influence correlation to physical test. This paper presents 4 specific factors: spot weld representation, weld thickness, weld strength, and metal forming effects around spot welds.
There are many ways in which a spot weld can be modeled within an FEA model from mesh independent beams to mesh dependent hex clusters. While each modeling technique comes with its unique sets of advantages and disadvantages, a method is chosen to best balance correlation, model setup timing and computation time.
Dependent on the way the thickness of the spot weld is represented, artificial moments can be induced which misrepresents structural behavior.
The assigned yield strength of the spot weld influences the behavior of the joint. Simply assigning the yield strength to the parent metal yield strength can underestimate weld forces of the joint.
Metal forming effects are inherent to formed components that alter the virgin metal. Typical factors include strength gains or losses due to work hardening, thinning, thickening and residual stress. Therefore, if a spot weld is located on an area of severe thinning, it will lose joining strength.
This paper describes how to overcome the 4 types of limitations through alternative spot weld modeling techniques and discusses correction factors for quasi-static analysis load cases using DYNA-3D[1]. A Roof Strength evaluation is used to verify these parameters.