VERITY Weld Fatigue Method in FE-SAFE Using ANSYS

It is well known that stress concentration in welded joints (and notched structures) dominates fatigue behavior of welded structures. However, traditional finite element methods are not capable of consistently capturing the stress concentration effects on fatigue behavior due to their mesh-sensitivity in stress determination at welds resulted from notch stress singularity. Any use of an artificial radius is too arbitrary for the results to be reliable in fatigue design in practice. In this presentation, a robust stress analysis procedure recently developed at Battelle and extensively validated by various industries will be presented. The method is called VerityTM mesh-insensitive structural stress method which serves as a FE post-processing procedure to commercial FE packages such as ANSYS. The VerityTM method has been integrated into fesafeTM and available from Safe Technology Ltd. The method is based on the mapping of the balanced nodal forces/moments along an arbitrary weld line available from a typical finite element run into the work-equivalent tractions (or line forces/moments). In doing so, a complex stress state due to notch effects can then be represented in the form of a simple stress state in structural mechanics in terms of through-thickness membrane and bending components at each nodal location. The resulting structural stress calculations are mesh-insensitive, regardless of element size, element type, integration order used, as long as the overall geometry of a component is reasonably represented in a finite element model. A series of simple and complex examples will be represented to demonstrate the meshinsensitivity of the structural stress method, covering MIG seam welds, laser welds, resistance spot welds, etc. In addition to its mesh-insensitivity, the effectiveness of the structural stress parameter has been further validated by collapsing several thousands of fatigue tests available from literature into a single curve, referred to as the master S-N curve. Additional applications of the structural stress method will may also be touched upon. These include:
• Treatment of low cycle fatigue
• Treatment of multi-axial fatigue
• Solder fatigue in electronic packaging

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