Fatigue Assessment & Test Correlation of Seam Welded Joints using Force Based Equivalent Structural Stress Solid Weld Approach

The fatigue life of typical welded structures is governed by the stress concentration at welded joints & small crack propagation from some pre-existing discontinuities at notched regions. There are numerous weld fatigue assessment approaches available which are unified using commercial fatigue software codes in conjunction with traditional finite element methods. However, FEM stress-based approaches predict extensively conservative results. Considerable efforts & subjective decision making is required to arrive at desired level of weld life correlation with physical test results, in terms of weld life and failure location. This is majorly because of inconsistency & inaccuracy in capturing the hot spot stress results due to stress singularities occurring at the notched regions owing to the mesh sensitivity. Hence to address these concerns, a force based equivalent structural stress solid weld approach in commercial weld fatigue code fe-safe VERITY™ was used for developing correlation with physical test results. For this study, the DOE matrices of product use cases for open and closed welds were chosen to accommodate the mix of weld fatigue assessment parameters such as weld algorithm, mesh size, survival probability, loading & weld direction. Weld fatigue correlation was assessed in terms of failure life cycles & location. The key findings from these product use cases for open and closed welds were identified based on the inferences drawn on multiple physical test correlation evidences. For getting a better correlation between weld life simulation results with that of physical test results, specific weld analysis parameters, guidelines were streamlined. Assessment of weld subjected to complex combination of normal & shear structural stresses has also been studied & decision factors identified. The outcomes of this study helped to reduce the number of failures in physical test by addressing & tracking failure beforehand in CAE and thereby saving cost involved in redesign and revalidation.