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

Abstract

<div class="section abstract"><div class="htmlview paragraph">The stress concentration at welded joints and small crack propagation from some pre-existing discontinuities at notched regions control the fatigue life of typical welded structures. There are numerous FEM stress-based weld fatigue assessment approaches available commercially which unify FEM stresses with various fatigue software codes embedded with international weld standards. However, FEM stress-based approaches predict extensively conservative results. Considerable efforts &amp; 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 &amp; inaccuracy in capturing the hot spot stress results due to stress singularities occurring at the notched regions owing to the mesh sensitivity, modeling complexity.</div><div class="htmlview paragraph">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. This paper presents detailed study using this mesh-insensitive weld fatigue assessment approach. 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 &amp; weld direction. Weld fatigue correlation was assessed in terms of failure life cycles, failure mode &amp; location, mesh sensitivity and result interpretation quality. 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. For open welds, end capping traction effects were studied for different loading circumstances. For closed welds, throat failure mode has been identified &amp; simulated. Assessment of weld subjected to complex combination of normal &amp; shear structural stresses has also been studied &amp; decision factors identified. The outcomes of this study helped to reduce the number of failures in physical test by addressing &amp; tracking failure beforehand in CAE and thereby saving cost involved in redesign and revalidation.</div></div>