The utility of laser scanning welds for improving fatigue assessment

Abstract

Welded joints are a common source of fatigue failures. Traditional fatigue assessment approaches usually describe the weld with an idealized geometry defined by the weld flank angle and the weld toe radius. By doing so, the actual stress concentrations are not considered in such fatigue life predictions. 3D laser scanning technology offers an opportunity to more accurately represent the weld geometry, and accordingly perform fatigue assessment on more accurate representations of weld geometry. This manuscript explores the benefit of incorporating scanned weld geometries into linear elastic stress analysis for fatigue life prediction. Additionally, the capabilities to explain experimental scatter of six different fatigue indicator parameters have been quantified. Using experimental data from 28 tests across three geometries, a total of 60 deterministic and probabilistic fatigue models were assessed using both scanned and idealized weld geometries. The use of scanned weld geometries is found to substantially improve fatigue prediction when using local fatigue indicator parameters. However, if nonlocal fatigue indicator parameters are employed, the use of scanned weld geometries does not display a benefit. In total, the use of nonlocal fatigue indicator parameters with idealized weld geometry offer the greatest accuracy across the three cases examined. Thus, for linear elastic fatigue life assessment, the use of a nonlocal parameter in the fatigue life model is more motivated than utilizing 3D scanned weld geometry. Regardless of how the weld geometry is included, the signed von Mises equivalent stress led to the most reliable fatigue life predictions overall for the specimens considered in this work.