The influence of specimen length on the residual stress and fatigue life

This paper studies the influence of specimen length on residual stress redistribution and fatigue life in welded cruciform joints made of steel grade S355. It uses numerical methods to simulate the common practice in fatigue testing, where specimens are cut from a larger welded plate assembly. A transient thermo-mechanical finite element model is used to simulate the welding and cutting processes, enabling a detailed analysis of residual stress relaxation due to reduced structural constraints when cutting the specimens. Fatigue life is assessed using linear elastic fracture mechanics, incorporating residual stress effects from the finite element simulations via a mean stress correction. Results show that shorter specimens exhibit reduced residual stress and increased fatigue resistance. For assemblies with a single pass weld, a minimum specimen length of 40 mm is recommended for deriving reliable S–N curves for welded joints in fatigue standards. The findings are in good agreement with experimental data and highlight the importance of specimen size in fatigue testing protocols. • Finite element simulations quantify welding and cutting effects on residual stress. • Cruciform joints cut to a small length have reduced residual stresses. • Fatigue life is assessed using fracture mechanics including residual stress effects. • Cruciform joints cut to a small length have increased fatigue resistance. • We advise specimen lengths ≥ 40 mm for deriving S–N curves of single-pass welds.