Multiaxial fatigue behaviour of laserbeam-welded thin steel and aluminium sheets under proportional and non-proportional combined loading

Laserbeam-welded overlapped tubular joints made from structural steel St35 (S235 G2T), artificially hardened aluminium alloy AlSi1MgMn T6 (EN AW 6082 T6) and self-hardening aluminium alloy AlMg3.5Mn (EN AW 5042) were investigated under combined proportional and non-proportional axial and torsional loading with constant amplitudes in the range of 2 x 10(4)-1 x 10(7) cycles. The multiaxial fatigue behaviour of these joints was assessed by the notch stress concept with the reference radius r(ref) = 0.05 mm. The equivalent stresses, especially considering the fatigue life reducing influence of non-proportional loading in comparison to proportional loading, were calculated by a recently developed hypothesis, which is called the Stress Space Curve Hypothesis (SSCH). This hypothesis is based on the time evolution of the stress state during one load cycle. (C) 2010 Elsevier Ltd. All rights reserved.