Low cycle fatigue behaviour of welded T-joints in high strength steel

The present paper investigates the low cycle fatigue of fillet welds made of high strength weldable steel, Weldox S1100. The investigation was inspired by lifting equipment used in the wind turbine industry, where mobility calls for light weight, making high strength steels the preferred material candidate. Quite often the number of operations for this type of equipment is within a few thousand operations or less before the equipment is obsolete. 4 point bending tests were carried out at stress amplitudes between 500 MPa - 1500 MPa and at a stress ratio of R = −1. The results showed that at N ≈ 1000-3000 cycles there is a distinct drop in fatigue strength, indicating a change of slope of the ΔS − N curve. It is also shown that the ultimate tensile strength may be used as the basis for constructing ΔS − N curves from static material data.