A FRACTURE-MECHANICS BASED FATIGUE LIFE PREDICTION FOR WELDED-JOINTS OF SQUARE TUBES

Square tubes of mild and low alloy steels are extensively used in vehicle structures and offshore platforms. Despite this fact the fatigue behaviour of welded nodes of these tubes is not sufficiently known, especially in thin sections. The paper presents the results of fatigue life predictions based on fracture mechanics, in non-load carrying T and also load carrying cruciform joints. The fatigue life prediction models include crack initiation and crack propagation. The stress intensity factor formulations were obtained using the weight function solution for semi-elliptical surface cracks with the stresses computed using a three-dimensional finite element program. The prediction results are compared with experimental results and a good agreement was obtained. The tube material was mild steel St 37 (DIN 17100). The loading modes were in-plane three point bending and cantilever bending or tension.