Fatigue Life Assessment of Cut Edges in High Strength Steel

Abstract: The interests in more effective and lighter structures have increased the use of high strength steels for higher performances. Plate materials are optimized so thinner structures and higher material strengths are reached, this leads to the cut quality might be a new issue. In this investigation steel thickness of 6 and 16 mm with minimum yield strength from 355 to 960 MPa are fatigue tested with constant amplitude tensile loading. The specimens were cut using waterjet and also with thermally cut methods such as plasma and oxygen. Before fatigue testing the cut surfaces were measured and roughness Rz values were obtained. Empirical and analytical results of the surface roughness influencing the fatigue strength for different steel strengths are presented. Since thermal cutting methods have been developed over the years the FAT values are higher for those IIW are recommending. When the quality of the cut surface can be kept high the fatigue strength will also be higher than those recommended. This means having a cutting process that provides smooth surfaces such as waterjet and plasma cutting the fatigue life will be longer.