Fatigue behaviour of high strength S690 steel and their welded sections under symmetric cyclic actions

Abstract

This paper presents an experimental investigation into fatigue behaviour of high strength S690 steel, and their welded sections. A total of 48 cyclic tests were carried out on cylindrical coupons of two different types of high strength S690 steel, namely, the S690-TM steel and the S690-QT steel, and their welded sections. These cyclic tests were conducted as i) load-controlled tests, and ii) strain-controlled tests over a range of 104 to 107 cycles to provide test data to demonstrate their resistances against fatigue fracture under practical situations, such as bridge structures. Both scanning electron microscope observations and metallographic analyses were conducted on typical fractured coupons to examine micromechanics of fatigue fracture of these high strength steel and their welded sections. It should be noted that while both the load- and the strain-controlled tests provide engineering data for generation of design S-N curves commonly adopted in fatigue assessment of bridge design, the strain-controlled tests provide additional information to quantify their fatigue behaviour including stiffness degradation, crack initiation and propagation, and fracture. All the test data of the steel plates and their welded sections of the S690-TM and the S690-QT were found to lie significantly above the design S-N curves for fatigue assessment given in EN 1993–1–9, AISC 360 and GB 50017, especially for those data which numbers of cycles are larger than 106. In addition, these high strength S690 steel possess superior fatigue performance, when compared with those of the normal strength S355 steel reported in the literature.