Fatigue testing of butt-welded high strength square hollow sections strengthened with CFRP

This paper presents a study on the residual stress, hardness and fatigue behaviour of butt-welded high strength square hollow section (SHS) steel tubes strengthened with carbon fibre reinforced polymer (CFRP). SHS tubes, with a nominal yield stress of 780 MPa and an ultimate tensile strength of 860 MPa, were butt-welded using the Gas Tungsten Arc Welding (GTAW) welding method. The hardness in the heat affected zone (HAZ) dropped to around 80% of that of the parent metal of the SHS steel. The strength in HAZ of the butt-welded SHS tubes is about 93% of that of the parent metal of the SHS tube. The residual stress of the butt-welded SHS tubes is about 20-50% 25-45%of the yield stress along the longitudinal direction and 15% of the yield stress along the transverse direction. The fatigue life of CFRP strengthened butt-welded SHS beams was extended for about 5 times comparing to the butt-welded beams without CFRP strengthening.