Fatigue life of CFRP laminate strengthened high-strength steel plates under fatigue loadings

Carbon fiber reinforced polymer (CFRP) sheets and laminates are effective and practical for strengthening steel with initial damages under fatigue loading due to its advantageous strength and fatigue resistance. Unfortunately, studies of cracked high-strength steel plates strengthened by CFRP laminates are still limited. This paper studies the strengthening efficiency of CFRP laminate on cracked Q345, Q460 and Q690 steel plates under fatigue loading. It is found the fatigue life by CFRP laminates is increased to 1.53 to 3.84 times as that of un-strengthened specimen. Compared with CFRP sheet with the similar reinforcement stiffness, CFRP laminate strengthened specimens exhibit longer fatigue life under low stress range (195 MPa), and shorter fatigue life under high stress range (240.5 and 402.5 MPa). The difference is due to the matched adhesive of CFRP laminates (Araldite-2015) has lower elastic modulus but higher strength and ductility compared with matched adhesive of CFRP sheets (E2500S). Thus the material property of adhesive is a key factor determining fatigue life under different range of fatigue loadings. Crack propagation and different failure modes were observed. Serious debonding around the crack tip occurred, which leads to a further study.