Fatigue tests of cracked steel plates strengthened with UHM CFRP plates

Carbon fibre reinforced polymer (CFRP) has shown promise for improving the fatigue performance of steel structures. Previous studies have indicated that increasing the Young's modulus of CFRP can be beneficial for decreasing the stress intensity factor at the fatigue crack tip. In this project, ultra high modulus (UHM) CFRP plates with Young's modulus of 460 GPa were adopted to study their fatigue repair effectiveness. A series of fatigue tension tests was carried out on steel plates with an initial crack in the centre. Five strengthening configurations were used and a constant amplitude fatigue loading was applied to all the specimens. The beach marking technique was utilized to record the fatigue crack propagation. The effects of CFRP bond length, bond width and bond locations on the fatigue performance of cracked steel plates were also studied. The experimental results show that UHM CFRP plates can greatly increase the fatigue life of cracked steel plates by a factor ranging from 3.26 to 7.47. When CFRP plates cover the whole crack surface, the fatigue crack of the steel plate is arrested. The strengthening effectiveness of UHM CFRP plates is also compared with those using high Young's modulus CFRP sheeting and normal Young's modulus CFRP plates with or without prestressing.