Fatigue of center cracked steel plates with UHM CFRP plate strengthening

Composite materials have led to great advances in improving fatigue performance of steel structures over conventional strengthening methods. High modulus carbon fibre composites (CFRP) make this fatigue strengthening more promising by decreasing stress intensity factor range at the fatigue crack tip to a large extend. In this study, an ultra high modulus (UHM) CFRP plate, with a modulus of 460 GPa, was adopted to strengthen initially center cracked steel plates. CFRP strengthened steel plates were tested under fatigue loading to investigate the effectiveness of the composites on preventing fatigue crack propagation and extending the fatigue life. Five strengthening configurations were adopted by changing both the patch length and patch width. Both single-sided and double-sided strengthened specimens were tested. A crack detection method of ''beach marking” was adopted during the fatigue tests, to monitor and record the crack propagation against fatigue cycles. Experimental results show that the application of UHM CFRP substantially reduces crack growth rate and prolongs fatigue life up to 8 times more than that of un-strengthened steel plates. It was also found that double-sided strengthening is more efficient than single-sided one. CFRP bond width, bond length and bond locations have considerable influences on the fatigue performance of strengthened steel plates.