Study of stress intensity factor of a cracked steel plate with a single-side CFRP composite patching

Composite fiber patching techniques have been considered as alternatives to traditional methods of strengthening and fatigue crack repair in steel structures. It is known that the fatigue strength of a cracked steel element depends on the stress intensity factor (SIF) at the crack tip which is a function of the stress/strain distribution of the plate. This paper presents an experimental study of tension tests of cracked steel plates repaired by single-side carbon fiber-reinforced polymer (CFRP) patching in investigating the strain distribution in the vicinity of the cracked region. The test parameters included patch length, patch width, tapered end, and axial stiffness ratio of adherend. It is shown from the test results that the single-side CFRP patching applied onto the cracked steel plate decreased the crack tip strains significantly in the patched face and increased the strains in the unpatched face. Finite-element analyses of the specimens using both the three layers model proposed by previous researchers and a modified three layers model proposed in this study were conducted to examine the strain distributions in the vicinity of the crack. In general, the strain distributions of the specimens were predicted well by the finite-element analyses using either model. The finite-element results showed that the SIF at the crack tip through the plate thickness was significantly reduced except on the unpatched side and the modified three layers model was able to capture the nonlinear SIF variation through the thickness of a cracked steel plate with single-side patching. Meanwhile, the three layers model overestimated the SIF on the patched side and underestimated the SIF on the unpatched side by about 10% on average compared to those of the modified three layers model. Based on the finite-element analysis results of the modified three layers model, it is shown that the width and the length of patching had only a marginal effect on the SIF. On the other hand, the effect of the number of layers of patching on the reduction of SIF was more pronounced.