Stress intensity factor and fatigue analysis of cracked cruciform welded joints strengthened by CFRP sheets considering the welding residual stress

In order to investigate the strengthening effect of carbon fiber reinforced polymer (CFRP) on the fatigue performance of cracked cruciform welded joints, numerical analyses and fatigue tests were presented. Considering the effects of initial crack depth, CFRP modulus, and CFRP thickness, three different methods were employed to assess the SIF ranges of unrepaired and CFRP sheets repaired cruciform welded joints, and a new formula to calculate the SIF range was fitted via numerical results. Two different welding residual stresses obtained from literatures were taken into account to evaluate the effective SIF range. Fatigue life predicted results were determined via the modified Paris equation considering two different crack closure factors. The results demonstrate that the SED method can be successfully and conveniently used to estimate the SIF range, the accuracy of the new equation is verified. CFRP sheets can decrease the SIF range of the crack tip and extend the fatigue life, and the maximum increase in the fatigue life reaches 66%. The effect of different CFRP sheets is nearly the same owing to a small stiffness ratio. Fatigue strength of cracked cruciform welded joints strengthening with CFRP sheets at 2 million cycles increases by 26% compared to that of specimens without CFRP. Good agreement with experimental results indicates that the residual stress B and the Schijve model are recommended to predict the fatigue life of cruciform joints.