DIC-based monitoring on debonding crack propagation in wrapped composite joints

Abstract

Wrapped composite joint is an innovative technique which connects steel hollow sections through bonding such that the fatigue performance is improved compared to welded joint. In this paper, a DIC-based method of monitoring surface strains is proposed to quantify the debonding crack propagation within the composite wrap layers during high cycle fatigue loading. A constant strain threshold was used to obtain crack length based on strain distribution curves extracted from DIC. Sensitivity analysis of such threshold showed that within the ‘steady strain slope’ region, the influence of threshold choice on calculated crack length is insignificant, but a good choice of threshold can help obtain more stable results. During cyclic loading, it was found that stiffness degradation and crack development of the joint is arrested due to friction effect at the cracked interface. Static tests after cyclic loading showed that the joint can still sustain its original static resistance.