Step repaired coupons involving Abrasive Water Jet machining

Carbon/epoxy coupons are machined, repaired, and tested to estimate the behaviour of a step-lap repair. The repair process involves Abrasive Water Jet machining to obtain regular steps with a depth equal to ply's thickness. Digital Image Correlation using stereovision, as well as FEM simulations, are used to study the release of the residual stresses during machining. Machined plates are repaired by co-bonding epoxy-carbon plies with reconstruction plies in autoclave. The chosen stacking sequence for the repair plate is the same than the initial one, with one ply shifting, in order to improve loading transfers. Then tensile coupons are cut from repaired plates and tested under tensile load. Experimental results show that repaired coupons reached 70% of the load achieved by healthy ones. Fracture seems to occur in the interface between two 0 degrees plies, for all types of coupons. For this type of repair, comparison between experimental and numerical data allows to obtain a fracture criterion based on an ultimate shear stress in the bonding.