Study on impact damage mechanisms and TAI capacity for the composite scarf repair of the primary load-bearing level

Abstract

As composite material plays a leading role in aircraft, composite bonding repair has been extensively applied. Among composite bonding repairs, the scarf bonding repair is widely adopted and has high repair efficiency especially in primary load-bearing structures. However, the impact damage tolerance and impact damage mechanisms were not considered for repaired structure integrity design yet. This paper experimentally and numerically studied the scarfed bonding repair of the advanced CFRP, which may suffer a low velocity impact load in service. At the central location of adhesive zone, impact energy and response regularity were studied to reveal the competition failure mechanism for inner kinds of materials. In the impact procedure, double force peaks phenomenon and four typical phases were found. Tension after impact (TAI) capacities were also tested to explain the impact damage effects on residual strength. The adhesive damage has strong influence over tension after impact capability. The most easily broken location in the bonded zone is the feathered tip on the back of impact point. The critical impact energy 23J exists for this size of specimen. When the impact energy is higher than the critical 23J, except for the composites damage, the adhesive damage can be observed at the second force dropping. The scarfed adhesive damage occurred at the scarf feathered tip of back side.