Residual strength of centrally cracked metal/fiber composite laminates

The residual strength of metal/fiber composite laminates (MFCLs) with a central crack is studied. The laminate is a sandwich with a fiber reinforced epoxy ply (prepreg) in the middle and an aluminum alloy layer on each of the outer surfaces. Dugdale strip yielding zones in the aluminum layers at the crack lip are assumed to take into account ductile deformations of the metal layers. It is also assumed that a strip damage zone in the prepreg layer is developed at the crack lip reflecting matrix cracking and fiber breakage and pull-out. Residual strengths for the centrally cracked laminates are calculated numerically. It is found that the residual strength of CARALL (carbon fiber reinforced polymer/aluminum laminate) is always higher than that of ARALL(R) (using aramid fiber instead of carbon fiber) for both infinite and finite width plates in the range of initial crack lengths considered. The strengths of CARALL with high elongation (HE) fiber are also higher than those of their metal counterparts. The results for ARALL predicted from the present model agree well with the existing experimental observations. The residual strength results for cracked MFCLs suggest that CARALL, especially with HE fibers, may replace aluminum alloys in lower aircraft wings and fuselage because of its higher residual strength and lower density. However, its fatigue resistance, impact residual properties and resistance to corrosion and other environmental effects need to be studied thoroughly.