Tensile and fatigue behavior of Al-based metal matrix composites reinforced with continuous carbon or alumina fibers: Part II. Quasi-unidirectional composite cross-ply laminates

The mechanical behavior (tension, fatigue, and notch sensitivity) of Al-based metal matrix composite (MMC) cross-ply laminates is investigated. The two selected laminates, K139/A357 and N610/AU2, are reinforced by continuous K139 (carbon) or N610 (alumina) fibers. These multiplies consist in the stacking of (quasi-unidirectional) quasi-UD preforms oriented at 0, ±45, and 90 deg, the thermomechanical behavior of the corresponding quasi-UD composites being reported independently (Part I). The investigated cross-ply laminates exhibit attractive static and cyclic performances and a low notch (circular hole) sensitivity. High-resolution microfractography has led to a better understanding of the fracture mechanisms of these materials. In this respect, the role of the transverse bundles is dominant in the tensile and fatigue failure of both laminates. However, the failure surfaces are completely different: long fiber pullout in the K139/A357 laminate and much more planar areas in the N610/AU2 laminate. Due to the rather low notch sensitivity, a large portion of the specimen section was already highly damaged during a non-negligible part of the fatigue life: debonded interfaces in the K139/A357 laminate and multicracked and “crumbled” matrix in the N610/AU2 laminate. These mechanisms are in good agreement with the weak interface in the first case and the very low yield stress of the AU2 matrix, much lower than the fatigue limit of the N610/AU2 laminate, in the second case. Moreover, compared to the quasi-UD composites, the stress concentration around the notch allows further exacerbation of the fatigue mechanisms, much more intense than that attained in “model” composites.