Damage tolerant fatigue behavior of laminated metallic composites with dissimilar yield strength

Abstract Aside from other demands, damage tolerance is an important design criterion for cyclically stressed components of commercial aircraft, such as the fuselage or wings. Heterostructured materials, such as laminated metal composites (LMCs) produced by the accumulative roll bonding process (ARB), can be tailored to provide high resistance against fatigue crack growth by utilizing material heterogeneities at interfaces. In this study, the influence of the layer thickness and dissimilar yield strength at interfaces on the fatigue crack growth behavior in LMCs is investigated systematically to derive design criteria for highly damage tolerant laminated composites. A linear rule of mixture behavior is introduced as a benchmark for the damage tolerant behavior of the laminated composites. The crack growth rates of the laminated composites at elevated stress intensity ranges are significantly reduced compared to both the rule of mixture concept and the behavior of the monolithic constituents. This is explained by the onset of toughening mechanisms at the vicinity of interfaces and the formation of complex crack networks. The extent of crack growth rate reduction due to toughening mechanisms depends on both the yield strength ratio as well as layer thickness of the laminated composites. A comprehensive understanding of the mechanisms responsible for the damage tolerant behavior was provided by determining the size of the plastic zone ahead of the crack tip using finite element analysis. An addition to the Paris crack-growth law was suggested, accounting for the additional influencing factors to accurately describe the significantly improved fatigue crack growth behavior of laminated composites.