Damage tolerance is a critical aspect designing components subjected to cyclic loading for various commercial applications such as the aviation industry. Especially in safety-relevant areas, increasing the service life of components without compromising on safety is of fundamental importance. For this reason, laminated metallic composites (LMC) are of particular interest due to their numerous advantages including an improved strength-to-weight ratio and tailored mechanical properties compared to monolithic materials [1,2]. Among others enhancing the resistance against fatigue crack propagation due to toughening mechanisms is very promising. This feature is based on the so-called material inhomogeneity effect at interfaces. By introducing a gradient in hardness or elastic properties at the interfaces, the resistance against crack propagation is increased due to the formation of a complex 3D-crack network with toughening mechanisms such as crack deflection, bifurcation or bridging [3].

In this work, monolithic materials, Al/Al-bimetals and Al/Al-LMCs with a hardness gradient were fabricated via the accumulative roll bonding process to develop a better understanding about the role of the layer architecture and interface density on the fatigue crack growth. Therefore, fatigue tests were performed for both the soft/strong and the strong/soft transition using a 3-pont-bending setup. The fatigue crack growth rate was effectively reduced compared to the monolithic materials in crack arrester orientation. Subsequent post-mortem light microscopy investigations revealed the various fatigue crack paths of the different samples. The different layer structures and interface densities led to different toughening mechanisms like crack deflection and crack bifurcation both in the bimetals and in the LMCs.

[1] D. R. Lesuer, et al. , “Mechanical behaviour of laminated metal composites,” Int. Mater. Rev., vol. 41, no. 5, pp. 169–197, 1996.

[2] F. Kümmel, et al. , “Ultrafine-Grained Laminated Metal Composites: A New Material Class for Tailoring Cyclically Stressed Components,” Adv. Eng. Mater., vol. 23, no. 7, p. 2100070, 2021

[3] P.M. Pohl, et al. , “About the Role of Interfaces on the Fatigue Crack Propagation in Laminated Metallic Composites,” Mater., vol. 14, 2021