EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Accumulative roll bonding (ARB) was first introduced by Saito et al. in 1998 [1]. In recent years, this process was used to produce ultrafine-grained (UFG) multilayered laminates out of a variety of material combinations [2]. Laminated metal composites (LMCs) can be tailored towards the exhibition of a variety of extrinsic toughening mechanisms and thus show promising potential for applications in damage tolerant components [3].
This research project focuses on the fatigue crack growth (FCG) in LMCs consisting of different Al-alloys with dissimilar hardness (AA1050 and AA5754) manufactured using the ARB processing route. LMCs with 50/50 volume fraction and different layer thickness of 625μm, 325μm, 150μm and 75μm were produced.
FCG results show significantly enhanced damage tolerant FCG behavior for LMCs in crack arrester orientation compared to a) specimen of monolithic constituents as well as b) a rule of mixture concept calculated from the FCG properties of the monolithic constituents. This behavior can be attributed to enhanced extrinsic toughening mechanisms in LMCs consisting of materials with dissimilar hardness [4]. The hardness gradient at the interfaces as well as the orientation of the interfaces perpendicular to the direction of crack growth lead to pronounced retardation of crack propagation when the crack approaches the interfaces in these LMCs. The prevalent toughening mechanisms were identified as a) crack deflection when the crack approach the interfaces from the softer towards the harder layers and b) crack bifurcation when the cracks approach the interfaces from the harder towards the softer layers. 3D-reconstruction of the crack network post-mortem obtained by X-ray micro computed tomography (µ-CT) show that these mechanisms can be observed throughout the entire volume of the laminated architecture.
These findings are of particular interest in order to understand mechanisms of FCG in LMCs and to tailor the laminate architectures and compositions for damage tolerant applications.