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Lecture

WEB Damage tolerant fatigue behavior of Al/Al-Laminates produced by ARB - Influence of layer thickness and hardness gradient at interfaces

Friday (25.09.2020)
12:50 - 13:05 S: Structural Materials 1
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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 two different Al/Al-Systems (AA5754/AA1050 and AA5754/AA5005) manufactured using the ARB processing route. LMCs with different layer thickness of 625μm, 325μm, 150μm and 75μm were produced. The volume fraction of the laminate components in the specimen’s valid FCG region (a/W = 0.3–0.7) was 50/50 for each system and architecture. Specimen with SEN(B)-geometry in crack arrester orientation were extracted from the rolled metal sheets.

In order to quantitatively study the influence of layer thickness and hardness gradient at interfaces, the FCG-tests of the LMCs were performed at different ΔK levels using ΔK=const. control to have a macroscopically constant crack driving force throughout the laminate architecture. Crack length during the experiments was measured as surface crack length using crack propagation gauges with a grid spacing of 100μm glued to the specimen and fed back to the control loop of the servohydraulic MTS810 testing machine.

First results show enhanced damage tolerant fatigue crack growth behavior for LMCs in crack arrester orientation compared to specimen of monolithic constituents. In order to properly classify the results, a linear rule of mixture concept of the constituent monolithic FCG properties using the same volume fraction as the LMCs serves as a benchmark.

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 LMCs. This is due, among others, to stress redistribution and crack deflection.

These findings are of particular interest in order to understand the underlying mechanisms involved in FCG in LMCs and thus to tailor the laminate architectures and compositions for damage tolerant applications.

Speaker:
Dipl.-Ing. Philip Pohl
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Additional Authors:
  • Dr. Heinz Werner Höppel
    Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
  • Prof. Dr. Mathias Göken
    Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)