Cyclic deformation and damage behaviour of the spring steel wire reinforced aluminium alloy EN AW-6082

The demand for lightweight materials used for constructions in automotive applications, e.g. space frames, requests for composite materials such as reinforced aluminium extrusions with a high specific stiffness and strength. This contribution shows that a spring steel wire reinforcement content of 11.1 vol% leads to a significant increase in fatigue life of monofilament composite extrusions based on the aluminium alloy, EN AW-6082, in heat treatment state T4 under stress controlled fatigue loading. As groundwork, the cyclic deformation and damage behaviour of the unreinforced matrix material is investigated in detail. Beside the determination of three stages of deformation and damage, the reason for the high fatigue strength in comparison to the quasi-static offset yield strength is also clarified. The main aim of the research focusses on the description of the mechanisms and mechanics of constituent deformation and damage evolution of 11.1 vol% spring steel wire reinforced EN AW-6082, which is presented quantitatively and qualitatively by metallographic means. The three stages represent the deformation and damage of the matrix material, whereas the fourth stage is characterised by the fatigue of the reinforcing element. Based on the knowledge of the quasi-static behaviour of the single components and the fatigue behaviour of the single matrix material, a new lifetime model is deduced from the strain response in order to predict the fatigue life for unidirectionally reinforced material systems.