In-situ investigations of structural changes during cyclic loading of aluminium by high resolution reciprocal space mapping

A major failure reason for structural materials is fatigue-related damage due to repeatedly changing mechanical loads. During cyclic loading dislocations self-organize into characteristic ordered structures, which play a decisive role for the materials lifetime. These heterogeneous dislocation structures are identified by high resolution reciprocal space mapping. The synchrotron technique using high energy X-rays was applied successfully in-situ during cyclic deformation of macroscopic aluminium samples at the Advanced Photon Source to reveal the structural reorganization within single grains embedded in the bulk material during cyclic deformation. As evident from the changes in the radial profiles of four grains, the adaption of the deformation structure to cyclic deformation is completed already after 800 cycles. Individual subgrains have been followed through a 7350 tension-tension cycles while monitoring macroscopic stress and strain during cyclic loading. The elastic back strains of subgrains are Gaussian distributed with larger subgrains showing larger back strains. The detailed characterization of the microstructure during cyclic loading by in-situ monitoring of the internal structure within individual grains facilitates the understanding of materials behaviour during cyclic deformation.