These ones are small; those ones are far away: A comparison of macro and in-situ micro tensile testing techniques

An aluminium AA7020 alloy was investigated in both the as received cold rolled condition and in the w-temper condition after heat treatments in both macro tensile and in-situ micro tensile tests to verify test parameters for in-situ testing to improve understanding of the validity of micro results to bulk properties. A variety of macro scale geometries conforming to ISO standards, and micro scale geometries were tested in the as received cold rolled condition to identify the optimal thickness of tensile samples to replicate bulk physical properties. Both macro and micro DIC (digital image correlation) techniques were utilised to confirm accurate strain paths in said geometries. W-temper specimens were then subjected to interrupted EBSD (electron back-scattered diffraction) scans during in-situ tensile tests to understand the microstructural evolution of the material during deformation and understand what impact the pauses in deformation have on physical properties. This study identified that for accurate physical properties to be derived from in-situ micro samples they need to be thinned to achieve a width to thickness ratio of around 5, and that interrupted tests significantly alter the UTS (ultimate tensile strength) and strain to failure so need to be combined with non-interrupted tests to derive accurate properties.