An In-Situ Investigation of the Strain Partitioning and Failure Across the Layers in a Multi-Layered Steel

Layered composites consisting of dissimilar materials have shown tremendous improvements in balancing strength with ductility. The details of strain partitioning across the layers, resulting in high ductility even in the brittle layer, are not well understood. This study aims to quantify strain partitioning and understand the failure of rolled sheets of alternating austenite and martensite layers through in situ tensile experiments. A novel high density speckle pattern with the sample surface as background is generated to resolve strain within and across the interface at the microscale. Simultaneous imaging of both the layered and top surfaces was performed to correlate strain and understand the localization leading to failure. Microstructural analysis and numerical simulations were performed to further understand the role of phase transformation and predict the stress–strain response, respectively. Both axial and transverse strain field heterogeneity was observed across the layers, with pronounced strain partitioning in the transverse direction and steep gradients near the interfaces. The restriction to the growth of micro-deformation sites in the thin austenitic layers led to a long neck region with local strain as high as 40