Additional hardening in harmonic structured materials by strain partitioning and back stress

Deformation behavior of a harmonic structured material (HSM), core-shell 304L stainless steel, is investigated using micro-digital image correlation (micro-DIC). High strain-partitioning between core and shell is observed. Because the grain boundaries with a grain-size gradient in HSM induce high deformation-incompatibility, strain peaks are detected near core-shell boundaries and in grain boundaries of cores. This incompatibility is compensated by geometrically necessary dislocations, generating back stress. The back stress is measured using tensile unloading-reloading testing. This investigation demonstrates higher back stress and strain hardening rate in HSMs than homogeneous materials, resulting in enhanced ductility. [GRAPHICS] IMPACT STATEMENT Core-shell structure with grain size gradient leads to strain partitioning and high back stress hardening in HSMs. micro-DICwas utilized to observe the local strain distribution.