Structural and microstructural influence on deformation and fracture of dual-phase steels

Abstract

The objective of this work is to demonstrate that the mechanical response of multiphase materials is fundamentally different in an imposed deformation field that is homogeneous, versus in an imposed deformation field that is heterogeneous, at a length-scale greater than the microstructural length-scale. To this end, we focus on two dual-phase steels with significantly different nominal chemical composition and microstructure. The mechanical response of the steels is characterized by in-situ SEM tensile tests of flat dog-bone and single-edge notch specimens. The experimental results show that the dog-bone specimens of the two steels exhibit very similar mechanical response but the mechanical response of their single-edge notch specimens differs significantly. This is in contrast to any classical analysis that will predict the same mechanical response in the presence of a notch for two materials that give the same mechanical response under uniaxial tension. The high resolution in-situ tests coupled with microstructure-based digital image correlation and finite element analysis are then used to elucidate how the interlacing of imposed heterogeneous deformation field and material microstructure affects the mechanical response of these steels. Our results clearly highlight that a mechanistic analysis of multiphase materials under imposed heterogeneous deformation field must involve explicit consideration of the length-scales associated with the material microstructure.