Measures of Bulk and Grain Strain in Deformation Processes

This study illustrates a method of measuring internal total strain based on the observation that networks of internal boundaries within a polycrystalline material deform locally in a manner congruent with the local metal flow. Appropriate measurements of the development of the spatial anisotropy of such networks with increasing deformation provide a basis for defining several measures of the local total strain. These quantities, called “grain strains” when the boundaries observed are grain boundaries, can serve as an experimental measure of the internal total strain at various locations in a specimen for comparison with computations based on finite element models using various constitutive relations or phase field simulations of grain growth or deformation. Experimental measurements of grain strains at the center of a ferritic steel sheet rolled in nominally 10% increments to 50% total reduction in thickness illustrate the method and correlate well with corresponding strains based on measures of the change in thickness of the sheet and the assumption of plane strain.