Multiresolution investigations of thermally aged steels using spherical indentation stress-strain protocols and image analysis

In recent work, our research group has developed and demonstrated novel multi-resolution protocols capable of extracting indentation stress-strain (ISS) curves from tests on individual microscale constituents (e.g., phases, grains) as well as bulk properties of material microstructures. In addition, we recently developed protocols for design of consistent segmentation of micrographs. This work combines these recent advances in multi-resolution spherical indentation and image segmentation protocols to address the current challenges in the critical evaluation and advancement of physics-based composite models. These new research avenues are identified and demonstrated through a case study on thermally aged ferrite-pearlite steel samples, where the respective indentation yield strengths of the microscale constituents (i.e., ferrite, and pearlite) and the bulk yield strength of the samples were estimated from ISS tests measurements. The constituent volume fractions were extracted from segmented optical microscopy images. It is shown that the multi-resolution indentation yield strength and volume fraction measurements are highly consistent with the homogenization estimates from simple composite theories.

Automated summary

This article introduces a novel multi-resolution protocol that can extract indentation stress-strain curves from tests on microscale constituents and design consistent image segmentation protocols. A case study on thermally aged steel samples demonstrates the accuracy of this approach in estimating the mechanical properties of microscale constituents and the bulk properties of the samples.