Microscopic Strain Mapping: Functional Diversity and Their Demands

This paper reviews recent demands and developments of microscopic strain mapping towards understanding plasticity-related fracture mechanisms in metals. After development of the most solid strain mapping method, i.e., micro-grid method, various strain mapping methods with different demands have been proposed. For instance, to satisfy the requirements of strain accuracy, spatial resolution, temporal resolution, view field range, strain limit, etc., digital image correlation (DIC) method, sampling moiré method, and photonic opal crystal film have been developed and improved. Furthermore, to understand true origins of fractures, regressive strain mapping, three-dimensional strain mapping, and post-mortem strain mapping have been increasingly required for the situations of “nobody knows the crack nucleation site before cracking”, “stress-driven cracking occurs on a plane strain condition (specimen interior)”, and “in some instances, only a fractured sample is available”. For these demands, DIC method on replicas, computed-tomography-based strain mapping technique, and orientation-based strain analysis have been developed. In this paper, based on our recent works, the state-of-the-art techniques of strain mapping in metals are briefly introduced.