A direct crack sizing approach from DIC strain analyses under elasto-plastic and dynamic conditions

Abstract

This paper proposes a novel approach to quantify the crack size from strain fields measured from digital image correlation (DIC), by extrapolating the positions at peak strain or peak strain increments identified along paths parallel to the crack plane. The proposed approach does not require data in the immediate vicinity of the crack tip, where DIC measurement is usually less accurate. This study utilizes the modified boundary layer model to demonstrate the strain pattern underpinning the crack size from HRR theory and the single edge notched bend model to verify the crack sizing accuracy from the strain fields. The experimental study further validates the proposed method in plane-sided and side-grooved specimens and evaluates the plastic wake effects on the crack-sizing accuracy for propagating cracks under elasto-plastic conditions. The proposed method identifies the crack tip location directly without measuring the elastic compliance, which enables fast and convenient crack sizing under challenging conditions such as the impact tests. This study demonstrates enhanced fracture resistance of the S550 material under increasing loading rates using the proposed crack sizing method.