Measurement of the M-integral for a Hole in an Aluminum Plate or Strip

A method using Digital Image Correlation (DIC) is proposed to measure the M-integral in an elastic rectangular plate and elastic–plastic strip made of LY12 Aluminum where a hole is located at center as a defect. The path-independence property of the M-integral is verified by selecting a few of closed contours to evaluate the M-integral. It is found that the measured values of the M-integral are path-independent when the closed contours are far from the nonlinear plastic zone. In contrast, large deviations occur in determining the M-integral among different integral contours when the contours pass through the plastic zone. The present study demonstrates that DIC method used by the ARAMIS 4 M instrument and the proposed smoothing technique for evaluating the measured displacements do provide the effective tools to measure the M-integral in describing the local damage of elastic and elastic–plastic materials. This technique could be extended to measure the M-integral for other complicated damage, e.g., multiple defects with different shapes in a local region.