Determination of Mixed Mode Delamination Crack Initiation using Acoustic Emission Measurements

A novel approach for the determination of the initiation of mixed mode delamination crack on glass/epoxy DCB specimens is presented. In the present study, acoustic emission measurements were used to identify the onset of delamination using different signature acoustic emission features. The acoustic emission was also utilised to track the crack front during all tests. Both, the acoustic emission features, as well as the crack front localisation indicate two different regions denoted as region I, and region II. It was observed that the cumulative sum of the acoustic emission features in region I shows a slow increase (both in the AE features and in the crack front localization), whereas in region II there was a rapid increase on acoustic emission and a progressive advance of the crack front. Furthermore, the initiation as obtained from the acoustic emission measurements was used to define and calibrate a new simpler approach for the determination of mixed-mode delamination crack initiation. The new approach, which is both faster and simpler, is based on the deviation from linearity of the load (or moment) vs displacement curve.