Delamination evaluation of composite laminates with different interface fiber orientations using acoustic emission features and micro visualization

This study aims to investigate the sequence of initiation and evolution of different damage mechanisms during the DCB standard test procedure on specimens with different interface fiber orientation using Acoustic Emission (AE) data analysis and microscopic imaging methods. For this purpose, a series of experiments based on standard ASTM D5528 were performed on 24 layer glass epoxy multidirectional specimens with ±ϑ/05 As As layup, in which ϑ is 0. 30. 45 and 60. The acoustic data were then acquired with two AE sensors and the whole test procedure was observed by two digital cameras, which were focused on specimen edges. The results show that the initiation and evolution process of matrix cracking as the first activated damage mechanism greatly depends on the interface fiber orientation. Also, load-displacement curves and AE data can be well correlated with microscopic observation in all stages of damage initiation, evolution and propagation. Although the standard nonlinear point as crack initiation onset predict an equal fracture energy for all cases, however AE analyses and microscopic observations show early damage initiation and evolution in 45 and 60-degree interfaces.