Acoustic emission-based identification and interfacial fiber bridging and delamination damage mechanisms in twill/unidirectional composite materials

Abstract

Interlaminar damage in carbon fiber reinforced polymer (CFRP) laminates is a common form of damage in engineering applications, with interlaminar fracture toughness commonly used to characterize its ability to resist crack propagation. In double cantilever beam (DCB) tests of CFRP laminates, the intensity of fiber bridging phenomena depends on the structure and orientation of fibers on either side of the delamination. To further elucidate the mechanism of fiber bridging phenomena in delamination crack propagation, DCB specimens with pre-fabricated cracks on either side composed of twill-weave (TW) fiber layers and unidirectional (UD) fiber layers were employed to study the delamination behavior of two fiber orientations. An unsupervised k-means clustering algorithm was employed for identifying damage modes from acoustic emission(AE) signals under different failure modes, and the relationship between the interlaminar fracture toughness of the specimens and interlaminar micro-damage was analyzed. Scanning electron microscopy (SEM) was used to reveal the micro-mechanisms of damage. The results indicate that the trend of interlaminar fracture toughness of the specimens is positively correlated with the peak amplitude of AE signals. Cluster analysis categorizes AE signals into matrix damage (including matrix cracking, interface debonding, and fiber pull-out) and fiber bridging damage (fiber breakage). Cluster analysis revealed that differences in interlaminar fracture toughness among interfaces stem from varying matrix fracture modes. Acoustic AE technology was used to distinguish the lamination mechanism between specimens from micro and macro perspectives, which provides an important basis for determining the mechanical properties of composite laminates.