Tensile test and damage mechanism analysis of carbon fiber laminates with different countersunk angles

In this study, a combination of numerical simulation and experiment was used to systematically investigate the mechanical response characteristics and damage mechanisms of countersunk hole angles (60°, 90°, 120°) on filled-hole composite laminates and countersunk hole laminates under axial tensile loading. Based on acoustic emission technology to monitor the damage evolution in real time, the damage patterns under static tensile conditions were identified and classified by combining with K-means clustering algorithm. A three-dimensional finite element model was constructed by ABAQUS platform, integrating 3D Hashin failure criterion, B-K damage criterion and zero-thickness cohesive layer method, and the VUMAT subroutine was used to characterize the material failure behavior. The results show that the countersunk hole angle significantly affects the location of delamination damage initiation. Four main damage modes were observed experimentally: fiber/matrix debonding (0-110 kHz), matrix cracking (110–250 kHz), delamination (250–350 kHz) and fiber breakage (350–400 kHz). The tendency for different damage modes to occur in the laminate changes as the countersunk hole angle changes. A comparative analysis of FHT and OHT for compression plates shows that countersunk bolts reduced stiffness and ultimate load but increased failure displacement. The results provide an important theoretical basis for the structural optimization of composite laminates.