Ultrasound investigation of pseudo-ductility of carbon fiber reinforced polymers at ± 45° layup

Fracture processes in carbon fiber reinforced plastics significantly depend on the architecture of the laminate reinforcement. For ± 45° angle-ply laminates of carbon fiber reinforced plastics, mechanical loading is accompanied by pseudo-ductility. This mechanism is characterized by the nonlinear stress-strain behavior under unidirectional loads. Bending stress combines compressive and tensile stresses. A transition between them is not linear, and destruction processes in carbon fiber reinforced plastic structure having layers angled at ± 45°, are interesting and not completely understood. The paper presents the experimental results of bending damage of a laminate with stacking sequences of [(± 45°)₂/0°]S and [(± 45°)₂/90°]S. High-frequency acoustic microscopy is used to visualize the bending damage development. Layer-by-layer ultrasound imaging shows localization of fiber fractures, microcrack nucleation, growth and association with interlayer delamination.