Influence of off-axis ply orientation on the axial compression behaviour of CFRP tubes

Abstract

This paper presents an experimental investigation of the compression behaviour of Carbon Fiber Reinforced Plastics (CFRP) tubes with different off-axis ply orientations. A series of compression tests with effective end-reinforcement were conducted on [0₄/±theta] CFRP tubes, with θ equal to either 0°, 30°, 45°, 60°, or 90°. Various failure progressions and fracture morphologies were measured using a high-speed camera and a scanning electron microscope. The failure modes and mechanisms of CFRP tubes with different stacking sequences were analysed in detail. The results indicate that the off-axis ply orientation greatly influences the compression behaviour. The adopted end-reinforcement ensures that nearly all of the CFRP tubes fail within the gauge length. When θ < 45°, the tubes exhibit various failure modes, and the scatter of strength is large. However, when θ ≥ 45°, the sole failure mode is a shear fracture of the inner 0° layers, and their scatter of strength is minor. A new shear failure mechanism is instrumented: the shear fracture direction changes from inclining along the circumferential direction to inclining along the radial direction when θ varies from 45° to 90°. The failure strength and off-axis ply orientation display a complex non-linear relationship. When θ = 60°, the compression strength becomes maximum at an average value of 602 MPa, and the scatter of strength is 2.71%.