Fatigue Behavior of Carbon Fiber Woven Composite Laminates with Different Off-Axis Angles Studied by Combining Infrared Thermography

This study employed infrared thermography to investigate the fatigue properties of plain-woven composites under various off-axis orientations. The specimens underwent constant amplitude fatigue loading at stress levels set at 80%, 75%, and 70% of the ultimate tensile strength, maintaining a stress ratio of 0.1. The experimental findings indicated a decline in both tensile strength and fatigue life as the off-axis angle increased. Among the four off-axis specimens, only the 45° off-axis samples demonstrated stiffness enhancement under low-stress fatigue loading. This enhancement was attributed to the rotational reorientation of fibers, compensating for the stiffness reduction caused by fatigue damage. Infrared thermography identified damage in off-axis specimens primarily at the edges due to the free-edge effect. Furthermore, interrupted specimens were tested late in the fatigue life, revealing more pronounced damage at the specimen edges.