Revealing low temperature-mechanical coupling failure mechanisms in CFRP laminates with in-situ observations

The number of layers and ply orientations determined the service performance of carbon fiber-reinforced polymer (CFRP) materials. Under low-temperature service conditions, the unclear weakening mechanism of mechanical properties of CFRP aggravates the failure risks of aerospace structures. In present work, the unclear correlation between layers with alternating orientations and the tensile-failure mechanisms of CFRP, the low temperature-mechanical coupling micromechanical behavior, and the failure mechanism of CFRP was experimentally revealed by using a horizontal testing instrument integrated with a low-temperature loading module and real-time optical imaging function. Based on various temperatures in a range from −40 °C to room temperature (RT) and two strain rates, the gradually decreasing trends of tensile strength, Young's modulus, and elongation after fracture with decreasing temperature are obtained. Three failure modes including fiber brittle fracture, fiber pull-out, and interface debonding are proposed to reveal the low temperature-mechanical coupling failure mechanism. Low-temperature asynchronous shrinkage of carbon fiber and epoxy resin promoted the transition from fiber brittle fracture to delamination at the interface. The proposed instrument could establish the approximatively actual service conditions involving low temperature and mechanical load.