Temperature-dependent interlaminar behavior of unidirectional composite laminates: Property determination and mechanism analysis

Delamination damage is a critical concern for composites—especially for aircraft structures—considering their complex service conditions, which include extreme temperatures and impact threats. This study considers the effect of temperature (−20°C to 110°C) on the mode-I interlaminar failure behavior for unidirectional carbon/epoxy composite laminates, through a series of experiments. A simple double compliances method (DCM) without the measurement of crack length was employed to determine mode I interlaminar fracture toughness, and the accuracy of DCM at different temperatures was validated by comparing the results obtained from DCM with those calculated using ASTM methods. The comparison indicates that fracture toughness values determined from DCM are consistent with those from ASTM methods, and the predicted crack lengths from DCM show little difference with experimentally measured crack lengths. The experimental results reveal the significant sensitivity of mode I interlaminar failure behavior with the environmental temperature. Both the peak load and initial interlaminar fracture toughness increases with the increase of test temperature. It is found that propagation fracture toughness shows different temperature sensitivity at high temperatures (50°C to 110°C) than that under low temperatures (−20°C to 25°C). The crack propagation speed tends to be a constant value during the tests and decreases with the increase of test temperature. The fractography analysis illustrates a transition of the mode of failure from fiber–matrix interface debonding at lower temperatures to matrix cleavage at higher temperatures.