An experimental study of large scale model composite materials under thermal fatigue

The effects of temperature cycling on the structural integrity of polyester matrix composites were investigated using a large scale model composite. The damage of composites during the heating and cooling phases was observed when subjecting the composites to thermal cycling using an especially designed temperature cycling apparatus. Results of the tests revealed that cracks were initiated at the fiber/matrix interface near the free surface as early as after one thermal cycle. Deterioration of the composites was found to occur only during the cooling phase of the thermal cycle. Fiber protrusion was also observed, with fibers protruding from the surface of the matrix at both ends of the specimen. Fiber/matrix debonding, initiated at the same time as fiber protrusion, progressed with increasing number of thermal cycles, and was found to arrest at approximately the same number of cycles as the number at which the progression of protrusion was found to terminate. The magnitude of the resulting fiber/matrix separation when the protrusion is stabilized was found to be equal to approximately three times the diameter of the fiber. (C) 1999 Elsevier Science Ltd. All rights reserved.