Acoustic Emission Characteristics Of C/SiC Composites During Complicated Environments

Carbon fiber reinforced silicon carbide composite (C/SiC) is one of important promising structure materials that can meet the need of the thermal-part of aero engines. Because of multi-constitute and characteristics of knitting and preparation, its mechanical behaviors and damage mechanics were extraordinary complicated. So the traditional method cannot be adapted to the research on damage evolution of composites. However, acoustic emission (AE) can deal with the problem effectively. The whole damage evolution of C/SiC composite during monotonic tensile, thermal-shock, fatigue and creep at high temperature were inspected in real-time by AE. The different failure modes of C/SiC composite were described by AE parameters and its rules of damage evolution were also revealed. The main contents and conclusions are as follows,[1] The damage evolution of C/SiC composite during monotonic tensile at room temperature was investigated by AE. The results showed that AE signals of C/SiC composites mainly came from matrix crack, interface debonding and fiber breakage. The parameters, such as duration, energy and frequency, of AE signals produced by different damage modes were different.[2] The damage evolution of C/SiC composite during thermal shock at different atmosphere was investigated by AE. The growth and expansion of crack occur in the course of cooling. At argon atmosphere, the thermal shock damage to C/SiC composites was limited and there existed a critical thermal shock cyclic times. At corrosion atmosphere, C/SiC composites were corrupted by corrosive gas continuously, and the cyclic thermal-stress degraded the mechanical properties of C/SiC composites. [3] The damage evolution of C/SiC composite during fatigue at hightemperature was investigated by AE and the main damage mechanism was understood. Under the condition of cyclic fatigue load, matrix crack, interface of fiber/matrix debonding, sliding, fiber breakage and fiber pull out occurred. These damage patterns effected and combined each other. As a result, the rigidity and strength of C/SiC composites descended and the other physical properties were changed.[4] The damage evolution of C/SiC composite during creep at high temperature was investigated by AE and the main damage mechanism was understood. During the creep at high temperature, the AE cumulative energy coordinates with the creep strain. So, the behaviors of C/SiC composites during creep at high temperature, could be described by AE cumulative energy. The creep strain of C fiber controlled the whole creep strain of C/SiC composite. The difference of interface status could cause great change of strain during creep.