Nondestructive evaluation (NDE) and mechanical behavior of continuous fiber reinforced ceramic matrix composites (CFCCs)

In order to encourage wide applications of CFCCs, nondestructive evaluation (NDE) of CFCCs is vital to characterize the integrity of the composites. Up to the present time, relatively little work has been performed on the NDE of CFCCs and on relating the NDE results to the understanding of mechanical behavior of CFCCs.; Various types of NDE techniques, such as ultrasonic testing (UT), X-ray computed tomography (CT), acoustic emission (AE), and infrared (IR) thermography, were applied to investigate defect distributions, to characterize the type and location of flaws in the composites, and to assure the manufacturing quality as well as to guarantee the reliability during the fabrication and/or service periods of CFCCs. The fracture behavior of CFCCs were also investigated using NDE technologies for a mechanistic understanding of failure mechanisms of CFCCs. Those NDE techniques were employed to characterize inherent damages and the damage evolution, before, during, and after mechanical testing. The NDE results were used to develop an understanding of fracture mechanisms of CFCCs. Prior to mechanical testing, UT, CT, and IR thermography were used to investigate the initial defect information of CFCC samples. Both AE sensors and an IR camera were used to assess the amount of damages and monitor in-situ damage evolution during monotonic tensile and cyclic fatigue tests. After mechanical testing, ultrasonic C-scans, CT, and IR thermography were performed on fractured CFCC samples for quantitative analyses of the progressive damage. Also, optical microscopy (OM) and scanning electron microscopy (SEM) studies were conducted to investigate the fracture mechanisms of CFCC samples, which were related to the NDE results.; In this investigation, quantitative relationships among the physical properties determined from various NDE techniques were formulated. Moreover, the relationship between the NDE results and fracture behavior of CFCCs was presented to explore the integrity and mechanical behavior of CFCCs. The understanding of the correlation between the NDE results and structural performance of CFCCs was the focus of this research. This investigation also explores the feasibility of using NDE techniques as the integrity assessment means for CFCCs. Furthermore, the relationship among experimental NDE results was compared with theoretical predictions.; Ultimately, the results of this research could provide invaluable information to aid in the fabrication, development, and selection of reliable CFCCs for structural applications.