In-situ Observation Techniques for Interfacial Strength Properties of Continuous Ceramic Fiber Reinforced Ceramic Matrix Composites

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The purpose of the present study is to develop in-situ observation techniques using optical microscopes (OM), scanning electron microcscopes (SEM) and scanning acoustic microscopes (SAM) to characterize the fiber/matrix interfacial properties of continuous ceramic fiber reinforced ceramic matrix composites.First, matrix cracking behavior was observed in randomly-oriented carbon fiber reinforced borosilicate glass matrix composites, with or without precracks introduced during fabrication. Monotonic and repeated (load-unload-reload) tensile as well as four-point bending tests were conducted to identify the microscopic fracture process and mechanisms, using replica techniques (to observe matrix crack evolution), unloading modulus measurements, and AE analysis.Secondly, damage observations were conducted for the same randomly-oriented carbon fiber reinforced borosilicate glass matrix composites with thermal-shock induced matrix cracks, using replica, OM,SEM and SAM.Their in-situ observatio … More ns were also conducted during tensile tests with AE measurements. Finite element analysis provided the transient stress values to determine the fracture criteria. Microscopic fracture process and mechanisms were identified through the above study.Thirdly, in-situ OM observations were conducted for notched four-point bending specimens of unidirectional SiC (PCS) (Nicalon) fiber reinforced borosilicate glass matrix composites. Fiber/matrix interfacial strength was controlled by changing the thickness of carbon coating on SiC fibers. Then, the effects of coating thickness on microscopic damage progress and mechanisms were studied to establish the model for damage evolution. The fracture criteria were determined using finite element analysis.Fourthly, single fiber push-out and pull-out experiments were conducted for SiC (CVD) (Textron) fiber reinforced mullite matrix composites. Fabrication conditions (hot-press temperature and pressure) were changed to obtain different interfacial strength values. SEM observations and AE measurements were used to quantify the fiber pull-out behavior. Stress and energy criteria were applied to determine the debonding initiation.Finally, the importance of experimental microfracture mechanics was emphasized for ceramic matrix composites, based upon the above studies. Less