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

本研究的目的是利用光学显微镜（OM）、扫描电子显微镜（SEM）和扫描声学显微镜（SAM）等原位观察技术来表征连续陶瓷纤维增强陶瓷基复合材料的纤维/基体界面特性。首先，观察了随机取向碳纤维增强硼硅酸盐玻璃基复合材料的基体开裂行为，无论在制造过程中是否引入预裂纹。采用复制技术（观察基体裂纹演化）、卸载模量测量和声发射分析，进行了单调和重复（加载-卸载-加载）拉伸以及四点弯曲试验，以确定微观断裂过程和机制。其次，采用复模法、OM法、SEM法和SAM法对相同的随机取向碳纤维增强硼硅玻璃基复合材料进行了热冲击裂纹损伤观察。在拉伸试验中用声发射测量进行了更多的现场观测。有限元分析提供了瞬态应力值来确定断裂准则。通过上述研究，确定了微观断裂过程和机理。第三，对单向SiC (PCS) （Nicalon）纤维增强硼硅玻璃基复合材料的缺口四点弯曲试样进行了原位OM观察。通过改变碳化硅纤维表面碳涂层的厚度来控制纤维/基体界面强度。然后，研究涂层厚度对细观损伤过程的影响及其机理，建立损伤演化模型。采用有限元分析确定断裂准则。第四，对SiC (CVD) （Textron）纤维增强莫来石基复合材料进行了单纤维拉伸和拉伸实验。改变制备条件（热压温度和压力），得到不同的界面强度值。利用扫描电镜观察和声发射测量来量化纤维的拔出行为。采用应力和能量准则确定脱粘起始。最后，在上述研究的基础上，强调了实验微断裂力学对陶瓷基复合材料的重要性。少

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