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

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)对连续陶瓷纤维增强陶瓷基复合材料的纤维/基体界面特性进行了原位观察。通过单调和重复(加载-卸载-再加载)拉伸和四点弯曲试验，利用复型技术(观察基体裂纹的演化)、卸载模量测量和声发射分析，确定了微观断裂过程和机制；其次，利用复型、光学显微镜、扫描电子显微镜和扫描电子显微镜对相同的随机取向碳纤维增强硼硅酸盐玻璃基复合材料的热震损伤进行了观察，并对其进行了…原位观察在拉伸试验中用声发射测量也进行了更多的ns。有限元分析提供了确定断裂判据的瞬时应力值。第三，对单向碳化硅(PCS)(尼卡隆)纤维增强硼硅酸盐玻璃基复合材料的缺口四点弯曲试件进行了原位金相观察。通过改变碳化硅纤维表面碳涂层的厚度来控制纤维/基体的界面强度。然后，研究了涂层厚度对微观损伤过程和损伤机理的影响，建立了损伤演化模型。第四，对碳化硅(CVD)(德事隆)纤维增强莫来石基复合材料进行了单纤维顶出和拉出试验。改变制备条件(热压温度和压力)以获得不同的界面强力值。用扫描电子显微镜观察和声发射测量对纤维的拔出行为进行了量化。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。较少

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