Evaluation method development for ceramic matrix composites towards damage tolerance design in micro gas turbine

本研究的目的是建立微型燃气轮机运行环境下碳/碳和陶瓷基复合材料微观变形和断裂特征的定量评价方法。具体地说，(1)热冲击试验方法，(2)高温冲击力学试验方法，(3)高温蠕变试验方法，(4)高温机械载荷氧化试验方法。利用这些方法，定量地阐明了微断裂(萌生、发展和积累)与力学性能(刚度和强度)之间的关系。研究结果如下：(1)选择水淬火试验方法作为C/C和陶瓷基复合材料的热冲击试验方法，研制了带红外加热器的分离式霍普金森压杆试验系统。该系统支持高达1300℃环境的冲击测试。(C)…已开发出更多具有两个液压执行机构的新型试验机。该系统可以在力和位移控制条件下工作。这台机器配备了红外线加热器，可以在机械载荷高达1300℃的情况下进行氧化试验。(D)通过耦合Griffiths断裂力学和裂纹萌生缺陷尺寸分布，提出了单丝强度尺寸效应的新模型。例如，对几种规格长度的Tyranno ZMI陶瓷单丝进行了拉伸测试，结果表明，模型估计与导出的数据在可接受的误差范围内吻合，而单模威布尔模型的估计显示出一定程度的偏差。(E)澄清了C/C复合材料中低纤维效率不取决于制造过程中纤维的降解，而取决于纤维/基质界面强度。(F)开发了对环境影响小的C/SiCo复合材料的制造工艺。结果表明，氧化气氛下生成的氧化物增大了纤维/基体的界面强度，导致强度下降。较少

The object of the present study is to develop the quantitative evaluation method of microscopic deformation and fracture characteristics of carbon/carbon and ceramic matrix composites under the environment where the micro gas turbine is operated. Specifically, (1) thermal shock test method, (2) impact mechanical test method under high temperature, (3) creep test method under high temperature and (4) oxidation test method with mechanical loading under high temperature have been developed. Using these methods, the relation between the micro-fractures (initiation, progress and accumulation) and the mechanical properties (stiffness and strength) are clarified quantitatively. The obtained results are as follows.(a) Water quench test method was selected as the thermal impact tests for C/C and ceramic matrix composites and has been developed.(b) Split Hopkinson pressure bar testing system with infrared heater has been developed. This system enables the impact tests up to 1300℃ environment.(c) … More New testing machine with two hydro-electric actuators have been developed. This system can be operated under the force and displacement control conditions. This machine has been instrumented with the infrared heater which enables the oxidation tests with mechanical loading up to 1300℃.(d) A new model on monofilament strength size-effect has been presented through coupling a Griffiths fracture mechanics and a distribution of crack initiating flaw size. As an example, Tyranno ZMI ceramic monofilaments were tensile tested on several gauge lengths to have revealed that the model estimations have fitted the derived data within acceptable error level, while single-modal Weibull model estimations showed a level of discrepancy.(e) It is clarified that the low fiber efficiency in C/C composites do not depend on the degradation of the fiber during the manufacturing process, but depends on the fiber/matrix interfacial strength.(f) The manufacturing process of C/SiCO composites with low environmental impact has been developed. It is clarified that the oxides generated under the oxidation atmosphere enlarged fiber/matrix interfacial strength, which results in the decrease in strength. Less