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性的定量评价方法。具体来说，发展了(1)热冲击试验方法，(2)高温下冲击力学试验方法，(3)高温下蠕变试验方法，(4)高温下机械载荷氧化试验方法。利用这些方法，定量地阐明了微裂缝（起裂、发展和聚集）与力学性能（刚度和强度）之间的关系。所得结果如下：(a)选择了水淬试验方法作为碳/碳复合材料和陶瓷基复合材料的热冲击试验，并建立了水淬试验方法。(b)研制了带红外加热器的分离式霍普金森压力棒测试系统。该系统可在1300℃环境下进行冲击试验。已研制出具有两个水力电动执行器的新型试验机。该系统可在力和位移控制条件下运行。本机配有红外加热器，可在1300℃的机械负荷下进行氧化试验。(d)将Griffiths断裂力学与裂纹起裂裂纹尺寸分布相结合，建立了单丝强度尺寸效应的新模型。例如，对Tyranno ZMI陶瓷单丝进行了几种规格长度的拉伸测试，结果表明模型估计在可接受的误差范围内拟合了导出数据，而单模态Weibull模型估计则显示出一定程度的差异。(e)阐明了C/C复合材料中纤维效率低并不取决于纤维在制造过程中的降解，而是取决于纤维/基体界面强度。(f)开发了低环境影响的C/SiCO复合材料制造工艺。结果表明，氧化气氛下产生的氧化物使纤维/基体界面强度增大，从而导致纤维/基体强度下降。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