【作者】 张鸿；

【导师】 宋迎东；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2009， 博士

【摘要】 陶瓷基复合材料是未来高推重比航空发动机的重要候选材料之一。为促进陶瓷基复合材料在航空发动机上的工程应用,必须对陶瓷基复合材料的失效机理和失效模型进行研究,以发展适合于陶瓷基复合材料力学行为和损伤分析的研究方法。本文基于能量释放率的裂纹偏转准则,采用虚裂纹闭合技术计算了基体裂纹在界面处不同传播路径的能量释放率,考察了弹性错配参数、基体裂纹扩展长度、基体裂纹相对扩展长度及热膨胀系数等对裂纹偏转的影响。结果表明:当不考虑温度、热匹配、界面等因素的影响时,双向基体裂纹偏转比单向基体裂纹偏转更容易发生;高温下陶瓷基复合材料基体裂纹扩展的失效模式是由外载荷和温度引起的闭合力共同决定的,只有外载荷大于温度引起的闭合力,裂纹才能进一步扩展。从细观层面解释陶瓷基复合材料在拉伸载荷下的宏观力学行为与基体开裂、界面脱粘和纤维断裂三种基本失效模式之间的关系。在陶瓷基复合材料应力应变曲线离散化方法的基础上提出陶瓷基复合材料失效过程结构离散化方法,将正交层合陶瓷基复合材料的失效过程离散为单向纤维增强陶瓷基复合材料的失效过程,单向纤维增强陶瓷基复合材料的失效过程离散为基体裂纹、界面脱粘、纤维断裂占主导地位细观失效模式控制的阶段。开展了单向纤维增强C/SiC复合材料在常温和高温环境下的单向拉伸试验研究。设计了常温和高温拉伸试件及相应试验夹具,成功实施了单向纤维增强C/SiC陶瓷基复合材料的常温和高温单向拉伸试验,得到材料的弹性模量、拉伸强度以及应力应变曲线。观察试件断口形貌和界面形貌,分析材料的失效模式和损伤演化过程。将基体裂纹、界面脱粘、纤维断裂等单一失效模式的失效准则和损伤演化规律融入宏细观统一本构模型中,建立耦合损伤的陶瓷基复合材料宏细观统一本构模型,用于预测陶瓷基复合材料的拉伸应力应变响应和损伤演化过程。更多还原

【Abstract】 Ceramic matrix composites are potential candidate materials for future aero engine of a high thrust to weight ratio.Comprehensive research of failure mechanisms and failure models must be conducted to promote engineering application of ceramic matrix composites,and to develop performance prediction methods and damage research technology of ceramic matrix composites.An energy criterion based the energy release rates is used to study matrix crack deflection at interface in ceramic matrix composites.The energy release rates of possible crack paths are estimated by applying the virtual crack closure technique, and the effects of elastic mismatch parameters, the crack growth length, the relative crack growth length, and thermal expanding coefficient are analyzed on crack deflection of the matrix. The results show that double matrix crack are more likely to expand than single matrix crack if not consider the effects of temperature, thermal expansion match and interface performance.Failure models of matrix crack at the interface depends on closing forces caused by load and temperature at high temperature,and matrix cracks at the interface can be able to expand only the closing force caused by load is greater than that caused by temperature.Analyzed failure mechanism of ceramic matrix composites under uniaxial tensile loading and studied the mechanical relation between common characteristic of the stress-strain response and three dominant damage modes: matrix cracking, interface debonding and fiber breakage through analyzing the damage microstructure. Based on discrete regions method of stress-strain curve, discrete structure method is set up to divide laminated ceramic matrix composites into unidirectional ceramic matrix composites, and to divide stress-strain curve of unidirectional ceramic matrix composites into different regions which characterize three dominant damage modes.Unidirectional tension testing methods and testing systems for unidirectional C/SiC composite are studied. Specimen geometries and gripping fixture are designed, and the tensile test of unidirectional C/SiC is conducted successfully. Elastic modulus, strength and stress-strain curves of test are obtained. In-situ of damage evolution and fracture are researched by analyzing the fracture surfaces of damaged specimens.Assembled unified macro- and micro-mechanic constitutive model with failure criterias and damage evolutions of three dominant damage modes, a unified macro- and micro-mechanic constitutive model coupled with damage is improved to predict macro-mechanical properties of unidirectional and Laminates ceramic matrix composites.更多还原