Fracture Mechanism and Strength Evaluation of Functionally Graded Materials Taking Account of Inhomogeneity and Gradation of Microstructure

为了将陶瓷-金属功能梯度材料（FGM）应用于耐热结构材料，建立考虑FGM微观结构不均匀性和梯度性的强度评价方法，明确FGM在机械和热载荷作用下的断裂机制和强度是十分重要的。本研究建立了功能梯度材料的数值计算方法和小试样的室温-高温试验方法，并对陶瓷-金属功能梯度材料的断裂行为和强度进行了研究。主要研究结果如下：1.基于细观力学和互穿组织基体的概念，建立了两相复合材料的模型。将该模型与有限元法相结合，建立了考虑功能梯度材料微观组织不均匀性和梯度性的数值计算方法。2.采用粉末冶金法制备的功能梯度材料直径约为30 mm，厚度约为10 mm。3.采用粉末冶金法制备了不同成分的非梯度复合材料和功能梯度材料，并分别采用部分稳定氧化锆（PSZ）和奥氏体不锈钢（SUS 304）制备了功能梯度材料。研究了这些材料在室温到高温下的弹性模量、断裂强度、断裂韧性和裂纹扩展行为，明确了显微组织的不均匀性和梯度对材料断裂行为的影响，提出了基于细观力学和断裂力学的功能梯度材料断裂行为预测方法和强度评价方法。

In order to apply ceramic-metal functionally graded materials (FGMs) as heat resistive structural materials, it is important to establish evaluation method of strength taking account of inhomogeneity and gradation of microstructure in FGMs and to make clear their fracture mechanism and strength under mechanical and thermal loading. In this investigation, numerical method for FGMs and test method for small specimens at room temperature to elevated temperature were established, and fracture behavior and strength of ceramic-metal FGMs were examined. Obtained results are summarized as follows.1.A model of two-phase composites is developed based on the micromechanics and concept of matricity for interpenetrating microstructure. By incorporating this model into a finite element method, the numerical method taking account of inhomogeneity and gradation of microstructure in FGMs is established.2.The size of FGMs fabricated by powder metallurgy is about 30mm in diameter and 10mm in thickness. The tests method to evaluate fracture mechanism, fracture toughness and crack growth behavior by small specimens under at room temperature to elevated temperature is established.3.Non-graded composites with deferent composition and FGMs are fabricated by powder metallurgy using partially stabilized zirconia (PSZ) and austenitic stainless steel (SUS 304). Elastic moduli, fracture strength, fracture toughness and crack growth behavior are examined for these materials at room temperature to elevated temperature and influence of inhomogeneity and gradation of microstructure is made clear.From the above results, method to predict the fracture behavior in FGMs and method to evaluate strength of FGMs are suggested based on the micromechanics and fracture mechanics.