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

为了实现陶瓷-金属功能梯度材料作为耐热结构材料的应用，建立考虑陶瓷-金属功能梯度材料微观组织的不均匀性和层次性的强度评价方法，弄清其在机械载荷和热载荷作用下的断裂机理和强度是非常重要的。在本研究中，建立了功能梯度材料的数值计算方法和从室温到高温的小试件试验方法，考察了陶瓷-金属功能梯度材料的断裂行为和强度。主要研究成果如下：1.基于细观力学和互穿组织匹配的概念，建立了两相复合材料的力学模型。将该模型与有限元方法相结合，建立了考虑功能梯度材料微观结构不均匀和渐变的数值计算方法。2.粉末冶金法制备的直径约为30 mm、厚度约为10 mm的功能梯度材料。建立了从室温到高温下小试件的断裂机理、断裂韧性和裂纹扩展行为的测试方法。3.采用粉末冶金方法制备了不同成分和功能梯度材料的非梯度复合材料。研究了这些材料从室温到高温的弹性模量、断裂强度、断裂韧性和裂纹扩展行为，明确了微观组织的不均匀性和梯度对断裂行为的影响，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定方法。

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.