Fundamental Investigation on Crack Behavior in Particulate-Dispersed Functionally Graded Material

本课题以功能梯度材料（FGM）为研究对象，分析了梯度对FGM断裂力学参数和裂纹尖端奇异场的影响，并对复合材料和FGM的力学性能和断裂韧性进行了实验研究。所得结果总结如下.采用基于Tohgo-Chou-Weng本构关系的有限元方法，对颗粒弥散型功能梯度材料中的裂纹进行了弹性和弹塑性分析。得出了以下结论：（1）梯度材料的力学性能梯度对裂纹的应力强度因子有影响。(2)与非功能梯度材料一样，功能梯度材料裂纹尖端的弹性和塑性奇异应力场基本上由断裂力学参数（K和J）描述，而非功能梯度材料裂纹尖端的材料力学性质则由裂纹尖端的材料力学性质描述。(3)奇异场的大小随力学性能梯度的增大而减小。这表明断裂力学的适用性，如小范围屈服条件和J积分的有效性受到梯度的影响.对7种玻璃颗粒增强尼龙66复合材料进行了拉伸试验和断裂韧性测试。复合材料的应力应变响应、力学性能和断裂韧性取决于颗粒的体积分数和颗粒与基体的界面处理.采用热压连接法制备了4种玻璃颗粒增强尼龙66复合材料功能梯度材料，并对其进行了三点弯曲试验和断裂韧性测试。建议在考虑梯度的基础上对功能梯度材料的强度进行评价，并指出功能梯度材料的断裂过程可能与非功能梯度材料不同。

In this project, in order to make clear the crack behavior in a functionally graded material (FGM), analytical work on influence of gradient on the fracture mechanics parameters and crack tip singular field, and experimental work on the mechanical properties and fracture toughness in composites and FGMs were carried out. Obtained results are summarized as follows.1. Elastic and elastic-plastic analyzes of a crack in a particulate-dispersed FGM were carried out using a newly developed finite element method based on Tohgo-Chou-Weng's constitutive relation. The following conclusions are derived : (1) The stress intensity factors of a crack in FGM is affected by the gradient of mechanical properties. (2) The elastic and plastic stress singular fields around a crack-tip in FGM are basically described by the fracture mechanics parameters (K and J) as well as in non-FGM,using the mechanical properties of the material at the crack-tip. (3) The size of singular field decreases with an increase in the gradient of the mechanical properties. This suggests that the applicability of fracture mechanics such as small scale yielding condition and validity of J-integral is affected by the gradient.2. Tensile tests and fracture toughness tests were carried out on seven kinds of glass particle reinforced nylon 66 composites. The stress-strain response, mechanical properties and fracture toughness of the composites depend on the particle volume fraction and the treatment of interface between the particles and matrix.3. FGMs were made by joining four kinds of glass particle reinforced nylon 66 composites by hot press, and three point bending tests and fracture toughness tests were carried out on the FGMs. It was suggested that the strength of the FGM should be evaluated based on the analytical results taking account of the gradient and the fracture process in FGM can be different from that in non-FGM.