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

本项目为明确功能梯度材料（FGM）的裂纹行为，对梯度对断裂力学参数和裂纹尖端奇异场的影响进行了分析，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：1。采用基于Tohgo-Chou-Weng本构关系的有限元方法，对颗粒分散FGM的裂纹进行了弹性和弹塑性分析。得到以下结论：(1)FGM裂纹的应力强度因子受力学性能梯度的影响。(2) FGM中裂纹尖端周围的弹塑性应力奇异场基本由断裂力学参数K和J来描述，而非FGM中则利用裂纹尖端处材料的力学性能来描述。(3)随力学性能梯度的增大，奇异场尺寸减小。这说明小尺度屈服条件等断裂力学的适用性和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试验。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体积分数和颗粒与基体界面的处理。采用热压法将4种玻璃颗粒增强尼龙66复合材料连接在一起，制备了fgm，并对其进行了三点弯曲试验和断裂韧性试验。建议在分析结果的基础上考虑梯度对FGM的强度进行评价，FGM的断裂过程可能与非FGM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.