颗粒增强金属基复合材料变形强化中的应变梯度效应

 针对单轴压缩实验，根据颗粒增强金属基复合材料中颗粒和基体两相的局部变形协调条件，并通过简单的位错模型，确定出与变形协调相应的几何必需位错密度，进而导出一种颗粒强化-应变梯度律。从中可以清楚地看出，颗粒增强金属基复合材料的强化由材料的微结构特征几何参数l和基体应变梯度联合控制。对于颗粒含量一定的复合材料，颗粒越小，应变梯度越高，强化效果越好。这一结果揭示了，颗粒强化及尺寸效应主要是通过应变梯度效应来表现的。这也同时说明，应变梯度可能是控制材料变形与断裂的重要因素之一。

STRAIN GRADIENT EFFECTS ON THE STRENGTHENING BEHAVIORS OF PARTICLE REINFORCED METAL MATRIX COMPOSITES

Although much efforts have been made to understand the relationship between microstructures and deformation behaviors of particle reinforced metal matrix composites(PRMMCs) during the past several decades,there are still some phenomena remained to be understood,one of which is size effects in PRMMCs.Recently,many experimental results demonstrate that reinforcing particle sizes have a significant influence on yield and flow stresses of PRMMCs.However,various micromechanical models which are based unpon homogenization technique for particulate composites predict particle volume fraction effects on deformation behavior of composite materials but show an independence of particle sizes.According to this observation,a strengthening strain gradient relation for particle reinforced metal matrix composites was developed by making use of the concept of geometrically necessary dislocation and proposed dislocation model.A comparison with existing experimental results demonstrates that the relation predicts a dependence of yield and flow stresses of composites on reinforcing particle sizes.From this relation,we found that the strengthening effect of mechanical behavior of composites is controlled by both characteristic microstructure geometrical parameters and strain gradient in matrix.For a given PRMMCs,the strengthening effect of the composite is completely controlled by particle size or strain gradient in the matrix.This tells us that the strain gradient in matrix may be an important factor controlling deformation and fracture behavior of heterogeneous material systems.Moreover,effects of characteristic microstructure geometrical parameters on deformation localization of PRMMCs are also discussed. [WT5HZ]