碳纳米管增强纳晶基复合材料力学行为的多尺度研究

The interactions between the reinforcement and grains play a significant role in the mechanical behavior of carbon nanotubes (CNTs) -reinforced nanocrystalline matrix composites. The continuum mechanics theory, finite element method as well as experiments will be adopted in this project. The effects of microstructures of the composites on their mechanical properties will be discussed in multiscale study. On a micro level, the influence of elastic stress fields around the cross section of the reinforcement on the distribution range of geometrically necessary dislocations induced by thermal expansion mismatch between CNTs and the matrix will be quantitatively analyzed. Meanwhile，the dependences of the mobility and stability of dislocations emitted from a crack tip on microstructures of aligned-CNTs are established. In addition, the variations of fracture toughness of the composites with microstructures and orientations of the reinforcement are determined. On a macro level, a dislocation density based model is developed to quantitatively describe the effect of matrix grain size on the mechanical response of the composites. The comparisons between the predictions and experimental results are also performed. In addition, a three-dimensional finite element model will be constructed to reveal the influence of matrix grain size and shape on the strengthening role of the reinforcement and mechanical behavior of the composites. The project provides necessary foundations of theories for preparing CNTs-reinforced metal matrix composites with both high strength and good ductility.

在碳纳米管增强纳晶基复合材料中，增强相与晶粒的相互作用对复合材料的力学行为存在显著影响。本项目利用连续力学理论并结合有限元和实验方法，多尺度研究碳纳米管增强纳晶基复合材料微观结构对其力学行为的影响。在微观尺度上，定量分析碳纳米管横截面周围弹性应力场对增强相与基体之间热膨胀系数错配引起几何必须位错分布范围的影响。同时，建立裂纹尖端位错运动及稳定性与定向排列碳纳米管微观结构之间的定量关系，揭示复合材料断裂韧性随增强相微观结构及取向的变化规律。在宏观尺度上，提出可用于定量分析基体晶粒尺寸对复合材料力学性能影响的三相复合模型，并用实验进行验证。此外，构建碳纳米管增强纳晶基复合材料的三维有限元模型，揭示晶粒尺寸及形状对碳纳米管强化效果及复合材料力学响应的影响。本项目为制备出具有高强度和良好韧性的碳纳米管增强金属基复合材料提供了必要的理论支撑。

碳纳米管因其独特的力学、物理和化学性质，成为国内外研究的热点。碳纳米管在众多领域内被认为具有广阔的应用前景，其中之一是人们利用其优异的力学性能，将其作为增强相制备碳纳米管增强金属基复合材料。但同时，作为微米级增强相，碳纳米管的强化效果还没有达到预期目标。实验中已观察到碳纳米管与基体之间相互作用对复合材料的微观结构及力学行为存在较大的影响，这种影响在基体晶粒尺寸在纳米范围内时尤为显著。但由于实验条件的局限，实验中难以测得一些重要参数对上述复合材料力学性能影响的定量关系，更加难以揭示这些因素的相互影响机理。本项目利用连续力学理论并结合有限元，多尺度研究碳纳米管增强纳晶基复合材料微观结构对其力学行为的影响。在微观尺度上，定量了分析碳纳米管横截面周围弹性应力场对增强相与基体之间热膨胀系数错配引起几何必须位错分布范围的影响。同时，建立了裂纹尖端位错运动及稳定性与定向排列碳纳米管微观结构之间的定量关系，揭示了复合材料断裂韧性随增强相微观结构及取向的变化规律。在宏观尺度上，提出了可用于定量分析基体晶粒尺寸对复合材料力学性能影响的三相复合模型。此外，构建了碳纳米管增强纳晶基复合材料的三维有限元模型，揭示晶粒尺寸及形状对碳纳米管强化效果及复合材料力学响应的影响。本项目为制备出具有高强度和良好韧性的碳纳米管增强金属基复合材料提供了必要的理论支撑。