纳晶双峰材料的本构行为及损伤机理研究

Though exhibit higher hardness, yield strength and better wear resistance in comparison with conventional coarse-grained materials, nanocrystalline materials usually exhibit low tensile ductility and fracture toughness. In order to quantitatively design nanocrystalline materials with high tensile ductility and fracture toughness, through mechanics behavior testing, computer simulations and deformation damage mechanisms study on such materials which are prepared in our laboratory, this project project intends to achieve the following objectives: 1)systematically detect the reasons of causing early failure of this materials; 2）based on self-consistent and strain gradient theories, build constitutive models which are dependent on loading modes and the material microstructures (grain size distribution, lattice distortion and grain anisotropy); 3) by coupling nanocrystalline finite element technique and microstructures of nanocrystalline bimodal material, analysis the local and global mechanical response under different loading conditions; 4) master the deformation damage inhibition mechanisms, depending on loading modes and the materials microstructure, develop damage and failure models, obtain stress intensity factors near crack tip that account for fracture toughness. The above research results will play an important promoting role in designing nanocrystalline materials with high tensile ductility and fracture toughness, optimizing microstructure design in nanoscale, promoting the development of new microstructural mechanical theory and industrial applications of nanocrystalline materials.

虽然纳晶材料相比普通粗晶材料具有较高的硬度、屈服强度及良好的耐磨性能，但该种材料通常呈现出较差的室温延展性和断裂韧性。为了寻求定量设计既有高强度又具备高延性的纳晶材料，本项目拟通过对实验室制备的纳晶双峰材料的力学性能测试、计算机模拟及变形损伤机理研究: 1)系统探究该种材料过早失效的原因; 2)构建基于自洽理论及应变梯度理论的与纳晶双峰材料微结构（晶粒尺寸分布、晶粒各向异性和晶格畸变）及加载方式相关的本构方程；3)采用纳晶有限元技术耦合材料的微结构，分析不同加载方式下纳晶双峰材料整体与局部力学行为的关系；4)掌握纳晶双峰材料变形损伤受抑制的规律，建立与材料微结构及加载方式相关的微观损伤力学模型并获得裂纹尖端的应力强度因子。有关这方面的研究对于定量设计既有高强度又具备高延性的纳晶材料、纳米尺度下微结构设计、新型微结构力学理论发展及最终工业应用等都将有着重要的推动作用。

虽然纳晶材料相比普通粗晶材料具有较高的硬度、屈服强度及良好的耐磨性能，但该种材料通常呈现出较差的室温延展性和断裂韧性。为了寻求定量设计既有高强度又具备高延性的纳晶材料，本项目制备了纳晶双峰材料并进行了力学性能测试、计算机模拟及变形损伤机理研究，得到了如下结果1)采用高压烧结方法制备了块体纳晶双峰材料，该材料纯度高，缺陷少，杂质少。2)构建了应变梯度理论的与纳晶双峰材料微结构（晶粒尺寸分布、晶粒各向异性和晶格畸变）及加载方式相关的本构方程；3)掌握纳晶双峰材料变形损伤受抑制的规律，建立了与材料微结构及加载方式相关的微观损伤力学模型并获得裂纹尖端的应力强度因子；4)研究了纳晶双峰材料的微尺度导热行为，并建立了与晶粒尺寸相关的导热模型。有关这方面的研究对于定量设计既有高强度又具备高延性的纳晶材料、纳米尺度下微结构设计、新型微结构力学理论和微尺度导热理论的发展及最终工业应用等都将有着重要的推动作用