含缺陷功能梯度材料及梯度多层结构表面抗磨损性能的理论及实验研究

With the widely use of functionally graded materials (FGMs) in aerospace and other fields, the mechanical properties of FGMs are attracting more and more attention and research. The intact assumption is usually made in the existing researches on the surface/interface mechanical properties of graded materials. However, the influence of defects, whose existence is inevitable for any materials, on material properties cannot be ignored. Taking FGMs and graded multilayered structures with defects as the main research object, the main motivation of the present project is to study the surface wear resistance of graded materials and structures of different defects. Firstly, a series of valid theoretical models with a single crack defect, whose location and angle should be considered, will be proposed to analyze the effect of loading types, gradient laws and finite dimension of graded materials and structures. Based on the single crack defect model, the contact behaviors of graded materials and structures with multiple crack defects will be systemically investigated by considering the effect of multiple crack defects and the interaction between them. Finally, indentation experiments on graded materials and structures will be carried out, and the results will be compared with the theoretical ones. The underlying physical mechanisms of crack extension and arrest by the graded materials and structures will be explained. The results in this project should be helpful to provide more reliable theoretical guidance and proof for the optimum design and quality inspection of graded materials.

随着功能梯度材料在航天等众多领域得到重要应用，其力学性能的研究受到越来越多科研工作者的关注。已有梯度材料表界面力学研究大都基于无缺陷理想假设。然而任何材料都不可避免缺陷的存在，缺陷对材料性质的影响不容忽视。本项目以含缺陷的功能梯度材料及梯度多层结构为研究对象，主要研究不同缺陷梯度材料及结构的表面抗磨损性能。首先考虑单裂纹缺陷在梯度材料及结构中位置及方向，建立系列接触力学理论模型，系统分析载荷形式、材料梯度变化规律、结构尺寸等因素对其表面接触力学特性的影响；基于单裂纹缺陷模型，进一步分析多裂纹缺陷的影响，考虑裂纹间的相互作用及影响，系统研究含多缺陷梯度材料及结构接触力学特性的综合响应。最后，开展与理论模型相应的含缺陷梯度材料及结构的压痕实验，与理论模型结果比较，揭示梯度材料及结构中裂纹扩展及抑制的物理机制。该项目的研究有望为梯度材料及结构的优化设计和服役监测提供更直接的理论指导。

在梯度材料制备和加工过程中，各相间结合界面不完美、粗糙度、弱界面等缺陷不可避免，此时，缺陷的存在对梯度材料抗磨损性能的影响将不容忽略。因此，本项目以含缺陷梯度材料及梯度多层结构为对象，开展了含缺陷梯度材料及梯度多层结构接触力学性能的理论和实验研究，探索了含缺陷梯度材料接触性能的主要影响因素。首先，建立了含单个缺陷的梯度材料摩擦接触模型，理论得到了接触区的正应力、横向正应力以及保持垂直压入所施加弯矩的大小。再次，建立了含多缺陷的薄膜/梯度材料基底结构的接触力学模型，理论得到了接触区应力和应力奇异性指数以及缺陷处的应力集中系数。进一步，开展了功能梯度材料的缺陷不敏感分析，发现该类梯度半空间的纳米黏附接触，缺陷不敏感更加依赖于接近表面的材料性质，此外，考虑了表面粗糙度和材料梯度性质对接触行为的影响。我们还利用激光熔覆制备了梯度合金涂层，研究了它硬度和耐磨性能。最后，数值分析研究了单轴拉伸条件下，梯度胶结结构弱界面的强度问题。该项目的研究有望为梯度材料及结构的优化设计和服役监测提供更直接的理论指导。