增强相非均匀分布钛基复合材料设计理论及强韧化机理

Existing composite theories and models only take account of a uniform distribution and the overall volume fraction of the reinforcement，a uniform distribution inevitably leads to an elastic property close to the theoretical lower bound, consequently, these theories offer little guidance to the design of the microstructures of metal matrix composites (MMCs). The project aims to develop theories that can accommodate controlled inhomogeneous reinforcement distribution within a matrix, hence a new microstructual parameter - local volume fraction will be introduced for the prediction of elastic properties of composites with different types of reinforcement distributions, namely, layered, clustering, network, and bi-continuous structures. This will afford new approaches to the strengthening and toughening of MMCs. To verify the developed theorem, a spatial distribution algorithm will be developed together with multiscale cohesive-zone model and macro/micro-failure constitutive relations for numerical analysis to inform the influence of reinforcement distribution and structural parameters on the mechanical behavior of the designed composites, these structural parameters will be in turn optimized for the preparation of specific composite for particular engineering applications. Based upon the theoretical predications and numerical analysis, experimental exploitation will be conducted and focused on the design and fabrication of Ti matrix composites with network and layered structures that are highly sought after by aerospace sector. Microstructural examinations and mechanical testing will be carried out to relate the local volume fraction, network dimension and layer thickness to the composite properties. Crack initiation and propagation will be analyzed to inform the fracture mechanisms. The ultimate goal is to elucidate the strengthening and toughening mechanisms of the designed Ti matrix composites and provide useful insight into the design, fabrication and engineering application of this new class of MMCs.

现有复合材料理论仅考虑增强相的均匀分布和整体体积分数，而均匀分布不可避免地导致复合材料弹性模量接近理论预测值的下限。本项目通过引入增强相可控非均匀分布和局部体积分数的概念，发展能够囊括增强相不同分布状态 (层状、团聚、网状、双连通)的复合材料设计新理论，为金属基复合材料提供新的强韧化途径。发展增强相非均匀分布的空间弥散算法，建立多级非线性界面模型及宏微观失效本构关系，采用数值模拟，揭示增强相分布状态及结构参数对性能的影响规律，验证复合材料设计理论。针对航空航天与两机专项迫切需求的轻质耐热钛基复合材料，以网状结构与层状结构为例，设计并制备具有不同结构参数（网状尺寸、层厚、局部体积分数）的复合材料，通过分析测试及计算模拟，获得结构参数对组织、力学性能、裂纹扩展与断裂机理的影响规律，揭示增强相可控非均匀分布钛基复合材料强韧化机理，为此类金属基复合材料的设计、制备及应用提供理论基础与试验依据。

高新技术发展要求钛基复合材料在高强度的基础上具有良好的塑韧性，然而传统的复合材料无法有效解决强韧性倒置的瓶颈问题，而基于增强相空间分布的构型设计，是突破这一瓶颈的有效途径。本项目基于调控增强相空间非均匀分布的新思路，建立了网状、层状结构复合材料模量理论预测模型，阐明了提高增强相局部体积分数对构型强化的促进作用，并发展了基于增强相空间分布的构型化复合材料损伤理论，分析了增强相空间分布对初生微裂纹扩展的抑制作用，证实了增强相非均匀分布设计具有强韧化金属基复合材料的潜力；建立并验证了界面失效模型与基体本构模型，发展了非均匀分布增强相几何模型的构建方法，并建立了多种构型化复合材料有限元模型，结合有限元方法预测了构型化复合材料的变形、损伤断裂行为及其宏观力学性能，揭示了增强相非均匀分布钛基复合材料构效关系，指导了复合材料的结构设计；针对航空航天与两机专项迫切需求的轻质高强韧钛基复合材料，完成了网状、层状复合材料结构设计及其制备工艺研发，通过调整结构参数实现了对综合力学性能的调控，实验证实了增强相非均匀分布的强韧化作用，并进一步发展了多级多尺度构型设计，实现了二级网状结构及层网复合结构；系统研究了构型化复合材料的增强相承载行为、基体协调变形行为、损伤和微裂纹钝化行为，构型设计可有效延迟偏转主裂纹扩展，阐明了增强相可控非均匀分布设计的强韧化机理。本项目为发展基于增强相空间分布的新一代高性能复合材料提供了科学依据、设计策略和制备技术，其中通过粉末冶金工艺制备的高强韧钛基复合材料已经初步应用到了工业领域，展现了性能提高和减重的潜力。