梯度纳米晶粒/孪晶材料的本构建模及微结构优化设计

The conflict relationship between strength and ductility has seriously restricted the engineering application of materials. The gradient nanograined / nanotwinned materials exhibit an excellent combination of strength and ductility through the introduction of twin boundaries and gradient sub-structures. However, comparing to the rapid progress in material processing techniques, characterization and performance test, successful constitutive models are still missing up to now. Meanwhile, no general rules are available for guiding the design scheme of such materials, which are still investigated generally according to the trial-and-error method. Considering the lack of both “constitutive model” and “microstructure optimization” for gradient nanograined / nanotwinned materials, the goal of this project is to establish a strain gradient crystal plasticity model and the corresponding finite element implementation framework, which can reflect the anisotropy, heterogeneity and multi-scale feature of the gradient nanograined / nanotwinned materials, and to explore the proper microstructure manipulations to optimize the macroscopic mechanical properties, which is based on the connection between microstructure and macroscopic mechanical responses of gradient nanograined / nanotwinned materials. Such goal can be accomplished through the “bottom to up” multi-scale modelling method, where the construction of constitutive model is based on the dynamic evolution of microstructure using discrete dislocation dynamic simulation. Research activities and the achievements of this project will not only enrich the multi-scale constitutive descriptions, but also serve as the theoretical reference in the microstructure design, property optimization and engineering application for gradient nanograined / nanotwinned materials. All these will certainly have important scientific significances and provide more opportunities for engineering applications.

材料强度-韧性的“倒置”关系是制约其工程应用的主要瓶颈。梯度纳米晶粒/孪晶材料通过孪晶界和微结构梯度构筑实现了强韧兼顾。但是，梯度纳米晶粒/孪晶材料“本构理论”的发展严重滞后于材料的制备、表征和性能测试，材料“微结构设计”仍以试凑法为主。本项目针对梯度纳米晶粒/孪晶材料“本构关系”和“微结构优化设计”研究方面的不足，旨在通过“自下而上”的多尺度本构建模方法，基于离散位错动力学模拟揭示材料微结构动态演化，建立综合反映梯度纳米晶粒/孪晶材料各向异性、非均匀性、多尺度特征的应变梯度晶体塑性本构理论及其有限元实现框架，进而揭示材料微结构与宏观力学行为关联，并在此基础上探索梯度纳米晶粒/孪晶材料的微结构调控，以提高其力学性能。本项目研究不仅有助于丰富材料本构理论的多尺度描述，还可以为高性能梯度纳米晶粒/孪晶材料的微结构调控、性能优化和工程服役提供理论参考，具有重要的科学意义和广阔的工程应用前景。

材料强度-韧性的“倒置”关系是制约其工程应用的主要瓶颈。梯度纳米晶粒/孪晶材料通过孪晶界和微结构梯度构筑实现了强韧兼顾。本项目从微结构尺度到宏观尺度的层层递进，采用多尺度模拟的手段，并结合宏观力学性能测试和微结构表征，深入研究了梯度结构材料的宏微观力学行为。在微米尺度，基于离散位错动力学模拟揭示了晶界/孪晶界对材料力学行为的影响。在细观尺度，建立了综合反梯度纳米晶粒/孪晶材料各向异性、非均匀性、多尺度特征的塑性本构理论及其有限元实现框架，进而揭示材料微结构与宏观力学行为关联，并在此基础上探索梯度纳米结构材料的微结构调控和力学性能提升。在项目执行期，共发表论文20篇，培养博士毕业生1名，硕士毕业生2名。本项目取得的研究成果丰富了材料力学行为的多尺度描述，为高性能梯度纳米晶粒/孪晶材料的微结构调控、性能优化和工程服役提供了理论参考，具有重要的科学意义和广阔的工程应用前景。