复杂载荷下二维原子晶体的微观断裂

With the discovery of graphene and other 2D atomic crystals (2DAC), and their applications in the strengthening and toughening of composites, the mechanical properties of 2DAC under complex loading has drawn the attention of researchers. However, it's still rarely reported on the studies of 2DAC fracture using micromorphic continuum theory. This project will focus on the fracture behaviors of 2DAC, such as graphene and hexagonal boron nitride, under complex mechanical and coupled thermo-mechanical loading. According to micromorphic theory, we will firstly determine the basal element of 2DAC and its internal length scale, and then construct a thin plate model of micromorphic by deriving the governing equations and constitutive relations based on balanced laws. Secondly, we will determine the material constants by performing a constrained optimization algorithm to match the phonon dispersion relations from atomistic calculations or experimental measurements. Thirdly, combining with atomistic modeling and related experiments, we will study crack initiation and propagation and other mechanical behaviors, and derivate the mechanics expressions of 2DAC, e.g. stress intensity factor, fracture toughness and the mixed mode fracture criterion etc. Finally, we will try to explore the underlying mechanisms of dislocation, topological defect formation and energy dissipation around crack tip. In this project, the microscopic fracture mechanisms of 2DAC will be revealed and their fracture laws will be routed as well. Combining theoretical analysis, multiscale calculations and experiments, the physical mechanical behaviors of 2DAC will be studied, which will provide a theoretical basis for capturing its fracture properties and engineering applications, and will promote the development and new understanding of the classical fracture theory.

随着石墨烯等二维原子晶体被发现，并逐渐在复合材料强韧化上得到应用，其复杂载荷下的力学性能引起研究者的关注，但仍鲜见利用微态连续介质理论研究二维晶体断裂的报道。本项目拟以石墨烯、六方氮化硼等为重点对象，选取适于微态理论的基元体、确定其内部特征长度，并根据均衡定律推导主导方程、建立本构关系，构造微态薄板模型，利用第一原理计算和实验获得的声子色散关系，通过应变能密度约束优化，确定材料常数，研究复杂力、热-力耦合载荷下二维晶体的断裂行为，结合原子力学计算模拟和相关试验，分析其裂纹萌生、扩展等力学行为，获得应力强度因子、断裂韧性、复合断裂准则等表达形式，探索裂尖位错、拓扑缺陷形成及能量耗散等机制，揭示微观机理，总结断裂规律。本项目采用理论分析、多尺度计算和试验相结合的方法，研究二维原子晶体的物理力学性质，所得结果将为掌握二维晶体的断裂特性及其工程应用提供理论依据，并促进对经典断裂理论的新理解和发展。

石墨烯等二维原子晶体具有优异的力学性质，在复合材料强韧化上逐渐得到应用，其复杂载荷下的力学行为引起研究者的关注。本项目利用微态连续介质理论及分子力学模拟,研究了二维晶体动态断裂。首先，以石墨烯、六方氮化硼为重点对象，选取适于微态理论的基元体、确定其内部特征长度，并根据均衡定律推导主导方程、建立本构关系，构造了微态薄板模型，利用第一原理计算和实验获得的声子色散关系，通过应变能密度约束优化，确定了材料常数。其次，结合原子力学计算（分子动力学、分子结构力学）模型模拟和相关试验数据，研究了复杂力载荷下二维晶体的动态断裂，分析了裂纹萌生、扩展、非稳定等力学行为，获得断裂韧性值、动态裂纹尖端原子应力场分布，裂纹转折/分叉临界速度与裂尖环向应力关联，探索了裂尖位错、拓扑缺陷形成及能量耗散等机制，揭示了裂尖非线性区尺寸与裂纹非稳定扩展内在联系。本项目所得结果将为掌握二维晶体的断裂特性及其工程应用提供理论依据，并将促进对经典断裂理论的新理解和发展。