体心立方结构金属裂纹尖端缺陷萌生的多尺度模拟

Crack propagation has been the focus of intensive researches since Griffith proposed the criterion of brittle fracture due to its fundamental role in structural applications. Recently, the desire of creating ultra-strength materials motivates researchers to further study the microscopic mechanisms of crack initiation and propagation with the help of the latest experimental and numerical simulation methods The project will be included as follows：The generalized stacking fault (GSF) and twinning fault energy (GTF) of body-centered cubic (BCC) rare metal Tantalum (Ta) are investigated based on the Embedded Atom potential. The quasicontinuum (QC) multiscale method is used to investigate the anisotropic fracture behavior of BCC metal tantalum loaded in Mode I and II. The processes of dislocation defects initiation and development are investigated. Different fracture mechanisms are discussed from microscopic to continuum perspectives to have a deep understanding of brittle and ductile fracture. Particularly, some of these fracture mechanisms are compared with the experimental results. Both isotropic and anisotropic critical stress intensity factor are derived and compared for different crack orientations. A straightforward criterion that is proved to be applicable is used to distinguish brittle fracture from ductile fracture.

纳米材料和结构的微观力学响应是现今力学和凝聚态物理科学的前沿研究方向之一。由于缺乏有效的分析方法及对体心立方结构金属纳观位错变形缺乏分析，使得现今无法对体心立方结构金属变形破坏机理具有更深刻的认识。本项目将采用多尺度分析技术，结合晶界广义堆垛层错能和多层广义孪晶能计算，模拟大尺寸体心立方结构金属钽Ⅰ、Ⅱ型裂纹尖端扩展，了解其位错发射的运动规律，分析金属钽裂纹尖端缺陷萌生，全位错的分解以及扩展位错形成机理，探讨不同晶向下裂纹扩展韧脆变化机理，并结合裂纹尖端微观力学分析，提出新的裂纹脆塑性扩展判定方法，并进行相应实验观察验证。本课题的完成对体心立方结构金属钽的纳观与宏观多尺度模拟方法的应用，加深对体心立方结构金属变形破坏机理的理解，丰富金属微观断裂破坏理论必将起到积极作用。

本项目对纳米材料金属结构裂纹尖端缺陷萌生进行多尺度模拟，以达到对金属变形破坏机理更深刻的认识。本项目采用多尺度分析技术，开展了钽、铁、钨三种体心立方金属裂纹的多尺度模拟，结合晶界广义堆垛层错能和多层广义孪晶能计算及提出的裂纹脆塑性扩展判据，进行韧脆性分析以及体心立方金属钨Ⅱ型微观裂纹的多尺度模拟研究；进行了纳米材料表面凹坑缺陷尺寸效应的多尺度分析，用准连续介质多尺度方法模拟表面缺陷对纳米压痕位置的影响，以及楔形压头顶角度对纳米压痕变形的影响；进行纳米材料摩擦的桥域多尺度模拟分析及基于多尺度方法的纳米薄膜材料摩擦过程中压头深度与速度效应研究；滚动接触润滑疲劳的多尺度建模与仿真，以及热超构材料等方面的研究。本课题的完成对纳米材料结构的纳观与宏观多尺度模拟方法的应用，加深对纳米金属结构变形破坏机理的理解，丰富金属微观断裂破坏理论必将起到积极作用。