脆性材料冲击破坏过程的三维格点—弹簧模拟

As a typical brittle material, transparent ceramics might suffer serious compression fracture and functionality failure when they receive high energy density pulse. Understanding its mechanical responses at the component crystalline grain scale through discrete simulations is useful to guide the design and optimization of the micro-structure of transparent ceramic which might help to improve its plastic deformability. For the purpose of predicting the mechanical response of shocked transparent ceramics, this proposed project is designed to develop an 3D lattice-spring model which includes translational, rotational and fracture functions. For the calculations of the normal and tangential contact forces, the classic Hertz theory is corrected by introducing two geometrical structure factors so as to account for the stress coupling effect between crystalline grains due to the multi-body surface contacts. An in the rotational direction, resisting moments are taken into account to represent the limited rotational deformation between crystalline grains. The developed 3D lattice-spring model is then applied to simulate the shock failure of transparent ceramics with different micro-structures. The influences of micro-structure on the shock response of materials are thoroughly evaluated through analyzing the stress and strain fields, crack propagation, spatial distribution of cracks, et al. The anticipated results of the present project will not only significantly intensify our knowledge of the complex mechanical response of brittle materials under shock impaction, but also provide the theoretical basis for the design and optimization of the microscopic structure of transparent ceramics.

作为一种典型的脆性材料，透明陶瓷在受到高能量密度脉冲作用时易发生压缩破坏，导致其功能失效。基于离散数值模拟，从微观晶粒尺度研究材料的力学响应特性，有助于指导透明陶瓷材料的微结构设计优化，进而提高其塑形变形能力。本研究项目致力于发展包含平动、转动和断裂模式的三维格点-弹簧模型以从微观晶粒尺度开展透明陶瓷冲击响应的数值模拟研究。为考虑晶粒间多体面接触所导致的应力耦合效应，在法向和切向力计算上引入几何结构因子以修正经典的Hertz接触力模型；在转动方向上引入一转动阻碍扭矩以实现微观晶粒间的有限旋转变形。基于所发展的三维格点-弹簧模型，模拟研究不同微结构脆性材料的冲击破坏过程，通过分析应力应变场、裂纹扩展模式、裂纹空间分布等，探索微结构影响宏观冲击响应的机理。预期的研究结果不仅有助于加深对脆性材料冲击加载下复杂力学响应特性的认识，也有望为透明陶瓷制备中的微结构优化设计提供理论依据。

作为一种典型的脆性材料，透明陶瓷在受到高能量密度脉冲作用时易发生压缩破坏，导致其功能失效。基于离散数值模拟，从微观晶粒尺度研究材料的力学响应特性，有助于指导透明陶瓷材料的微结构设计优化，进而提高其塑形变形能力。本项目首先发展了离散态试样的快速数值方法，建立了含平动、转动和固体键断裂的三维离散单元法接触模型，并开发了相应的程序。随后以脆性陶瓷材料为研究对象，模拟研究其在拉伸和压缩作用下的力学响应特性、材料内部孔洞相互作用规律、材料力学属性与孔洞属性的关系、裂纹扩展特性等，以及针对颗粒物料模拟研究其堆积、流动特性等，并通过与文献中报道的理论分析/数值模拟/实验测量结果对比，检验了所建立离散单元法接触模型及所开发程序的可靠性和准确性。在此基础上，模拟研究了陶瓷材料在冲击加载下的力学行为，考察了孔洞、弱界面等冲击波剖面、材料损伤、裂纹扩展等的影响。模拟结果表明，孔洞的引入会显著提高材料在冲击加载下的塑性变形能力，增强对冲击波能量的吸收，延缓/避免材料整体功能性的失效。分析结果表明，这主要是因为孔洞的引入为晶粒提供了自由运动空间，孔洞的塌缩导致孔洞周围形成剧烈损伤，从而有效地耗散了能量，进而保护了材料的整体完整性。本项目的研究成果为透明陶瓷材料可能的微结构优化以提高其在冲击加载下的力学性能，提供了思路与方向。