爆轰加载下金属熔化破碎问题的多尺度模拟

Dynamic behaviors such as phase transition, melt and fragmentation could occur in metals under explosive loading, which is one of focus of most concern in fundamental research of weapon physics currently. However, understanding of the formation and evolution progress for this problem is still insufficient, due to the complicated mechanism and limitations of current research capacity. In this project, multiscale method is adopted to study the melt and fragmentation of metals under explosive loading by coupling molecular dynamics and material point method. Multiphase equation of state and damage model will be introduced, and microscopic molecular dynamics method is used to obtain macro physical parameters needed in continuum model. In this way, an accurate and reliable multiscale method and corresponding numerical program can be established to apply to simulate spalling and fragmentation of melted metals under explosive loading. Further, deeper understanding can be obtained of nucleation, growth and coalescence of void during the early stage of spall fracture. The interaction process and internal mechanism between material properties and stress wave will also be studied. The velocity of free surface and spatial density distribution of fragments in later stage will be compared with experimental results to improve the proposed multiscale method and material model. Therefore, the systematic study in this project will contribute to deeper understanding of the whole process of phase transition, melt and damage evolution in metals under explosive loading.

爆轰加载下金属材料将发生相变、熔化、破碎等一系列物理现象，是当前武器物理基础研究关注的焦点之一。由于金属熔化破碎问题的复杂性和现有实验诊断能力的局限性，目前对该问题的形成演化物理机制认识还存在明显不足。本项目针对金属（Pb或Sn）熔化破碎问题开展模拟研究，引入能描述金属相变的多相物态方程以及涉及熔化破碎过程的损伤模型，利用微观分子动力学方法获取物理模型对应的参数；结合适用于模拟大变形和材料破坏问题的物质点方法，构建一种可准确可靠模拟金属熔化破碎问题的层级多尺度方法。利用实验获得的自由面速度剖面和破碎物质分布等关键数据，验证和完善物理模型和多尺度方法。进一步，应用该多尺度方法系统研究熔化破碎形成早期阶段空穴萌生、生长、贯穿演化过程以及固-液转变与应力波相互作用耦合的物理机制，获得对已有实验结果的清晰认识。

本项目针对爆轰加载下低熔点金属材料熔化破碎问题开展了系统的数值模拟研究，项目组首先构建了包含多相本构及状态方程、相变动力学、损伤演化的物理模型，实现了低熔点金属熔化破碎问题数值模拟能力。进一步，针对低熔点金属开展了飞片冲击加载下的层裂实验和爆轰加载下层碎裂实验，获取了低熔点金属的层裂损伤及熔化破碎过程中的关键物理数据，完成了物理模型及参数校验。最后通过开展系统的数值工作，深入分析了低熔点金属熔化破碎问题中早期熔化过程及断裂方式，中后期多种稀疏波共同作用下不同的层裂破碎特征及内部机制，以及间隙因素对爆轰加载过程的影响，最终实现了对爆轰加载下低熔点金属熔化破碎问题中冲击加-卸载波与材料性能耦合作用过程及机制的深入认识。