爆炸加载柱壳剪切断裂演化过程主控应力机制研究

The fracture properties of the shells have been studied by many researchers in the recent years. The onset and evolutions of the self-organized shear fractures of metal cylindrical shells under explosive loadings are affected by many factors such as the characteristics of the impulsive loadings, the dynamic behavior of the materials, the geometry of the shell structures, etc. In this proposal, the crack initiations and propragations of the self-organized shear fractures which occur in cylindrical metal shells driven by either explosive or implosive loadings will be studied. The characteristics of the stress state of the cylindrical metal shell, which varies with the developing of the shear deformation and fracture, will also be investigated. Experimental research will be conducted to help distinguish the shear fracture process of the shells, which may be divided into three stages: 1) the initiations and evolutions of multiple-adiabatic shear bands, 2) the onset of shear crackings from shear bands, and 3) the growth and propagations of the multiple shear cracks that cause the ultimate break-up of the shell. Furthermore, stress analysis will be conducted to understand the unloading process of zones neighboring the multiple shear bands (or cracks). This analysis, combined with the 2-dimensional or 3-dimensional numerical-simulations, will identify the transition criteria of the shear deformation/localization/failure stages of the shells under explosive loadings., The research on one hand will significantly improve the understanding of the fracture and fragmentation behavior of the explosively loaded cylindrical metal shell, on the other hand, it will help for the design and the evaluation of protecting structures against explosive loadings.

爆炸载荷作用下金属柱壳的剪切型断裂的发生及单旋破坏现象受到载荷、材料、结构几何及尺寸特征等诸多因素影响，引起广泛关注。本申请拟对爆轰加载下金属柱壳中单旋型剪切断裂的萌生、裂纹传播、以及剪切裂纹贯穿后柱壳的滑移碎裂过程进行分析，获得柱壳特征应力分布随其膨胀/压缩进程的变化关系。结合实验，对作为剪切裂纹前驱的多重绝热剪切带的生成和演化、剪切带发展为剪切裂纹、多重剪切裂纹的扩展和演化等的物理条件进行识别；结合二维或三维数值分析，对爆炸加载下柱壳剪切断裂过程的各个阶段进行划分和定义，提出柱壳变形过程中描述剪切带（或裂纹）的行为以及剪切带（或裂纹）附近局部卸载区应力场的物理限制条件或模型建议。本研究对于金属柱壳破坏规律理解、结构的可靠设计与理论分析具有重要意义。

金属圆管作为一种轴对称结构是武器战斗部中应用最广泛、最具代表性的构型，其爆炸膨胀碎裂过程及其破坏机理的受到动态破坏研究及军事领域的关注。早期，基于拉伸断裂假设提出 的“Taylor断裂判据”，由于存在拉剪混合断裂等其它破坏方式，回收的试件并不能很好的支撑“Taylor断裂判据”。国内中国工程物理研究院胡海波、汤铁钢等实验揭示金属柱壳存在剪切及单旋剪切断裂模式，且具有取向的绝热剪切带自组织单旋特征。直接采用动态宏观热塑性本构的温度失稳机制对柱壳爆炸剪切失稳起始和形成进行有限元模拟，无法描述实验结果，存在问题。本项目开展金属柱壳外爆破坏特性及其数值模拟方法研究，主要工作包括：（1）金属柱壳外爆破坏的实验测试分析，并对试样碎片的宏观特征、微观损伤、绝热剪切带及裂纹起始及传播特征开展观测，结果显示金属柱壳膨胀破坏存在多种破坏模式。45钢及TC4钛合金柱壳双剪切与单旋剪切断裂受材料及试样剪切局域化演化过程影响。（2）设计帽型剪切及压缩试样对金属材料绝热剪切带起始、扩展问题开展系列实验研究，测试分析了剪切带形成、发展过程的温度、应变局域化演化特性；研究结果显示TA2、TC4钛合金绝热剪切起始时绝热温升低于390K，揭示材料热软化可能不是绝热剪切带起始及扩展的控制因素；采用剪切软化模型实验表征了绝热剪切形成、扩展的软化特性，计算与实验结果吻合较好。（3）采用实验及有限元结合的方式系统探讨了金属柱壳外爆剪切断裂模形成及影响因素，结果显示：爆轰作用下载荷特征及机加工缺陷（切削纹或残余应力）等会导致柱壳界面不稳定发展，进一步会引起变形局域化演化是剪切破坏的主控机制。并进一步探讨了爆炸载荷特性、几何缺陷、切削残余应力特征等对柱壳膨胀断裂破坏模式转变影响的规律。有限元分析揭示：不仅仅应变率及材料强度（Grady-Kipp公式），材料绝热剪切带内的软化特性也影响剪切自组织间距特征。另外，在一定条件下，缺陷分布周期特征控制碎片（绝热剪切带间距）尺寸。这些为金属柱壳破坏规律理解及数值模型建立提供了重要参考，具有学术及应用意义。