炸药冲击响应的二维细观离散元模拟

【作者】 于继东；

【导师】 王文强；

【作者基本信息】 中国工程物理研究院 ， 流体力学， 2007， 硕士

【摘要】 细观结构对炸药的冲击响应具有重要影响,颗粒尺度的数值模拟是目前研究这一问题的主要手段。本文用离散元方法模拟了冲击作用下颗粒炸药和塑料粘结炸药中热点的形成和发展。首先利用Voronoi拼图建立了可近似反映炸药实际细观结构的离散元几何模型。相应地改进了离散元程序DM2,使之适应本文模拟的要求。并改进了原有的法向作用力模型,即用换算后的Hugoniot关系取代原有的中心作用力关系,用物理的体积粘性取代原有的法向振荡阻尼。此外,引入“代表体元”的概念对体应变和剪应变进行了新的定义和计算。在此基础上,开展了炸药冲击响应的二维细观离散元模拟。利用文献给出的物理参数,得到了基本合理的计算结果。在可对比的算例中,热点的温度范围与文献给出的基本一致。在本文的算例中,粘塑性变形是温度局域化的主要原因,而摩擦和体积粘性等机制影响很小。通过对比颗粒炸药和塑料粘结炸药,发现粘结剂的缓冲作用可降低炸药颗粒的热点温度。对不同几何形状炸药部件与固壁碰撞的模拟表明,加载方式和边界条件对热点的温度影响较大,而对热点的空间分布影响相对较小。对孔洞塌缩的热点形成机制的计算结果表明,孔洞塌缩可使当地温度显著提高,温升主要是由于应力波对孔洞周围的加载—卸载—再加载导致炸药颗粒剧烈的粘塑性变形。更多还原

【Abstract】 Mesoscopic structures significantly affect the shock response of explosives. Presently this problem is mostly investigated through grain scale numerical simulations. In this thesis, the discrete element method has been used to simulate the formation and development of hot spots in shock loaded granular and plastic bonded explosives.The geometrical part of the discrete element model that mimics the mesoscopic structure of explosives was created based on the Voronoi tessellation. Correspondingly, the discrete element code DM2 was modified to satisfy the special needs of this study. Improvements were also made on the original normal force model. That is, the central force was replaced by a modified Hugoniot relation, and the artificial damping was replaced by the physical volumetric viscosity. In addition, the idea of representative volume element has been used to redefine both the volumetric and the shear strains.Based on the above efforts, two dimensional mesoscale discrete element simulation of shock response of explosives has been performed. Reasonable results were obtained by using the physical parameters from the literature. The temperature scale of hot spots is comparable to that in other works. In this study, viscoplastic deformation is the main cause for temperature localization, whereas the effects of friction and volumetric viscosity are very small. By comparing the granular and the plastic bonded explosives, it was found that the cushioning effect of the binder can reduce the temperatures of hot spots. Simulations of explosives of different shapes impacting on a rigid wall showed that the loading method and boundary condition affected the temperatures of hot spots more than affecting their spatial distribution. For explosive sample with a void inside, it was found that void collapse can significantly raise the local temperature. The reason for this is the severe viscoplastic deformation in materials surrounding the void due to loading, unloading, and reloading of the stress wave.更多还原