基于力-热-化耦合细观热点模型的PBX炸药低冲击点火机制研究

Low-shock ignition in explosives could cause the killing and injuring of person and loss of economics and failure of the explosive weapon during attack or defense. Therefore, safety research of explosives under low-shock loading has become important and imminent. The investigation of explosive ignition and hot-spot mechanisms involves in the coupling of mechanical, thermal, and chemical processes, and spans mesoscale and macroscale, which makes the problem become more complex and challenging. Based on the mechanical experiments and mechanical constitutive model obtained in previous work about a Polymer Bonded Explosive(PBX)，this investigation is going to study further on the forming of hot-spots due to pore collapse and crack friction，and establish the corresponding mechanism codes，both of which will be implemented into LS-DYNA codes，and achieve the combination of the macroscale Finite Element Method (FEM) and the mesoscale.hot-spots mechanisms by coupled mechanical-thermo-chemical formulation.Two types of low-shock ignition tests will be designed and performed for the PBX and the ignition thresholds are obtained. The results of the ignition tests are used to calibrate and validate the ones of numerical simulation. The validated FEM could be used to simulate the ignition of the PBX under various low amplitude loadings. Finally, a numerical modeling method which could predict the safety of explosives under low amplitude loadings and exhibit the mesoscale hot-spot mechanisms will be established. This investigation will be significant for preventing accidents of explosives and safety evaluation of weapon under battle.

炸药低冲击下的意外点火会造成严重的人员财产损失及战场上弹药武器攻防战斗力丧失，低冲击下炸药安全性研究成为重要且亟待解决的课题。研究涉及力学、热学和化学反应的耦合，尺度横跨宏观到细观，给课题研究带来更强的复杂性和挑战性。本项目针对一种高聚物粘结炸药（PBX），基于前期进行的力学实验和力学本构关系研究结果，深入研究孔洞塌缩和裂纹摩擦两种细观损伤机制下热点形成过程，形成相应的计算程序，并将其与本构模型一起嵌入LS-DYNA软件中，实现宏观有限元软件与力-热-化耦合细观损伤热点模型的跨尺度结合。设计并开展炸药低冲击点火实验，获得炸药点火的临界加载条件，采用实验结果对数值模拟结果进行标定、验证。验证后的有限元软件可用于对各种低冲击下炸药点火情况进行数值模拟，最终建立一套反映细观损伤热点机制的炸药低冲击下安全性预测方法。这对弹药安全事故预防及实战使用的安全性评估具有重要作用。

深入了解炸药在低冲击加载下的点火机理对炸药的安全性研究是十分重要的。炸药在低冲击加载下首先会形成局部热点，这些热点的进一步发展将导致炸药点火并向更高的反应烈度演化。本研究以理论分析，数值模拟和实验验证相结合的方法，建立了一套细观物理机制清晰、能有效预测宏观加载下炸药安全性响应的宏细观结合的数值模拟方法。首先，针对孔洞塌缩和裂纹面摩擦这两种热点形成机制建立细观分析模型，推导模型控制方程，并与已有的PBX炸药的本构模型相结合，从而建立包含多种热点机制的细观和宏观相结合的本构模型。将该本构模型嵌入到LS-DYNA程序中，在描述低冲击加载下的PBX炸药的力学性能的基础上进一步预测炸药的点火性能。使用该计算模型对落锤撞击实验和平板撞击实验进行了模拟，给出了不同加载情况下导致炸药点火的主要热点形成机制。然后，设计了低冲击加载点火实验和剪切加载点火实验，来对上述计算模型进行验证。低冲击加载点火实验中，基于分离式霍普金森压杆实验平台（SHPB）建立了SHPB-砧骨实验，来研究PBX炸药在低幅值长脉宽加载下的点火情况。并用基于物质点-有限体积法（MPM-ICE）的Uintah程序对该实验仿真模拟，与实验结果相结合，共同给出了某PBX炸药的临界点火判据。最后基于离散元(DEM)方法，对PBX炸药的在低冲击加载下的热点生成情况进行模拟，初步验证了离散元方法在模拟炸药点火及后续反应烈度演化过程的可行性。