【作者】 李俊玲；

【导师】 卢芳云； 谭多望；

【作者基本信息】 国防科学技术大学 ， 力学， 2012， 博士

【摘要】 随着现代高性能武器系统的飞速发展，弹药的安全性问题日益突出，新型常规武器对炸药装药的起爆性能提出了更高的要求。高聚物粘结炸药（PBX）是一类具有较高能量密度、优良机械性能和较高安全性能等的高能复合材料，在国防和国民经济等领域广为使用。然而，即便是PBX这类钝感炸药，意外爆炸事件也时有发生。为适应高性能武器装备发展的需要，研究钝感高能炸药的各项性能就显得尤为重要。PBX炸药本身结构复杂，加之其在发挥效能前的服役过程中所受力学环境复杂，研究PBX炸药的力学性能，特别是动态力学性能是目前研究炸药安全性的一个重要课题。本文旨在研究PBX炸药的动态力学响应和损伤的产生和发展规律。采用霍普金森压杆（SHPB）作为主要的实验平台，研究PBX炸药的动态压缩和拉伸力学特性，并观察PBX炸药受动态加载后的细观损伤形貌，最终建立含细观损伤的本构关系，为研究含能材料的安全性提供一定的理论支撑。本文主要有三个部分，第一部分为PBX炸药力学性能的基础研究，从宏观层次观察了损伤的发展及其在应力应变曲线上的反映。从实验结果看PBX炸药这类材料具有典型的力学脆性，脆性材料的损伤模式一般以微裂纹的产生和发展为主，要研究其损伤特性就需要观察内部细观裂纹的发展变化。因此，第二部分采用巴西实验为主要加载方式对PBX炸药的细观损伤演化过程进行了实验和数值模拟研究。在获得了PBX炸药的损伤特性之后，需要对其发展规律进行数学描述。在本文的最后一部分，采用微裂纹扩展区损伤本构模型来描述PBX炸药内部微裂纹演化发展对宏观应力应变曲线的影响。详细的研究内容如下：第一部分的内容主要为PBX炸药的宏观动态力学响应研究。首先针对PBX炸药这类破坏应变很小的脆性材料，改进传统的SHPB测试方法以获得更为准确的实验结果。采用半导体和石英晶体联合测试技术提高实验信号的信噪比；采用不同脉冲和不同波形整形器进行加载研究PBX炸药的宏观损伤力学特性，发现PBX炸药的损伤发展对冲击加载比较敏感，且极限加载应变率很低。根据PBX炸药的一维压缩应力应变曲线特点，建立了对PBX炸药单轴压缩下的唯象本构描述，能较好地反映PBX炸药从加载到破坏后卸载过程中的应力应变关系。为精确标定半导体的灵敏度系数和石英晶体的压电系数，将改进的激光微位移速度干涉系统用于SHPB系统杆中质点速度的测试。结果表明，激光干涉方法标定的系数比传统方法标定的系数要小10%左右。由于激光微位移速度干涉仪可采用多点同时测量，本文尝试直接测量SHPB实验中试样两端的速度历史，获得材料的应力应变响应并拓展到中应变率实验的测试。为研究PBX炸药的组成结构对其力学性能的影响，对三种PBX炸药的力学性能进行了对比研究，获得了三种炸药各力学参数随温度的变化情况，分析了PBX炸药中各成分对力学量的贡献。结果表明，各材料的动态模量、强度随温度的升高而减小，而破坏应变基本保持不变。三种PBX炸药中，PBX3具有较特殊的破坏模式，力学性能相对稳定。TATB的加入对HMX有很明显的钝感作用，对PBX炸药的整体宏观力学性能有很大的改善。第二部分的主要内容为PBX炸药的细观损伤发展的实验研究和数值模拟研究。采用准静态和动态巴西实验对磨抛后的PBX炸药进行加载，回收试样观测PBX炸药的细观损伤发展情况。结果表明，PBX炸药中裂纹是主要的损伤形式。静态加载时，微观裂纹主要为界面脱粘裂纹，宏观裂纹主要为穿晶断裂裂纹；界面脱粘裂纹在加载早期即可形成，但不影响材料对外界的承载能力；穿晶断裂可能是试样破坏的主要原因。动态加载时，观察到的微裂纹和宏观裂纹均为穿晶断裂。采用离散元数值方法模拟PBX炸药在巴西实验过程中的裂纹扩展过程。为验证该方法的有效性，用HMX炸药晶体的参数作为均匀材料的基本参数，模拟均匀材料在巴西实验过程中的应变场分布，符合巴西实验的理论分析结果。建立能反映PBX炸药细观结构的模型，并模拟了PBX炸药圆盘试样受巴西实验加载后的响应情况。模拟结果表明：沿晶断裂先于穿晶断裂出现；带有沿晶裂纹的试样依然能承受加载；晶体出现断裂后试样内部结构失稳，表现为宏观失效；颗粒尺寸小的试样抗拉性能增强，在微裂纹形成后的很长一段时间还能承受加载，直到穿晶裂纹出现。第三部分为PBX炸药的含细观损伤本构关系研究。采用裂纹的张开，闭合裂纹的摩擦滑移以及翼型裂纹的弯折扩展等机制来描述PBX炸药的本构行为。考虑单轴压缩加载的计算结果表明，采用裂纹扩展区概念发展的含细观损伤本构关系能反映PBX炸药的应力应变曲线的基本形状。最后，对该模型进行了理论改进以用于描述动态加载时材料的响应。在今后的工作中将发展该模型用于LS-DYNA模拟中，为武器效应评估提供理论支撑。更多还原

【Abstract】 As modern high-powered weapon systems develop so fast, the safety problem ofthe explosive gradually becomes more and more spiculate. New-style normal weapongives higher requirement of explosives’ detonation initiation behavior. Polymer-bondedexplosive (PBX) is a kind of high energetic composite, having higher energy density,better mechanical behavior and higher safety property. Therefore, they are widely usedin many areas like national defense and civil economy. However, unexpectedexplosions occur sometimes even if the insensitive explosives were used. To satisfy therequirement of high property weapon equipments, it is crucial to investigate eachproperty of the insensitive explosives. Because PBX has complicate structure and itusually undergoes very complex mechanical state before explosion, to study PBX’smechanical behavior, especially the dynamic mechanical behavior is an important taskfor researching the safety behavior of PBX. This thesis aims at the research on thedynamic response and damage evolution. Using Split Hopkinson Pressure Bar (SHPB),we studied the dynamic compressive and tensile behavior of PBX, obtained the damagefeature at meso-scale of recovered specimen, and finally constructed the constitutiverelation involving the meso-damage evolution.There are three parts in the thesis. The basic mechanical researches of PBX wereperformed firstly. Damage developments and its influences on stress-strain curves wereexperimentally observed. From the experimental results, it can be inferred that PBX istypically brittle. The according damage modes are mainly micro-cracks’ initiation andspreading, and development of PBX’s inner micro-cracks needs to be experimentallyobtained for the investigation of damage evolution of PBX. Hence, in the second part,the experimental and numerical studies of PBX’s meso-damage evolution were carriedout by way of Brazilian test. After the obtainment of the damage feature of PBX, themathematical description of the evolution law is necessary to be founded. Therefore, atthe last part, the micro-crack development region constitutive model was adopted todescribe the influence of inner micro-cracks’ evolution on the macro stress-strain curve.Follows are the details.The first part mainly works on the macro dynamic response of PBX. Themeasurement of the SHPB tests was improved to obtain more accurate data, because thefailure strain of PBX was quite small. Using quartz crystal as stress gauge andsemiconductor strain gauge together, high Signal-to-Noise signals were obtained. Usingdifferent wave length and pulse shaper, it was found that the damage evolution wassensitive to impact loading, and the range of the loading strain rate was small due to thelow strain rate limit. According to the feature of the stress-strain curve, constitutive equations were developed and they could describe the stress-strain relation including theunloading stage after failure. Laser micro-displacement velocity interferometer wasdeveloped to accurately calibrate the coefficients of semiconductor and quartz crystalslices, by measuring the particle velocity of the bars directly. Results show thecoefficients obtained by laser interferometer are smaller by10%than that obtained bytraditional methods. Because the laser interferometer system can realize multi-pointmeasurement, the velocity history of specimen’s two ends can be obtained directly.Moreover, it is still can be developed to measure the signals of long pulse at middlestrain rate loading cases.Mechanical behaviors of three PBXs are compared by taking high temperatureSHPB tests to investigate the influence of the components on the whole mechanicalresponses. Several mechanical parameters’ variations with temperature were obtainedand the contributions of PBXs’ each component to mechanical parameters wereanalyzed also. Results show the dynamic modulus and the failure strength decreases asthe temperature rises, but the failure strain changes little. Among the three PBXs, PBX3has unique failure mode and most stable mechanical behavior. The addition of TATBcan insentisize HMX obviously and improve the macro mechanical properties of PBXgreatly.The second part concerns about experimental and simulative investigation of themeso-damage evolution. At first, the quasi-static and dynamic Brazilian tests wereperformed on polished PBX and the meso-damage features of recovered specimen wereobserved using optical microscope. It is found that cracks are the main damage mode inPBX, like many brittle materials. In case of quasi-static loading, most microcracks areinterface debonding cracks, and macrocracks are mainly transgranular fracture cracks.The interface cracks may initiate at early stage of loading and they have little influenceon specimen’s sustainability. Transgranular cracks may be the primary cause ofspecimen’s macro-failure. In case of dynamic loading, the observed macro-cracks andmicro-cracks both exhibit transgranular fracture.Discrete element method was adopted to simulate the cracking process of PBXduring Brazilian tests. To prove the validity of this method, homogenous material modelwas built using HMX’s parameters. The strain distributions of the disk specimen duringBrazilian test were obtained and they were similar to the theoretic analysis of Braziliantests. Meso-structure of PBX was presented. Specimens with different particle size weremodeled under the loading of Brazilian test. Simulation results show that interfacecracks occur before transgranular cracks, and specimen with interface debonding crackscan sustain the applied loading, also. The specimen fails at macro-scale after the crystalfractures. Specimen with smaller particle size can sustain for a long time withmicrocracks before transgranular cracks occur.The third part focuses on the constitutive relation concerning the meso-damage evolution. The damage evolution contains the cracks’ splaying, the friction and slidingof closed cracks and the bending spread of wing cracks. Computing results in case ofuniaxial compression loading show that this constitutive model can describe themechanical behavior. At last, the model was developed for the use in dynamic loadingcase theoretically. In further work, the model will be developed for the use inLS-DYNA.更多还原