【作者】 陈荣；

【导师】 卢芳云； 夏开文；

【作者基本信息】 国防科学技术大学 ， 力学， 2010， 博士

【摘要】 高聚物粘结炸药（Polymer Bonded Explosive,PBX）装药在常规武器战斗部及火箭推进剂中具有广泛应用。在制造、运输及发射等过程中往往要承受复杂应力过程,甚至是强动载。在不同作用下炸药装药的力学响应及损伤发展是炸药发生意外起爆的源头,严重影响着武器弹药的安全和可靠。因此,需要系统研究PBX炸药装药在复杂应力条件下的力学响应,这是深入认识起爆机理、研究弹药安全性的基础。论文首先介绍了本研究在实验方法方面的创新。建立的压拉通用Hopkinson杆实验系统将传统的Hopkinson压杆及Hopkinson杆拉杆集成到一个系统平台。单次加载技术保证了实验过程中试样只受到一次加载。基于夹心弹的可控双脉冲加载系统,可实现两个加载脉宽之间的距离以及两个脉宽的幅值比例可调。将同步高速摄影与数字图像相关相结合的技术引入到Hopkinson杆实验中来,得到了加载过程中试样表面的应变场。自行建立了激光光通量位移计测量系统,并将其应用到Hopkinson杆实验中。本文以某压装PBX炸药试样为研究对象,系统研究了其在复杂应力加载下的力学响应。在进行传统准静态加载及常规Hopkinson杆动态加载实验的基础上,结合激光光通量位移计应变测试技术及石英晶体应力测试技术,建立了材料在中应变率加载下的力学性能测试方法。对于平台Brazilian实验采用数值标定的方法将试样的中心应变和横向平均应变结合起来,建立了一种非接触式测量试样拉伸应变的方法。与同步高速摄影结合数字图像相关的方法对比,该方法具有可比拟的实验精度,但是能够得到更为完整的应变历史曲线。将实验结果与直接拉伸实验及半圆盘三点弯拉伸实验结果进行比较,前两者吻合较好,而由于半圆盘三点弯拉伸实验中试样沿断裂方向拉伸应力分布不均匀,需要采用非局域化的方法修正后才能与前两者吻合。论文通过准静态、中应变率以及高应变率加载实验,获得了不同初始密度（1.5、1.6和1.7 g/cm³）不同应变率(10^-4～10³ s^-1)下该PBX炸药试样的应力-应变曲线,论文最后建立了反映试样初始压装密度和应变率效应的本构模型。研究结果表明,该PBX炸药试样的压缩和拉伸破坏应力均随着初始压装密度以及加载应变率的增加而增加。通过对被动围压及主动围压实验中试样与加载介质之间的摩擦效应的分析表明,被动围压实验中试样与加载介质之间滑动配合能够有效地减小摩擦对实验结果的影响,而主动围压实验中试样与加载介质之间的摩擦对实验结果影响较小。在动态围压加载条件下,该PBX炸药试样轴向应力和围压应力均随着初始压装密度以及加载应变率的增加而增加。随着围压应力的增加试样的破坏模式由应变软化转变为应变硬化。在考察试样动态强度的基础上,本文进一步建立了Hopkinson杆加载带预制裂纹的半圆盘三点弯试样来测试材料动态I型断裂参数的实验方法。该方法在一次实验中能够得到包括起裂韧度、传播韧度、表面能和裂纹传播速度在内的所有I型裂纹相关参数。采用同步高速摄影结合数字图像相关技术得到了在动态加载下带预制裂纹的该PBX炸药半圆盘三点弯试样表面的位移场以及应变场历史。该PBX炸药试样的Ⅰ型起裂韧度及传播韧度均随着加载率及试样密度的增加而增加。试样的表面能及传播韧度均随着裂纹传播速度的增加而增加,且存在裂纹传播的极限速度。论文最后根据压缩、围压和拉伸的实验结果,得到了PBX炸药试样的非线性破坏准则,加载-再加载实验结果与理论模型吻合较好,可以为工程应用与仿真计算提供材料模型和参数支持。通过分析材料强度、韧度、表面能等力学参数之间的相关性,得到了试样的破坏机理,结果表明试样的颗粒破坏强度远大于颗粒间的脱粘强度。宏观测到的试样拉伸强度与界面脱粘强度相近,而压缩强度介于两者之间。更多还原

【Abstract】 Polymer bonded explosives （PBX） are used in a wide variety of applications, ranging from rocket propellants to the main explosive charges in conventional munitions. Of great concern to explosive researchers is the possibility of accidental ignition during manufacture, transport or handling. It is thus essential to obtain a complete description and understanding of the mechanical response of PBX. This description and understanding are necessary for modeling those events that may cause unwanted ignition of the energetic materials and the resulting hazards.A method is proposed to combine the traditional Split Hopkinson Pressure Bars and Split Hopkinson Tensile Bars in a newly developed Hopkinson Pressure-Tensile Bars. A momentum-trap system is introduced to ensure single pulse loading during tests. The controlled multi-pulse loading is carried out by a stuffed striker, and the dwell time and amplitudes of pulses can be accurately controlled. The strain field of the specimen is estimated by the Digital Image Correlation （DIC） processing of the photos which are taken by a synchronous high speed camera. In addition, a self made laser gap gauge （LGG） is developed in the experiment.The modified Hopkinson bar system is developed to measure material responses at intermediate strain rates (1 10² s^-1). In this work, the insituation Hopkinson bar technique is proposed, where the LGG is adopted in the traditional Hopkinson bars system to measure the sample deformation and an X-cut quartz stress gauge to measure the dynamic load directly. For the flattened Brazilian disc （FBD） test, the LGG is used to monitor the transverse expansion of the disc perpendicular to the loading axis, from which the average tensile strain is deduced. The numerical simulation reveals a linear relationship between the tensile strain at the center of the specimen and the average tensile strain. This scaling factor is not sensitive to the material elastic parameters. This method is as accurate as the DIC process, but the latter is limited by the number of frames of the high speed camera. The results are then compared to those from other two methods, the direct tension with‘dog bone’specimen and the semi-circular bending （SCB） tension test. The results from the first two methods are coincident with each other, while the result of the SCB test has to be properly adjusted by a‘non-local’failure approach due to the stress gradient along the fracture path. The mechanical properties of the PBX at three density levels （1.5, 1.6, 1.7 g/cm³） are tested under strain-rates ranging from 10^-4 to 10³ s^-1. A constitutive relation has been established based on the experimental curves, including the features such as mass density, strain, strain-rate et al. The results show that the mechanical behaviors of the PBX bear obvious rate-dependence, and the corresponding compression/tension failure stresses increase with the original density or the loading strain rates.Two types of confinement, the passive confinement using jacket and the active confinement using pneumatic pressure vessel, are used in the triaxial test. The friction between the specimen and the confinement medium is analyzed for both methods. There is noticeable difference in the jacket confinement due to friction, and sliding fit with lubrication could minimize the friction error. However, the friction-induced error is ignorable in the pneumatic pressure vessel method as long as the confinement stress is fixed during tests. Both the axial strength and the corresponding confinement stress increases proportionally as the rising of original density or strain rates. There is a change from strain softening after the maximum at the lower confining pressures to work hardening at larger strains at the higher confining pressures.Fracture initiation toughness, fracture energy, fracture propagation toughness, and fracture velocity are key dynamic fracture parameters. A method is proposed to simultaneously measure these parameters for mode-I fractures in SHPB testing with a notched SCB specimen. The crack propagating process is monitored by a synchronous high speed camera, and thus the strain field history is observed by DIC process. Both the initiation toughness and the propagation toughness are found to increase linearly with increasing loading rates. The propagation fracture toughness also increases with the fracture velocity, and a limiting fracture velocity is obtained.A dynamic failure criterion is set up to reveal the nonlinear effect of PBX. Parameters are obtained based on the experimental results of compression, tension and confinement. The model could potentially be implemented in commercial software such as ABAQUS and LS-DYNA. The failure modes are discussed in terms of various theoretical models. The results suggest that the debonding strength is much smaller than the crystal fracture strength. The measured tensile strength is similar to the debonding strength while the compression strength is somewhere between them.更多还原