【作者】 林谋金；

【导师】 沈兆武； 马宏昊；

【作者基本信息】 中国科学技术大学 ， 工程力学， 2014， 博士

【摘要】 传统含铝炸药中的铝通常以粉末形式加入到炸药中,以提高含铝炸药的爆炸威力,但同时也提高了炸药的机械感度,降低了炸药的安全性。铝粉的粒径要求在微米或纳米量级,加工工艺较为复杂,而且粉尘对环境的污染严重,还存在粉尘爆炸的危险,同时铝粉比表面积较大,其活性随着储存时间增加而降低。另外炸药在运输、存储和使用过程中受到各种机械形式作用,炸药在各种机械作用下的力学行为变得日益重要。针对上述问题,将传统含铝炸药(RDX/Al)中的铝粉用铝纤维替代,得到新型铝纤维炸药。与传统含铝炸药相比,铝纤维的加入能改善含铝炸药的成型性,同时增强了含铝炸药的力学性能并提高含铝炸药的安全性。本文通过对铝纤维炸药的研究,有利于加深对含铝炸药爆炸性能认识,具体研究内容如下：通过铝纤维炸药与传统含铝炸药的空中爆炸实验,得到压力时程曲线,并对曲线进行小波分析。小波分析表明信号去噪后的信噪比主要与分解的层数有关,而小波基的选择对信噪比影响相对较小。通过对信噪比、均方根误差与去噪效果综合判断,文中最终采用Daubechies小波系中的db4对空中冲击波压力时程曲线信号进行处理。通过小波分析可以获得冲击波信号在各频带的细节信息,d4对应的频带(781kHz～1562kHz)上存在周期性干扰信号,d9与d12对应的频带上明显存在三处突变信号,分别为入射冲击波、二次击波与反射冲击波。空中爆炸的冲击波能量分布主要处于0-8E5Hz频率范围内,该频率范围也为滤波的截断频率提供参考。铝纤维炸药的二次击波超压幅值和到达时间与铝粉炸药相近,而铝纤维炸药的二次击波到达时间早于基体炸药(RDX),说明二次击波的超压幅值与到达时间与炸药类型有关。使用压制铝纤维的铝纤维炸药冲击波冲量与传统含铝炸药相当,其相对于RDX提高了18%。将含有不同铝纤维含量的铝纤维炸药与含有不同铝形态的含铝炸药进行水下爆炸实验,得到冲击波压力时程曲线与脉动压力时程曲线,并对这些曲线进行分析计算。使用压制铝纤维的铝纤维炸药(20%)压力峰值、比冲击波能、冲量略低于传统含铝炸药或与传统含铝炸药相当,但铝纤维炸药的爆速与比气泡能略高于传统含铝炸药的爆速。铝纤维炸药(20%)的冲量相对于RDX提高了14%-21%。铝纤维炸药的第一次气泡脉动周期时间略高于传统含铝炸药,但铝纤维炸药的气泡脉动压力峰值与压力冲量都低于传统含铝炸药,其原因需要进一步研究。低含量铝纤维对铝纤维炸药的压力峰值影响较小,高含量铝纤维对铝纤维炸药的压力峰值影响较大。铝纤维炸药的爆速随着铝纤维的含量增加而减小,与铝纤维二次反应放出的能量未能支持爆轰波阵面的传播有关。铝纤维炸药的第一次脉动周期时间与比气泡能随着铝纤维含量的增加而增大,铝纤维炸药的脉动压力峰值与脉动压力冲量随着铝纤维含量的增加而减小。铝纤维炸药的比冲击波能随着铝纤维含量的增加而先增大后减小,即铝纤维含量为20%时,铝纤维炸药比冲击波能最大。将含有不同铝纤维含量的铝纤维炸药进行力学实验,通过对实验结果进行分析,结果表明铝纤维炸药的压缩极限应力与残余强度随着铝纤维含量增加而增加。对不同含量的铝纤维炸药弹性模量进行拟合计算,得到铝纤维的增强系数为8.19,说明铝纤维显著增强铝纤维炸药力学性能。SHPB实验采用波形整形技术对入射波进行整形,延长其加载时间,使试样在破坏前达到应力平衡,同时实现常应变率加载,另外可以获得比较光滑的入射波,降低应力波的弥散效应,消除高频振荡,明显改善加载波的质量。SHPB实验表明：铝纤维炸药的压缩极限应力具有应变率效应,随着铝纤维含量增加,铝纤维炸药的压缩极限应力的应变率效应开始减弱。采用正态分布函数对不同含量的铝纤维炸药在准静态下的应力应变曲线进行拟合,拟合效果较好。低于20%含量的铝纤维炸药在SHPB实验后都己粉碎,高于20%含量的铝纤维炸药在SHPB实验后还能保持较好的完整性,说明高含量的铝纤维炸药具有一定的抗过载能力。SPH-FEM耦合方法克服了网格畸变问题又能保证计算效率,文中通过MATLAB与LS-DYNA程序生成水下爆炸的SPH-FEM模型并进行模拟计算。在建模过程中,SPH粒子区域最终采用球形,为了保证球体区域上的最外围的一层粒子都严格落在球面上,即在最外层球面上生成的SPH粒子坐标与ANSYS生成的有限元网格坐标能很好地对应上,从而使SPH粒子与有限元网格进行良好接触耦合,SPH粒子将采用新方法生成,并成功解决粒子穿透有限元单元以及接触面部分网格畸变问题。通过对铝纤维炸药水下爆炸过程进行模拟,将模拟计算得到的远场压力时程曲线与实验得到的压力时程曲线进行比较,结果表明数值模拟得到的压力峰值与实验得到相应位置的压力峰值高度一致,说明文中采用SPH-FEM耦合方法对铝纤维炸药水下爆炸模拟具有一定的可靠性、优越性和精确性,从而进一步获取铝纤维炸药近场的冲击波压力时程曲线。另外将离铝纤维炸药不同距离的压力峰值按指数衰减函数进行拟合,其拟合效果良好。更多还原

【Abstract】 Traditionally, aluminum is incorporated in the composite explosives in the form of powder, which is expected to result in improving the blast performance of composite explosives due to superior heat of formation. However, impact sensitivity is improved owing to aluminum powder becomes hot spots in composite explosives. In addition, aluminum particle size ranges from nanometer to micrometer, which may lead to the problems of environmental pollution, complex production process, and dust explosion during the production process. The activity of aluminum powder decreases with an increase in storage time because the specific surface area of aluminum powder. Explosives is subjected to all kinds of loading under different environment, such as productive process, packing, handing, transportation, launch, and so on. Mechanical properties of explosives become increasingly significant. A new non-ideal composite explosive is proposed by replacing aluminum powder in traditional aluminized explosives with aluminum fiber. The disadvantage of traditional aluminized explosives may be solved by using aluminum fiber in composite explosive and the better mechanical properties may be obtained because aluminum fiber is used in the new composite explosive. It is helpful to understand the detonation mechanism of traditional aluminized explosives by the study of aluminum fiber explosive.The pressure history curves of aluminum fiber explosive and traditional aluminized explosives are measured by air blast experiments and the curves are analyzed by wavelet analysis. The results show that the decomposition levels have a great effect on the signal to noise ratio after denoising and the wavelet kernel function has less effect on the signal to noise ratio after denoising. Based on the comprehensive judgment of signal to noise ratio, root mean square error and denoising effect, the signals of pressure are processed by db4of Daubechies wavelet series. Details of shock wave signal in each frequency band can be obtained by the wavelet analysis. There are periodic interference signal in d4(781kHz to1562kHz) and three obvious mutation signals, the incident shock wave, secondary shock wave and the reflected shock wave, in d9and dl2. The energy of air blast shock wave is mainly distributed in the0-8e5Hz, which could provide a reference for filter. The amplitude and occurring time of secondary shock wave of aluminum fiber explosive as same as traditional aluminized explosives and the occurring time of secondary shock wave of aluminum fiber explosive is earlier than matrix explosives (RDX), which shows that the amplitude and occurring time of secondary shock wave is associated with the types of explosive. The shockwave impulse of aluminum fiber explosive is close to that of the traditional aluminized explosive. Compare with RDX, the impulse of aluminum fiber explosive increase by18%.The pressure-time curves for the shock wave and bubble pulse of aluminum fiber explosives and traditional aluminized explosives are measured by underwater explosion experiments. The peak pressure, impulse, shock wave energy and bubble energy are obtained by analyzing the curves. The peak pressure, impulse and shock wave energy of aluminum fiber explosive are close to that of traditional aluminized explosives. The detonation velocity and bubble energy of aluminum fiber explosive are greater than that of traditional aluminized explosives. Compare with RDX, the shock wave impulse of aluminum fiber explosive increase by14%-21%. The first pulsation period of aluminum fiber explosive is close to that of traditional aluminized explosives, but the peak pressure and impulse of bubble pulse are lower than that of traditional aluminized explosives. The low content aluminum fiber has less effect on the peak pressure of aluminum fiber explosives, but the high content aluminum fiber has a significant effect on the peak pressure. Detonation velocities of aluminum fiber explosives are decreased with an increase of Al fiber contents. It indicates that the potential of secondary reaction of aluminum fiber and detonation products does not support the detonation propagation. The first pulsation period and bubble pulse of aluminum fiber explosive are increased with an increase of Al fiber contents. The peak pressure and impulse of bubble pulse are reduced with an increase of Al fiber contents. The shock wave energy of aluminum fiber explosive increased firstly and then decreased with an increase of Al fiber contents. The specific shock energy of aluminum fiber explosive is maximum when the content of aluminum fiber is20%.The mechanics experiment of aluminum fiber explosive was carried out by MTS and SHPB. The analysis of experimental results shows that the ultimate stress and residual strength of aluminum fiber explosive are increased with an increase of Al fiber contents. The reinforcement coefficient is8.19, which obtained by fitting experimental data of elastic modulus. The fitting effect on experimental data is satisfactory. The coefficient shows that the enhanced effect of aluminum fiber on RDX is marked. The loading time of SHPB is extended by pulse shaping technique, which ensures the dynamic stress equilibrium in the specimen and to obtain a constant strain rate. The shaping technique could improve the quality of the incident wave and reduce dispersion effects of stress waves. The ultimate stresses of aluminum fiber explosives are related to strain rate by the analysis of experimental results. The relationship of ultimate stresses and strain rate is weakened with an increase of Al fiber contents. The normal distribution function is taken to fit stress strain curves of aluminum fiber explosive in a quasi-static state. The aluminum fiber explosive is destroyed under shock loading when the aluminum fiber contents below20%and the aluminum fiber explosive keep integrity under shock loading when the aluminum fiber contents more than20%. It indicates that aluminum fiber explosive has anti-overload ability.SPH-FEM coupled method could overcome the problem of mesh distortion and improve computational efficiency. The model (SPH-FEM) of underwater explosion is established by MATLAB and LS-DYNA. The region of SPH is a sphere. In order to ensure that the coordinates of particles are agreeing with the grid coordinates of the element on the sphere. The particles of SPH are generated by a new method. The method solves the problem of mesh distortion in the zone of cube tip and penetration of SPH particles to FEM element. After underwater explosion of aluminum fiber explosive was simulated by using the SPH-FEM model, the pressure-time curves of numerical simulation and experiment were compared and the result show that the peak pressure of numerical simulation can match with that of experiment. It indicates that the model of the underwater explosion is presented to testify the validity and precision of SPH-FEM coupled method. The pressure-time curves of aluminum fiber explosive in near-field are obtained by numerical simulation. The decaying exponential function is adopted to fit peak pressure of aluminum fiber explosive at different positions and it is excellent in fitting.更多还原