【作者】 田勇；

【导师】 刘石；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2010， 博士

【摘要】 炸药熔铸成型是将炸药加热熔化,由一定的工艺处理后将熔融态炸药注入容器或模具(其中固相含量一般高达40%-70%),经过短暂流动逐渐冷却固化成具有一定形状、尺寸的成型方法,是当前国内外一种广泛使用的装药成型技术,主要适用于TNT单质炸药或以TNT为液相载体的混合炸药。熔铸过程伴随着十分复杂的物理变化过程,其中一个最重要和最受关注的变化就是物态变化,即熔融态炸药熔铸到模具中后,随着温度降低,液相炸药将逐渐结晶变成固体,而这一过程将在很大程度上决定熔铸成型体的质量特性,并进而影响装药的使用性能。长期以来,由于TNT结晶行为与形态的复杂性和缺乏能够有效监测结晶过程的可视化非破坏检测手段,对炸药熔铸结晶成型过程的认识仍主要依赖于传统的相变分析和热力学分析,以及对成型体最终质量检验推演获得的经验知识。对于深入分析成型过程、优化熔铸工艺和提高成型体质量而言,还迫切需要寻求精密、有效的在线非破坏检测方法以实现对熔铸炸药成型过程结晶与质量特性演化的深入观察研究。因此,本论文探索以超声、CT技术为主导,结合内部温度场测试技术,研究深入炸药熔铸成型过程的各种内部参数及其分布测量的监测评价方法,开展数值模拟和仿真,探讨浇铸成型机理及异常形成机制。研制并利用热电偶内置法研究了浇铸成型过程的温度分布,获得了熔铸炸药冷却凝固过程的温度变化曲线,显示出物质相变与温度拐点出现之间的关联。结果表明单质TNT炸药凝固降温过程中越靠近模具中心部位在凝固点温度保持时间越长,TNT/RDX混合炸药冷却过程在凝固点温度保持时间很短,在靠近中心部位才有明显的时间保持；熔铸成型中加冒口与不加冒口对温度动态变化的影响有明显不同,最明显区别是最终凝固的区域不同,加冒口熔铸成型的区域较不加冒口炸药熔铸成型的区域明显上移。设计多通道超声透射方法并在线监测了炸药凝固成型过程,得到了凝固成型过程的声衰减、声速和波形特征变化规律,其中波形和声速的变化与炸药固／液相界面物理特征和凝固速度密切相关,而声衰减的变化则与炸药结构变化(含气孔和裂纹)和炸药密度的高低密切相关。凝固速度随着凝固层的推进而逐渐减慢,并显现了炸药凝固后裂纹的产生与扩展导致声衰减值降低至稳定的现象以及纯TNT凝固过程不断形成的缩松导致衰减值快速降低的现象,表明了设计的超声透射技术及其炸药凝固特性与其声学特性的内在联系能有效地揭示炸药熔铸凝固成型规律并在线诊断出产品质量的优劣。利用x射线CT研究了熔铸炸药凝固成型结构,获得了熔铸TNT/RDX炸药成型过程中三维结构信息。结果表明炸药自然凝固呈现以模具中心轴线为中心,从模具壁开始由外及里的逐层凝固规律,且靠近模壁TNT为细小晶体,随着凝固的继续逐渐形成粗大结晶体,造成大量孔隙并导致成型炸药疏松,在保温、不补缩状态下凝固后细小缩孔率一般7%左右,但添加RDX固相颗粒后TNT炸药基本凝固成细小等轴晶,炸药密实性得到大幅提高,药柱底部与上部密度差一般小于2%；单质TNT结晶体取向与凝固过程中内部热应力的分布密切相关,呈现较为明显的取向特征,一种取向基本沿径向排列,另一种基本沿轴向排列,模具尺寸越大这种排列规律越明显；越靠近模壁部位缩孔越少、CT值越高,相应密度值越高,而越靠近中部则由于形成较密集的微缩孔,CT均值则降低越明显,相应密度值降低也越明显；TNT混合炸药(RHT-902和RHT-906)成型药柱中一般都存在气孔,气孔是在浇注到模具的过程产生的,且成型药柱内部会产生横向和纵向裂纹,其中纵向裂纹一般穿过中轴线,横向裂纹多数处于药柱中部,并证实裂纹的产生通常发生在炸药全部凝固后。研究了炸药熔铸过程温度、粘度、传热等参数的因素对浇铸的物质相变及其异常产生的影响,数值模拟了浇铸成型过程中的温度和应力分布以及以出现缩孔等异常情况,模拟结果表明：粘度降低药柱中的缩孔情况略有改善,固化过程中的应力略有减小；换热系数降低,药柱内部温度变化明显趋缓,可能产生缩孔的区域变小,产生热应力也略有减小；模具温度提高后对内部中心的质量无改进效果,温度变化的拐点有延后现象。在上述试验基础上探讨了炸药熔铸成型过程中裂纹、气孔、缩孔异常产生的基本问题,并分析了炸药熔铸凝固机制及影响因素、不同工艺条件以及RDX含量对TNT结晶形态、微细结构以及成型质量的影响,探讨了工艺优化措施,为进一步研究TNT/RDX熔铸成型结构与性能关系奠定一定的理论基础。综上所述,本文提供了一种综合的测量和观察炸药凝固成型过程的方法,较为系统地研究了凝固成型过程的一些机制问题以及不同物理量之间的内在联系,这些为炸药熔铸成型工艺改进和提高提供了重要的技术基础,并具有重要的实际指导意义。更多还原

【Abstract】 Energetic materials (simply named explosives) casting is a widely used molded technique. In this way explosive is heated and melted with solid phase rate up to 40%-70%, then injected in mould using some treatment technology, and last solidified to cast products with some shape and dimension. It is mainly applied in TNT pure explosive or TNT liquid carrier mixed explosive.Explosive casting process involves many complicated physical changes, and phase change is the most important and attended change, which is liquid explosive solidification as temperature descends.This process can determine the casting quality characteristic at a large extent and accordingly affect the performance. For the complexity of crystallization, the understanding of explosive casting process mainly lies on the phase change and thermodynamics analysis.So it is urgent for on-line nondestructive test method to realize crystallization process and quality study. This paper studies test evaluation method of inner parameters and their distribution of explosive casting process based on ultrasonic and CT technique, and investigate the analysis method of abnormity through numerical simulation.The temperature distribution in the casting process was studied with thermocouple inner-laid method. The temperature change curves show that there is an association between phase change and temperature inflexion. The results indicate that the temperature at freezing point is held longer at closer center position for pure TNT while the holding time is very short for TNT/RDX mixed explosive and only obvious holding at center part during cooling process. The riser added will obviously affect the dynamic change of the temperature and the final solidification regions.The change rules of sound attenuation, sound velocity, and waveform character were obtained by on-line multichannel ultrasonic technique during explosive solidification process. Changes of waveform and sound velocity are related to solid and liquid phase interfacial character and solidification rate. And change of sound attenuation is related to explosive configuration such as pores and cracks and the density. The result shows that axis solidification rate is bigger than radius solidification rate of cylindrical casting explosive and solidification rate reduces with time. Acoustic data show that formation and growth of cracks induce ultrasonic amplitude rapid reduce then keeping stable, and shrinkages induce ultrasonic amplitude rapid reduce in TNT solidification process.The results show that acoustic characteristic has internal relation with explosive solidification characteristic and can online diagnose product quality.This paper studies cylindrical solidification structure of casting explosive with x-ray CT and obtains 3-D structure of crystallization in the melted TNT/RDX casting process.The results show that the solidification is from the outer to the inner along central axis line. Fine crystals and compact explosive are got near the wall of mould.Bulk crystals are formed along with solidification which induce many pores and porosity of casting products.Shrinkage rate is about 7% under heat preservation and no repair while density can be largely enhanced when RDX grain is added and isaxis crystal is formed.The density difference between upper and down is less than 2%.The crystallization tropism of pure TNT is relative with inner thermal stress and one is radial and another is axial. The shrinkage is less near mould wall and CT value is higher and density is bigger. The micro shrinkage is dense at central section. There are some pores produced during casting in TNT mixed explosive (RHT-902 or RHT-906) and longitudinal and transverse crack are brought at explosive pole. And the cracks are approved to be produced after entire solidification.The influence of temperature and viscosity and heat transfer on phase change of explosive casting is studied.Temperature and stress distribution and shrinkage etc. are simulated. The results show that reducing viscosity can decrease shrinkage and stress, and reducing heat transfer coefficient can make temperature change slower which reduced the area of shrinkage and thermal stress.Increasing mould temperature has no improvement effect on inner quality and the inflexion point of temperature change will cause time delay phenomena.The basic issues are discussed during explosive casting including crack, pore, shrinking hole based on above test.Casting mechanism and effect factor are analyzed and the infection of different techniques and RDX content for micro structure and quality are also studied.This can establish some theory basis for studying the relationship of structure and performance of TNT/RDX casting explosive.Above all, this paper provides an integrated measuring method of explosive casting and solidification process and studies mechanism of molded rules and inherent relation between different physical parameters. These provide important technology basis for explosive molded technology improvement and have important guiding significance.更多还原