强冲击载荷下岩石损伤特性实验研究

通过在一级轻气炮驱动的平板碰撞实验台进行冲击损伤实验 ,对软回收样品进行超声波测试 ,研究了强冲击载荷下两种典型岩石损伤特性 .结果表明 ,岩石的动态损伤与冲击速度和超声波衰减系数α有关 ,后者较好地反映了岩石的损伤程度 ,可作为构造岩石损伤模型的主要参量     

岩石动态损伤特性的实验研究

利用一级轻气炮技术,对２类岩石进行冲击损伤实验,并对软回收样品进行了超声波测试,得到岩石的动态损伤与冲击波速和超声波传播特性的关系．结果表明声波衰减系数可作为描述岩石动态损伤的主要参量．     

Ultrasonic Evaluation of the Impact Damage of Polymer Bonded Explosives

The damage properties of polymer bonded explosives under dynamic loading were studied by using ultrasonic evaluation. Explosive samples were damaged by a low-velocity gas gun at different impact velocities. Ultrasonic examination was carried out with a pulse through-transmission method. Spectra analyses were carried outby using fast Fourier transform. Characteristic ultrasonic parameters, including ultrasonic velocities, attenuation coefficients, spectra area and master frequency, were obtained. The correlation between the impact damage and ultrasonic parameters was analyzed. A damage coefficient D was defined by considering a combination of ultrasonic velocity and amplitude. The results show that ultrasonic parameters can be used to quantitatively assess the damage extent in impacted plastic bonded explosives.     

Experimental Investigation on Spall Fracture of 30CrMnSiNi2A Steel

Spall fracture is a damage that occurs in a body when two rarefaction waves interact and produce enough dynamic tension breakage,and then the spall zone is founded in the interior of the target.Behavior of materials in the spall phenomenon is strongly affected by the stress level,time of loading and so on.The spall properties of 30CrMnSiNi2A steel loaded by a gas gun were investigated using the planar impact experiment and the two-wave structural profiles of free surface velocities of specimens were recorde...     

冲击载荷下脆性岩板损伤断裂演化的实验模拟研究

在矿山运输系统中,井壁围岩冲击损伤破坏对经济和安全效益的影响是至关重要的,因为动态冲击载荷对井壁围岩和支护结构会产生严重的削弱破坏作用,室内研究表明,岩石样品如岩板在动态载荷的冲击作用下会失效。为研究在低速冲击载荷作用下,脆性岩石损伤断裂的演化过程,利用分离式霍普金森压杆(SHPB)装置中压缩气体发射球体子弹对脆性岩板进行变角度冲击损伤实验,岩板受到冲击后,边缘出现凹坑,表面裂纹从撞击凹坑直达岩板边缘,实验中样品的表面裂纹能有效代表试样内部的开裂状况,能有效反映冲击能量的耗散、破裂区面积与裂纹表面积随入射能量呈非线性增长趋势,同时与入射角度相关,但当破裂区面积急剧下降时,裂纹表面积反而急剧上升,表明裂纹的发生发展有明显的孕育期,在入射能量达到临界值前,主要表现为裂纹孕育增长,在达到临界值后,发生宏观断裂破坏,裂纹面积呈负增长,破裂区面积增大。实验结果分析表明在实际工程中,围岩和支护结构的抗冲击的最优化设计角度范围在15°～30°。     

玄武岩纤维布Whipple防护结构超高速撞击损伤分析

针对加入玄武岩纤维织物对Whipple防护结构损伤产生的影响进行了实验研究.探讨了将玄武岩纤维织物作为航天器空间碎片超高速撞击损伤防护结构的增强材料用于航天领域的可行性.实验采用的基本构形为Whipple防护结构,玄武岩纤维布按不同方案布置在结构中.实验分析表明,玄武岩纤维布的防护作用在于:其发生击穿破坏时,击穿孔处的纤维束产生的断裂和孔边处纤维束产生的变形消耗和吸收了撞击物的撞击能量;破坏时,玄武岩纤维束中逐次断裂的纤维丝与撞击物的撞击除了对撞击物产生切割作用外还在撞击物中产生高频的间歇冲击波,两者都对撞击物产生碎化作用;玄武岩纤维布自身的破坏不会再产生新的大碎片.     

受外来硬物低速撞击的弹性板撞击接触力的予报公式和实验研究

本文在大量实验的基础上,用半经验、半解析方法给出了受外来硬物撞击的弹性板撞击接触力的计算公式.采用气体发射撞击试验机对三种不同厚度的A_3钢板在1米/秒至4米/秒的速度范围内进行了撞击力测定实验,并对实验结果进行了简单分析.理论予报与实验结果吻合的很好.     

Experiments and simulation of low-velocity impact characteristics on carbon fiber composite lattice core sandwich structures

Since composite sandwich structures are susceptible to low-velocity impact damage,a thorough characterization of the loading and damage process during impact is important.In the present paper,the low-velocity impact response of carbon fiber composites lattice structures is investigated by experimental and numerical methods.Impact tests on composite plates are performed using an instrumented drop-weight machine(Instron 9250HV)and a new damage mode is observed.A three-dimensional finite element model is built by ABAQUS/Explicit and user subroutine(VUMAT)to predict the peak loading and simulate the complicated damage problem.The numerical predictions are in good agreement with the experimental results.     

新型基因枪微弹材料可行性初步研究-Ⅱ

基因枪在未来临床基因转导中很有前途,但目前所用微弹材料金、钨都属于重金属,其长期存在于人体的安全性尚无法估计,曾提出用羟基磷灰石(HAP)微粒来代替金或钨微粒。报告了两种HAP微粒的制备以及它们对DNA的负载及其影响因素研究的结果,以期对HAP在基因枪中的应用研究奠定基础。用化学沉淀法和热处理研磨法制备HAP微粒,调节pH负载DNA后,用红外光谱、同步热分析仪、透射电镜等方法表征负载。结果表明,可在一定条件下实现HAP对DNA的高效负载。     

混凝土率相关单轴塑性损伤本构的开发及应用

为了对爆炸作用下钢筋混凝土(reinforced concrete,RC)构件动力响应进行简化分析,需要合理描述混凝土和钢筋的应变率效应,而LS-DYNA中缺乏能够考虑混凝土应变率效应的单轴本构模型,因此,结合Faria单轴塑性损伤模型,通过黏性规则化方法调整率无关模型的损伤阈值演化律以考虑应变率效应,并利用LS-DYNA将该模型编制为用户材料子程序VUMAT.以单个单元测试了高应变率下材料的基本性能;基于纤维模型模拟了RC梁在爆炸、冲击作用下的动力响应.结果表明:该本构模型能反映混凝土受拉应变率效应高于受压应变率效应的事实,同时也能较准确地模拟爆炸与冲击作用下RC梁的动力响应.     

Kevlar织物增强复合材料层合板冲击损伤特性研究

采用空气炮实验装置，渗透剂增强的X射线照相法和高强光背射法，对中心受到横向冲击的Kevlar/环氧层合板的冲击损伤情况进行了研究，借助于有限元程序对层合板的应力状况进行分析，计算，讨论了冲击速度，铺层角，弹丸质量变化时材料的破坏机理与特征，其研究的结果对抗弹复合材料的设计与合理使用具有指导意义。     

Experimental and numerical investigations on the tensile mechanical behavior of marbles containing dynamic damage

To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage, multiple impact loading tests were performed on the disc marble samples, and then static Brazilian tests were conducted for the damaged samples. Besides, coupling modeling technology of finite difference method (FDM)—discrete element method (DEM) was used to carry out the numerical investigation. The results show that after multiple impacts, more white patches appear on the surface, and some microcracks, macro-fractures as well as pulverized grains are found by optical microscopic. The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample. The interaction between grains in the damaged sample becomes intense in the subsequent static loading process, causing a relatively large strain. The volume of the fragments falling off around the loading points becomes larger as impact number increases. As the dynamic damage increases, the absorbed energy of sample during the static loading first decreases and then tends to be stable. Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.     

某些身管武器连发射击过程中膛壁温度分布

本文用高速气流沿半有界平板的湍流做为火炮发射过程中火药燃气流对炮膛的对流換热模型,导出连发射击过程中膛壁温度分布的数学模型。对任何火炮,只要知道其压力曲线和速度曲线,就可求得连发射击过程中膛壁温度分布。为改善武器的使用条件、身管强度设计及发射过程中热損失的分析提供理论根据。文中所用換热模型和数学模型已由53式7.62mm步枪的单发射击实测結果证实是可信的。     

硝酸铵对炮口焰的影响研究

从理论上研究了硝酸铵对发射药燃烧产物组成的影响;采用高速摄影仪进行炮口焰拍摄,采用炮口焰面积、炮口焰最大直径、积分光密度对炮口焰进行表征.研究结果表明:在发射药中加入硝酸铵,可以明显降低燃烧产物中可燃气体含量,减小炮口焰;配方中,硝酸铵含量为70%时,与单基药相比,可燃性气体含量降低了98.4%.混装发射药中硝酸铵含量达到25%时,与制式药相比,炮口焰面积减小了44.7%,最大直径减小了31.4%,积分光密度减小了44.7%.     

Relation of Damage Variable and Gas Permeability Coefficient of Concrete under Stress

Compressive stress and tensile stress were applied to concrete specimens using test rigs designed by RILEM TC 246-TDC. Ultrasonic wave velocity and autoclam permeability system were used to characterize the damage variable and gas permeability coefficient of concrete, respectively. The experimental results show that the strain value of concrete increases with the increasing of stress level and loading time. The damage variable and gas permeability coefficient of concrete under compressive stress decrease at first and increase after a threshold value between 0 and 0.6. When the concrete is under tensile load, the damage variable and gas permeability coefficient increase with tensile stress, with a significant increase from 0.3 to 0.6 tensile stress. There is a strong linear relationship between the damage variable and the gas permeability coefficient, suggesting both as good indicators to characterize the damage of concrete under stress.     

有保护层的岩石冲击损伤实验研究

利用一级轻气炮，对有保护层和无保护层的砂岩、花岗岩和大理岩试件进行冲击实验，并对试件进行冲击压力测试和声波测试，利用试件端面产生的冲击压力波形分析保护层对冲击作用的影响，利用实验前后的声波速度变化情况衡量岩石试件的损伤度。实验结果表明，在其它实验条件基本一致时，有保护层的岩石试件所受的冲击压力比无保护层时降低了60％左右；波速降低率也明显减小，损伤度降低率在14．8％～48．2％之间。说明保护层能够对受冲击作用的岩石起到很好的保护作用。     

碳纤维复合材料冲击损伤的激光错位散斑检测

采用激光错位散斑检测技术,对含有冲击损伤的碳纤维层压板进行检测实验,分析了错位方向、错位量和加载时间对检测结果的影响。实验结果表明,激光错位散斑检测技术能够快速、准确的定位含有冲击损伤碳纤维复合材料层压板中的损伤位置;对有明显纵横比的冲击损伤而言,错位方向与其纵向一致将对损伤范围和程度判定产生较为明显的影响;错位量大小应控制在需要检测的最小冲击损伤的半径到直径之间,在提高检测灵敏度的同时避免由于错位量过大导致的误检和漏检;热加载时间过长或过短都会导致漏检,在实际检测过程中应结合被检物实际情况具体分析。     

铝双层板结构高速撞击防护性能实验

采用非火药驱动二级轻气炮发射球形铝质弹丸,对铝双层板结构进行高速撞击实验研究,从而模拟空间碎片对航天器防护结构的高速撞击作用.实验得到了该铝双层板结构的前后板在不同速度区间的高速撞击损伤模式.获得了弹丸撞击速度在0.5~5.0 km/s时该铝双层板结构的撞击极限曲线,并与Christiansen方程的预测撞击极限曲线进行比较,同时分析了后板材料的屈服强度对铝双层板结构高速撞击防护性能的影响.     

冲击荷载下岩石动态损伤演化研究

I型裂纹破坏为岩石材料在冲击荷载作用下的主要破坏方式.通过假设岩石材料宏观上是一个均匀连续体,而细观上其内部则包含了大量随机分布的微裂纹等损伤缺陷;研究了岩石材料在冲击荷载下裂纹的成核、发展以及内部损伤演化规律;借助于宏细观相结合的理论建立了表征岩石材料细观结构及其损伤演化过程中的某种特征参量与宏观力学参数之间的关系方程.     

Dynamic Properties of Fiber Reinforced Cement Mortar

Based on the shear wave tracing(SWT) technique proposed by Tang Z P, particle velocity gauge and the dual internal measurement for pressure and shear waves (IMPS) system are applied to investigate the responses of fiber reinforced cement subjected to impact loading. Series of experiments are conducted. The results show that there exist four critical points, A, B, C, D, in p - V Hugoniot curves. They correspond to the Hugoniot elastic limit (I/EL) of the material, the critical point for shear strength limit and transition from damage state to failure state, void collapse, and solid compression, respectively. The critical point B is difficult to be aware of and never reported. However, it can be clearly disclosed with SWT method. Based on the analyses of shear strength, it can be concluded that the transversal wave, especially the unloading transversal wave, is especially important for the dynamic damage investigation of brittle materials.