Reliability estimates for flawed mortar projectile bodies

The Army routinely screens mortar projectiles for defects in safety-critical parts. In 2003, several lots of mortar projectiles had a relatively high defect rate, 0.24%. Before releasing the projectiles, the Army reevaluated the chance of a safety-critical failure. Limit state functions and Monte Carlo simulations were used to estimate reliability. Measured distributions of wall thickness, defect rate, material strength, and applied loads were used with calculated stresses to estimate the probability of failure. The results predicted less than one failure in one million firings. As of 2008, the mortar projectiles have been used without any safety-critical incident.     

Impact deformation of polymeric projectiles

Post-impact deformation of projectiles is studied in relation to flyer-plate thickness and standoff distance from a rigid anvil, without significant penetration and perforation of the flyer plate. A close-range photogrammetric measuring technique is used to determine the final profiles of polymeric cylindrical projectiles. This non-destructive measurement technique is utilized to study the effects of projectile nose geometry on the high rate deformation process, at speeds ranging from 100 to 600 m/s, in connection with metal sheet deformation during impact spot welding. An Imacon ultra-high speed camera is used to photograph the deforming polymeric projectiles.     

The electromagnetic θ gun and tubular projectiles

Unlike the better known rail gun, the θ gun applies the propelling force along the length of its projectile. This is shown to allow much greater acceleration of high fineness ratio projectiles for a given barrel pressure, allowing much shorter barrels for military applications. A computer code which simulates performance of the θ gun is described and experimental results from a few simple, low energy experiments show close agreement with code predictions. Trajectories and aerodynamic heating for three candidate military projectiles are calculated for vertical and horizontal atmospheric launches where initial velocity is as high as 3 km/s. The calculations indicate that in some cases a thin layer of heatshield (ablator) will be required to control projectile heating.     

空化器形状对超空泡射弹尾拍运动影响的数值研究

为研究空化器形状对超空泡射弹尾拍航行时运动特性的影响,基于有限体积法和Mixture多相流模型,结合动网格技术构建了三维自由尾拍运动仿真模型,在两种长径比下比较了平头弹、凹口弹、锥头弹的尾拍运动特性,并分析了其水动力影响因素。结果表明:较小长径比下,平头弹可以保持运动稳定,凹口弹和锥头弹易失稳,主要是由于空化器产生的空泡尺寸差异导致其临界失稳攻角依次降低。较大长径比下,临界失稳攻角消失,三种头型射弹均能保持尾拍稳定,锥头弹在速度较高时以“单侧尾拍”保持稳定,速度降低后以“双侧尾拍”保持稳定,而平头弹和凹口弹始终以“双侧尾拍”保持稳定;锥头弹由于“单侧尾拍”会产生与初始扰动方向相反的垂直位移,而平头弹和凹口弹由于弹头升力产生与初始扰动方向相同的垂直位移。     

Hypervelocity penetration of ceramics

The penetration resistance of alumina was found to decrease with velocity for armor-piercing bullets. However, it was relatively independent of velocity for rods and fragment-simulating projectiles. These results are explained in terms of compressive yielding caused by high velocity pointed projectiles.     

The ballistic performance of metal plates subjected to impact by projectiles of different strength

In this paper, the ballistic performance of monolithic, double- and three-layered steel plates impacted by projectiles of different strength is experimentally investigated by a gas gun. The ballistic limit velocity for each configuration target is obtained and compared based on the investigation of the effect of the number of layers and the strength of projectiles on the ballistic resistance. The results showed that monolithic plates had higher ballistic limit velocities than multi-layered plates for projectiles of low strength regardless their nose shape, and also the ballistic limit velocities of plates decreased with the increase of the number of layers. Moreover, monolithic plates showed greater ballistic limit velocities than multi-layered plates for ogival-nosed projectiles of high strength, and also the ballistic limit velocities of plates decreased with the increase of the number of layers. However, monolithic plates had lower ballistic limit velocities than multi-layered plates for blunt-nosed projectiles of high strength, and also the ballistic limit velocities of plates increased with the increase of the number of layers. The differences in the ballistic limit velocities between various impact conditions can be related to the transitions of perforation mechanisms and failure models of plates and projectiles.     

Effects of density ratio and diameter ratio on critical incident angles of projectiles impacting granular media

The dynamic behavior of projectiles upon impact with granular media was recorded using two high-speed video cameras for capturing different angles. We used steel, brass, tungsten carbide spheres, and alumina ceramic spheres with diameters in the range of 6–20 mm as the projectiles and polystyrene beads (6 mm in diameter) and glass beads (1.7 mm in diameter) as the granular media. Upon impact, the projectiles penetrated the media, rebounded from the media, or were deflected such that their resulting motion was in a horizontal direction. Post-impact motion of the projectiles depended on the impact angles of the projectiles, the density ratio (bulk density/projectile density), and the diameter ratio (granular diameter/projectile diameter) and not on the impact velocity. The post-impact motion of the projectiles did not follow a clear trend in terms of the transient angle; instead, we observed the existence of a transient region. On the basis of the area of the transient regions, an empirical equation was derived for determining the critical angle of projectiles (the angle at which they can penetrate the granular media) as a function of the density ratio and the diameter ratio.     

Experimental impacts above 10 km/s

In the proceedings of the last symposium, recent work on a technique for launching small projectiles to hypervelocities above 10 km/s using an inhibited shaped charge was presented [1]. In the interim, experiments have been conducted using the inhibited shaped charge to launch aluminum, nickel, and molybdenum projectiles. This paper presents the results of the impact tests, as well as discusses the shaped charge design modifications for the nickel and molybdenum launchers. Radiographs are presented of the impacting projectiles, as are post test photographs of various targets. The data are unique in that they represent low L/D projectile impacts into both monolithic blocks and spaced plates at velocities above 10 km/s. The aluminum projectiles are being launched at 11.25±0.20 km/s, the molybdenum projectiles at 11.72±0.10 km/s, and the nickel projectiles at 10.81±0.10 km/s.     

Perforation of flexible laminates by projectiles of different geometry

This paper investigates the response of flexible laminates to ballistic impacts by projectiles of various geometries, namely, flat-ended, hemispherical, ogival (CRH 2.5) and conical (30° half-angle) projectiles. The laminate of interest is Spectra Shield^® comprising [0°/90°] extended chain polyethylene filaments embedded in a thermoplastic resin. Ballistic tests show that flat-ended projectiles cut the laminate through a shearing action, effectively punching a circular hole in the laminate whereas hemispherical projectiles perforate the laminates by stretching the Spectra filaments to failure resulting in a rectangular hole in the laminates. While the manner in which they are perforated are different, many similarities are observed in specimens perforated by flat ended and hemispherical projectiles such as the formation of a generator strip, the extent of delamination, the creasing of the laminate, tearing of the laminate at the edges, etc. Ogival and conical projectiles, on the other hand, perforate the laminates with minimal delamination and tearing of the specimens. Interestingly, the region of the specimens affected by the projectiles appears to increase in size instead of becoming more localised at higher impact velocities as often reported for most ballistic impacts events, including the ballistic perforation of woven fabric. This suggests flexible laminates are more effective in dissipating energy than woven fabric in the application of flexible armour.     

A new hypervelocity shotgun

This paper presents a technique for launching multiple, hypervelocity projectiles in a predictable pattern. The technique has been successfully applied to collections of 4–42 projectiles launched at velocities of 2 to 5 km/s. The projectile dispersion is obtained by impairing a pre-determined radial impulse to the collection of projectiles as the sabot exits the gun muzzle.     

Predicting the fragmentation onset velocity for different metallic projectiles using numerical simulations

For cubes and spheres under high velocity impact there exists for each system of projectile and target, a threshold velocity that is just sufficient to shatter the projectile. This velocity, usually above 2km/s for metallic projectiles, is known as the fragmentation onset velocity. To determine the fragmentation onset velocity experimentally, a number of experiments in which the impact velocity of the projectile is varied in a controlled manner needs to be conducted [1]. In the work described in this paper, the numerical analysis code AUTODYN was used to simulate the impact of stainless steel and tantalum projectiles onto transparent targets in an attempt to simulate the onset of fragmentation. Using the meshfree SPH method for discretizing the spatial domain of the projectile and a simple failure model that allows the critical spall stress of the material to vary with the local material and loading conditions, encouraging results were obtained, with the fragmentation onset velocity for both projectile/target configurations being reasonably well predicted. In addition, further experiments conducted at TNO-PML, to determine the fragmentation onset velocity for tungsten projectiles, will be reported.     

Cavity and crater depth in hypervelocity impact

We discuss the depth of cavities and craters caused by hypervelocity impacts as a function of impact parameters such as impact velocity, projectile and target densities, and projectile diameter, in two extreme cases: the penetration of intact projectiles at low impact pressure and the hemispherical excavation at very high impact pressure. The relations between the depth and the impact parameters are obtained. Then, previous experimental results are compiled; crater depth normalized by projectile diameter and the ratio of projectile and target densities is plotted for glass, plastic, and metal projectiles and metal, rock, ice, foam, sheet-stack, and aerogel targets. The trends of the data are consistent with the relations in the extreme cases.     

Penetration of hard layers by hypervelocity rod projectiles

The penetration resistance of hard layers, such as ceramics and hardened steels, struck by high velocity long rod projectiles can be characterized by the depth of penetration (DOP) test. The DOP test can be used to calculate average penetration resistance, which can be expressed as R_T. The tests can also be used to compute differential efficiency. For hard materials, these values differ markedly from those for conventional armor steel (RHA). Implications for the effectiveness of hypervelocity penetrators are that the optimum velocity for energy efficient penetration will be much higher for hard materials than for RHA. Furthermore, ceramics will continue to substantially outperform armor steels, while high hardness steels will lose their relative advantages against long rod projectiles above 3 km/s.     

RCS-based ballistic limit curves for non-spherical projectiles impacting dual-wall spacecraft systems

Ballistic limit curves (BLCs) for dual- or multi-wall spacecraft wall systems impacted by spherical projectiles exist for a variety of impact conditions. However, meteoroids and orbital debris particles can take any shape, and non-spherical projectiles can be more damaging than equal mass spherical projectiles under the same impact conditions. In a recent study, a series of BLCs for a typical dual-wall configuration impacted by a variety of non-spherical projectiles were developed and presented in terms of equivalent spherical projectile diameter as a function of impact velocity. In order to be more consistent with debris environment predictions and to be useful for spacecraft design, such BLCs need to be drawn in units that are consistent with environment flux models used in that design process. In this paper, we have recast the equivalent spherical projectile diameter BLCs and now present them using radar cross-section (RCS) diameter as the characteristic length parameter. The recast BLCs are seen to be more tightly grouped and are not as spread out as they were when plotted using equivalent spherical projectile diameter. Thus, the effect of projectile shape on penetrating ability is shown to be somewhat reduced when considering characteristic length as the size parameter as opposed to an equivalent mass diameter.     

Studies on the role of microstructure on performance of a high strength armour steel

This investigation describes and analyses the experimental results pertinent to the ballistic performance of two apparently identical low alloy high strength steel plates against deformable lead projectiles at a velocity about 840 m/s. All the tests are carried out at normal impact angle, i.e. zero obliquity. One plate stopped all projectiles fired at it. However, the other plate failed to stop the projectiles at some locations. Both the plates were subjected to detailed analysis using standard metallurgical techniques to identify the cause of failure in one plate. The experimental results presented include the variation in the microstructure, hardness and retained austenite of the two target plates. The study concludes that the failure is caused by the decrease in resistance of the plate possibly due to higher retained austenite and coarser martensitic structure.     

Review of impact fusion concepts [EM launchers]

The authors review the main features of the impact fusion concept in which gram-sized metallic projectiles from electromagnetic launchers collide around heavy-hydrogen fusile gas to produce thermonuclear plasma whose pressure brings the projectiles to rest, providing a pulse of fusion power during the `turnaround' of the projectiles. They discuss the concepts of nonmagnetic as well as magnetically insulated, impact fusion, showing how its potential advantages as an inertial confinement system could be realized. Of particular interest is magnetically insulated impact fusion, where the decreased plasma heat loss may allow lower impact velocities, consistent with the nearer-term state of the art of electromagnetic launchers. Also considered is the concept of mechanical helicity injection that allows both convenience and flexibility in producing the final magnetic configuration     

Superpenetration

The present paper is focused on a discussion of the physical possibility of superdeep penetration of hyperspeed macroscopic projectiles into solid materials. We present a survey of some papers on superdeep penetration, experimental data on the superdeep penetration of microparticles, and the theoretical analysis of this phenomenon. We make a conclusion that the superdeep penetration of individual projectiles is a resonance-type phenomenon which may exist only in a narrow band of high subsonic velocities close to the Rayleigh speed when projectiles form inertial self-propagating cavities. The implementation of superdeep penetration on the macroscale would open the door for the development of fast under-ground crafts. Department of Mechanical Engineering, Florida International University, Miami, USA. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 1, pp. 76–80, January–February, 1996.     

Pits in Metals Caused by Collision With Liquid Drops and Rigid Steel Spheres

A pit-depth-versus-velocity equation developed earlier was tested further with experimental data obtained using target plates of electrolytic tough pitch copper, 1100–O aluminum, and 2024–O aluminum, the static strength properties of which were measured by testing tensile specimens. The projectiles used to produce the pits were mercury drops, waterdrops, and steel spheres. It was found that the numerical constants in the equation for projectiles that flow during and as a result of the collision are different from those for projectiles that do not flow (hardened steel spheres). Curves calculated using the equation were found to be in acceptable agreement with experimental pit-depth-versus-velocity data for collisions of the indicated projectiles with target plates of the three metals used with the exception of the case of steel-sphere impingement against 2024–O aluminum alloy. In this case work-hardening of the target metal seems to foster a mode of pit formation that was not considered in the development of the pit-depth-versus-velocity equation.     

卵形头部弹丸侵彻钢筋混凝土的工程解析模型

在球形空腔膨胀模型的基础上,将钢筋混凝土中的钢筋网结构所在混凝土等效为高强混凝土层,其余部分按素混凝土层处理,得到了计算卵形头部弹丸侵彻钢筋混凝土的分层工程分析模型。用分层分析模型计算了最终侵彻深度,侵彻过程中弹丸的位移时程曲线,速度时程曲线和加速度时程曲线。将计算结果与实验数据和按球形空腔膨胀模型计算结果对比分析,结果表明分层分析模型能够较真实的反映弹丸侵彻钢筋混凝土过程中的运动状态。     

废旧炮弹销毁设计与实践

为了安全有效、完全彻底销毁收集到的废旧炮弹,先对衢州市公安机关收集的废旧炮弹进行检测、鉴定,确定属于非生化类和非放射性炮弹后,根据待销毁废旧炮弹的性质和销毁工作要求,提出了坑内爆炸法销毁方案。按照销毁场地选择原则,选择了一处大型矿山中部的废弃石料堆填区,设置多坑安放待销毁废旧炮弹,采取毫秒延时导爆管雷管起爆技术,同时击发起爆的方式,共销毁迫击炮炮弹60枚,炮弹尾翼2枚,鱼雷463枚,手榴弹62枚,手雷16枚,穿甲弹2枚,航弹1枚。着重阐述了待销毁废旧炮弹的装卸搬运、安全警戒、爆后检查等各个工作环节,并对爆破振动、爆炸冲击波和弹片冲击的最小安全距离进行了安全校核。通过充分的准备、精心的设计和精细的施工组织,使得衢州市公安机关每一次销毁废旧炮弹工作安全、顺利完成,没有发生任何事故和产生次生灾害,为类似销毁工作提供参照。