Penetration mechanics of yawed rods

The penetration of rod projectiles is a function of impact yaw. Armor steel targets were struck at 0° obliquity by long steel rods at ~2.15 km/s and various angles of yaw. Crater dimensions varied systematically with yaw angle. Trenching behavior was observed for yaw angles exceeding about 30°. Analysis indicates that the rods collapsed into the targets with no significant rotation, and that penetration chiefly depends on the parameters D and $\text{D}\text{sin θ}$ (where D is rod diameter and θ is yaw angle).     

Impact of conical tungsten projectiles on flat silicon carbide targets: Transition from interface defeat to penetration

Normal impact of conical tungsten projectiles on flat silicon carbide targets was studied experimentally and numerically for half apex angles 5° and 5–15°, respectively, and comparisons were made with cylindrical projectiles. A 30 mm powder gun and two 150 kV and four 450 kV X-ray flashes were used in the impact tests. The numerical simulations were run with the Autodyn code in two steps. In the first, the surface loads were determined for different impact velocities under assumed condition of interface defeat. In the second, these surface loads were applied to the targets in order to obtain critical states of damage and failure related to the transition between interface defeat and penetration, and the corresponding critical velocities. In the impact tests, interface defeat occurred below a transition velocity, which was significantly lower for the conical than for the cylindrical projectiles. Above the transition velocity, the initial penetration of conical projectiles differed markedly from that usually observed for cylindrical projectiles. It occurred along a cone-shaped surface crack, qualitatively corresponding to surface failure observed in the simulations. The transition velocity for the conical projectile was found to be close to the critical velocity associated with this surface failure.     

半球形头弹不同角度冲击下编织复合材料板的侵彻特性

利用一级气炮发射半球形头弹冲击2 mm厚的编织复合材料层合板,冲击角度为0°、30°和45°,通过高速相机记录弹靶撞击过程并得到弹体速度数据。利用拟合公式处理试验数据,得到不同冲击角度时的弹道极限值,并和理论模型结果进行对比。分析了冲击角度对靶板弹道极限、能量吸收率和失效模式的影响。结果表明：45°斜冲击时的靶板弹道极限最高,正冲击次之,30°斜冲击最低。相同冲击能量时,45°斜冲击的能量吸收率最高,低能量（<80 J）冲击时,30°斜冲击比正冲击能量吸收率高,高能量（>80 J）时,正冲击更高。正冲击时,靶板正面因剪切失效而形成圆形凹坑,背面因纤维拉伸失效形成菱形鼓包,斜冲击形成椭圆形扩孔,且其面积随冲击角度增加而增加。     

Tumbling of hypervelocity rods induced by impact with oblique plate targets

We investigated the cause of tumbling by hypervelocity rods after impact with oblique plate targets. The projectiles were strong rods, length to diameter ratio of 6 to 10, prepared from aluminum (10 tests) or steel (5 tests), launched at velocities of 4.2 to 4.8 km/s, and impacted into like material targets. The rods had little or no initial yaw (the average yaw was 1.8°). The residual projectile properties of length, tumbling rate and radial velocity were measured and evaluated in a simple model for rod tumbling. The model is based on the observation that plastic shear continues at the nose of the rod for a finite time after target perforation. Based on the observed tumbling rate, duration of plastic flow and the inertia of the residual rod an implicit determination of the shear strength of the rod was obtained. The calculated shear strength was in fair agreement with static shear values.     

A numerical comparison of the ballistic performance of unitary rod and segmented-rods against stationary and moving oblique plates

The purpose of this paper is to investigate the ballistic performance of segmented-rods against stationary or moving oblique plates. To do this, a series of three-dimensional numerical simulations for the impact characteristics of segmented-rods (5 of L/D=1) into stationary or moving oblique thin-plate targets is conduced. To provide a base line data, an L/D=5 unitary rod projectile which has the same mass and kinetic energy is also considered. The ballistic characteristics of the projectiles are evaluated by examining the crater profile in a thick witness target that is placed behind the oblique plate. The impact velocities considered are 1400, 1800 and 2200 m/s. The results for the test range show that the unitary rod projectile shows better performance in the moving oblique target than the stationary one and the segmented-rods always show slightly better performance in the stationary target. From the impact velocity of 2200 m/s, the outstanding penetration performance of the segmented-rods can be observed. This trend is due to the interaction between the reactive plate and projectile. The extent of the interaction relies on the relative velocities of the plate and projectiles, the plate angle and extended total length of the segmented-rods     

钝头弹高速斜侵彻中厚背水金属靶板的机理研究

为探讨高速钝头弹斜侵彻中厚背水金属靶板的机理,根据不同的受力状态及耗能机制,结合中厚背水靶板抗高速斜侵彻特点,通过厚度等效,将斜侵彻转化为相应的正侵彻。然后,将整个侵彻过程分为压缩镦粗、剪切压缩和剪切扰动三个阶段。基于三阶段侵彻机制,建立了钝头弹高速斜穿甲中厚背水金属靶板后的瞬时余速计算模型,并讨论了该计算模型的局限性。采用该模型计算了3.3 g立方体弹丸斜穿甲5 mm背水钢板后的瞬时余速,理论计算值与试验结果及相应的仿真计算值均吻合较好。由于该模型考虑了靶后水介质的动支撑作用及动能耗散等效应,在一定的适用范围内,能对钝头弹高速斜侵彻中厚背水金属靶板的瞬时余速进行合理地预测,具有一定的理论价值和工程应用价值。     

刚性卵形头弹撞击角度对编织复合材料层合板侵彻特性的影响

利用一级气炮发射卵形头弹撞击2 mm厚度的编织复合材料层合板,撞击角度分别为0°、30°和45°,通过高速相机记录弹靶撞击过程,并获得弹体速度数据。基于拟合公式处理试验数据,计算获取弹道极限,分析撞击角度对弹道极限、靶板能量吸收率及其失效模式的影响规律及机制。结果表明：弹体撞击角度为45°时,靶板弹道极限最高,其次为0°,撞击角度为30°时最小。随着冲击角度增加,层合板损伤形状从菱形逐渐转变为椭球形,损伤面积随冲击速度增加而增大,且45°冲击时层合板损伤面积最大,0°和30°冲击时损伤面积近似相等。弹体初始撞击角度对靶体失效模式存在影响,弹体撞击角度为0°时,纤维断口主要是剪切应力导致的横截面。撞击角度为30°时,纤维断口主要是剪切应力和拉伸应力导致的斜截面。45°斜撞击时,纤维断口主要是拉伸应力导致的横截面。     

Controlled tumbling of projectiles— II. Experimental results

This paper presents the techniques and results of the experimental investigation concerned with the production of controlled tumbling of blunt cylindrical projectiles and the effect of this feature on impact targets placed in the subsequent trajectory of the striker. This work complements the theoretical approach described in the previous paper [Controlled tumbling of projectiles—I. Theoretical model. Int. J. Impact Engng7, 101–115 (1988)]. The tumbling was achieved when the projectile, initially translating along its axis of symmetry, struck the free edge of a deflector plate clamped on the other three sides with varying degrees of overlap.     

The application of the integral theory of impact to model penetration of hypervelocity impact

The Integral Theory of Impact (ITI) (Swanson and Donaldson, 1978) is a unique formulation of the equations of motions of projectiles to describe the penetration process. The model requires only basic material properties, no empirical data is needed. The original model was modified to divide the penetration process into three consecutive phases. The new model has successfully modeled impacts over a wide range of velocities, at normal or oblique impact, for infinite or finite targets. In order to better match the experimental observations of impacts in the hypervelocity range, it was necessary to include a thermal softening effect on flow stress. For finite targets, the back-face effect is proposed to be a function of both penetration velocity and the speed of sound, extending the model's applicability to hypervelocity penetration.     

Dislocation wall formation during interdiffusion in thin bimetallic films

Transmission electron microscopy observations are described of the diffusion-induced behaviour of misfit dislocations originally present in the interface of thin bimetallic films. Experiments were carried out with specimens consisting of a layer of approximately 500 Å Cu vapour deposited onto an electropolished Ni substrate approximately 1000 Å thick. Diffusion anneals were performed in situ in the electron microscope at annealing temperatures in the range 450–600°C. The dislocation behaviour in Cu/Ni bicrystals with originally a (100) interface was photographed and video-recorded. A cross-grid of misfit dislocations parallel to 〈110〉 directions was present in the original interface. The Burgers vectors were of type $\text{1}\text{2}$a〈110〉 lying in the interface. During diffusion the misfit dislocations became distributed in the diffusion zone. When $\text{2Dt}$ (where D is the diffusion coefficient and t is the annealing time at a given temperature) exceeded a value of 40–50 Å, the dislocations started to align vertically forming dislocation walls along 〈110〉 directions parallel to the original interface. This resulted in a dislocation cell structure. Lengthwise the dislocation walls grew with shocks. The elastic strain energy of a finite edge dislocation array was estimated. Using this result an energy criterion for the formation of dislocation walls was derived. From this criterion it followed that dislocation wall formation may start to occur when $\text{2Dt}$≈ 45 Å, in good correspondence with the experimental results. Some additional observations of recrystallization phenomena during interdiffusion are reported.     

Some general features of random elastic scattering spectra

The dependence of the yields and the shapes of the energy distribution spectra generated by projectiles elastically scattered from smooth-surfaced random solid target materials on the stopping power of the material, on the scattering cross section and on the geometry of the experimental arrangement is computationally investigated. The effects of such secondary phenomena as straggling, angular beam divergence and loss of beam intensity with increasing penetration depth are neglected. General arguments demonstrate that these spectra are quite sensitive to the energy dependence of both the stopping power and the cross section, but to different extents depending on the geometry of the experimental arrangement. If the arrangement is such that the observed projectiles must travel a much larger path length to leave the target material after scattering than they travel to reach the scattering site, then the stopping power plays the dominant role in shaping the spectrum. Specifically, the spectrum tends to follow strongly the shape of the reciprocal of the stopping power versus energy curve. When the arrangement is such that these path lengths have the opposite relationship, then the cross section comes into strong competition with the stopping power in shaping the spectrum. These features are illustrated by the spectra calculated using two model stopping powers and simple power-law cross sections. One model assigns simple power-law energy dependence to the stopping power, while the other model assigns an energy dependence which approaches $\text{E}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ at low energies and E^-1 × ln E at high energies.     

Crystal data for two new phosphate-tellurates : Te(OH)6·2TlH2PO4·Tl2HPO4 and Te(OH)6·2TlH2PO4. Crystal structure of Te(OH)6·2TlH2PO4

We describe chemical preparations and give crystal data for two new phosphate-tellurates : Te(OH)₆·2TlH₂PO₄·Tl₂HPO₄ and Te(OH)₆·2TlH₂PO₄. Both are monoclinic with the following unit cell dimensions : a = 13.68(1), b = 6.317(5), $\text{c}\text{= 11.36(1)}\text{A}\text{?}$, β = 110.18(1)°, Z = 2, D_x = 4.82, S.G. = Cm for the first one, a = 6.285(5), b = 14.74(1), $\text{c}\text{= 7.844(5)}\text{A}\text{?}$, β = 113.38(1)°, Z = 2, D_x = 4.14, S.G. = P2₁/n for the second one. Crystal structure of the second salt shows, as in the already described phosphate-tellurates, the coexistence of independent TeO₆ octahedra and PO₄ tetrahedra in the atomic arrangement.     

The effect of interdiffusion on moiré patterns of thin bimetallic films

Observations are described of a diffusion-induced change in the spacing of moiré fringes from thin bimetallic films at low temperatures where the diffusion coefficients are small (<10^-15 cm² s^-1). Experiments were carried out with specimens consisting of a layer of approximately 400 Å Cu vapour deposited onto an electropolished Ni substrate approximately 1000 Å thick. After annealing in the electron microscope at different temperatures an increase in the average spacing M of the moiré fringes was observed. It was found that $\text{1?}\text{M}{}_0\text{M}$ varies linearly with t^{$\text{1}\text{2}$}, where M₀ is the original moiré spacing and t is the annealing time at a given temperature. According to a highly simplified model of electron diffraction the diffusion coefficient can be obtained from the slope of the $\text{1?}\text{M}{}_0\text{M}$versus t^{$\text{1}\text{2}$} plot. From experiments at 450°C, 500°C and 550°C the frequency factor D₀ and the activation energy Q for diffusion were established: D₀ = 0.2 cm² s^-1, Q = 54.6 kcal mol^-1. These values are in good agreement with published data for volume diffusion in the Cu-Ni system at higher temperatures.     

Tungsten long-rod penetration into confined cylinders of boron carbide at and above ordnance velocities

The purpose was to investigate the influence of impact velocity and confinement on the resistance of boron carbide targets to the penetration of tungsten long-rod projectiles. Experimental tests with impact velocities from 1400 to 2600 m/s were performed using a two-stage light-gas gun and a reverse impact technique. The targets consisted of boron carbide cylinders confined by steel tubes of various thicknesses. Simulations were carried out using the AUTODYN-2D code and Johnson–Holmquist's constitutive model with and without damage evolution. The experimental results show that the penetration process had different character in three different regions. At low-impact velocities, no significant penetration occurred. At high-impact velocities, the relation between penetration velocity and impact velocity was approximately linear, and the penetration was steady and symmetrical. In between, there was a narrow transition region of impact velocities with intermittent and strongly variable penetration velocity. In the lower part of this region, extended lateral flow of the projectile took place on the surface of the target. The influence of confinement on penetration velocity was found to be small, especially at high-impact velocities. The simulated results for penetration velocity versus impact velocity agreed fairly well with the experimental results provided damage evolution was suspended below the transition region.     

Crystallography of epitaxially grown molybdenum on sapphire

Molybdenum thin films were deposited onto (0001), ($\text{1012}$) and (10$\text{12}$) sapphire substrates by electron-beam evaporation in ultrahigh vacuum. The surface morphology and crystallographic orientation of these films were characterized by electron microscope replication and reflection electron diffraction. The effect of the crystallographic plane of the sapphire substrates as well as that of the deposition rate on the crystallographic orientation of the deposited molybdenum films were examined in the temperature range 25°-1000°C. The epitaxial temperature range was 600°-900°C for basal plane substrates and 300°-1000°C for ($\text{1}$012) and (10$\text{1}$2) substrates. The orientation of the deposited film was strongly dependent on that of the sapphire substrate.     

Numerical simulations of oblique-angle penetration by deformable projectiles into concrete targets

Numerical simulations of oblique-angle penetration by deformable projectiles into concrete targets are performed in this paper by using the three-dimensional finite element code LS-DYNA, into which a combined dynamic constitutive model which can simultaneously describe both the compressive and tensile damage of concrete is implemented. As a consequence, the ballistic trajectories and the depths of penetration under different oblique angles (from 10° to the ricochet angle) are obtained. Moreover, the damage distribution of concrete after oblique penetration is procured, which can really reflect the tensile and compressive damage of concrete. The numerical results for the depths of penetration are compared with experimental data obtained by previous authors and show good agreement.