Yaw impact of rod projectiles

The purpose of this numerical study is to investigate the penetration regimes for L/D 30 tungsten-alloy rod projectiles for cases where the impact yaw angle varies from 0 to 90° and for impact velocities from 1.4 to 2.6 km/s. The target is modeled as a semi-infinite or half-space block of rolled homogeneous armor (RHA) at zero obliquity. For cases of mild interference, the penetration channel is still deep and narrow but may be skewed with respect to the original shot-line. While penetration is degraded the efficiency of the rod projectile remains relatively high. With increasing yaw angle the rod may deform due to transverse loading to the extent such that it contacts and produces gouges on the opposite side of the penetration channel. Additionally, lateral loading may induce angular acceleration to the extent such that the tail of the projectile rotates (in the plane of symmetry) and also contacts the opposite side of the penetration channel. In the next discernible penetration regime, the long-rod deforms under transverse load but the tail does not rotate significantly. It is seen that nearly the entire rod length experiences the lateral load with the result that the original shot-line is significantly altered. The deformed rod, again, has multiple contact or loading points (or regions) and the resultant angular acceleration appears to be insufficient to induce rotation of the projectile tail. Thus, rather than ricochet, the projectile cuts a significant slot into the target. Finally, for very large yaw angles the crater becomes indistinguishable from one produced by a side-on or 90° impact even though the impact yaw angle may be significantly less than 90°.     

Target damage from highly oblique hypervelocity impacts of steel spheres against thin laminated targets

Target hole sizes and geometries were measured for a series of highly oblique hypervelocity impacts of steel spheres against thin laminated targets. The impact velocity was nominally 4.6 km/s for most of the experiments with a few tests conducted at 7.3 km/s. Impact obliquity ranged from 60° to 80° from the normal to the target plane. Projectiles were stainless steel spheres with masses of 222 g, 25 g, and 1 g. Targets were laminated MX-2600 silica phenolic bonded to a 2024-T3 substrate. Target thickness, t, was varied to give thickness to projectile diameter, d, ratios of t/d = 0.6 and 0.3 for each projectile. CTH Eulerian wavecode calculations of selected tests were performed to improve our understanding of the experimental results.     

Ballistic limit for oblique impact of thin sandwich panels and spaced plates

Ballistic perforations of monolithic steel sheets, two-layered sheets and lightweight sandwich panels were investigated both experimentally and numerically. The experiments were performed using a short cylindrical projectile with either a flat or hemispherical nose that struck the target plate at an angle of obliquity. A total of 170 tests were performed at angles of obliquity 0–45°. The results suggest that during perforation by a flat-nosed projectile, layered plates cause more energy loss than monolithic plates of the same material and total thickness. There was no significant difference in the measured ballistic limit speed between monolithic plates and layered plates during oblique impact perforation by a hemispherical-nosed projectile.     

Penetration dynamics of rods from direct ballistic tests of advanced armor components at 2–3 km/s

The penetration of semi-infinite steel and spaced-plate armors by continuous and segmented rods has been analyzed and measured by direct ballistic tests, hydrocode calculations, and hydrodynamic models at velocities from 2 to 4 km/s. An empirical equation of rod penetration in semi-infinite steel was formulated from hydrodynamic models of rod impact. Penetrations predicted by the equation agreed well with measured values. Increasing the spacing between segments from one to two diameters increased the penetration significantly (20%). Structures to support and align the segments can either increase or decrease the penetration, depending on their design. The relative penetrations of continuous and segmented rods depend on the parameters selected for the comparison: the segmented rod having greater penetration for equal mass and diameter and vice versa for equal mass and length. Tests of segmented rods penetrating spaced-plate armor showed that the armor is defeated by the front segment (or segments) punching a hole in the front plate (or plates) that allows the remaining segmented rod through intact to attack the main armor.     

Measurement of small angle fiber misalignments in continuous fiber composites

In aligned, continuous fiber composites the fibers actually wander with small angular misalignments about the mean direction. These misalignments are suspected of having a significant influence on several mechanical properties, such as longitudinal compression strength and tensile modulus. A technique is presented for measuring the volume fraction distribution of fiber misalignment angle in the range of ±10°, with an estimated resolution of ±0·25°. The method can provide a full bivariate distribution, which includes both in-plane and out-of-plane misalignments. Data from a carbon fiber composite, APC-2, are given as an illustration. Misalignment distributions for prepreg, a 0/90 laminate, and a unidirectional laminate are given. It is found that the distribution in the prepreg is axially symmetric, but changes upon laminations, the changes depending on stacking sequence. In this particular material most of the fibers are found to lie within ±3° of the mean fiber direction. Distribution standard deviations range from 0·693 to 1·936 degrees.     

An elastic–plastic thermal stress analysis of aluminum metal–matrix composite beams

In this study, an elastic–plastic thermal stress analysis is carried out on steel fiber-reinforced aluminum metal–matrix composite beams. Temperature is chosen to vary linearly. It is zero and T₀ at the upper and lower surfaces, respectively. The beam is fixed by two rigid planes at the ends. The solution is performed at 0°, 30°, 45°, 60° and 90° orientation angles. The plastic region is expanded at the lower side of the beam. It is found that the intensity of the residual stress component of σ_x and the equivalent plastic strain are maximum at lower surface of the beam. The residual stress is found to be greatest for the 0° orientation angle. In addition, the intensity of the equivalent plastic strain is the greatest for the same angle.     

Penetration of limestone targets by ogive-nosed VAR 4340 steel projectiles at oblique angles: experiments and simulations

In this paper, we document the results of a combined experimental, analytical, and computational research program that investigates the penetration of steel projectiles into limestone targets at oblique angles. We first conducted a series of depth-of-penetration experiments using 20.0 g, 7.11-mm-diameter, 71.12-mm-long, vacuum-arc-remelted (VAR) 4340 ogive-nose steel projectiles. These projectiles were launched with striking velocities between 0.4 and 1.3 km/s using a 20-mm powder gun into 0.5 m square limestone target faces with angles of obliquity of 15° and 30°. Next, we employed the initial conditions obtained from the experiments with a technique that we have developed to calculate permanent projectile deformation without erosion. With this technique we use an explicit, transient dynamic, finite element code to model the projectile and an analytical forcing function based on the dynamic expansion of a spherical cavity to represent the target. Due to angle of obliquity we developed a new free surface effect model based on the solution of a dynamically expanding spherical cavity in a finite sphere of incompressible Mohr–Coulomb target material to account for the difference in target resistance acting on the top and bottom sides of the projectile. Results from the simulations show the final projectile positions are in good agreement with the positions obtained from post-test castings of the projectile trajectories.     

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.     

A fracture mechanics approach to the residual strength behavior of ballistically damaged high hardness laminar composite steel

Welded and unwelded specimens of an air-melted laminar composite steel armor were tested for degradation of strength from ballistic impact. Specimens were impacted with cal. 0.30 AP and ball projectiles at various velocities and 0-degree obliquity. During impact, specimens were tensile loaded from 0 psi to the preload that would result in specimen failure at impact. Specimens that did not fail upon impact were pulled to failure to determine residual strength.

Damage due to cal. 0.30 impact maximized at approx. 2.25 in. laterally for ball and 1 in. for AP at a velocity near the ballistic limit. Preload increased the damage slightly. Impacts near the weld produced no detectable degradation of the weld.

Damage near the maximum resulted in residual strengths near 20% of the original σ_M. Fracture mechanics analysis showed that residual strengths could reasonably be predicted by assuming that all damage could be modeled as a center notch through the hard face.     

Effect of interlayer on stress wave propagation in CMC/RHA multi-layered structure

Due to the significance of the propagation of stress wave in composite armor during projectile–target interaction, the characteristics of stress wave propagation in multi-layered composite structure under impact load were investigated by traditional Split Hopkinson Pressure Bar system in this study. The effect of interlayer characteristic on the stress wave propagation was discussed. The results show that the interlayer properties between CMC and RHA steel play an important role in the propagation of wave. Compared to “CMC/RHA” structure without interlayer, the tungsten carbide interlayer can increase stress level in CMC layer remarkably, while silica gel layer has an opposite effect, and epoxy resin adhesive layer has no distinct effect on the propagation of stress wave. The increased compressive stress level in CMC layer is very useful when the CMC layer served as the face plate of a composite armor. During the impact process of the projectile to the armor, the anti-penetration capability of the face plate of the composite armor can be improved when in the compression stress state. In the comparison ballistic testing conducted with 7.62 mm armor piercing projectiles, the protection efficiency of the “CMC/WC/RHA” composite armor is about 36% higher than that of the “CMC/RHA” structure, which is in good correlation with the stress wave measurement results.     

装甲防护材料抗侵彻性能研究现状

目的分析装甲防护材料抗侵彻性能的研究现状,为改进复合装甲的结构设计提供参考。方法对装甲防护材料的抗侵彻研究现状进行论述,并对其应用情况进行分析。结果分别阐述了金属材料(装甲钢、铝合金和钛合金)、陶瓷复合靶板以及纤维增强复合材料(玻璃纤维、芳纶纤维和超高分子量聚乙烯纤维)的抗侵彻研究现状,并介绍了其应用情况。结论随着战场环境的日益更新和武器装备的飞速发展,单一的装甲防护材料已难以适应战场环境的不断变化,装甲防护材料将朝着强韧化、轻量化、智能化及多功能化发展。     

层间混杂复合材料装甲板防弹性能及其防弹机制

为研究层间混杂复合材料装甲板的防弹性能及其防弹机制,采用钢芯弹侵彻层间混杂复合材料装甲板。以超高分子量聚乙烯（Ultra high molecular weight polyethylene,UHMWPE）纤维、对位芳香族聚酰胺纤维作增强纤维,水性聚氨酯（Waterborne Polyurethane,WPU）树脂和环氧树脂（Epoxy resin,EP）作基体,采用热压工艺制备单向（Unidirectional,UD）结构的层间混杂复合材料装甲板。研究混杂比例、防弹面和树脂基体对混杂复合材料装甲板防弹性能的影响以及弹击后混杂复合材料装甲板的破坏形貌,分析混杂复合材料装甲板的防弹机制,并对复合材料装甲板的破坏机制进行了分析。结果表明:混杂复合材料装甲板的防弹性能优于其任一单一纤维复合材料装甲板;WPU的防弹性能要优于环氧树脂;以UHMWPE纤维复合材料充当防弹面时,混杂复合材料装甲板具有更好的防弹性能;纤维拉伸变形和装甲板分层是纤维复合材料装甲板主要的吸能方式。      

Effect of precursor solution on the formation of perovskite phase of Pb(Mg1/3Nb2/3)O3 thin films

Precursor solutions for Pb(Mg_1/3Nb_2/3)O₃ (PMN) synthesis were obtained by Pechini's method. The influence of the concentration of organic materials on the phase formation has been studied. For this purpose, PMN solutions were prepared with different precursors and were characterized by thermogravimetric and differential thermal analysis. The obtained solutions were deposited onto a Si (100) substrate by dip coating and pre-treated in a hot plate at 300 °C for 1 h. The films were annealed at 600, 700, 800 and 900 °C for 1 h and characterized by X-ray diffraction. The perovskite phase was formed after annealing at 600 and 700 °C when the solution of PMN was prepared with a lower amount of organic material and starting with niobium oxide. By increasing the temperature to 800 or 900 °C, only the formation of pyrochlore phase was observed. With the solution prepared from niobium ethoxide, only the presence of pyrochlore phase was observed independently of the annealing temperature.     

Effect of distance from the support on the penetration mechanism of clamped circular polycarbonate armor plates

A 1.91-mm thick circular polycarbonate plate of 115 mm diameter was impacted by a spherical steel projectile of 6.98 mm diameter at its center. Subsequent impacts were made at 10, 20, 30, 40, and 50 mm radii of the plate. Dent dimensions for the damaged plate were measured using optical microscope. For a constant projectile velocity of 138 m s⁻¹ which was below the perforation limit of the plate under investigation, a maximum thickness reduction close to the edge support was observed. The experimental work was modeled into explicit finite-element analysis program LSDYNA for simulations. LSDYNA was able to predict the dent depth and reduction in plate thickness at impact points precisely. In this research, the effect of the impact location distance from the supports on the damage mechanism of circular polycarbonate armor plates is investigated. The target plate was subjected to constant velocity projectile impacts starting at the plate midpoint and varying the impact distance from midpoint towards the clamped edge. Failure of plate is predicted close to the constrained boundary under uniform conditions.     

Influence of processing conditions on bending property of continuous carbon fiber reinforced PEEK composites

The purpose of this study is to achieve an optimum fabrication condition for the continuous carbon fiber reinforced PEEK matrix composites based on a micro-braiding fabrication method. The composite plates were fabricated at three processing temperatures (380, 410 and 440 °C) and three holding times (20, 40 and 60 min), respectively, with a total number of nine different fabrication conditions, and their bending properties were investigated in terms of thermal and fracture characterizations. As a result, the bending performance of the fabricated composites was significantly affected at the 440 °C temperature. Although no significant change in the bending performance was seen at the 380 and 410 °C with all the holding times, the thermal and fracture characterizations implied a degradation of the PEEK matrix property during the fabrication process. In order to avoid the matrix degradation and the decrease of mechanical properties, a lower fabrication temperature with a shorter holding time should be recommended for the carbon/PEEK composites fabricated by the micro-braiding method.     

Aluminum foam integral armor: a new dimension in armor design

Closed-cell aluminum foam offers a unique combination of properties such as low density, high stiffness, strength and energy absorption that can be tailored through design of the microstructure. During ballistic impact, the foam exhibits significant non-linear deformation and stress wave attenuation. Composite structural armor panels containing closed-cell aluminum foam are impacted with 20-mm fragment-simulating projectiles (FSP). One-dimensional plane strain finite element analysis (FEA) of stress wave propagation is performed to understand the dynamic response and deformation mechanisms. The FEA results correlate well with the experimental observation that aluminum foam can delay and attenuate stress waves. It is identified that the aluminum foam transmits an insignificant amount of stress pulse before complete densification. The ballistic performance of aluminum foam-based composite integral armor (CIA) is compared with the baseline integral armor of equivalent areal-density by impacting panels with 20-mm FSP. A comparative damage study reveals that the aluminum foam armor has finer ceramic fracture and less volumetric delamination of the composite backing plate as compared to the baseline. The aluminum foam armors also showed less dynamic deflection of the backing plate than the baseline. These attributes of the aluminum foam in integral armor system add a new dimension in the design of lightweight armor for the future armored vehicles.     

The effect of geometric scale on impact induced fragmentation, and its application to the design of dual plate armor

An analysis is presented which predicts that, for a fixed impact velocity, impact induced fragmentation becomes more severe as geometric scale increases. Test data is presented which supports this prediction, and which allows calculation of material dependent coefficients. The analysis was based on a minimization with respect to radius, for an expanding body, of a total energy density term (expansion kinetic energy per unit volume plus surface energy per unit volume). The test configuration was a steel sphere impacting an aluminum plate, with fragmentation recorded by a stack of spaced witness panels. The tests were run at full and half scale. Correlation between testing and analysis was achieved for the number of fragments perforating the front witness panel when a term analogous to a threshold energy was introduced. While the fragment count showed a dependence on geometric scale, the relative depth of penetration (number of witness panels perforated) did not. This suggested that the targets were fragmented, but that the projectile remained in one piece. A reduction in penetration depth with increasing impact velocity was seen, and was attributed to increased projectile deformation. For cases where the projectile would fragment (for example, if a harder target material were used), the effect of geometric scale on the performance of dual plate armor is predicted by analysis. The prediction is that, for impact velocities where projectile breakup at the outer plate of dual plate armor is a factor, the armor required to stop a large scale projectile can be lighter, on a relative basis, than the armor required to stop a small scale projectile.     

The effect of misalignment errors in optical elements of VUV polarimeter

We have designed a Vacuum Ultra Violet polarimeter for Indian Synchrotron Radiation Source Indus-1. This polarimeter will be installed on a toroidal grating monochromator-based beamline. Polarimeter consists of four-mirror phase retarder and three-mirror linear polarizer. Three-mirror linear polarizer has glancing angles of incidence 23°, 46° and 23°, working in 200–1100 Å wavelength region, with linear polarizence greater than 90%. Detailed ray-tracing analysis was carried out to find the effect of various misalignment errors in each of the optical element of the polarimeter. It is found that misalignment errors in optical element of the polarimeter affect only the beam spot position and do not affect the spot size, polarization state and photon flux of outgoing beam, substantially. Accuracies in the linear and angular positions of optical elements in phase retarder and linear polarizer must be very precise to perform ellipsometric experiments. Tolerance limit for various misalignment errors has been obtained. Required accuracy in angular position around X-axis is more than that required in angular position around Z-axis.     

Numerical analysis and modeling of jacketed rod penetration

A computational study to assess terminal ballistic performance issues of adding a steel sheath, or jacket, to a depleted uranium (DU) penetrator has been performed. The CTH hydrocode was used to model DU penetrators with steel sheaths of various thicknesses against semi-infinite rolled homogeneous armor (RHA), finite RHA, and oblique plate targets. Guided by the initial results, additional semi-infinite RHA simulations were performed to support the development of a generalized penetration model for jacketed rods. The model computes RHA penetration as a function of impact velocity and normalized jacket thickness (thickness over diameter) and compares very favorably with experimental DU and steel data. The model indicates that “bulk” density (areal density) can considerably underestimate jacketed rod penetration. In addition, some insight into the penetrator and target flow shape factors (k_p and k_t) is obtained.     

A three-dimensional FE analysis of large deformations for impact loadings using tetrahedral elements

 A three-dimensional dynamic program for the anaysis of large deformations in contact-penetration problems is developed using the finite element Lagrangian method with explicit time integration. By incorporating a tetrahedral element, which allows a single-point integration without a special hourglass control scheme, this program can be more effective to the present problem. The position code algorithm is used to search contact surface. Eroding surfaces are also considered. The defense node algorithm was slightly modified for the calculation of contact forces. A study of obliquity effects on metallic plate perforation and ricochet processes in thin plates impacted by a sphere was conducted. It is well simulated that on separation of two parts of the sphere, the portion still within the crater tends to perforate, while the portion in contact with the plate surface ricochets. This deformation pattern is observed in experiments, especially at high obliquities. A long rod that impacts an oblique steel plate at high impact velocity was also simulated in order to study the dynamics of the rod caused by the three dimensional asymmetric contact. The agreement between simulated and experimental results is quite good. Fracture phenomena occuring at high obliquity deserves further investigations. Received: 20 February 2002 / Accepted: 20 September 2002