Caliber Projectiles Research Articles

Numerical modeling of the impact behavior of new particulate-loaded composite materials

Ballistic efficiency and cost are the main considerations in the design of lightweight armors. Metallic materials have the drawback of their high density. Mixed armors, of ceramic tiles backed by a metallic plate, are an efficient shield against low and medium caliber projectiles since they combine the light weight and high resistance of a ceramic with the ductility of a metal. The drawback is their high cost. The authors developed a new material composed of ceramic particles and a polymeric matrix. It fills the gap between metallic and ceramic materials and could be interesting for applications in which weight is not the primary concern and cost benefits are welcome. A model of the mechanical behavior of this composite is presented in this paper, implemented in a numerical code and validated by experimental results.

Heat as a Factor in the Penetration of Cloth Ballistic Panels by 0.22 Caliber Projectiles

This report explores the possibility that heat plays a role in the penetration of cloth ballistic panels by 0.22 caliber projectiles. We postulate that heat is generated by friction between the surface of the projectile and the yarns, between yarns, and between filaments within a yarn in advance of and in the path of the projectile. Evaluations by light microscopy, polarized light microscopy, and scanning electron microscopy show heat- induced damage in fibers in the path of and several layers preceding the layer at which a 0.22 caliber projectile comes to rest. Polarization microscopy of impacted yarns reveals differences in birefringence within the fibers close to the hole made by the projectile compared with the same fiber at a greater distance from the hole. Heat is an energy sink, and depending on how, when, and where it is generated, can degrade the ballistic performance of the yarns. The quantitative importance of heat in affecting ballistic panel performance is elusive: consequently, the discussion presented here is largely qualitative.

Modelling of the adhesive layer in mixed ceramic/metal armours subjected to impact

Abstract The effect of the adhesive layer, used to bond ceramic tiles to a metallic plate, on the ballistic behaviour of ceramic/metal mixed armours is analysed mathematically and experimentally. Two types of adhesives, polyurethane (soft adhesive) and rubber-modified epoxy resin (rigid adhesive), and different thicknesses, are considered in the study. Numerical simulations were made of low calibre projectiles impacting on alumina tiles backed by an aluminium plate, using a commercial finite difference code. Full-scale tests were carried out to check the influence of the adhesive. An engineering model was also developed to provide a preliminary design tool taking account of the influence of the adhesive.

MODELING PENETRATION OF CERAMIC/METAL LIGHTWEIGHT —1 ARMOURS BY SMALL AND MEDIUM CALIBER PROJECTILES

In this paper, an analytical model is developed to describe the penetration of ceramic/metal lightweight armours by small and medium caliber-projectiles, 4 respectively. Both the projectile and back plate materials are assumed to behave as rigid-perfectly plastic with respect t9, .their nominal stress-engineering strain relationships. Two modes are associated with the back plate and the projectile, respectively, during the penetration 'Ptocess; these are erosion and rigid The model identifies three main phases for the penetration of a lightweight armour; these are: (i) ceramic fragmentation, (ii) penetration of fragmented ceramic and (iii) penetration of back plate. Phase (i) consists mainly of one stage, whereas the other two, i.e. phase (ii) and phase (iii), consist mainly of different penetration stages, respectively. The current penetration stage is ascertained according to the relative velocities between the projectile mass and the mass of remaining ceramic and/or the mass of the back plate ahead of projectile. The main equations representing each penetration stage are derived based on momentum conservation principle. The present model is capable of predicting the time-histories of the velocities of the moving masses and the projectile penetration depth through ceramic/metal lightweight armour as well as post-perforation results. Matching predicted results of the present model with the experimental and numerical results of other investigators serves to determine the flow stress of the ceramic material globally. The present results are concerned with design optimization of ceramic/metal lightweight armours capable of defeating small and medium caliber projectiles. The influence of ceramic thickness and strength as well as back plate thickness and strength on the ballistic limit of the armours considered is presented and discussed. Moreover, the effect of ceramic thickness on projectile remaining mass and residual velocity are discussed.

Analytical modelling of normal and oblique ballistic impact on ceramic/metal lightweight armours

This paper presents a new analytical model developed to simulate ballistic impact of projectiles on ceramic/metal add-on armours. The model is based on Tate and Alekseevskii’s equation for the projectile penetration into the ceramic tile, whilst the response of the metallic backing is modelled following the ideas of Woodward’s and den Reijer’s models. The result is a fully new analytical model that has been checked with data of residual mass and residual velocity of real fire tests of medium caliber projectiles on ceramic/metal add-on armours. Agreement observed between experimental and analytical results confirmed the validity of the model. Therefore, the model developed can be a useful tool for optimisation of ceramic/metal armour design.

Electro-optical target system for position and speed measurement

This paper introduces an electro-optical target system (EOTS) covering the speed range from subsonic to supersonic. This microcomputer-based system has a novel structure and shows the capability of precisely detecting the position as well as the velocity of small calibre projectiles in real time. A prototype EOTS whose target area is 1 m2 has been constructed and tested. A speed accuracy of better than 0.3% was achieved. A position accuracy, mainly dependent on the spacing between photodiodes in EOTS, of better than 1 mm on a target area of 1 m2 was also accomplished.

Projectile perforation of multi-layered beams

A combined analytical and experimental study has been performed on the ballistic resistance of layered targets, in particular of flat, relatively thin beams with clamped ends in spaced and laminated (i.e. in contact without bonding) conditions. The theoretical analysis combines the effect of structural deformation with the mechanism of perforation. This requires a redefinition of the ballistic limit velocity as the initial impact velocity for which the post perforation velocity and the structural deformation velocity of the impact point would be equal at the same time. The ballistic tests were based on commercially pure and alloy (6061-T6) aluminum target specimens of various thicknesses and configurations, and used 0·22 in. caliber projectiles which struck the targets perpendicularly at their center with a velocity of 375 msec. The results for the velocity drop show fairly good agreement between experiments and predictions, and greater ballistic resistance of the laminated configuration.

Impact Behaviour Of Lightweight Armours

Lightweight armours are being increasingly introduced as protective structures against small and medium calibre projectiles, as well as explosive fragments in such different applications like body jackets, helmets, aircraft cockpit seats, military vehicles and ships. Performance of composite armours ceramic/metal and ceramic/composite shows a clear improvement with respect to monolithic metal armours. The paper illustrates the experimental behaviour of several composite armours under impact of small calibre projectiles. Also, analytical models simulating the experimental behaviour of ceramic/metal and ceramic/composite armours are described, showing the possibilities of such models for helping the designer of protective structures impacted by small and medium calibre projectiles and fragments. Transactions on the Built Environment vol 22, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509

Ballistic Impact On Ceramic/composite Armours

Ceramic/composite armours are being increasingly utilised as protective structures against medium calibre projectiles due to its high efficiency compared to monolithic steel armours. Armour design optimisation use to be helped by the utilisation of different design tools, either analytical models that simulate the penetration process by one-dimension al simple equations or numerical hydrocodes that simulate the process by finite element or finite difference methods. An accurate description of the ballistic impact of a medium calibre projectile onto a ceramic/composite armour is far from being fully solved neither by existing analytical models nor by commercial hydrocodes, due to the lack of data of the mechanical behaviour of materials involved, and specially of failure criteria at high strain rates. The paper presents some advances on the simulation of the penetration process of medium calibre projectiles on ceramic/composite armours, both by analytical and numerical approaches, that agree well with empirical data, thus providing design tools that permit optimum armour design with a reduced number of actual firing tests.

Space correlation measurements in the fluctuating turbulent wakes behind projectiles.

Measurements of the space-time correlations in the turbulent wake behind 0.22 caliber projectiles traveling at 4000 fps were made with a pair of anemometers. A wide range of turbulence frequencies and thus averaging time requirements were encountered over the 20,000 diameters of the wake that were considered. The measured convection velocities were somewhat lower than the theoretical mean wake velocities, which were calculated for the blunt and slender projectiles by the Lees-Hromas-Webb (LHW) method. The space integral scale increased with X/D in agreement with the LHW calculation. Taylor's hypothesis produced space integral scales that were in a remarkable degree of agreement with the cross-correlation results, considering the high-turbulence intensity of the flow.

Hot-wire measurements of wake turbulence in a ballistic range.

Introduction 4 N experimental program to obtain local measurements -L*of wake turbulence behind projectiles by means of a hotwire anemometer has been initiated, and preliminary results have been obtained. It is worth emphasizing that the measured turbulence was local, the sample being no longer than the length of the hot wire (0.05 in.). This length is much shorter than the sampling length of the various summing techniques (schlieren, interferometer, etc.), which produce integrated information only after the beam has passed completely through the wake once or twice. Inasmuch as the available data from local turbulence measurements behind projectiles is very limited, the present results are unique in producing a quantity of valuable information in a short time. The kind of turbulence observed in wakes behind projectiles bears some similarity to the homogeneous shear-flow turbulence that can be analyzed theoretically. In both situations, the turbulence is stimulated initially and then decays. On the other hand, projectile wakes exhibit intermittency and compressibility effects that are not amenable to theoretical treatment at present. Local properties of wake turbulence, such as correlation length scales, are needed for the radar backscatter problem. Backscatter has been estimated analytically, using assumptions of self-preserving turbulence. Current needs for comparable measurements are striking. As a first step, the present measurements behind 0.22caliber projectiles traveling at 4000 fps have been accomplished with modest expenditures. Turbulent time scales were derived from records of hot-wire heat loss. These correlation time scales exhibit acceptable trends over 10,000 diameters of projectile travel, but they are not immediately convertible into the needed space scales.