Explosively Formed Projectile Research Articles

Applied research of shaped charge technology

For special requirements of penetrating rock, we have developed a shaped charge jet device, from which a rather uniform and wide jet can be generated. The mass of shaped charge explosive is less than 2.5kg. The profile and velocity of the jet are measured with an X-ray technique. We have simulated the formation and penetration process of the jet with a 2-D HELP code, which provides important reference data in designing the shaped charge. A series of penetration tests into rock at different strengths has been carried out. The penetration tests to the rock with a strength about 600kg/cm2 show that the average diameter of the hole entrances is 63.5 mm; the average penetration depth of the holes with internal diameters of more than 35 mm is about 1311 mm, the average total penetration depth of the holes is 1531 mm; the coning of the holes are less than 1.4 %. All the results of the tests indicate good penetrating performance. Additionally, we have designed an explosively formed projectile (EFP) testing device with the explosive of 450g, a liner of 150g and 60mm-diameter. Performance tests and experiments of penetrating multilayer steel plates have been conducted. The EFP penetrates throughout the whole steel target that consists of five layers of 6-mm-thick A3 steel plate spaced in a range of two meters. The diameters of penetrating holes range from 41mm to 46mm. The mass of EFP recovered behind the target is about 98g.

Aspects of dynamic recrystallization in shaped charge and explosively formed projectile devices

Under a shock wave, a shaped charge (SC) liner or an explosively formed projectile (EFP) device transforms into a jet and a slug. At various laboratories, it was found that the transformation was closely related to extensive plastic flow occurring at high strain rates. Along with the shape trans-formation, there is evidence of changes in hardness, strength, grain configuration, microstructure, and resultant texture in the slug when compared to the starting liner. This article examines the effect of material parameters on jet and slug formation. Based on microstructure (metallography and trans-mission electron microscopy) and texture data, an analysis is made of the recovery and recrystalli-zation processes which are believed to be closely associated with the deformation. Grain rotations and shifts in texture are described from the starting liners to the recovered slugs. While fully re-crystallized grains are found in a “soft” recovered copper EFP slug, only partial recrystallization is achieved in a tantalum counterpart. The difference in extent of recrystallization of copper and tan-talum EFP slugs is analyzed. An attempt is made to explain the difference in terms of the deformation structures between the two types of metal. Experimental evidence tends to support a grain rotation concept for recrystallization phenomena.

Dynamic-loading-induced damage in tantalum and Armco iron

The deformation behaviours of tantalum and Armco iron were investigated. Taylor cylinder, explosively formed projectile (EFP) and tensile tests were conducted on Armco iron and electron-beam-melted tantalum. The deformation and damage mechanisms were deduced from observations by optical, scanning and transmission electron microscopy. Hydrocode-EPIC2 was used to simulate the deformation process. Distinct adiabatic shear bands, extensive twins and voids were observed in Armco iron Taylor cylinders and EFPs. Tantalum was found to be more resistant to the formation of voids and twins but exhibited less strain hardening. Massive diffused deformation bands were observed in tantalum EFPs. The factors which caused the different behaviours of these two metals are discussed.

An investigation of shock-induced damage in oxygen-free high conductivity copper

Shock-induced damage in soft-recovered explosively formed projectiles (EFP) of oxygen-free high conductivity copper was investigated using transmission electron microscopy, scanning electron microscopy and optical microscopy. A high volume fraction of voids and extensive adiabatic shear bands were observed in the centre, around the longitudinal axis of the EFPs. The premature fracture of some projectiles was found to be caused by flow localization and the development of adiabatic shear bands in locations other than the centre of the projectiles. The fracture path followed the trace of a shear band.

Advances For Modelling Of Geological Materials

Geologic material models have been developed, based on static triaxial data, that improve hydrocode modelling capabilities in the assessment of Kinetic Energy warheads against soil and concrete targets. Recent work has demonstrated that the flow and failure of geological materials under confinement are strongly dependent on the load path and strain rate. This paper will describe test methods that are currently being developed by DERA to generate new models that are also predictive for shaped charge, Explosively Formed Projectile and contact explosive loading against such targets. Existing GREAC (Gauged REACtive Confinement) and Hoek cell methodologies have been used to determine the physical states that control the path dependent response of concrete. The variation of the state variable has been determined under different hydrostatic loading conditions and this behaviour will form the basis from which the computational algorithm can be constructed. Elements of the supporting test programme will utilise the newly developed Stabilised Hoek Cell and this will be extended to a high pressure testing technique. Plate impact techniques will be developed to directly determine the equation of state of geologic materials and investigate the failure mechanisms (such as failure waves). A dynamic triaxial test rig will be developed in order to investigate the high strain rate behaviour of concrete. The new geologic material models will be validated against precision instrumented trials, covering a range of warhead mechanisms. Transactions on the Built Environment vol 32, © 1998 WIT Press, www.witpress.com, ISSN 1743-3509