Manfred Held

Disturbance of Shaped Charge Jets by Bulging Armour

Bulging armour is an interesting and relatively often used protecting system which is typically not too much published. The patent of the author was filed 1973. The principle function is already described in detail in his overview paper on ‘‘Armour’’ 1993 on a number of interlayer materials, as the dependence on impact angles (Fig. 11 and Fig. 12 of Ref. 2). ‘‘Spall’’ armour – called in this earlier publication – is identical to ‘‘bulging’’ armour. Israeli authors presented a theoretical consideration to this topic in 1992 and again together with some experimental results in 1995. A very nice numerical parametric study was recently published by Rosenberg 1998. Experimental results with a numerical support to this topic are given by Thoma et al.. This paper does not describe the used materials. The author assumes that it was not a totally passive system but also not a fully detonative explosive reactive armour system. It was maybe something between these two extremes, called in USA ‘‘Self-Limiting Explosive Reactive Armour’’ or ‘‘Non-Explosive Reactive Armour (NERA)’’. In this present paper two tests are described with two ‘‘new’’ base inert materials – Dyneema – between two metal plates.

Comparison of Rectangular and Round Momentum Gauges for Blast Impulse Measurements

Measuring the blast contour method of the horizontal displacement of momentum gauges made of cylinders with 70 mm diameter and 50 mm, respectively 100 mm length or rectangular cross section of 25 mm width and 50 mm height with the Held momentum method gives very well corresponding results with regard to the measured impulse densities in the four selected radii of 0.25 m, 0.5 m, 0.75 m and 1.00 m. This confirms the validity of the selected test method.

Stopping Power of Explosive Reactive Armours Against Different Shaped Charge Diameters or at Different Angles

The experimental results of three different explosive reactive armour arrangements with singleand double-sandwiches are described against shaped charges of 64 mm, 96 mm, 144 mm and 200 mm base diameter under 60 NATO-angle and the 96 mm diameter shaped charge additional under the angles of 40 and 30 . Larger shaped charges give, as expected, more penetration capability. However, the 200 mm, not so precise shaped charge, only gives similar results compared to the 144 mm precision shaped charge. The stopping power depends extremelly on the angle of the shaped charge axis to the reactive armour containing small layer thicknesses of high explosives.

Momentum Theory of Explosive Reactive Armours

The deviations of the jet of a shaped charge or of the rod of a KE-round by the flying plates of an Explosive Reactive Armour (ERA) are described by a simple momentum equation. This continuous consideration does not describe the non permanent event at all, as the plates pulsate or act iteratively especially against shaped charge jets. Nevertheless, they give a good trend analysis concerning angles of the ERA-sandwich changing with respect to the direction of attack, jet or KE-round velocities and densities of plates or attackers.

Radial Crater Growing Process in Different Materials with Shaped Charge Jets

The equations of Szendrei/Held for the radial crater growing process as a function of time can also be inverted to get the target strength Rt if the maximum crater radius rcm is known. With this method the strength was calculated for an aluminum target to 300 N/mm2 and for glass fiber reinforced plastic to 405 N/mm2, which are at least very reasonable values. By using these values for Rt, the comparison of the radial crater growth process with carefully arranged and analysed experiments by the Ioffe Institute is showing good agreements.

Glass Armour and Shaped Charge Jets

Summary 115 mm shaped charges were fired at a constant built-in standoffs of 3 caliber against on both sides with steel plate covered glass targets from 0 to 60 NATO angles. The residual jet tip velocities and the disturbed jet regions have been analyzed from double flash X-ray pictures of the residual jet behind the target. Surprisingly under small angles the tip regions and under large angles the residual jet velocity regions have been more disturbed. This can be explained by the fact that under small angles the closure effect of glass is efficient but no more under large angles. But here the cover plates of the glass sandwich are effective as bulging armour. From the penetration time measurements, compared to the theoretical penetration potential, and together with the jet fan the jet velocities, which are no more perfectly penetrating can be defined. From this can be derived an induction time or how fast the armour will start to interfere with the passing jet.

Jet Initiation of Covered High Explosives with Different Materials

Cover-plate materials are influencing the build-up distances and delay times of high explosive charges in contact to the barrier, loaded by shaped charge jets. Materials with strong bulging behavior give long build-up distances, as steel and ceramics, with subsonic perforation velocities in contrast to materials with low sound velocities and therefore supersonic penetration velocities, as lead.

Time–Distance Plots for ERA‐Design

Time–distance plots are good design tools for reactive armour layouts, either against APDSFS (Armour Piercing Discarding Sabot Fin Stabilized) rounds or against shaped charges. They give clear answers to the given interaction times, necessary plate lengths and useful air gap distances in front and behind the ERA (Explosive Reactive Armour)-sandwiches.

Blast Effects of High Explosive Charges Detonating in Cylindrical Steel Tubes

Summary Described are tests of cylindrical high explosive charges with an L=D ratio of 2, centrally detonating in steel tubes of different radii and wall thicknesses to measure the bulge respectively the damaging effects of these steel tubes. The results can be described with analytical equations. For a protecting container with minimum weight the radius should be as large as possible, because the necessary tube wall thickness is quadratically decreasing and therefore the weight of the tube is linearly decreasing with increasing tube radius.

Tests of Unconfined Single Fragment Generators

A single fragment cannot be accelerated very well and undisturbed by an unconfined high explosive charge. The converging shock and release waves eject a higher number of very small spall debris of the fragment in the firing and target direction. This means, the fragment is considerably deformed and looses some mass. In addition, the release waves reduce the high pressure zone after the fragment very fast. Therefore, only moderate velocities are achieved.