2018 Insensitive Munitions and Energetic Materials Technology Symposium
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An Explosive Fragment Projector for IM testing
G.G. Goviazin, R.E. Ceder, T. Eliash
Rafael, Manor – Advanced Defense Technologies Division
ISRAEL
Email: talel@rafael.co.il
Abstract
Fragment Attack (FA) testing, as described in STANAG 4496, calls for a specific fragment
shape, material and velocity. Usually this is achieved by accelerating a fragment in a long
barrel, powder or light gas gun. This method requires heavy infrastructure, binding FA tests
to stationary facilities. At Rafael, the need for a mobile FA test apparatus had led us to use
specially designed Explosively Formed Projectiles (EFP) as substitutes for the STANAG
fragment. We call this method Modified Fragment Impact or MFI. In this method the EFP has
the needed mass and velocity but is roughly spherical in shape and made of copper rather
than steel. Another advantage of this method, besides being portable, is its accuracy both in
velocity and in aim.
The objective of this work is to develop a new explosive charge and test set-up that will have
the advantages of our EFP test method while projecting a fragment at the velocity, with
shape, mass and material as required by the STANAG. The design process includes both
hydrocode calculations and characterization of the performance through testing of selected
designs.
Introduction
The Fragment Attack (FA) test is described in STANAG-4496 [1]. This procedure specifies a
steel fragment of 18.6 g, made of mild steel, 14.30 mm in diameter and 15.56 mm in length,
with a conical nose. The specified impact velocity is 2530 m/s. An alternate velocity of 1830
m/s is also specified in the STANAG. The means for accelerating the fragment to the desired
velocity is usually a long barrel powder gun or a light gas dual stage gun. While this is a
precise and common method, it requires a considerable investment in heavy infrastructure
and maintenance. Typical setup time needs to account for activities such as sighting shots,
propellant conditioning etc. [2, 3]. In addition, cost considerations require the gun to be
protected from the detonation of the test item.
An alternate method which is relatively low-cost and mobile is the use of Explosively Formed
Projectiles (EFP). This method was suggested for IM testing in the past for both copper and
mild steel projectiles [4,5,6]. The disadvantage of this method is that the shape of the
fragment differs from the STANAG requirements. At Rafael, the need for a mobile FA test
apparatus has led us to use this method which we call Modified Fragment Impact or MFI [7].
In addition to its mobility, the tight manufacturing tolerances of the EFP charge yields
consistent fragment velocity and shape thus reducing the need for a pre-test shot.
Several other designs were suggested as explosive fragment projectors such as the
explosively driven light gas gun [8] or an explosive charge specifically designed for this
purpose [9] which was based on the work of Held [10, 11]. These designs have the
advantages of being portable and inexpensive but used a large explosive charge of ~4 kg
and ~5-8kg respectively, resulting in an undesirable parasitic blast in the test arena.
The need to decrease the amount of high explosive incorporated in the test, served as
motivation for the present work. By maximizing the effect of the charge confinement, we
aimed to accomplish this goal. This approach, however, can decrease the explosive amount
up to a certain physical limit. In order to decrease the explosive mass beyond this limit, we
employed the Munroe effect by constructing a shaped charge like design. We will present
the hydrocode simulations and experimental results achieved.
