Logo from Scott Cunningham.
Logo from Scott Cunningham.
he quality of armour plate must obviously be assessed primarily in terms of its ability to stop armour piercing projectiles, but an important secondary requirement is that, when defeated, the plate shall not fail in such a way that fragments become detached and so add to the lethality of the attack. These two requirements are not independent, since both depend upon the mode of deformation and fracture of the plate when penetrated. It does not follow that the type of plate giving the most desirable form of failure necessarily offers the greatest resistance to penetration.1
When considering the various types of plate failure it may prove helpful to bear in mind the obvious fact that complete perforation of a plate cannot occur by deformation alone. Some form of fracture must also occur, and the type of plate failure which takes place is very largely determined by the nature and position of the first fracture.1
When a projectile is fired into a plate of about one calibre thickness or more, the front of the plate almost invariably has either a petalled appearance, or a crater where the petals have sheared off, whether perforation is complete or not. If the plate is thick enough to stop the projectile, the impression in the plate beyond the crater is a mould of the projectile’s form. On the other hand, if the projectile perforates the plate, the last stages of the hole formation may occur in a variety of ways, giving one of four main types of back damage, or, sometimes, a combination of two or more of these:1
Penetration may proceed to the stage where the projectile breaks through the back of the plate and forms back petals. These are normally larger and fewer than the front petals, and they may remain attached to the plate, or may break away as they are bent back by the projectile.
Alternatively, a plug of approximately shot diameter may shear out, giving a roughly cylindrical hole right through the plate and a slight lip on the back face.
A third type of back damage occurs with RHA and is caused by the breaking away from the back of the plate of a disc of metal up to several calibres in diameter and usually half a calibre or so in thickness.
A fourth type of back damage which may occur is the breaking away of irregular flakes from the back of the plate. This most commonly occurs with cast armour.
Formation of Petals on Plate Front
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