Logo from Scott Cunningham.
Logo from Scott Cunningham.
ast armour does not display the laminar weakness which may occur in rolled armour, but may have a general low level of elongation under tensile stress due to intergranular weakness or inclusions. Thus it is not uncommon to find cast armour which is quite as ductile as rolled armour when subject to shear stresses in the absence of tensile stress, but which is capable of little elongation in tension. This combination of properties tends to favour star cracking and back petalling, but may cause flaking if the internal weakness of the plate is too pronounced.1
Cast armour tends to fail by back petalling or flaking.
The way in which flaking occurs is best seen by analogy with discing. As in the case of rolled plate, annular cracks may be started in a cast plate by incipient plugging. Since there are no preferential planes of weakness, however, the cracks do not spread outwards parallel with the plate face. Instead they proceed towards the back face in the same way as the edge crack on a disc in rolled plate, but with greater initial outward inclination due to the high component of stress parallel with the projectile axis. When no secondary breakup occurs this can result in a large symmetrical flake, although in practice further break up usually occurs due to the brittle nature of plates which fail in this way, and several flakes detach.1
Discing and flaking are often used loosely and may sometimes be interchanged.
A distinction has been made here between discing and flaking, however the terms may sometimes be interchanged. In particular, in reports of trials on tank armour it will be found that the term flake will be applied in cases where disc would be used in the present article.1
Failures Peculiar to Thin Plates
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