Editing Spall (section)

==Mechanical spalling==
Mechanical spalling occurs at high-stress contact points, for example, in a [[ball bearing]]. Spalling occurs in preference to [[brinelling]], where the maximal [[shear stress]] occurs not at the surface, but just below, shearing the spall off.

One of the simplest forms of mechanical spalling is plate impact, in which two waves of compression are reflected on the free-surfaces of the plates and then interact to generate a region of high tensile stress inside one of the plates.

Spalling can also occur as an effect of [[cavitation]], where fluids are subjected to localized low pressures that cause vapour bubbles to form, typically in pumps, water turbines, vessel propellers, and even piping under some conditions. When such bubbles collapse, a localized high pressure can cause spalling on adjacent surfaces.

===Anti-tank warfare===

[[File:Armour plating from HMS New Zealand.JPG|thumb|A chunk of armour knocked from [[HMS New Zealand (1911)|HMS ''New Zealand'']]{{'}}s 'X' turret during the [[Battle of Jutland]] on display at the [[Torpedo Bay Navy Museum]] in Auckland. Caption reads, &quot;The chunk of armour plating you see here was [[gouge (chisel)|gouge]]d out of X turret by a German shell.&quot;]]

In [[anti-tank warfare]], spalling through mechanical stress is an intended effect of [[high-explosive squash head]] (HESH) anti-tank [[Shell (projectile)|shells]] and many other munitions, which may not be powerful enough to pierce the armour of a target. The relatively soft warhead, containing or made of plastic explosive, flattens against the armour plating on [[tank]]s and other [[armoured fighting vehicle]]s (AFVs) and explodes, creating a [[shock wave]] that travels through the armour as a compression wave and is reflected at the free surface as a tensile wave breaking (tensile stress/strain fracture) the metal on the inside. The resulting spall is dangerous to crew and equipment, and may result in a partial or complete disablement of a vehicle and/or its crew. Many AFVs are equipped with [[spall liner]]s inside their [[vehicle armour|armour]] for protection.

A [[kinetic energy penetrator]], if it can defeat the armour, generally causes spalling within the target as well, which helps to destroy or disable the vehicle and its crew.<ref>{{cite web | url=http://science.howstuffworks.com/m1-tank3.htm | title=How M1 Tanks Work: Sabot| date=7 May 2002}}</ref>

An early example of anti-tank weapon intentionally designed to cause spallation instead of penetration is the [[wz. 35 anti-tank rifle]].