text: 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.