The twisting of polished cylinders beyond the elastic limit results in the formation of surface cracks in the smooth surface. These surface cracks scatter light in a characteristic way. For small plastic deformations, the light scattering properties of the surface depend linearly on the permanent twist angle. Therefore, light scattering may be used as a kind of strain gauge.
© 1986 Optical Society of America
Richard R. Zito and William S. Bickel, "Light scattering from twisted metal cylinders," Appl. Opt. 25, 1833-1836 (1986)