The Mechanism of Spalling ¹

A study has been made of the stresses and fractures developed in a solid when rapidly heated or cooled. The stresses were measured in bakelite specimens by the photoelastic method. High stresses in all cases were found to occur near the surface of the solids, but no high tension stresses were present when the specimens were being heated. A number of vitreous clay spheres and bricks were heated and cooled rapidly and the nature of the cracks was noted. In practically every case the fractures occurred as predicted from the measured stresses. Torque‐deflection curves were obtained for a number of fire brick in torsion at different temperatures. The temperature at which plastic flow occurs for every material tested was approximately the same as the temperature of the initial deflection under compressive loads in a standard load test.