The optical study of percussion figures

Abstract

The application of optical interference methods to the study of the small local deformations occurring in impact is indicated as likely to lead to an extension of our knowledge of such deformations. As an illustration of the usefulness of the method, interference photographs showing the surface deformations produced by the percussion of a polished steel ball on a thick glass plate are reproduced. The photographs show the percussion figure to consist of three distinct regions. a: A central area which remains plane and practically undisturbed except for a small permanent lowering of its level. b. A narrow annular region of fracture showing severe injury to the surface. c. A sudden elevation of the surrounding surface which slopes down gradually to the general level of the plate at the outer margin of the area of internal fracture.