Abstract
The problem of a circular aperture in a thin plate under tension, is set briefly in a historical background. Relevant published work is surveyed and various ways of strain measurement are examined with a view to their usefulness in plastic and elastic regions of a metal plate. The method of a thin photoelastic layer, bonded to the metal surface, is selected; its advantages and difficulties are investigated. The design is given of an apparatus which has been constructed to stretch a thin metal plate in either one direction or in two directions at right angles. A reflection polariscopic was arranged above this tensioning table for examining bonded specimens in polarised light, strains being measured from the photoelastic patterns obtained. Plastic and elastic regions, surrounding the central circular hole of each specimen, were examined by this means. The method of oblique incidence has been developed for use with a bonded layer, in order to separate the individual principal strains. Results are given for a single tension and for two equal tensions using aluminium alloy L71. The strains obtained for a single tension are compared with an experimental and a theoretical work. The plastic elastic boundary (using Tresca's yield condition) and the measured values of strain, in the case of equal tensions, are compared with theoretical works.