Device for the determination of biaxial-symmetrical residual stresses in metallic, disk-shaped specimens

Abstract

A device is described for the determination of the residual stresses in metallic disks up to 3 mm thickness due to axi-symmetric surface treatments on both faces. The apparatus is designed to measure normal stresses at any point on planes 0r:tho~onal to the disk in the cases, normally occurring in practice, of compreSSIve tnternal stresses on carburized, nitrided, chromed, peened, etc., surfaces. The method consists of the electrochemical thinning of the disk, making the sample act as a rotating anode in a special electrolytic cell with floating cathode. During the operation, the spontaneous deformations of the disk are caref~lly compe~sated for by use of an annular bending load which guarantees a suffiCIent plananty of the outer surface of the disk. The electrolytic cell develops a plane attack front only on the internal surface; parallelism between the two faces is assured by accurate mechanical seating. The determination of the stress field is carried out by relating the bending of the disk, or the values of the ~ounter-bending load applied to compensate for this bending with the unknown tnternal stresses. Two analytical treatments are thus developed, each of which is abl~ to prov~de a measure of the internal stresses starting from experimental data whIch are dIfferent, but which are obtained in the course of the same test and are able to provide a check.