The Measurement of Dynamic Strains Using Birefringent Strips

An experimental study is presented of the bonded birefringent strip as a means of observing transient deformations on the surfaces of opaque bodies. The particular situation investigated consists of a birefringent sheet bonded to a metal rod in which a strain pulse is initiated by a small explosive charge. Major emphasis is placed upon the study of two problems associated with the use of the technique. The first is the development of a reliable method of interpreting the observed photoelastic fringe patterns. The second is an evaluation of the influence the sheet has on the strain pulse in the bar. Satisfactory agreement is obtained between the strain profile at the rod-sheet interface determined by using a birefringent strip and the profile given by resistance-wire strain gages.