PHOTOELASTIC DETERMINATION OF ELASTIC AND PLASTIC DEFORMATIONS AND OF CRYSTAL FRAGMENTATIONS IN METALS,
REDSTONE SCIENTIFIC INFORMATION CENTER REDSTONE ARSENAL ALA
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The paper describes a new method of measuring local deformations created on the surface of metallic or other types of specimens subjected to loads. The method is based on the incidental birefringence acquired by plastic materials subjected to stresses. To measure the surface deformations, the specimen under study is coated with a strongly photoelastic plastic material which follows exactly the deformations of the metal. By measuring the birefringence of the coating, it is possible to calculate the deformation of the metal in the elastic and in the plastic range. Thus, the photoelastic coating fulfills the functions of an infinite number of extensometers, distributed uniformly on all the points of the surface under study. It is possible to pinpoint with high accuracy the start of the plasticizing process, the effect of the geometric shape of the specimen, the crystal fragmentation made according to the metal used, the weak areas of welded, forged or riveted pieces. The precision of the method is about 0.00005 for the relative elongation.