An X-Ray Method of Measuring Poisson's Ratio

Abstract

The paper describes the measurement of Poisson's ratio in metals by an X-ray diffraction method. The specimen, which is a small tensile test piece, is examined at various loads by a high-angle “back-reflection” X-ray technique. At any load (the value of which need not be known) X-ray patterns are obtained for various angular settings of the specimen relative to the incident X-ray beam, and, for each setting, the shift of the diffraction lines from their original position gives the strain in a direction normal to the reflecting crystallographic planes. The strains corresponding to various angular settings of the specimen, for any one load, give a linear graph when plotted against a simple function of the orientation of these crystallographic planes, and from this graph the value of Poisson's ratio is directly obtained.

Experimental results are quoted for the aluminium alloy known as “Hiduminium RR.56”. The results obtained for various elastic loads are consistent within the experimental error, the resulting value of Poisson's ratio being 0·36.

It is concluded that the method described is capable of an accuracy at least as good as that of the ordinary mechanical method, and that it has the additional advantage of providing values which apply to a single set of crystallographic planes in a polycrystalline metal.