The application of moiré rotational mismatch techniques to strain analysis

Abstract

Theoretical and technological aspects of moiré fringe techniques when applied to problems of strain analysis are discussed. An outline is given of the methods of determination of direct and shear strain distributions of elastic and plastic orders of magnitude from the formation of moiré patterns resulting from the superposition of two gratings of straight parallel lines. The rotational mismatch technique is discussed and shown to give strain directly. Reference is made to the use of master gratings, to the ‘photo-resist’ and ‘stripping film’ techniques for the reproduction of these gratings and to some of the photographic difficulties encountered. The advantages of the moiré techniques over conventional methods of strain evaluation employing extensometers, strain gauges and photoelastic materials are discussed and illustrated by results obtained during (1) uni-axial tensile tests on mild steel, brass and aluminium alloy, and (2) diametral compressive tests on cast iron discs.