A New Moiré Fringe-Strain Relation and A Method for the Determination of the Strain Sign

Abstract

The conventional moiré interfringe spacing-strain relation does not contain a factor for determining the strain sign. Therefore, in the case of complex strain fields, this equation can not give exact strain values.
In this paper, new equations for the fringe-strain relation are derived. These expressions contain new factors M_ii and M_ij (±1) for determining the strain sign. The factors can easily be determined by shifting the master grid in the direction perpendicular to the grid lines.
When the crossed grid is used, the discrimination of two kinds of fringes produced by X and Y grid is generally difficult. However, it is proposed that the above mentioned shifting method is also an effective means for the discrimination of both fringes.