Strain Measurement of Surface Coatings by the Scattered-Light Method

A method for measuring surface strains of real specimens is proposed using the scattering photoviscoplastic analysis with polyester coating. A major advantage of this experimental technique is that interference fringes in the vicinity of the adhesion plane bounding the real specimen and the coating can be observed. The difference in principal strains on the symmetric section of real specimen in two dimensional problems can be calculated using two kinds of scattered-light fringe patterns obtained by two different incidences of polarized light. For the demonstration of effectiveness of this method, surface strains of unnotched and semicircular notched plate specimens made of aluminum alloy were measured under uniaxial tension. For the unnotched specimen, measured longitudinal strains were consistent with ones calculated from the elongation of the gauge length. For the notched specimen, normal strains on the notched section were measured and the distributions were consistent with FEM analyses