Strain Measurement of Surface Coatings on a Three-Dimensional Body by the Scattered-Light Method

A method for measuring large surface strains of three-dimensional bodies under tension is proposed, which utilizes the scattered light technique with polymer coating. A major advantage of this method is that interference fringes at the boundary between a real specimen and coatings can be observed directly. The difference in normal strains and shear strain on the surface of real specimen in axisymmetric tension problems can be calculated from three kinds of scattered-light fringe patterns obtained by three different incidences of polarized light. For the demonstration of effectiveness of this method, surface strains of solid and circumferentially notched cylindrical specimens made of aluminum alloy were measured under uniaxial tension. For the unnotched specimen, measured longitudinal strains were well consistent with ones calculated from the elongation of the gauge length. For the notched specimen, distributions of the measured normal and shear strains on the notch surface were well consistent with FEM analyses