Visualization and quantification of quasi-static and dynamic surface slopes using a reflection-mode digital gradient sensor

Abstract

A full-field, reflection-mode Digital Gradient Sensing (DGS) technique capable of measuring small angular deflections of light rays reflected off specularly reflective planar surfaces is developed. The method is aided by 2D digital image correlation principle to quantify angular deflections of light rays. In this paper, the principle of the method is described and the governing equations relating light ray deflections to surface slopes are presented. The method is demonstrated by simultaneously mapping orthogonal surface slopes of a circumferentially clamped silicon wafer subjected to a central deflection. The curvature fields, proportional to stresses in thin plates, as well as surface topography are evaluated from the measured slopes. Subsequently, the method is demonstrated for studying a stress-wave dominant problem of a free, thin, compliant plate subjected to impact by a rigid spherical ball.