A programmable data-retrieval system for in-plane displacements from speckle photographs

The paper presents a computer-controlled system developed to scan a double-exposure speckle photograph (specklegram) of a loaded specimen and to print out in-plane displacement components as a function of specimen coordinates. This is accomplished using a microcomputer-controlled x-y translating table which incrementally scans the specklegram through a matrix of points defined by the user. The field size and interrogation density are user selectable. The overall system accuracy is + or - 2%, and the interrogation rate is 0.1 points per second. Consideration is given to each component of the system: a helium-neon laser, a specklegram holder and scan drive unit, a fringe scanner, and a computer-controlled data acquisition, control, analysis, and printout unit.