Measurement of in-plane displacement fields by a spectral phase algorithm applied to numerical speckle photography for microtensile tests

This paper describes a numerical method applied to speckle photography to m easure the inplane displacement field on a thin film and specially adapted to microtensile test. Speckle photography is chosen to avoid touching and s tressing the specimen. A Spectral Phase Algorithm particularly useful in th e case of small displacement or/and strain is compared with the Intercorrel ation and Double FFT methods. A final algorithm using first the Intercorrel ation method without interpolation and secondly the Spectral Phase Algorith m is then adopted to estimate with good accuracy the in-plane displacement field in quasi-real time during the microtensile tests. A first application of the method to the tensile tests performed on thin fi lms of electroplated copper of 18, 35 and 70 mu m of thickness is then pres ented.