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 measure the inplane displacement field on a thin film and specially adapted to microtensile test. Speckle photography is chosen to avoid touching and stressing the specimen. A Spectral Phase Algorithm particularly useful in the case of small displacement or/and strain is compared with the Intercorrelation and Double FFT methods. A final algorithm using first the Intercorrelation method without interpolation and secondly the Spectral Phase Algorithm 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 films of electroplated copper of 18, 35 and 70 µm of thickness is then presented.