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

¹ Laboratoire d'Optique P.M. Duffieux (UMR CNRS 6603 and IMFC, FRW 0067), Université de Franche-Comté, UFR Sciences et Techniques, route de Gray, La Bouloie, 25000 Besançon, France
² Laboratoire de Mécanique Appliquée R. Chaléat (UMR CNRS 6604 and IMFC, FRW 007), Université de Franche-Comté, UFR Sciences et Techniques, 24 rue de l'Épitaphe, 25000 Besançon, France

Corresponding author: patrick.delobelle@univ-fcomte.fr

Received: 25 November 1999
Revised: 5 June 2000
Accepted: 5 June 2000
Published online: 15 August 2000

Abstract

This paper describes a numerical method applied to speckle photography to measure the in- plane 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.