Flaw detection using temporal speckle pattern interferometry and thermal waves

Abstract

ABSTRACT This paper presents a temporal speckle pattern interferometry (TSPI) system which uses thermal waves to detectinternal defects. The system allows the measurement of out-of-plane thermoelastic displacements generated whena specimen is locally heated with a temporally modulated CO 2 laser. The defects can be detected by observing theperturbations which appear in the induced displacement “eld. Displacements are determined from the calculationof the optical phase distribution using a temporal phase shifting method and temporal phase unwrapping. Thedescription of the TSPI system is followed by the presentation of experimental results that demonstrate that thedetectability of certain type of ”aws is improved by the use of thermal waves.Keywords: temporal speckle pattern interferometry, nondestructive testing, fringe analysis, phase measurement. 1. INTRODUCTION Nowadays, digital speckle pattern interferometry (DSPI) is a well-established optical technique for full “eldmeasurement of surface displacements, deformations and vibrations. The displacement “eld is obtained from theevaluation of the phase change distribution of two speckle interferograms recorded after and before deformationof a diusely re”ecting object followed by spatial phase unwrapping.