Speckle Cross-Correlation Method in Measuring Fine Surface Displacements

Industrial applications need regular testing for the lifetime, movement, strength, and performance of manufacturing machines during production process. Since speckle photography is a simple economic technique, it is used in investigating object response under mechanical and thermal effects depending on the movement of the speckle patterns with respect to the deformation strength and direction. In the present work, the cross-correlation technique is used to analyze the speckle patterns by iterative method to define both values and directions of rigid body translation and expansion. In order to check the accuracy of the cross-correlation technique, the results are compared with the displacement values given by analyzing the Young's interference fringes resulted from the Fourier transformation of the speckle patterns. This noncontact technique is found to be accurate and informative depending on the stability and sensitivity of the optical system. This method of measurement is an effective tool in studying the hard cases of objects and machines under various effects. 1. Introduction The necessity to ensure the efficiency of machines and tools used in industrial applications requires regular testing of their ability to work under various effects such as vibration and temperature. The conventional methods of investigation require surface contact and could be limited to object materials and time of measurements. In order to maintain the quality of the object and to make the testing service possible any time and under any circumstances, it is important to use a simple nondestructive method in the investigation. Electronic speckle photography is a simple nondestructive technique used in investing object variation under different effects. The investigation using this technique is performed by analyzing several recorded images for the object surface before and after deformation. The variation of speckle patterns position and interference fringes’ visibility indicate the direction and the strength of the deformation that the object encountered. Previous work discussed methods for characterizing object displacement and surface roughness by analyzing Young’s interference fringes resulted by the Fourier transformation of the combined speckle images before and after deformation [1, 2]. This method is reliable in indicating value of displacement but not field of displacement. The cross-correlation method describes the displacement field by the maximum position of the cross-correlation function between the speckle patterns recorded before and after displacement or