Mikael SJÖDAHL

Division of Experimental Mechanics, Luleå University of Technology, 971 87 Luleå Sweden

(Received August 29, 1996; Accepted December 20, 1996)

The robustness to rigid body object motions of three optical systems used in the speckle strain gauge were experimentally investigated and compared with analytical results of the correlation. It was found that an out-of-plane motion of the object damaged the reliability of the strain measure when recording the objective speckle patterns while subjective speckle patterns were more robust. Besides out-of-plane object motions, the robustness of a free-space geometry and an afocal imaging configuration are approximately the same, while a telecentric imaging system is more robust to rigid body motions but more sensitive to deformation gradients (basically in-plane rotation and tilt). Results from a measurement of the relaxation in a lead-tin alloy used in organ pipes is also presented.

Key words : strain measurement, speckle strain gauge, correlation, speckle correlation, correlation robustness

*Presented at 1996 International Workshop on Interferometory (IWI '96), August 27-29, Wako, Saitama, Japan.