Optical EngineeringStrain and torque measurements on cylindrical objects using the laser speckle strain gauge
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First, the theory of diffraction field speckle displacement is extended to include speckle patterns arising from a cylindrical object subject to general deformation. Second, the usefulness of the derived relations are demonstrated by measuring the axial strain component on a Teflon cylinder and torque (shear strain) on a twisted steel cylinder. We performed real-time measurement of these quantities using the setup adopted for the laser speckle strain gauge. With this equipment, we obtained resolutions of 37.5 µ strain in the axial strain measurement and of 1.8 N m in the torque measurement. Both experiments agreed within 4% with simultaneous results obtained from an electrical strain gauge and with the known applied torque.