Results from real-time laser speckle-shift strain measurement system

A real-time two-color laser speckle-shift strain measurement system based o n the technique of Yamaguchi was designed, built, and tested at room temper ature. This noncontact 1-D system detects surface strain in a structural fi ber as it is pulled in a tensile test machine. Interference or speckle patt erns from the laser-illuminated fiber test specimen are recorded. As the fi ber is pulled, its speckle pattern shifts in proportion to the strain, tran slational, and rotational components of the sample deformation. Shifting sp eckle patterns are detected using two linear CCD arrays with image processi ng performed in realtime by a hardware correlator. Surface strain is detect ed in fibers with diameters on the order of 100 mu m and can be resolved to 20 mu m/m. This system was designed to be robust and compact and generally does not require surface preparation of the structural fibers. (C) 2000 So ciety of Photo-Optical Instrumentation Engineers. [S0091-3286(00)03502-9].