| Abstract: | A non-contact strain field measurement technique called dual-beam digital speckle photography is presented. The system facilitates strain measurements in rough environments and at elevated temperatures and can be used on materials where instrumentation of standard strain gauges are difficult. The system uses two symmetrically oriented laser illumination beams and an imaging system oriented normal to the object surface. The laser speckle field for each illumination beam is recorded simultaneously before and after object deformation. From these data sets it is possible to extract one strain component, e.g. xx, without the need of numerical differentiation. It is shown that the most important criteria is normal viewing but also that deviation from perfect symmetry in the illumination will affect the results. A dynamic strain field, acquired at 15 Hz, illustrates the system performance. The effect of oblique viewing and unstable lasers are also shown. |
