Elastic characterization of anisotropic materials by speckle interferometry

In this paper we present an experimental procedure for the elastic characterization of thin anisotropic plates. The procedure allows the determination of the elastic constants of isotropic materials (metals and ceramics) and orthotropic materials (composite laminae). Moreover, the flexural compliances of completely anisotropic uncoupled materials (most of composite laminates) can also be measured. The tests are carried out by applying a concentrated force to the specimen supported by three spheres. The stress components are evaluated by simply measuring the applied load, while the strain fields are measured by digital phase-shifting speckle interferometry. The experimental procedure is entirely controlled by a virtual instrument developed for this purpose in the National Instruments LabVIEW® environment, which runs on a personal computer interfaced with a standard black and white CCD camera. By means of the speckle interferometer, the whole field of the out-of-plane displacements is acquired; the curvatures, and hence the strain components, are obtained by two subsequent numerical differentiations. The numerical processing of the experimental data was carried out in the Mathematica™ environment. The results obtained on a steel specimen and on a composite laminate are reported.