Direct measurement of large-strain deformation fields by particle tracking

A hybrid particle image velocimetry/particle tracking velocimetry (PIV/PTV) method is described for direct measurement of large-strain deformation fields using plane-strain machining as the model system. PIV/PTV is shown to accurately measure displacements and velocities with a spatial resolution of similar to 1/10th of a pixel, which is an order of magnitude improvement over a comparable PIV-based method. For the configuration studied here, this translates to about similar to 400 nm in terms of displacement and similar to 80 mu m s(-1) in terms of velocity. Furthermore, the method is shown to be able to capture steep gradients in velocity, which are typical of deformation zones in machining. This enables accurate estimation of associated strain rates. Implications of the technique for measuring large-strain fields in deformation processes and indentation tests, and velocity gradients due to friction at sliding interfaces, are briefly discussed.