A new method to detect anisotropy and local variations in paper

The mechanical properties of paper were studied using holographic interferometry. Bending wave propagation in paper was generated by the impact of a small pendulum. Holograms were produced at various times elapsed after impact with the use of a double-pulsed ruby laser. Results show that this method can be used to detect anisotropy, to determine principle directions (machine and cross-machine), and to examine local variations in paper.