Mont A. Johnson
Yves H. Berthelot
School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405
Pierre Brodeur
Joe Gerhardstein
Inst. of Paper Science and Technol., Atlanta, GA 30318-5794
At present, the paper industry lacks an on-line, noncontact quality control system. Several studies indicate that there are strong correlations between paper strength and elastic stiffness properties. These elastic properties or elastic coefficients can be determined by measuring the velocities of propagation of various ultrasonic waves. Lamb waves, for instance, propagate in paper and appear to be sensitive to paper strength. Experiments have been conducted with a laser-based system to both generate and detect ultrasonic Lamb waves in copy paper. Results obtained regarding the relationship between the generation laser spot size, power density, and ultrasonic signal strength are presented. Paper damage is assessed at the generation spot. Phase velocity dispersion curves are produced for those modes that have sufficient signal-to-noise ratio. These dispersion curves are then compared to those predicted by ortotropic plate theory. [Work supported by OIP-GT.]