Laser-ultrasonic measurements of the elastic properties of a static and a moving paper web and of the web tension.

Non-contact, non-invasive laser-ultrasonic measurements of the tensile stiffness index (TSI) and orientation (TSO) of a paper web and of the applied tension to the web are reported. The generation of ultrasound in paper is performed in the damage free thermoelastic regime by using a short pulse TEA-CO[sub 2] laser. The 10.6 μm infrared wavelength of the TEA-CO[sub 2] laser generates a stable and reproducible source of ultrasound, which was verified for several types of paper. For generation and detection spots separated by a known distance, plate or membrane waves are generated and detected, and the in-plane modulus and the tension applied to the sheet are measured. By detecting waves propagating in various directions the anisotropy of the in-plane modulus is determined. For overlapping generation and detection spots, the compression modulus is measured. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]