Deformation and Warping in Magnetic Tapes by Laser Speckle Technique

Laser speckles appear as a pattern of fine randomly distributed dots resulting from multiple interference when an optically "rough" surface is illuminated by a coherent laser beam. By photographing a speckle pattern, the positions of all points on a surface are "fingerprinted" and any changes in posi tion can be detected with high sensitivity. Such speckle patterns can be used as a non-contact, nondestructive, quantitative tool to measure in-plane deforma tions in magnetic tapes subjected to tension. Because such tapes not only stretch but also warp, the obtained data reflect the projection of the deforma tion vector in the longitudinal plane of the tape. By geometrical relations, all three components of the deformation vector at any point of interest can be de termined. This article presents data that were obtained for a commercial com puter data cartridge tape (40 Mb Format). It is shown that with such data, stress-strain relations can be established and the overall deformation behavior of the material ...