Contribution to Guided Waves Analysis at Low Frequency in Thin Absorbing Plates with Application to the Non Destructive Testing of Paper

The paper is a cellulose fiber base material and consequently it is heterogeneous at different scales. In addition, the paper exhibits two preferential axes of fiber orientation, from which it is easy to define the characteristics of an elementary bi-dimensional fiber network. A third axis, perpendicular to the first, corresponds to the stacking direction of individual networks. Following the example of composite layered media modeling, the paper presents three perpendicular planes of material symmetry. In other words, the paper is commonly assumed to be an orthotropic material [1]. The paper presents also various mechanical behaviors such as elasticity, viscoelasticity, non-linear elasticity. Furthermore the paper properties depend on both the temperature and the hygrometry [2]. At last, paper materials exist in the form of sheets; their thickness (100 µm on average) is very small beside their other dimensions

Program overview

The interaction of Rayleigh waves with surface inhomogeneities has received considerable attention in recent years. Though of interest to the geophysics and microelectronics communities, the subject is particularly important to those involved in nondestructive testing. This is because of industry demands for more detailed and reliable characterizations of surface-breaking defects. Material interrogation using Rayleigh waves offers an effective means of detecting such inhomogeneities because energy is confined to the near-surface region. Flaws can be detected up to depths of one or two wavelengths, corresponding to 0.31–6.1 mm over a frequency range of 0.50–10.0 MHz [1]. The associated area of coverage is ten to one hundred square feet. The material need not be conductive, as required for electromagnetic methods, and is more sensitive than bulk wave ultrasonic testing to small cracks