Modes de flexion d'une plaque mince au voisinage d'un seuil de percolation

We examine the flexion modes of metallic thin plates excited acoustically. The plates are randomly degradated square lattices of bonds with a fraction of intact bonds a little above the percolation threshold p c . The variation of the frequency of the fundamental mode measured at different distances from threshold, evaluated by the electrical conductance of the grid, gives an estimate of the critical variation of the elastic modulus. We conjecture that the critical exponent of the electrical conductance should apply to the problem rather than the vector percolation one because of the absence of moments acting normal to the plates. However, the experimental data are insufficient to verify this proposal. On the other hand, there is an upper cut-off frequency of the resonant modes which decreases continuously as p c is approached from above. The variation is consistent with that of the loffe-Regel limit between extended modes and localised ones (fractons) On examine les modes propres de vibration en flexion d'une plaque mince sous forme d'un reseau de percolation de liens sur reseau carre juste au-dessus de son seuil de percolation