ON THE CROSSING POINTS OF LAMB WAVE VELOCITY DISPERSION-CURVES

Standard dispersion curves relating the phase velocity of Lamb waves t o the frequency-plate thickness parameter fd indicate that in some cas es symmetrical and antisymmetrical mode velocity curves cross each oth er. Viktorov's equations are used to show that the crossing points are points where the dispersion curves are discontinuous so that no disti nct Lamb mode exists for these particular velocity-fd combinations. Pr ocedures are given to predict how many such points exist and where the y are located in a given range of fd.