板および棒の中のP波の速度

抄録

Longitudinal primary waves which are called P waves in the present paper have their own velocities α, v_pl and v_rod respectively in a three, a two and an one dimentional media. The rule of conversion from v_pl to v_rod is equal to that from a to v_pl. Here, the transient from v_rod to a has been investigated experimentally as well as theoretically.
Several brass rods having various radii were used for the super sonic measurements. Onset of the longitudinal fundamental mode, namely the first mode, has the velocity equal to v_rod. Various higher modes ride on the fundamental one. Byond the fifth order, the maximum group velocities U_n, _max of the higher modes exceed v_rod and some of the rider waves become the forerunners against the fundamental mode. The higher the order of the mode, byond the fifth in case of the brass rod whose Poisson's ratio is 0.35, the larger the maximum group velocity which approaches α. The higher the order of the mode which we can observe, the more the forerunner which will appear. The curve connecting U_n, _max against wevelengths may be taken as the dispersion curve of P waves in a rod, where the order n is larger than five for Poisson's ratio of 0.35.