Dispersion of flexural elastic waves in honeycomb sandwich panels

Abstract

The phase velocity of flexural waves traveling along a 1-in.-thick honeycomb sandwich panel has been experimentally determined from 170 Hz to 50 kHz by using three techniques: measurement of resonant frequencies of beam-shaped samples in forced vibration, measurement of nodal spacing in standing wave patterns on beam-shaped samples, and measurement of the change in time delay of a particular phase feature of a wave packet as a function of propagation distance on large plate samples. The experimentally determined velocities ranged between 2.2×104 cm/sec at 170 Hz to 1.18×105 cm/sec at 40 kHz. This dispersion arises primarily from the geometrical effect of the finite thickness of the panel and agrees well with two theoretical models; a plate theory and an elasticity theory, each of which treats the core as a continuum. Above 40 kHz, the predictions of the two models differ greatly for the particular panel geometry studied. The experimental phenomena become more complex and appear to agree with neither model, quite possibly due to the neglect of the periodicity of the core. A brief description of these results is given. Subject Classification: 40.24; 35.26.