Lamb waves in sandwich structures: Anomalous dispersion and transverse (quasi) resonances

Guided waves propagating in three layered sandwich structures with extremely soft inner layer and thin stiff outer layers reveal peculiar phenomena related to the appearance of dual zero group velocities (ZGV) in the fundamental symmetric branch, transverse (quasi) resonances, and transverse energy fluxes, causing “ringing” of the plates and even material damage. The current research relates to sandwich plates, satisfying the so-called Wiechert condition. The analysis is based on the combined method comprising Cauchy sextic formalism and the exponential fundamental matrix method.