The Propagation Of Lamb Waves In Honeycomb Structures

A common approach to structural health monitoring is to mount a network of PWAS (piezoelectric-wafer active sensors) in which one sensor sends out a pulse of Lamb waves that the others receive. Any difference between the initial wave form and the received wave form indicates potential damage between the actuator and receiving sensor. This hybrid sensing method requires extensive access to the structure, which cannot always be granted. An alternative approach to this problem utilizes a single mounted PWAS and a laser vibrometer, which measures out-of-plane displacements from the specimen. The PWAS emits pulses of Lamb waves that can be received by the laser vibrometer at any point on the specimen, not just the points where sensors are mounted. This method also requires much less access to the structure, as only one sensor needs to be mounted. In this paper preliminary research on the interaction between Lamb waves and honeycomb “sandwich” structures using the hybrid sensing method will be presented. In an anisotropic honeycomb structure, the Lamb waves propagated in an anisotropic manner at a frequency of around 15 kHz. Damage simulating delamination can be detected using the hybrid sensing method at this frequency. At higher frequencies, such as 100 kHz, the outlines of the individual honeycomb cores can be seen on the videos produced by the laser vibrometer