In this study, a guided wave phased array beamsteering approach is applied to composite laminates. Current beamsteering algorithms derived for isotropic materials assume omnidirectional wave propagation. Due to inherent anisotropy in composites, guided wave propagation varies with direction and wavefronts no longer have perfect circular shapes. By examining slowness, velocity and wave curves for a given composite laminate, the wavefront from a single source can be described as a function of the angle of propagation and distance from origin. Using this approach, a generic delay and sum beamforming algorithm for composite laminates is developed for any desired wave mode. It is shown that anisotropic wave mode regions can be effectively used for beamsteering in certain directions with a linear array and performance similar or even better than isotropic case. However, the useful range of angles with a 1d linear array for anisotropic wave modes is quite small and other directions exhibit undesired grating lobes and large sidelobes.

The usage of ultrasonic guided Lamb wave approach in structural health monitoring has been prevalent and proven to be an effective method. During flight, aircraft or spacecraft structures sometimes experience rapid temperature changes. The propagation of guided Lamb waves can be affected by these abrupt changes. In this paper, the effects of rapid temperature variation, due to which a sharp temperature gradient is achieved, on the propagation of guided Lamb waves through aluminum and composite beams are compared. The heating and cooling cycles for gradual temperature changes are firstly obtained for comparison. An abrupt change in the temperature is brought out by heating the beam to an elevated temperature and rapidly cooling it using liquid nitrogen. The design guidelines for the experimental setup used in the research are provided. The effects of rapid change in the temperature on the piezoelectric wafer active sensors (PWAS) are measured. Two different adhesives between the PWAS sensors and the beams are tested and the results obtained from the experiments are discussed.