Real-time nondestructive evaluation of fiber composite laminates using low-frequency Lamb waves

Abstract

Amid the nondestructive evaluation techniques available for the inspection of composite materials, only a few are suitable for implementation while the component is in service. The investigation examines the application of Lamb waves at low-frequency-thickness products for the detection of delaminations in thick composite laminates. Surface-mounted piezoelectric devices were excited with a tone burst to generate elastic waves in the structure. Experiments were carried out on composite beam specimens where wave propagation distances over 2 m were achieved and artificially induced delaminations as small as 1 cm2 were successfully identified. The feasibility of employing piezoelectric devices for the development of smart structures, where a small and lightweight transducer system design is required, has been demonstrated. The resonance spectrum method, which is based on the study of spectra obtained by forced mechanical resonance of samples using sine-sweep excitation, has been proposed as a technique for measuring the A0 Lamb mode phase velocity. The finite-element method was also used to investigate qualitatively the dynamic response of laminates to wave propagation. Several locations and spatial distribution of the actuators were examined showing the advantages of using transducers arrays for the inspection of large structures.

Variation in the group velocity of Lamb waves as a tool for the detection of delamination in GLARE aluminium plate-like structures

“…To achieve this, a second set of specimens was analysed with lead zirconate titanate (PZT) embedded in the glass fibre reinforced resin matrix layer. Many researchers have commented on the benefits and advantages of using surface-mounted or embedded PZTs as actuators and sensors [6][7][8]. One clear advantage over the wedge method is that, unless, there is degradation of the adhesive layer between the PZT and the parent structure, the coupling force is always constant and very high; hence, the energy level transmitted to the parent structure is constant and a maximum, provided one the dominant frequencies is selected.…”

“…Finally, they employed finite element analysis to model qualitatively the response of laminate plates to wave propagation and substantiate their experimental results. D ıaz Vald es and Soutis [7] also mentioned the potential of using embedded piezoelectric elements during fabrication of the composite laminates.…”

“…There are many techniques available for detection of delaminations [4][5][6][7][8][9][10][11][12], however not all can be applied in practical situations. Non-destructive evaluation (NDE) has shown great potential over the past decade as it enables in situ structural health monitoring of the material.…”

“…The selective Lamb mode technique outlined by Grondel et al [8] was then shown to have a large sensitivity of the A 0 mode to composite damage. D ıaz Vald es and Soutis [7] investigated the application of Lamb waves in detecting delamination in thick composite laminates. They also evaluated the suitability…”

“…Numerous workers have investigated the use of Lamb waves for the ultrasonic inspection of structural components in numerical and experimental studies [1][2][3][5][6][7][8][10][11][12][13][14]. Attenuation of ultrasonic signals and changes in slowness (inverse of velocity) are two parameters that have proved to be powerful for damage detection purposes.…”