Nondestructive Evaluation of Laminated Composites Using Rayleigh Waves

Abstract

The design and implementation of a nondestructive method for evaluating interlaminar bonding during the in-situ thermoplastic tow placement process was developed. This method utilizes two piezoelectric transducers in a “pitch-catch” arrangement.Each transducer is mounted on an acrylic wedge which, in turn, is mounted on a steel mediator wedge. This “double wedge” assembly produces Rayleigh surface waves in a composite specimen without a gel couplant. The received signals are analyzed for changes in the Rayleigh wave speed. Poorly bonded top most plies cause the Rayleigh wave velocity to decrease by as much as 30%. Verification of this bond quality sensor is demonstrated under various tape laying conditions. In each specimen, the Rayleigh wave velocity was measured.The bond quality was assessed quantitatively with a peel test and qualitatively by visual inspection (photomicrographs). The Rayleigh wave velocity was compared with the strength and thickness of the bond between the top ply and substrate. The Rayleigh wave speed increases linearly with the top ply peel strength. Photomicrographs indicated that poorly bonded specimens have a resin rich region at the top ply/substrate interface. These tests demonstrate that the double wedge sensor can measure bond quality during in-situ consolidation of thermoplastic matrix composites.

8D-5 Tracking of Cracks in Fatigue Experiments Using Nonlinear Propagation of Multi-Sine Surface Acoustic Waves

“…Several authors successfully applied SAWs for the detection of cracks in different materials: metals [2], composites [3] and concrete structures [4]. The linear attenuation of the wave between two transducers placed on both sides of a crack can be used to detect the crack and determine its size [5].…”

Tracking of Cracks in Airplane Components Using Nonlinear Surface Wave Propagation Techniques

“…(7) Because possible many components should be monitored (as is the case for an airplane) the techniques should be easy to interpret, computationally simple and fast. And last but not least: (8) the application of the NDT technique should be guaranteed to be safe (at the structural and electronical level).…”

“…Indeed, the sensors and instrumentation are quite compact and because of the use of high frequency transducers a high sensitivity can be attained while being robust with respect to environmental noise. Several papers exist on the application of SAWs for the detection of cracks in metals [7], composites [8] and concrete [9]. In [10] and [11] an off-line and on-line method for detecting fatigue cracks using SAW was introduced.…”

Ultrasonic Non-Destructive Testing of Fibre Reinforced Composites

“…Detection of the Rayleigh wave could then be achieved via either a laser interferometer measuring the surface displacement, or air coupled transducers to detect the leaked energy. Alternatively a contact method for launching and detecting Rayleigh waves could involve a double wedge (acrylic/steel) setup [10] which does not require a coupling gel or immersion as the steel mediator is in direct contact with the sample.…”

“…The guiding nature of Rayleigh waves makes them a popular choice for surface probes [6,7,8]. Popular techniques for launching Rayleigh waves on FRC samples include laser ultrasonics [9] or double wedge arrangements with contact transducers [10].…”