Ultrasonic and vibration methods for the characterization of pultruded composites

Characterization of unidirectional fiber reinforced glass/epoxy pultruded composites using ultrasonics (high frequency, 1-5 MHz) and the impulse-frequency response vibration (intermediate frequency, 50-100 Hz) technique, is demonstrated here. This paper compares the response of both of these non-destructive test techniques to the changes in the pultrusion process variables and to the indeed contaminants introduced during manufacturing. The ultrasonic methods use multi-mode techniques of wave velocity and attenuation measurements to measure the viscoelastic constants of the pultruded composite while the vibration technique provides the dynamic flexural modulus and loss factor (damping) measurements. Quasi-destructive assays were also performed using a low frequency (1-50 Hz) Dynamic Mechanical Analyser (DMA) to verify the state of pultruded samples with induced contaminants (simulated porosity and interfacial debonding) and the results compared with the non-destructive measurements. Mathematical models to describe the influence of porosity and debonding agents on the material properties were derived based on statistical regression analysis procedures. Results indicate that the peak damping value of the tan δ curve obtained from the DMA is a sensitive parameter to detect abnormalities in the finished product. The ultrasonic velocity and dynamic flexural modulus measurements provide useful information on the stiffness characteristics while the attention and loss factor can be related to the anomaly-sensitive damping properties of the material.