ULTRASONIC AND VIBRATION METHODS FOR THE CHARACTERIZATION OF PULTRUDED COMPOSITES

Characterization of unidirectional fiber reinforced glass/epoxy pultru ded composites using ultrasonics (high frequency, 1-5 MHz) and the imp ulse-frequency response vibration (intermediate frequency, 50-100 Hz) technique, is demonstrated here. This paper compares the response of b oth of these non-destructive test techniques to the changes in the pul trusion process variables and to the induced contaminants introduced d uring manufacturing. The ultrasonic methods use multi-mode techniques of wave velocity and attenuation measurements to measure the viscoelas tic constants of the pultruded composite while the vibration technique provides the dynamic flexural modulus and loss factor (damping) measu rements. Quasi-destructive assays were also performed using a low freq uency (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-destruct ive measurements. Mathematical models to describe the influence of por osity and debonding agents on the material properties were derived bas ed on statistical regression analysis procedures. Results indicate tha t the peak damping value of the tans curve obtained from the DMA is a sensitive parameter to detect abnormalities in the finished product. T he ultrasonic velocity and dynamic flexural modulus measurements provi de useful information on the stiffness characteristics while the atten uation and loss factor can be related to the anomaly-sensitive damping properties of the material.