K. Balasubramaniam et al., ULTRASONIC AND VIBRATION METHODS FOR THE CHARACTERIZATION OF PULTRUDED COMPOSITES, Composites engineering, 5(12), 1995, pp. 1433-1451
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.