Papers by Author: Akihiro Wada

Abstract: Ultrasonic testing is applied to monitor the curing process of GFRP laminates used for rehabilitation of aged sewerage pipes. Instead of conventional method in which through-thickness ultrasonic wave is used, wheel type probes are adopted to transmit and receive in-plane Lamb wave. It is well known that wave velocity depends on the stiffness of the propagating medium, so that it could be used as cure index of resin. However, because of the relatively low signal-to-noise ratio of detected signals, determination of wave arrival time with zero-crossing detecting method leads to nonnegligible error. In order to improve the precision of measurement, AIC (Akaike Information Criterion) is introduced and the arrival time of Lamb wave is monitored in curing process. Two types of waveform, pulse and burst waves are examined to confirm the effect of waveform on the accuracy of measurement. It is found that the arrival time of Lamb wave decreases with the increase of cure degree, and approach asymptotically to constant value during post cure process. Also, AIC analysis with pulse wave is found to be more reliable to monitor the early stage of resin cure.

Abstract: In this study, partially debonded spherical particles in a particulate composite are analyzed by three-dimensional finite element method to investigate their load carrying capacities, and the way to replace a debonded particle with an equivalent inclusion is examined. The variation in Young’s modulus and Poisson’s ratio of a composite with the debonded angle was evaluated for different particle arrangements and particle volume fractions, which in turn compared with the results derived from the equivalent inclusion method. Consequently, it was found that by replacing a debonded particle with an equivalent orthotropic one, the macroscopic behavior of the damaged composite could be reproduced so long as the interaction between neighboring particles is negligible.