Original paper(Vol.49 No.5 pp.510)

Static and Fatigue Failure of FW-CFRP Tubes under Pure Torsion

Hiroshi Kawakami, Toru Fujii

Abstract:A series of strength tests on FW (filament winding) CFRP tubes was carried out to clarify the effects of fiber orientation (FW) angle and test temperature. The experimental results revealed that the static strength was lower than that theoretically predicted by the simple laminate theory based on the strength data for unidirectional coupon specimens. As the test temperature increased, non-1inearity in the stress-strain relationship became remarkable. Although the modulus obtained by using thin specimens is the same as that obtained by using thick specimens, the strength of thick specimens was higher than that of thin specimens. Thicker specimens are preferable to utilize their mechanical properties under torsional moment as much as possible although there exists an optimized dimension for a given angle and compositions of the specimen.
Fatigue tests were also conducted at room temperature and 140 degree C using thicker specimens. In the case of low temperature, modulus decay with respect to loading cycles was divided into three regions: initial region where the modulus decreases steeply soon after the test started, middle region where the modulus is almost constant, final region where the modulus again decreases abruptly followed by the final failure of the specimen. On the other hand, in the case of high temperature, there exists no middle region and the modulus continuously decreases with respect to loading cycle until the Anal region comes.

Key Words:CFRP, Filament winding tubes, Helical angles, Pure torsion, Elevated temperature, Static, Fatigue, Failure, Stress-Strain curves