Graphite/Epoxy [ ± 45]s Tubes. Their Static Axial and Shear Properties and Their Fatigue Behavior under Completely Reversed Load Controlled Loading

Abstract

Fixtures are described which are appropriate for static and fatigue testing of thin-walled composite tubes of 25.4 mm outer diameter and for use in an MTS servohydraulic tension-torsion system. The room temperature static ax ial and shear properties of tubes consisting of four layers of [ ± 45]s graphite epoxy were determined using axial and axial/shear clip-on extensometers where appropriate. Elastic moduli are equal in tension/compression (tor sion/reversed torsion). Ultimate tensile and compressive strengths are nearly equal. The torsional strength depends strongly on the direction of twist. Beyond the relatively small elastic range time-dependent deformation is observed which is also felt as a frequency effect on fatigue life under com pletely reversed axial load controlled loading. The room temperature axial fatigue strength amplitude at 105 cycles is approximately thirty percent of the ultimate strength.