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.