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.

Validating the Classical Failure Criteria for Applicability to the Notched Woven-Roving Composite Materials

“…P u p p o a n d E v e n s e n [ 25] ( ] is the global of 45 ∘ tenstion test (1) Main frame (2) Main shaft (3) Self-aligning bearing (4) Bending loading arm (5) Bending transducer (7) Torque transducer (8) Intermediate shaft (9) Deep groove ball bearing (10) Guide shaft (11) Twisting moment arm (6) Specimen (13) Twisting moment coupling (12) Bending connecting rod (14) Coupling shaft (15) Driven pully (16) Twisting moment loading arm (17) Bending moment loading arm (19) Motor table (20) V belt (21) Bending coupling plain specimen, the observed failure mode was a matrix-cracking mode normal to the loading axis and along the transverse fiber direction as shown in Figure 10. This may be attributed to brittleness of the matrix compared to the filling fiber fabrics.…”

“…In the present study, the principal fatigue stress components ( 1 , 2 , and 6 ) and the corresponding fatigue strengths ( 1 , 2 , and 6 ) are used in the failure criteria [19]. The values of the fatigue strengths 1 , 2 , and 6 are calculated from tests conducted on five-layer plates fabricated from the same constituent materials of the studied materials.…”

Design of Modified Tabs for Testing of Symmetric Composite Thin Walled Tubes Under Pure Torsional and Tensile Loadings

“…However, no attention was devoted to the tab and grip regions stress and strain distributions in the specimens during the tests. Krempl and Niu [12] studied designing biaxial testing fixture for testing of composite tubes subjected to combined axial and torsional load under completely reversed loading. They used wedged tabs to match with the fixtures designed to apply the desired loading.…”