Measuring How Overlap Affects the Strength of Composite Tubes in Bending-Torsion - Springer
A novel design for composite tubes possessing bend-twist coupling has been presented. The design requires a series of layers overlapping at two locations around the tube. This was suspected to create a weak point in the strength of the composite structure. To test this, multiple tubes possessing bend-twist coupling were constructed out of carbon fiber/epoxy prepreg. The tubes were then cut and prepared for torsional loading. A combined axial-torsion loading machine was used to steadily rotate the specimens while measuring torque and adjusting the cross-head to keep the axial load zero. DIC was used to measure the strains on the surface of the tubes. The results show the tubes fracturing with a lengthwise crack during an average torque of 44.2 lb-in (5.00 N-m). The location of the cracks and the stress at failure are consistent with failure occurring where the inner layers overlap. Micrographs of cross-sections are needed to confirm this. Further testing is also needed for the case of tension-torsion and compression-torsion that occurs during the bending-torsion the shafts would normally be subject to.
