Effect of excessive bending on residual tensile strength of hybrid composite rods

Excessive bending has been identified as a concern for the hybrid composite core that is currently being used as the structural member for the Aluminum Conductor Composite Core Trapezoidal Wire (ACCC/TW™) transmission line. In this work the flexure strength of the ACCC core was measured in a series of four point bend tests while monitoring acoustic emissions. To quantify the stress state within the rods and to evaluate its flexure strength, an analytic solution for the bending stress was derived and numerically verified using the finite element method. In the second part of the study several specimens that had been subjected to excessive bending were subsequently tested for their residual tensile strength. It was found that wrapping the ACCC core around a 1 m mandrel, which is a common loading condition in practice, will not generate significant structural damage in the composite core. It was determined that the diameter of the mandrel that would cause failure of the composite core is 467 mm. From this work it was found that excessive bending, up to 90% of the flexural strength of the ACCC core, had no detrimental effect on the residual tensile strength of the hybrid composite. It was observed that the majority of the micro-structural damage that was accrued during the excessive bending of the cores presented itself in the form of matrix damage without any significant fiber kinking.