Improved potted socket terminations for high-modulus synthetic-fibre rope

Summary

This paper describes research performed for the U.S. Navy to reduce the size and increase· the efficiency of terminations on high-modulus synthetic fibre ropes. The strength efficiency of resin-potted sockets decreases with increased rope size. The principal cause is deformation of the resin potting material, which permits the centre rope elements to contract relative to the outer rope elements near the cavity wall, thus increasing tension in those outer elements. ln aramid fibre ropes this action can also produce axial compression fatigue in the inner elements and thus cause failure after only a few thousand load cycles. This resin deformation can be decreased by dividing the potting cavity into smaller segments. Increasing the slope of the socket cavity can reduce radial pressure and improve holding efficiency. Placing a shaped body in the cavity can alter stress distributions to further increase termination efficiency. Tests with these improvements, conducted on 39 mm (1 Y:z in.) dia. six-strand aramid rope, showed that break strength increased by more than 50% and statistical variation of strength decreased from 19% to 4%. ln a cyclic tension test, after 200,000 cycles to 45% of that improved break strength, there was no strength reduction.