Evaluation of GRP rod and rope materials and associated end fittings

Abstract

An extensive and varied test program was carried out on four GRP rod and rope materials to evaluate tensile strengths, moduli of elasticity, flexibility at low temperatures, effects of simulated Aeolian vibration, and stress-rupture properties at moderate elevated temperatures both with and without high humidity. The effects of elevated temperature on long-term storage capabilities were investigated, and diametertemperature relationships were established for avoiding buckling due to storage in a coiled condition.The performances of five commercially available end fittings on these materials were examined in terms of the breaking loads attained in tensile tests. Using finite-element analyses, an improved end fitting was developed. With this end fitting the strength of the fitting-specimen system approaches the true tensile strength of the specimen for two of the GRP materials. An experimental stress analysis of the improved fitting was performed.

Fatigue and weatherability studies of aramid-fiber rope slings

“…Differences between the original free lengths of specimens of different styles reflect differences in the lengths of their end fittings, since all of the specimens were manufactured to have the same approximate length between the clevis pins on their end fittings. 4.…”

“…While the potting compound exhibited the flexibility, under normal environmental conditions, that NBS work has shown to be desirable [4], its degradation under the simulated weathering exposures was excessive.…”

“…These failures occurred at loads corresponding to 78, 89 and 101 percent of the respective breaking loads of the specimens*, and appeared to have been induced by the stress concentrations imposed by the end fittings. NBS work has shown that these stress concentrations can be reduced by using a more flexible potting compound [4]. Of course, it is not immediately obvious that a suitable potting compound can be formulated which is flexible under ordinary environmental conditions yet does not degrade rapidly under severe environments End-fitting parameters other than those related to the potting compound also merit discussion.…”

“…Studies involving fiberglass rope, for example, have shown that dead-end guy grips and potted, shear-type end fittings** both performed better than potted compressiontype end fittings [4]. Dead-end guy grips, unfortunately, exhibited low fatigue strengths when the cable specimens, to which they were attached, were cycled between a slack and a taut condition [5].…”

Non-metallic antenna-support materials

“…If tensile strengths of the materials are to provide a meaningful measure of product improvement, it is necessary to determine the tensile strengths accurately. However, previous work in this laboratory [1,2] has shown that the end fittings for these materials, which are available commercially, are not generally capable of withstanding the tensile forces which are required to fracture these materials in a true tensile mode. Hence, there has been a need, first, to develop end fittings, for use in the laboratory, which can gen-' erate the full tensile strengths of the materials.…”