Mechanical aspects of crimped glass reinforced plastic (GRP) rods

Nonceramic insulators (NCIs) with crimped metal end fittings were studied to understand the nature of the interfacial stresses at the rod-metal fitting interface. The study involved both experimental and computational aspects. Monotonic tension tests were performed on rod assemblies (bare rod with end fittings crimped) as well as full-scale composite insulators. Different rod formulations (E-glass, E-CR glass fibers, resins made of epoxy, polyester, and vinyl ester) were evaluated. The experimental results were used to calculate the stresses at the interface. It is shown that the onset of debonding/detachment of the rod from the end fitting can occur at load magnitude close to the proof-test load. Radial cracks in the rod can also develop in the crimped portion of the rod. A theoretical model for pullout was developed to validate the experimental observations. A companion paper identified the role played by imperfections in the GRP rod matrix and electrical stress on brittle fracture. It is concluded that imperfections caused by crimping, together with mechanical stress concentrations are a greater threat to brittle fracture than posed by imperfections in the GRP rod matrix and electric stress concentrations near the line end fitting, only if the housing does not protect the rod from the elements. This highlights the importance of good quality control in manufacturing, and complete protection of the rod by the polymer housing.