Mechanism of brittle fracture in nonceramic insulators

Abstract

The results of an investigation concerning a mechanism of brittle fracture in glass reinforced plastic (GRP) rods used in non-ceramic insulators (NCI) are presented. Commercial grade GRP rods and GRP rods from actual insulators were exposed to ultra-pure water (UPW) and acids while being subjected to mechanical stresses. The experimental results revealed that water has the potential of inducing stress corrosion cracking on the fibers and hence brittle fracture in the rods. It is observed that the fracture proceeded faster when the rods were exposed to UPW than when exposed to acids. Furthermore, a brittle fracture in an epoxy cross-arm, which was installed in a region where the formation of acids in the atmosphere can be neglected, is analyzed. Based on these evidences, it is postulated that the failure of in-service NCI in the brittle mode can occur under the influence of water and mechanical stresses, and that the failure is more likely to happen with water than with acids.

Water absorption and water vapor permeation characteristics of HTV silicone rubber material

“…One notes that (4) is identical to (3) in case that water molecules do not interact with the bulk material (i.e. α = 0 and β = 1).…”

“…Absorbed water can initiate degradation mechanisms like partial discharges [1], hydrolysis [1,3], glass fiber corrosion or ion exchange [2,3] which mostly coincide with a change of the dielectric, electric and mechanical properties of the core material. Furthermore, absorbed water is supposed to play an important role for the development of brittle fracture [3,4]. Although the core of composite insulators is protected by the sheath material, i.e.…”

Análise de falha em isolador polimérico

“…O mecanismo que possibilita o processo de substituição dos íons metálicos por íons de hidrogênio pode ter origem de diversas fontes como: chuva ácida, catalisador da resina em contato com a água dando origem a ácido carboxílico [4], penetração de ácido nítrico pela formação de dióxido de nitrogênio pelo efeito corona (equação 1) e posterior reação com a água [1, 6,7] e até mesmo mecanismos envolvendo apenas a água em reações de hidratação, hidrolise e troca iônica [8,9].…”

“…Estes resultados, somados à conhecida susceptibilidade à falha [9] do material empregado no núcleo composto (Eglass/epóxi), permitiram identificar a causa da fratura do isolador polimérico Figura 8: (a) Taxa de iniciação da trinca (estágio I) para compostos E-glass/polímero. (b) Taxa de extensão de trincas subcríticas (estágio II) para compostos E-glass/polímero [9].…”

Mechanical and electrical issues concerning the use of composite materials for the supporting core in transmission line conductors

“…This test was devised to simulate brittle fractures in fiberglass cores of composite conductors [4]. The conductor core was subjected to high purity water (Fig.…”