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An improved version of a brittle fracture model based on the formation of nitric acid in service through corona discharges, ozone, and moisture, is presented and used to explain different modes of brittle fracture. Throughout the work, the insulators are referred to as nonceramic insulators (NCIs). The information given is expected to help the insulator manufacturers and users design, manufacture,
The applicability of using flat composite plates and hollow core composite cylinders for moisture absorption testing of unidirectional glass/polymer composites used in high voltage composite (non-ceramic) insulators was examined. Two main issues were addressed in this work. First, the effect of specimen geometry (cylinders vs. plates) on moisture absorption by the composites was investigated both
The chemical environment responsible for the brittle fracture failure of composite (non-ceramic) insulators is determined. Also previously reported observations by the authors are verified. Five non-ceramic composite suspension insulators and one composite guide were subjected to FTIR analysis. Out of the six field failed units, five insulators showed significant levels of nitrate on their brittle
It was postulated in [1], based on experimental evidence, that brittle fracture failures of composite (non-ceramic) HV insulators could be caused by water and mechanical stresses. It was also claimed therein that the brittle fracture process was more likely to happen with water than acids. This postulation could be of major importance as its ramifications might affect the entire composite insulato
This paper describes water diffusion into and electrical testing of unidirectional glass reinforced polymer (GRP) composite rods used as load bearing components in high voltage composite (non-ceramic) insulators. The tests were performed following ANSI standard C29.11 Section 7.4.2 that can be used to evaluate electrical properties of composites. The unidirectional composite rod materials based on
Moisture absorption tests were performed on unidirectional glass/polymer composite materials used in high voltage composite (non-ceramic) insulators. The composites were based on E-glass, high seed count ECR-glass and low seed count ECR-glass fibers with modified polyester, epoxy and vinyl ester resins. The composites were exposed to a moist environment with a relative humidity of 80% at 50 °C, an
Unidirectional and woven graphite fiber (T650-35)/polyimide (PMR-15) composites with embedded aluminum inclusions were investigated for their aging behavior either in nitrogen or air at 315 °C for up to 1170 h. Residual strains and stresses in the inclusions were determined as a function of aging by performing X-ray diffraction (XRD) measurements. Subsequently, residual strains and stresses in the
Existing brittle fracture models have been reviewed and their applicability to explain the in-service brittle fracture failure of composite (non-ceramic) insulators is evaluated. It is shown that the only brittle fracture model that can explain all aspects of the brittle fracture process is a model based on the formation of nitric acid solutions in-service. The chemical cause of brittle fracture i
The effect of large bending loads on strains and stresses inside aluminum particles embedded in unidirectional and woven eight harness satin (8HS) graphite/PMR-15 composites has been examined. The stresses and strains in the particles were determined by performing X-ray diffraction (XRD) measurements. It has been shown in this work that when the composites are subjected to large four-point bending
Iosipescu shear tests were performed at room temperature and at 316-°C (600-°F) on woven composites with either M40J or M60J graphite fibers and PMR-II-50 polyimide resin matrix. The composites were tested as supplied and after thermo-cycling, with the thermo-cycled composites being tested under dry and wet conditions. Acoustic emission (AE) was monitored during the room and high temperature Iosip
This work evaluates the effects of static and cyclic loading conditions on the stress corrosion process in unidirectional glass/modified polyester composite in the presence of a nitric acid solution. The composites were investigated under static, cyclic, and static with overload conditions using a rectangular specimen with centrally positioned grooves. The stress corrosion process was monitored us
Stress corrosion experiments were performed on unidirectional ECR-glass/polymer composites with the modified polyester, epoxy and vinyl ester resins for the use in high voltage composite insulator applications. Two types of ECR-glass fibers were investigated with low and high counts of gaseous inclusions (seeds) within the glass. The stress corrosion tests were performed in nitric acid under four
Failure and stiffness properties of a woven 8 harness satin (8HS) graphite/PMR-15 composite have been investigated at room temperature and at 315°C by performing the ±45° tensile and Iosipescu tests. Acoustic emission has been monitored during testing. The critical loads for the initiation of damage in the composite have been determined. In particular, the specimen width effect has been investigat
The purpose of this research is to examine the effect of sandblasting on the initiation of stress corrosion cracking (SCC) in unidirectional E-glass/polymer composite materials with modified polyester, epoxy and vinyl ester resins. The composites with different amounts of surface damage due to sandblasting have been subjected to mechanical bending loads in the presence of nitric acid (pH=1.2). It
In this research the mechanical behavior of composite suspension insulators with crimped end-fittings manufactured by NGK has been evaluated. Two issues have been addressed in this study. Insulators crimped with the standard, high, reversed and constant high stress conditions have been analyzed for their crimping deformations, and the two and three dimensional compression profiles for the four dif
The purpose of this research has been to design an advanced numerical model that can be used to evaluate the mechanical behavior of composite insulators with crimped end-fittings subjected to axial tensile loads. Two issues have been addressed in this study. First, examples of insulator failures due to improper crimping have been shown and discussed. Second, comprehensive nonlinear two- and three-
The mechanical response of a woven eight-harness satin graphite/polyimide composite has been investigated by performing ± 45° tensile and Iosipescu shear tests at room temperature. Nonlinear finite element simulations of the tests have been conducted to determine internal stress distributions in the ±45° tensile and Iosipescu fabric specimens as a function of load. In the experimental part of this
This work is a continuation of the research recently presented in [1] and [2] on the determination of residual thermal stresses in graphite/polyimide composites with and without externally applied bending loads. In the previous work [1, 2] a combined experimental and numerical methodology for the determination of the residual stresses in unidirectional graphite/PMR-15 composites based on X-ray dif
The purpose of this research is to evaluate the mechanical response of eight harness satin woven graphite/polyimide composite specimens using the ±45 ° test. A series of tensile tests have been conducted at room temperature to evaluate the effect of specimen width as well as monotonie, progressive, and multiple loadings on the response of the composite specimens. Acoustic emission techniques have
A testing methodology for the determination of residual thermal stresses in the polymer-matrix of unidirectional polymer-matrix composites has been proposed in Ref. [1] [Benedikt B, Kumosa M, Predecki PK, Kumosa L, Castelli MG, Sutter JK. An analysis of residual thermal stresses in a unidirectional graphite/PMR-15 composite based on the X-ray diffraction measurements. Composites Science and Techno
