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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
The purpose of this research is to determine residual thermal stresses in a unidirectional graphite-fiberT/PMR-15 polyimide composite by using crystalline inclusions. X-ray diffraction (XRD) measurements have been made to determine residual stresses in embedded aluminum and silver inclusions placed between the first and second plies of six-ply unidirectional graphite/PMR-15 composite specimens. In
The purpose of this work is to establish the critical surface conditions leading to the initiation of stress-corrosion cracks on the assupplied surfaces of three unidirectional E-glass/polymer composites with modified polyester, epoxy and vinyl ester resins subjected to a nitric acid solution without mechanical loads. The composite materials considered in this study are commonly used in composite
The purpose of this research is to determine the resistance to stress-corrosion cracking (SCC) of three unidirectional (pultruded) E-glass/polymer composites based on modified polyester, epoxy and vinyl ester resins. The composites have been subjected to a nitric acid solution of pH 1.2 in a newly designed four-point bend fixture. The stress-corrosion process was initiated on the as-supplied surfa
BackgroundScintigraphy with technetium-99m-labelled dimercaptosuccinic acid ([99mTc]Tc-DMSA) is widely used for renal cortical imaging. Uptake of [99mTc]Tc-DMSA has been shown to correlate with glomerular filtration rate (GFR). Prostate-specific membrane antigen (PSMA) radiopharmaceuticals used for positron emission tomography (PET) show high renal uptake and are being investigated for renal imagi
Several studies have shown decreased cerebral blood flow (CBF) in Alzheimer's disease (AD). However, the role of hypoperfusion in the disease pathogenesis remains unclear. Combining arterial spin labeling MRI, PET, and CSF biomarkers, we investigated the associations between gray matter (GM)-CBF and the key mechanisms in AD including amyloid-β (Aβ) and tau pathology, synaptic and axonal degenerati
BACKGROUND AND PURPOSE: Myeloablative Total Body Irradiation (TBI) is an important modality in conditioning for allogeneic hematopoietic stem cell transplantation (HSCT), especially in children with high-risk acute lymphoblastic leukemia (ALL). TBI practices are heterogeneous and institution-specific. Since TBI is associated with multiple late adverse effects, recommendations may help to standardi
