Influence of hygrothermal environment on thermal and mechanical properties of carbon fiber/fiberglass hybrid composites

Acoustic metamaterials with negative dynamic mass density have been shown to demonstrate a five-fold increase in transmission loss (TL) over mass law predictions for a narrowband (100 Hz) at low frequencies (100–1000 Hz). The present work focuses on the scale-up of this effect by examining the behavior of multiple elements arranged in arrays. Single membranes were stretched over rigid frame supports and masses were attached to the center of each divided cell. The TL behavior was measured for multiple configurations with different magnitudes of mass distributed across each of the cell membranes in the array resulting in a multipeak TL profile. To better understand scale-up issues, the effect of the frame structure compliance was evaluated, and more compliant frames resulted in a reduction in the TL peak frequency bandwidth. In addition, displacement measurements of frames and membranes were performed using a laser vibrometer. Finally, the measured TL of the multi-celled structure was compared with the TL behavior predicted by finite element analysis to understand the role of nonuniform mass distribution and frame compliance.

Membrane-type metamaterials: Transmission loss of multi-celled arrays

The task of monitoring asset status and optimizing asset utilization for the T&D industry, given millions of assets and hundreds of thousands of miles of power lines distributed geographically over millions of square miles, seems particularly challenging if not impossible. Given the traditionally high cost of sensing and communications, the grid has minimal 'smarts' with much of the intelligence located at major substations. Dramatic reductions in sensor, computing and communications costs, coupled with significant performance enhancements has raised the possibility of realizing widely and massively distributed sensor networks (SNs) to monitor utility asset status. Under NEETRAC funding, a survey was conducted to review existing sensor technologies and products, and to estimate the possibility of extending these to realize distributed SNs. Possible applications for such SNs were also explored, as was the issue of cost point at which such networks would become commercially viable. This paper provides an overview of the highlights from the detailed survey that was conducted, and identifies 'gaps' in currently available sensor technologies, both from a performance and cost point.

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A Survey on Technologies for Implementing Sensor Networks for Power Delivery Systems

Unidirectional hybrid composite rods were conditioned in humid air to investigate the sorption kinetics and the effects of moisture on mechanical and physical properties. Sorption curves were obtained for both hybrid and non-hybrid composite rods to determine characteristic parameters, including the diffusion coefficient (D) and the maximum moisture uptake (M∞). The moisture uptake for the hybrid composites generally exhibited Fickian behavior (no hybridization effects), behaving much like non-hybrid composites. A two-dimensional diffusion model was employed to calculate moisture diffusivities in the longitudinal direction. Interfaces and thermally-induced residual stresses affected the moisture diffusion. In addition, the effect of hygrothermal aging on glass transition temperature (Tg), short beam shear strength (SBS), and tensile strength was determined for hygrothermal exposure at 60 °C and 85% relative humidity (RH). Property retention and reversibility of property degradation were also measured. Microscopic inspection revealed no evidence of damage.

Moisture absorption of unidirectional hybrid composites

Thermal oxidation of a unidirectional carbon-fiber/glass-fiber hybrid composite was investigated to determine oxidation kinetics and degradation mechanisms The epoxy composite rods were comprised of a carbon-fiber core and a glass-fiber shell A reaction–diffusion model was developed for each of the two hybrid sections to obtain the oxygen-concentration profile and the thickness of the oxidized layer (TOL) within the composite rods The TOL was measured experimentally for samples exposed at 180 °C and 200 °C for up to 8736 h, and measured values were similar to the modeling predictions The glass-fiber shell functioned as a protective layer, limiting the oxidation of carbon-fiber core A relationship was derived relating TOL to tensile strength of the hybrid composite The tensile strength remained essentially unchanged by thermal oxidation after 52 weeks of exposure Inspection of thermally aged capped rods showed no cracking after long-term exposures

Thermal aging of fiberglass/carbon-fiber hybrid composites

A new type of overhead conductor with a polymer composite core is evaluated in terms of the mechanical properties and operating characteristics. The conductor is composed of trapezoidal O'-tempered aluminum wires helically wound around a hybrid glass/carbon composite core produced by pultrusion. The conductor is intended for electrical power transmission, and is designated ACCC/TW, for aluminum conductor composite core/trapezoidal wire. Measurements of core properties and conductor sag at high temperatures were compared to conventional ACSR (aluminum conductor, steel-reinforced) of the same diameter. The tensile strength of the ACCC/TW was /spl sim/1.5 times greater than conventional ACSR of the same outer diameter. The CTE of the composite core was approximately 4 times lower than the steel core in ACSR. The ACCC/TW conductor exhibited a six-fold reduction in high-temperature sag compared with conventional ACSR (Drake) when operated at the same current. The ACCC/TW conductor also exhibited greater ampacity than ACSR conductor at all operating temperatures.

E.J. Bosze

Papers

A composite core conductor for low sag at high temperatures