Abstract
The thermal stability of a hybrid composite rod, made of epoxy-anhydride matrix reinforced with both unidirectional carbon and glass fibers, has been evaluated between 180 and 210 °C in different nitrogen/oxygen gas mixtures with several conventional but complementary laboratory techniques such as Fourier transform infrared spectrometry, thermogravimetry, differential calorimetry, optical microscopy, and three-point bending. Thermolysis predominates in the carbon-fiber core, where it induces an efficient chain scission process, leading to a decrease in the glass transition temperature and the formation of small macromolecular fragments, presumably diacids. These very polar fragments remain trapped in the carbon core, where they initiate micro-cavities when their concentration exceeds the solubility threshold. These micro-cavities accumulate in rich-matrix regions, where they coalesce to form apparent large cracks. They are thus responsible for the catastrophic decrease in elastic and fracture properties of the composite rod. In contrast, thermal oxidation affects a too thin superficial layer (typically 60 µm) of the glass-fiber shell to change significantly the global mechanical behavior of the composite rod. Based on these experimental observations, a kinetic model has been proposed to predict the initiation and development of damage in the composite rod. Its validity is successfully checked by comparing its predictions with the experimental results.
Highlights
The request for electricity increases constantly over the world
The aim of the present study is to evaluate the feasibility of a new conductor technology especially designed for the generation overhead lines. It consists of an aluminum conductor supported by a hybrid composite core made of epoxy matrix reinforced with both unidirectional carbon and glass fibers (Figure 1)
The present study focuses on the understanding of the thermal ageing of the composite rod at high temperature in different nitrogen/oxygen gas mixtures
Summary
The request for electricity increases constantly over the world. Faced with environmental and societal pressures opposed to the construction of new overhead power lines, electricity distributors need new technical solutions for increasing the nominal rating of the present lines. Several technical solutions are under study to avoid a catastrophic increase in the sag, but they will be selected by electricity distributors only if the long-term thermal stability of their different constituent materials is well demonstrated. The aim of the present study is to evaluate the feasibility of a new conductor technology especially designed for the generation overhead lines. It consists of an aluminum conductor supported by a hybrid composite core made of epoxy matrix reinforced with both unidirectional carbon and glass fibers (Figure 1). Carbon fibers have been selected for this application because of the very low value of their thermal expansion coefficient in the longitudinal direction [1], allowing to design lines with a sag almost independent of temperature variations. Carbon fibers have been replaced by glass fibers within the composite shell to avoid the galvanic corrosion of the surrounding aluminum conductor [2]
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