Abstract
1. The effect of the test temperature up to 2000°C in vacuum, on the mechanical properties of carbon fiber under different conditions of loading has been studied and their nonmonotonic character established. 2. It was shown that for a short-term test up to 1500–1700°C, the reversible changes in Young's modulus, caused by corresponding changes in the degree of orientation and density, can be explained by anisotropic thermal expansion of the fiber which is characteristic for solids of hexagonal structure. Beginning at higher test temperatures an irreversible plastic deformation of the fiber brings about a sharp decrease in its thermoelastic properties and strength. 3. The high temperature stress relaxation of the carbon fiber, which obeys the Maxwell equation for viscoelastic solids, was studied. The region of the relaxation spectrum which was disclosed is closely similar in the range of relaxation times to the λ-process in polymers associated with mobility of the supramolecular structure.
Published Version
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