Specific characteristics of mechanical relaxation in electron-irradiated carbon armored composites

Full text: Temperature dependences of internal friction and electric resistance in the samples of carbon-reinforced components with epoxy binder are experimentally studies in the temperature range of 20-300 deg. C, before and after irradiation by different doses of 2 MeV electrons. The two peaks are observed in temperature dependences of internal friction and electric resistance in the samples not subjected to irradiation: the first one appears at the temperatures f 85-100 deg. C the second one is observed in the temperatures of 230-260 deg. C. Appearance of these maxima, characteristics for multi carbon-armored composites, is associated with glassy structural transitions in the polymer binder inside of composite layer and the intermediate region between layers. A remarkable feature of the dependencies obtained is availability of the direct correlation of the internal friction and electric resistance maxima. In the case of low temperature peaks, this correlation results from the fact that polymer macromolecule segments are scattering centers for the current carriers; at the same time they are the structural elements that dissipate elastic energy of the sample mechanical oscillations. The glassy transition is accompanied by intense oscillations of molecule segments that lead to appearance of the peaks observed. Analysis of the dose dependencies of the peak heights shows that the main processes initiated by radiation in the composite at the doses up to 10 MGy are the feeble cross-linking of polymer macromolecules and intense carbon diffusion that causes disappearance of the electric resistance maximum at the heightened doses. The specificity of high-temperature peaks of internal friction in the samples studied in their stron widening, apparently associated with the superposition of different relaxation processes due to polymer transition from glassy to high-elastic and plastic state. Comparison of temperature dependences of internal friction and electric resistance for the different doses of electron irradiation shows that the same processes proceed in the basic composite layers and in the intermediate space between the layers. However, the processes in the basic layers require higher activation energy. Disorder that accompanies polymer transition to the plastic state causes more considerable increase in electric resistance than that caused by glass transition. Structural transitions in the polymer binder associated with radiation-induced cross-linking are more pronounced for the high-temperature transitions. Thus, radiation-induced structural alterations in the carbon-armored polymer composites lead to the non-standard dose and temperature dependences that can be used in different technological applications