THERMAL-DIFFUSIVITY MEASUREMENT OF SINGLE FIBERS BY AN AC CALORIMETRIC METHOD

An ac calorimetric method is applied to the direct measurement of ther mal diffusivity of single fibers. Theoretical analysis is presented, t aking into account the two-dimensional ac thermal wave for cylindrical systems and the effect of time delay at the temperature detecting sys tem. Experimental tests are performed using nickel and stainless steel wires about 20 mu m in diameter. The thermal conductivity of fibers a bout 10 mu m in diameter of the advanced materials, polyacrylonitrile- based carbon, TORAYCA, and aramide, Kevlar, is determined. The relatio nship between the thermal conductivity and electric conductivity and t he crystalline size of these fibers is discussed. For composite materi als made of carbon fibers, the observed thermal conductivity agrees wi th the thermal conductivity estimated using the values determined by t he present method. (C) 1996 American Institute of Physics.