Considerable
Different Frequency Dependence of Dynamic
Tensile Modulus between Self-Heating (Joule Heat) and External Heating
for Polymer–Nickel-Coated Carbon Fiber Composites
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Abstract
Dynamic
tensile moduli of polyethylene–nickel-coated carbon
fiber (NiCF) composites with 10 and 4 vol % NiCF contents under electrical
field were measured by a homemade instrument in the frequency range
of 100–0.01 Hz. The drastic descent of the storage modulus
of the composite with 10 vol % was verified in lower frequency range
with elevating surface temperature (<i>T</i><sub>s</sub>) by self-heating (Joule heat). The composite was cut when <i>T</i><sub>s</sub> was beyond 108 °C. On the other hand,
the measurement of the composite with 4 vol % beyond 88 °C was
impossible, since <i>T</i><sub>s</sub> did not elevate because
of the disruption of current networks. Incidentally, the dynamic tensile
moduli by external heating could be measured up to 130 and 115 °C
for 10 and 4 vol %, respectively, but the two composites could be
elongated beyond the above temperatures. Such different properties
were analyzed in terms of crystal dispersions, electrical treeing,
and thermal fluctuation-induced tunneling effect