Effect of temperature on fatigue strength of carbon nanotube/epoxy composites

The monotonic and fatigue tensile strengths of acid-treated carbon nanotube/epoxy composites with various carbon nanotube contents were experimentally studied at -25?, 0?, 25?, and 40?. Experimental results reveal that the monotonic and fatigue strengths of the nanocomposites decreased as the temperature increased. The temperature-dependent S-N curves of the nanocomposites with various carbon nanotube contents were experimentally determined. The fatigue strength exponents in the power laws that described the S-N curves were independent of the carbon nanotube content and the testing temperature, and the reciprocals of the fatigue strength coefficients were related to the testing temperature according to the Arrhenius model. Nanocomposites with higher monotonic strength had a lower pre-exponential factor and activation energy. The epoxy-based nanocomposites presented obvious cyclic softening and dynamic creep characteristics in the fatigue tests conducted at 40?. However, adding carbon nanotubes in the epoxy can diminish these phenomena significantly. The fracture surfaces demonstrated that the length of the pull-out carbon nanotubes increased with the testing temperature, indicating that a high temperature weakened the adhesion strength between the carbon nanotube surfaces and the polymer matrix.