The Effects of Loading Rate on Shear Mechanical Behavior of Carbon Nano Fiber/Epoxy Nanocomposites

Polymeric nanocomposites show a remarkable enhancement in mechanical, electrical and thermal properties in comparison with neat polymers. The effects of nano reinforcements on tensile and flexural mechanical properties are widely studied by many researches. Whilst the shear mechanical properties of polymers filled with nano particles needs more studies. The polymers and reinforced polymers with nano particles show significant nonlinear and strain rate dependent mechanical behaviors. In this research, first the influence of adding carbon nano fibers (CNFs) to an epoxy matrix has been investigated at static loading conditions. The effect of addition of various CNF contents, 0.15, 0.25 and 0.4 wt.% on the tensile and shear mechanical properties of epoxy is studied. Then, an optimized weight fraction (0.25 wt.%) which leads to the most enhancements in ultimate shear strength was determined. The shear mechanical behavior is studied by conducting pure torsional experiments. Moreover, the effects of loading rate on shear mechanical properties of neat epoxy and epoxy filled with the optimized weight fraction were studied. It is found that the loading rate can significantly affect the shear mechanical properties of nanocomposites. The ultimate torsional strength increased with increasing the applied strain rate while the ultimate tensile strength shows increasing at low strain rates and decreasing at relative high strain rates.