Abstract
Polypropylene (PP) material is preferred for engineering applications for its low density, coefficient of friction and cost. Fiber reinforcement of PP enhances its basic fatigue and tribological properties. However, directional shrinkage limits its usage in precision applications like gears. Carbon nanotubes (CNT) offer higher strength and lower shrinkage characteristics. The present study evaluates the influence of CNT reinforcement on the bending fatigue performance and shrinkage behavior of polypropylene gears. Unreinforced and 1 wt. % CNT reinforced PP gears (CNT-PP) were injection-molded and tested using inhouse developed servo motor driven bending fatigue gear test rig. Metrological inspections were conducted to quantify the accuracy of the micro-geometry of test gears. Pulsating tensile (R=0) load was applied at 10 Hz frequency in load controlled mode. The net surface temperature of test gear was measured using an Infra-red camera. The profile accuracy of CNT-PP gears was found to be superior to PP gears. Enhanced modulus and ultimate strength increased the bending strength of CNT-PP gears. Hysteretic heating diminished in CNT-PP gears due to the restriction of polymer chain mobility. Characteristic bending fatigue failure mode of straight root crack was observed. Failure morphology confirmed the ductile and brittle nature of PP and CNT-PP gears respectively.