Preliminary bending fatigue performance evaluation of asymmetric composite gears

In this work, symmetric gears 20°/20° and asymmetric gears 20°/34° were injection molded using unreinforced and 20% glass fiber reinforced polypropylene materials. To evaluate the bending fatigue performance of symmetric and asymmetric gears, a test rig was specially designed and developed and integrated with the servo hydraulic fatigue test facility. Gear teeth were subjected to constant, completely reversed deflection and the load required to maintain constant gear tooth deflection was continuously measured. Addition of glass fibers improved the bending load carrying capacity of both symmetric and asymmetric gears. Test gears exhibited superior performance at higher loading frequencies due to the strain rate sensitiveness of polymer based materials. The effective cantilever length of the gear tooth contributed to the improvement of the load carrying capacity of 34°/20° asymmetric gears over 20°/34° asymmetric gears as well as symmetric gears. The load carrying capacity of 20°/34° asymmetric gears were found to be superior to that of 20°/20° symmetric gears due to the increased gear tooth width at the root region.