Experimental and numerical investigation of the bending fatigue performance of symmetric and asymmetric polymer gears

Abstract

In this work, the bending fatigue strengths of injection-molded symmetric and asymmetric nylon 66 gears were evaluated experimentally, and the results were substantiated using numerical studies. The symmetric (20°/20°) and asymmetric (34°/20° and 20°/34°) configurations were subjected to bending fatigue tests under a load controlled mode. The bending stresses of the symmetric and asymmetric gears were predicted by quasi-static simulations using a commercial finite element analysis software. The form factor ([Formula: see text]) and the stress correction factor ([Formula: see text]) were computed using an adapted ISO method. The 34°/20° configuration exhibited the lowest bending stress and highest bending fatigue life among the tested configurations. The form factor exerted a decisive influence on the magnitude of the bending stress compared to the stress correction factor. For the considered loading conditions, deflection-induced load sharing occurred in the 20°/20° and 20°/34° configurations but was absent in the 34°/20° configuration. Failure analysis indicated that a high stress concentration caused multiple cracks in the fillets of asymmetric gears.

Effect of metal and polymer mating gears on the bending fatigue performance of asymmetric polymer gears

“…The rationale behind adopting these pressure angles is described in detail elsewhere. 17 The gear configurations are described by referring to the drive side pressure angle and coast side pressure angle (left to right). For example, the gear configuration 34 /20 indicates that the pressure angles on the drive and coast side are 34 and 20 , respectively.…”

“…A concise account of the test rig is provided in this section, as the test rig components are comprehensively described elsewhere. 17,18 The system was powered by a servo motor (BALDOR, BDM -100C -3250), which was regulated by a servo drive (Motiflex). The loading and control systems are connected to the human machine interface, which allowed the user to set the torque and cycling frequency.…”

“…In asymmetric polymer gears, deflection-induced load sharing improves the bending fatigue life when the drive side pressure angle is lower than the coast side. 17 Thus, it is essential for polymer gears to consider the deflection-induced increase in load sharing during the calculation of maximum bending stress.…”

“…30 The FEM is appropriate for this study, as it can consider the effect of gear materials on load sharing. In addition, FEM is useful for precisely locating the HPSTC in polymer gear pairs, 17 and predicting the bending stress with better accuracy compared to analytical methods. 31 Moreover, the lack of standard bending stress formulation for asymmetric gears necessitates the use of FEM to compare the bending stresses of symmetric and asymmetric configurations directly.…”

“…Asymmetric polymer gears exhibit higher bending fatigue strength compared to symmetric polymer gears. 17 Therefore, the objective of this work was to investigate the influence of mating gear material on the bending fatigue strength of asymmetric polymer gears. The bending fatigue life of polymer-polymer pairs of PA 66 asymmetric gears was determined experimentally using a test rig developed in-house.…”