Investigation of the experimental fatigue performance of the asymmetric spur gears under bending stress

In this thesis study, single tooth bending fatigue performance analysis studies were performed under the bending stresses of the symmetric and asymmetric gears. There are theoretical studies and finite element method analysis studies about asymmetric gears in literature but there is not enough experimental study to confirm the theoretical studies on the effect of the reduction in tooth root stress on fatigue performance. In this study, single tooth bending fatigue tests of symmetric and asymmetric spur gears were done and fatigue performances of gears were analyzed. Critical stress analyzes in the root region of tooth were calculated by referring to the approaches used in the literature. In order to carry out the experimental studies, a unique testing set design was carried out and the gears which were made of AISI 4140 material then were tested in this test apparatus. Gears to be tested specified as the symmetrical spur gears with 20°/20° pressure angle, asymmetrical spur gears with 20°/22° pressure angle and asymmetrical spur gears with 20°/25° pressure angle. Only the tooth of the symmetrical and asymmetric gears to be tested were left on the gear and the other tooth are removed during the design process and the gears were manufactured in this way. In the experiments, specified loads were applied to the tooth flanks from the highest point of single tooth contact and fatigue tests were done under variable stresses. Single tooth bending fatigue test results were presented as graphs based on both torque and root stress. According to the test results, a significant increase in fatigue strength of asymmetric tooth was obtained. According to the tests carried out at the same torque, a fatigue performance increase of 90 % was obtained statistically in asymmetric gears which has 20°/22° pressure angle compared with symmetric gears which has pressure angle 20°/20°. Tooth flank fracture damages have been observed in the asymmetric spur gear tooth which has 20°/25° pressure angle at the relatively high number of cycles. It has been determined that tooth flank fracture damage has affected the fatigue performance negatively. As a result of experimental studies, the effects of small changes in pressure angles on the gear tooth under bending stresses and the effects of fatigue on the tooth damage shape were determined. Single tooth bending fatigue test results were statistically evaluated and enhancement in the asymmetric tooth fatigue strength was detected.