Bending fatigue testing of gear teeth under random loading

Abstract

The gears in a gear box fitted in an armoured tracked vehicle for the purpose of power transmission and positioning of rotating heavy mass to the desired angle with high accuracy are subjected to fluctuating loads that are random in nature. One of the important modes of failure in cyclic loading conditions including random loads is fatigue failure. It is thus important from the design point of view to estimate the life of the gears under these conditions. The fatigue life of components subjected to sinusoidal loading can be estimated by using cumulative damage theories. Their extension to random load fatigue, though straightforward, may not be very accurate owing to inherent scatter exhibited by the fatigue phenomenon. It is therefore necessary experimentally to determine the fatigue life of randomly loaded components and establish the validity of the theoretical model. An electrohydraulic test rig has been designed and fabricated that is capable of generating different types of load pattern by adopting a suitable electronic circuit in the test rig. This paper presents the details of the test rig for random load generation, the test fixture for mounting the gear and the technique for testing the gear for bending fatigue life under random loading. A gear has been tested in the test rig under random loading conditions and also under constant amplitude conditions for bending fatigue, and the life of the gear has been obtained experimentally. Fatigue lives of the gear have also been estimated theoretically by employing linear cumulative damage theory using the peak count method.