Bending fatigue testing of gear teeth under random loading

The gears in a gear box fitted in an armoured tracked vehicle for the purpo se of power transmission and positioning of rotating heavy mass to the desi red angle with high accuracy are subjected to fluctuating loads that are ra ndom in nature. One of the important modes of failure in cyclic loading con ditions including random loads is fatigue failure. It is thus important fro m the design point of view to estimate the life of the gears under these co nditions. The fatigue life of components subjected to sinusoidal loading ca n be estimated by using cumulative damage theories. Their extension to rand om load fatigue, though straightforward, may not be very accurate owing to inherent scatter exhibited by the fatigue phenomenon. It is therefore neces sary experimentally to determine the fatigue life of randomly loaded compon ents and establish the validity of the theoretical model. An electrohydraul ic test rig has been designed and fabricated that is capable of generating different types of load pattern by adopting a suitable electronic circuit i n 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 f or testing the gear for bending fatigue life under random loading. A gear h as been tested in the test rig under random loading conditions and also und er constant amplitude conditions for bending fatigue, and the life of the g ear has been obtained experimentally. Fatigue lives of the gear have also b een estimated theoretically by employing linear cumulative damage theory us ing the peak count method.