Development of Accelerated Life Test Schedule for Rig Testing of Live Axles Based on Road Load Data and Its Correlation with Field

Drive components of live axle undergoes different loading conditions during field usage depending upon terrain conditions, vehicle loading and traffic conditions etc. During vehicle running, drive components of axle experiences variable torque levels, which results in the fatigue damage of the components. Testing of these drive components of axle on test rig for endurance life is an imperative part of axle development, owing to limitations of vehicle testing because of time and cost involved. Similarly, correlating field failures with rig testing is equally critical. In such situation, if a test cycle is derived correlating the field usage, rig testing can be effectively used for accelerated life testing and reliability prediction of these components. An approach is presented in the paper wherein test cycle is derived based on the data collected on vehicle in the field under service road and loading conditions. The data is collected in terms of propeller shaft torque or wheel torque, engine and transmission output speeds, transmission and axle oil temperatures etc. Above data is collected for few hundred kilometers in required terrains as per the road mix proposed for vehicle. This data is then processed and analyzed to determine the number of cycles of different torque levels equivalent to kilometers covered by vehicle during data collection activity. The analyzed data is then extrapolated for the stated life of vehicle or axle using acceleration factors based on S-N curves. A block test cycle is then prepared, comprised of a matrix of torques, number of revolutions or test durations and corresponding speeds, representing a duty cycle for the axle on a given vehicle. This method set forth an accelerated test approach effectively correlating with field failures of axle drive components like crown wheel-pinion, bearings etc.