Realistic Correlation of Damage Estimate in Axle Housing of Commercial Vehicles Using Road Load Data with Bench Testing Results and Failure Analysis to Overcome Hot Forming Losses

The present work deals with the damage life correlation of vehicle-level testing results of an axle housing for different road load conditions with the accelerated bench testing experiment results to reduce product development time. Also failure analysis is carried out to overcome the mechanical strength losses caused by the hot forming process during the manufacturing of housings. Commercial vehicle torture test tracks are built to reflect the forces similar to vehicle usage conditions from lighter to severe loadings. Strain data and calibrated force values are captured at the critical loading points in the axle for one cycle, at actual vehicle-driven speeds, to reflect the accelerated load values on five different track conditions. Damages estimation carried out based on the road loads reflects there will be no failure of axle housings till the acceptance of 120 repeats in different track combinations. Equivalent damage estimate at the component level using constant amplitude indoor servo hydraulic bench testing conditions with varying stress ratio “R” loading cycles reveals the crack initiation of housings before acceptance of 0.6 million stress cycles, which is contradictory to vehicle-level testing estimates. Failure analysis reveals component measured tensile strength values are lower than the designed. It was observed in further investigations the tensile strength loss of 18% is due to the hot forming process owing to induction heating at 700°C below the recrystallization temperature, followed by rapid cooling. Damage life estimate for the lowered tensile value after hot forming indicates failure for both vehicle and indoor bench testing, which reveals a good correlation between both the life calculation methods. An alternate proposal to overcome the fatigue strength loss leading to failure has been worked out with a localized increase of sections at banjo radius resulting in an additional weight penalty of 4.1 kg/axle housing.