Ultralight Axle Development-Fracture Mechanics Life Predictions (40% Weight Reduction) 2020-01-0179

This paper details the light weighting efforts of an axle drive with innovative design techniques on the pinion and ring assembly and the use of Fracture Mechanics technology. This premise of this work is that in order to obtain the lightest weight components the current methods of predicting life in manufactured components can be improved/extended with the use of a Fracture Mechanics technique (Crack Growth Theory). This technique assumes that all metal components are manufactured with a certain level of defects. These defect sizes can be quantified through multiple techniques (ultrasonic, and other). The processing can be improved to minimize the size of these defects with process improvements such as vacuum arc re-melting techniques.

Inclusions in the materials are the result of addition of elements in the steel melt that are added for easy of machinability. The vacuum arc (VIMAR process) is used to minimize the formation of these inclusions (Aluminum Oxide, …) and thus decrease the size and density of the defects. All materials have some level of defect in the manufacturing process. This paper addresses a method that allows life prediction based on material properties (base, premium, standard cleanliness, and clean materials) and residual stress requirements (shot peen, as processed), initial flaw size, and drive cycle.

The Fracture mechanics technique as used in this paper takes a standard hypoid axle gear design and determines the life that can be realized with the use of cleaner steels and additional processing to the steels such as single peening, dual peening and other methods. Initial size of the ring gear is a driver for the weight of an axle assembly. If the size can be reduced then the complimentary components (pinion gear, bearings, and housing) can also exhibit a weight reduction. These improvements can then be used to drive significant environmental fuel and emissions reductions.

Specific details of the light weight weighting effort were examined in the finite element analysis. Finite element tools were used to refine highly stressed areas of the product and special changes were performed to insure component life would exceed vehicle drive cycles.