Last modified: 2024-07-30
Abstract
Rigid axles are subsystems that are still widely used in modern heavy commercial vehicles due to their simple design, high load carrying capacity and ease of production. Drive axles used in trucks and buses not only distribute the vehicle weight properly to the chassis or vehicle structure, but also provide power transfer to the drive wheels. In this respect, rigid rear axles are considered as an important part of the power transmission systems of heavy commercial vehicles. The axle housing, which is the main load-carrying part of a conventional rigid drive axle, is mainly subjected to bending load throughout its service life, due to the forces acting from the wheels and suspension spring supports. Due to the effects arising from road irregularities and the driving dynamics of the vehicle, these loads and the stresses they create generally have dynamic characteristics. It is known from the literature that vertical dynamic loads may cause fatigue damage on the axle housing. To ensure the structural integrity of the axle throughout its service life, it is critical that the axle housing be designed to be lightweight as well as resistant to fatigue damage. In practice, the load carrying capacity and fatigue life of a new axle housing design under dynamic vertical forces are determined by vertical fatigue tests. In these tests, cyclic vertical loads are applied to the housing prototypes by hydraulic actuators and the test continues until a crack occurs.
Within the scope of this work, the effect of the position of the stiffening ribs used in the arm transition regions of a heavy-duty truck rear axle housing prototype on fatigue failure tendency was examined. In the vertical fatigue tests applied to the housing prototype, it was observed that the component withstood the targeted number of load cycles, however suffered fatigue damage at the lower stiffening rib - spring support connection area above this limit. In order to determine the effects of rib position on stress distribution of the part, firstly the vertical loading test was simulated using Finite Element Analysis (FEA). It was determined that the stress concentration region and the area where fracture occurred in the tests overlapped. Design improvement including relocating the stiffening ribs was applied to the housing model to decrease stress concentration at the critical regions. Results showed that it is possible to reduce the maximum stress at the crack initiation region by approximately 41%. It was also concluded that placing stiffening ribs at the upper region of the axle housing could enable a lighter design.