DEVELOPMENT OF ADVANCED STRUCTURAL DESIGN METHODOLOGIES FOR AXLES OF OFF-ROAD AND OFF-HIGHWAY VEHICLES

This work is a collaboration with Carraro S.p.A., a leading manufacturer of axles and transmissions for off-road and off-highway vehicles. Axles play a crucial role in these vehicles, performing functions such as power transmission, weight support, load absorption, braking, and steering. The axle components vary based on vehicle types, with off-highway vehicles using nodular cast iron castings and off-road vehicles using high-strength low-carbon steel tubes. The focus of this project is to enhance axle design methodologies, particularly in fatigue assessment of the external structure. Different approaches are employed for steel welded components and nodular cast iron. The Peak Stress Method (PSM) is used for fatigue assessment of steel welded joints, demonstrating reliability in estimating crack initiation locations. The PSM is applied to assess the welds of an off-road vehicle axle, and numerical constants are calibrated for NX Nastran, the FE software used by Carraro S.p.A. The second part of the work concentrates on the fatigue assessment of axles for off-highway vehicles with a focus on nodular cast iron components. The microstructure and mechanical properties of EN-GJS-500-7 nodular cast iron are evaluated through strain-controlled and load-controlled fatigue tests. The impact of casting processes on fatigue properties is considered, and correlations between microstructure-related parameters and static and fatigue properties are identified. A procedure for estimating properties based on quality controls is proposed. In conclusion, fatigue data for EN-GJS-500-7 cast iron are utilized to evaluate damage in strain-based spectra from field and laboratory fatigue tests on axles. A safety factor between laboratory tests and the overall vehicle life field spectrum is determined.