Failure analysis of an axle shaft in an airport ground support vehicle

In this study, failure analysis of an axle shaft in an airport ground support vehicle was carried out. Mechanism and causes of failure that occurred in the axle shaft, which was loaded only by torsion, were determined. Preventions have been proposed in order not to encounter same failure again. Macroscopic observation, numerical analysis, metallographic analysis, chemical composition analysis, hardness measurement and tensile test methods were used in failure analysis. In numerical analyses, axle shaft was modelled as a functionally graded material (FGM) to obtain results close to actual. The analysis results show that the axle shaft fracture is a torsional fatigue failure and type of fatigue life is low cycle fatigue. High surface roughness that occurs after machining of axle shaft is one of the causes of failure. High surface roughness that caused formation of stress concentrations decreased torsional fatigue strength of surface and caused crack initiation. Another reason for failure is selection of material with insufficient mechanical properties. Although torsional strength of axle shaft is increased by induction surface hardening, it has been found that yield strengths are not sufficient at depths from 9 mm to 14 mm. Making finish cut with low depth and even grinding in surface finishing process have been proposed as a prevention to increase surface quality, reduce surface roughness and stress concentrations in machining of axle shaft. In addition, using another material with higher yield strength (EN 37Cr4) have been proposed instead of EN 34Cr4 alloy steel as the axle shaft material.