Abstract: A horizontal stabilizer shaft fractured during fatigue test. Failure analysis indicates that the fracture mode of the shaft is fatigue fracture. Fatigue cracks initiated from the valley of the machining marks near the fillet of the inner surface of the hollow shaft. Scanning electron microscopy analysis discovers that there is a loose layer about 10-16 m on the inner surface of the used hollow shaft. Besides, many fatigue microcracks and holes are in the loose layer. The loose layer resulted from oxidation corrosion and fatigue damage in the use of the shaft which destroys surface integrity and weakens anti-fatigue properties of the shaft. Finite element analysis shows that the structural stress concentration and the local stress concentration resulted from the machining marks are the mechanical factors lead to fatigue failure. Comprehensive analysis shows that the loose layer and the structural stress concentration and the local stress concentration resulted from the machining marks are main reasons for fatigue fracture.

Key words: Fatigue fracture, Horizontal stabilizer, Stress concentration, Surface integrity