Study of the nature and causes of damage of 40KhN2MA steel propshafts

The nature and character of the destruction of the high-loaded airscrew shaft of the gas turbine engine made of steel 40KhN2MA are studied using the methods of scanning electron and optical microscopy and X-ray spectral microanalysis. We determined the chemical composition, microstructure and character of destruction of the flange part of the shaft. It is shown that chemical composition of the shaft material meets the requirements of the regulatory documents and defects of metallurgical origin are absent both in the metal of the shaft and in the fatigue fractures. All the identified cracks have been formed during operation, and developed according to the fatigue mechanism. Zones of fretting-wear and fretting-corrosion damage to the surface in the stud holes are the foci of the fatigue crack birth in the airscrew shaft. The cause of formation and development of the fatigue cracks in the shaft flange is a high level of contact stresses in the flange body, attribute to a poor quality of the interface of the splined joint due to significant fretting corrosion damage to the splines and vibration damages. A set of recommendations and measures aimed at elimination of the adverse factors is elaborated. To exclude the formation and development of fatigue cracks in the splined flange upon operation, we recommend to: optimize the tightening torque of the splined joint; introduce quality control of the interface between contact surfaces of the splined joint when replacing the airscrews; address the issue of dynamic balancing of the airscrews upon their production and repair.

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