Survey of fatigue failures in helicopter components and some lessons learnt

• The effect environment and stress has on fatigue of carburised steel has been studied.
• Both mean and alternating stress have been shown to influence failure mode.
• HCF performance was lowered when testing was carried out in elevated temperature oil.

The paper presents a comprehensive review of the failure investigations carried out within AgustaWestland Limited (AWL) over the last 30 years. The results of this survey show that fatigue accounts for approximately 55% of all failures in helicopter components. Although fatigue failures can occur in a wide range of components the types of factors responsible for initiation differ depending on the application of the part. This paper identifies the most common fatigue prone areas in the helicopter, how design considerations and certain key factors such as fretting can influence fatigue life. The importance of aircraft maintenance and quality control in the supply chain will also be discussed. Based on the survey, the paper will also illustrate several instances where fatigue failures have been eliminated through the application of novel surface engineering techniques, improvements in material & processes and modifications to the original design.