Examination Of Helicopter Hydraulic Tube That Experienced Fatigue Cracking Via Slip Mechanism

A helicopter hydraulic tube cracked under a flareless coupling sleeve as a result of fatigue. The fatigue initiated on the outer diameter surface in an area of wear and fretting. Crystallographic plane features were observed on the crack surface, which are typically associated with Stage I slip mechanism fatigue. However, the crystallographic plane features were observed across the entire thickness of the tube. Brittle fatigue striations were observed further along the crack surface, followed by ductile fatigue striations.