Failure Analysis of the Apache Mixer Pivot Support
Abstract
This report discusses a failure analysis of a mixer pivot support located on the AH-64 Apache Helicopter. The component was found to be broken in two pieces during an inspection. Visual inspection of the failed part revealed significant wear on surfaces that contacted the bushing and areas at the machined radius where the cadmium coating had been damaged allowing corrosion pitting to occur. Light optical microscopy showed that the crack origin was located at the machined radius within a region that was severely pitted. The hardness, chemistry, and microstructure of the electroslag remelted (ESR) 4340 steel used to fabricate the component conformed to required specifications and no apparent manufacturing defects were found. Electron microscopy showed that most of the fracture surface failed in an intergranular fashion with the exception of a shear lip zone which exhibited a dimpled morphology. The failure was set into action by hydrogen charging as a result of corrosion and was aggravated by the stress concentration effects of pitting at the radius and the high notch sensitivity of the material. Energy dispersive spectroscopy (EDS) determined that deposits of sand, corrosion, and salts were found within the pits. The failure mechanism was hydrogen assisted and was most likely a combination of stress corrosion cracking and corrosion fatigue.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1991
- Accession Number
- ADA240858
Entities
People
- Gary Wechsler
- Kirit J. Bhansali
- Marc S. Pepi
- Victor K. Champagne Jr.