Case Histories » Automotive

Axle Cracking

Cross-Section Showing Crack Initiation and Propagation
Polished Transverse Cross-Section Showing Crack Initiation and Propagation from both the Top and Bottom of the Axle
Magnified view of the thick iron oxide later lining the portion of the crack
High Magnified view of the thick iron oxide later lining the portion of the crack closest to the outer surface of the axle

Material

Chromium steel alloy.

Environment

Motorized vehicle.

Background

The axle was manufactured in Germany in 2005. Visual inspections revealed 36 out of 50 vehicles had a cracked front axle. The axle design has been used since the 1990s.

Service Life

Approximately 12 years.

Findings

Stress corrosion cracking was not responsible for the failure. Cracking had initiated from both the outer surfaces of the top and bottom of the axle beam. The longitudinal character of the cracking, in the thickest section of the axle beam, suggested a high-temperature failure process. The series of angular character micro cracks adjacent to the principal longitudinal crack suggested a high-temperature stress-rupture failure mechanism.