A landing gear lug fatigue case study — SEM fractography of beach marks and striations, a Neuber stress-concentration back-calculation at the crack-initiation scratch, and a root cause traced to a specific reaming and inspection process escape.
The project brief: a 4340 steel main landing gear trailing-arm lug was pulled from service after an eddy-current inspection found a crack at just 8,450 landings — 19% of its 45,000-landing design fatigue life. Framed as this program's baseline fatigue-investigation project, it walks the teardown fractography, the stress back-calculation that quantifies why the part failed so far short of its design life, and the manufacturing root cause behind the gap.
This module works the full investigation the way a failure analyst actually would: reading beach marks and SEM striation spacing to reconstruct the crack's growth history, back-calculating the local stress concentration at the crack-initiation scratch with Neuber's formula, and tracing that scratch to a specific worn-tool and inspection-method process escape — plus the fleet-scope corrective action that followed. The full worked numbers, complete findings table, and finished root-cause reasoning are part of the unlocked module below.