Failure Analysis of T-38 Brake Assemblies

Southwest Research Institute^® (SwRI^®) performed a failure analysis on various T-38C Brake Assemblies from different aircraft. The stators were found with cracks at the thermal relief holes. The rotors were confirmed to exhibit a friction wear coating comprised of Cu with alloying additions of Sn. The stators did not require a wear coating. The cross-sectional examination of the stators demonstrated a discontinuous, thin Cu coating of approximately 0.0006 inches (16 μm). This thin coating was a result of significant wear between the mating rotor and stator surfaces. The thin Cu coating exhibited significant debris, and lacked the porosity to be typical of a friction material. Coupled with wear mechanisms, elevated temperatures experienced during braking resulted in localized melting and solidification of the Cu-Sn friction wear coating over the worn/oxidized stator surfaces. The material dissimilarities between the transferred Cu layer and the underlying base metal of the stators facilitated galvanic corrosion mechanisms that resulted in discrete corrosion pits acting as fatigue crack initiators.