Morphology Analysis on Fatigue Failure of PTFE Pipe Caused by Cavitation Erosion

A dozen of polytetrafluoroethylene (PTFE) pipe leakage occurred on hydraulic system of a certain aircraft. Three-dimension microscope and SEM were used to analyzed macro and micro morphology of faulty PTFE pipe. The results showed that these PTFE pipes hade same failure characteristics and failure mode, which is named fatigue failure caused by cavitation erosion. The paper analyzed working condition of PTFE pipe, investigated failure mechanism of cavitation erosion, and concluded fractal characteristics of fatigue failure caused by cavitation erosion. Characteristic features of such failures included: 1) feature of damage zone were honeycomb-like caves macroscopically, 2) caves consisted of small fatigue zones microscopically, 3) cracks that propagate first at surface or subsurface and then parallel to the surface of pipe, and 4) fatigue striations on the fracture surfaces. Fatigue failure caused cavitation erosion of PTFE pipes could be described by shock wave mechanism.