Investigation of Main Rotor Spindle Assembly Retaining Rods from an Army Utility Helicopter

The purpose of this investigation was to determine the root cause of the differences noted in the fatigue test data of main rotor spindle assembly retaining rods fabricated from three different vendors, as part of a “second source” evaluation process. The Army Research laboratory (ARL) performed dimensional verification, and measured the respective surface roughness of the rods in an effort to identify any discrepancies. Next, mechanical testing was performed, followed by metallography, and chemical analysis. ARL subsequently mechanically tested specimens subjected to laboratory heat treatments at the required aging temperature.