Analysis and Improvement of Root Fracture Fault of Helicopter Blade Installation Bolt

In response to the root fracture of the installation bolt of helicopter blade, a comprehensive analysis was conducted using macroscopic morphology characterization, microscopic observation, and physical and chemical inspection methods to analyze the cause of the fracture and propose improvement measures. The analysis results show that the root fracture of the blade installation bolt is intergranular brittle fracture, and its internal residual stress is mainly generated during the cold extrusion forming process. Under the state of annealing softening, scratches are generated in the R zone of the bolt root after grinding and further expand into microcracks in subsequent processes, resulting in hydrogen-induced cracks during the cadmium plating process and ultimately fatigue fracture. In the light of analysis results, by adding control measures for cold extrusion forming molds, stress relieving processes after cold extrusion heat treatment, and adjusting the sequence of magnetic particle and heat treatment processes, the product quality can be effectively improved as well as the flight safety.