Study on fatigue performance of large-scale alloy steel bolts in control pitch propeller

During the voyage of the warship, the connection structure of pitch propeller will be subjected to various alternating loads, and the blade root bolt, as the main stress component, is prone to fatigue failure. According to the actual working situation of pitch propeller, a set of test loading device is designed in combination with MTS fatigue testing machine to study the fatigue performance of large-scale alloy steel bolts under working conditions. Combined with the monitoring of actual strain by dynamic acquisition instrument, 11 blade root bolts were subjected to constant amplitude fatigue test by fatigue loading device. The fatigue S-N curve of pitch propeller bolts is established. By analyzing the fracture morphology of three stress levels, the influence of loading stress level on fatigue fracture characteristics was studied. The test results show that the fatigue limit of the large-scale alloy steel bolts is 70.53MPa at 1×10⁷ cycles. Through the analysis of different loading stress levels, it is concluded that when the stress amplitude increases, the fatigue crack occurs faster, the transient fracture zone increases, and the crack propagation zone decreases with the proportion. Furthermore, the stress concentration effect of high-strength bolts is analyzed by establishing the finite element model of bolts, which provides a basis for optimization of large-scale alloy steel bolts.