Dynamic Investigation and Resonant Frequency Determination of Shaft Bending Fatigue Testing Machine

The testing machine of shaft bending fatigue is widely used to test the fatigue limit and life of various shaft-type parts in mechanical engineering. Machine dynamic characteristics and system bending resonant frequency are very important for the design, testing, and application of the testing machine, but existing complex finite element calculation and aimless large-range frequency scanning in testing are the available methods to solve these two problems helplessly and inefficiently. A novel analytical model of nonlinear coupling dynamic system is built for the fatigue testing machine in this paper. The nonlinear dynamic model is simulated and investigated numerically, then it is reasonably linearized and reduced as a linear one, and the corresponding error analysis and application range are presented. By using eigenvalue approximation, the shaft bending resonant frequency formula is obtained, then the formula is compared and verified with the results from the nonlinear system simulation and finite element software, and it can improve the machine design and testing efficiency obviously. The analytical dynamic modeling and linearizing, and the given mode resonant frequency approximating, also provide a reference for many similar vibration machines.