Fatigue Testing Of The Resonating Structure And Coupling Analysis Of Vibration Fatigue For Cracked Components

There are different modes of damage in any engineering structures, and most of them are cracks. Problems of vibration and fatigue are often produced by external force simultaneously. New scientific problems are produced due to coupling effect of vibration and fatigue. Based on the results of fatigue testing for the resonating structure, the cracked beam and the cracked plate are employed for coupling research of vibration and fatigue through vibration analysis and fatigue crack growth calculation in view of local complicane model. The vibration behaviors change as crack growth and the influence of vibration on fatigue crack propagation are discussed. The results and the main contributions are as following.In experiment, vibration-exciter-based fatigue testing system is designed and a fatigue testing method of the resonance controlled structure is proposed. Experiments are carried out for the typical components under different working conditions. Influences of dynamic characteristis on the structure fatigue life are discoveried through investigation of experimental phenomena and datas. The internal connecting link of vibration and fatigue crack growth is discussed.In theory, to begin with the local compliance model of the cracked beam is given in view of the fracture mechanics and energy principle. Local compliance expression of the uniformity cantilever beam subjected to a typical loading with common mode crack is given. In addition, a new analytical method of the vibration fatigue life for the cracked beam is proposed with the structural response changes as crack growth. In this analysis, the damping loss factor is introduced by complex elastic modulus, and the crack growth is analyzed by employing a Paris equation, and the coupling effect of vibration and crack growth is considered by vibration analysis and fatigue crack growth calculation cycle by cycle. It can be shown that the influences of frequency, damping and mode on vibration fatigue life are very obvious. Due to the influence of damping, the resonance fatigue crack growth rate decrease, and the first resonance has more contribution to fatigue crack growth than that of other mode vibration. What is more, the influence of the crack breathing behavior on vibration and fatigue are studied. During the coupling analysis, the breathing crack is depicted by the double linear spring model, and the cracked beam is simplied to single-degree-of-freedom system by Galerkin's method, and the parametric vibration equation is deduced by employing the varying stiffnes, and the friction damping loss factor is given based on the Coulomb friction model and the energy dissipation theory, and the crack propagation is analyzed by employing a modified Forman equation. Results indicate that the closing effect of the breathing crack adds average stiffness, and influences of parametric resonance on the vibration fatigue can't be ignored, and the friction damping has important influence on the life of vibration fatigue crack growth. Finally, an analytical model of the vibrating cracked plate is derived and the coupling effects of vibration and fatigue are investigated. In analysis, the crack is equivalented by an additional external force, and equation of the vibrating cracked plate is derived by using mechanical equilibrium principle, and the crack terms are obtained by using stress relational expression introduced by Rice and Levy. Galerkin's method is applied to reformulate the vibration equation of the bilateral cantilver cracked plate into single-degree-of-freedom system. Nonlinearity is introduced by formulations introduced by applying Berger's method. Results are presented in terms of natural frequency versus structural dimensions and crack length, and the structural vibration response of the cracked plate is calculated of cracked plate, and the influences of damping and exciting force on the life of vibration fatigue are discussed.Finally, a simple analytical method of the structural vibration fatigue life with coupling effect is proposed based on the theoretical research production, and the rationality of the analytical method is verified by the simulation results of the typical experimental component. Results indicate that this analytical method of the vibration fatigue life is simple, and it is a good idea for fatigue life analysis of engineering structures.