Analysis And Engineering Application Of Structure Fatigue

Fatigue fracture will happen when equipments bear a certain number of alternating load. Statistics have shown that 80 per cent of the structural damages were caused by the fatigue fracture. Therefore how to effectively prevent the machinery from fatigue fracturing during the time of services becomes an important subject.Fatigue fracture frequently occurs in the places in which there is the presence of stress concentration and the structural fatigue strength is weak, limited in certain region. For the pressure vessel subject to the circular load, the manhole's opening rate is somehow higher and that will not only destroy the continuity of the equipment, but also reduce the areas used to bear the load, resulting in high stress concentration and easier structural damage. For the bucket elevator used to transport cement, the loads of the pins in the hoist chains conclude alternating shear stress and bending stress, the maximal composition of forces and some metallurgical defects will make the centre of the pin weakest point in withstanding fatigue. Damages resulting from fatigue will endanger the normal business operation and production safety.This article firstly analyzed the stresses intensity and fatigue of the manhole in an oxygen cylinder according to the principles and methods of analytic design, using finite element method and ANSYS program. For one thing, an engineering problem was solved. For another, some general conclusions were obtained by examining the effects of some variables. That is, high stress concentration exists in the junction of the manhole and nozzle extending inside of opening. The stress can be reduced obviously by extending the nozzle inside the opening though the stress reduction effect will become different when the extending depth increases. The larger is the thickness of the tube, the smaller is the stress of the junction, except for the peak stress, but the stress declining rate will decrease.Secondly, the stress intensity of the pins was calculated and a comprehensive research on composition, microstructure, cracks and fracture surfaces was conducted. The research showed that the maximal bending stress of the pin's surface was larger than expected and some micro cracks were generated during the quenching, which resulted in fatigue damnification on the surfaces of the pins and fracturing finally. The bending stress and the initial size of the quenching cracks are the key factors that affect the crack growth life of the pin.