Research On The Spatial Crack Arrest In Metal Component By Using Electromagnetic Heating

In modern industry, metal is widely used in military affairs, aviation, aerospace, shipping, transportation, mechanical productions and many other industrial fields for the main original material. Cracks might be generated due to various reasons when metal components are being made or used, and the crack propagation results in that the fracture in a component takes place before the material intensity limit is come up to, thus this brings immeasurable losses to the practical productions and lives. Making use of electromagnetic heating effect to prevent crack propagation in metal components with cracks is a novel and effective method that can extend its lifetime, improved the security and reliability. Nowadays, for the technology of crack arrest by electromagnetic heating effect, the domestic and overseas studies are only limited in planar problems, but for the theory and experiment research of spatial problems are vacant. The article which is just based on this develops studies in three aspects of theoretical analysis, numerical simulation and experimental study. The content includes six parts as below:(1)Theoretical analysis of the temperature field is conducted in metal components with half-embedding circular cracks when an impulse current is switched on. The model of theoretical analysis is built, the current density functions around the crack tip is presented when a current is switched on, further more, temperature field and stress field functions are received when crack arrest by electromagnetic heating effect is proceeding. The model of numerical analysis is built, and making use of the software of Ansys the coupling course of thermal and electrical is simulated, in succession the temperature field is received. The results of theoretical analysis and numerical simulation are also compared.(2)The temperature field is analyzed theoretically for metal components with deep embedding elliptical cracks when an impulse current is switched on instantaneously. Using the similarity of current detour problems and fluid detour problems in the hydromechanics, the theoretical analysis model is built, and the functions around the forehead of the crack is gotten when crack arrest by electromagnetic heating effect is carried on. By concrete calculated examples, the effect relations of various parameters to the stress field are discussed. Theoretical analysis problems of spatial crack arrest by electromagnetic heating effect with practical significance are also solved.(3)The model of numerical simulation analysis is built for metal components with deep embedding elliptical cracks when an impulse current is switched on instantaneously. Using the method of the electric-thermal-mechanical ordinal coupling calculation, the numerical answers of instantaneous temperature field and thermal stress field in the nonlinear course are given. The exceeding unlinear problems result from the instant discharge time, great temperature gradient around the crack tip and material character parameters such as heat consistency, resistivity and heat conduction changing with the temperature in the course of crack arrest are discussed. The results of theoretical analysis are simulated, analytical contents are broadened based on the valid theoretical analysis, the temperature field is calculated when an impulse current is switched on instantaneously in metal components with deep embedding elliptical leaning cracks, the relations of the temperature around the crack tip and the leaning angle are discussed, simultaneously the current detour is simulated.(4)The crack arrest experimental study in metal components with spatial cracks is conducted on pulse current generator (model ZL-2) developed by the authors. Many standard tension test pieces(single straight crack, double straight cracks, single leaning crack) are produced. Firstly by the method of numerical simulation, the experimental discharge parameters are identified, and the experimental program is established. Experiments study the situation of crack arrest in standard tension test pieces with various spatial cracks, established the validity of the technology of crack arrest by electromagnetic heating effect, which approves the validity of spatial crack arrest in metal components by using elelctromagnetic heating.(5)By the method of ultrasonic detecting damnification, the position and configuration of the entire embedding crack in weld joint of the jointing structure are conformed, and the crack arrest by electromagnetic heating experimental study is also carried out. The method of pulse current discharge realizes the spatial embedding crack arrest by electromagnetic heating in weld joint, simultaneously the obdurability is improved. Fining microcosmic structure in the heat influence area is realized, the inside stress state of the weld joint is reformed, further more, the structure and performance of the jointing structure don't change.(6)The experiments of mechanical performance examination are carried out in standard tension test pieces after crack arrest. Through the PC-control universal tester,the study of stretch experiment is carried out in components before and after crack arrest, mechanical performance index is studied by contrast. Analysis of the macroscopical state and microstructure is carried out in the fracture after the component is snapped.Microcosmic structure analysis is carried out at the crack tip, the white-right layer which is coriaceous forms around the crack tip. Mechanical performance is improved after crack arrest. Also, Scanning Probe Microscopy is used to finish the mechanical testing for metal component after crack arresting at the nanometer scale. The research results in the dissertation demonstrated that the spatial half-embedding crack and embedding crack can be prevented in metal component by pulse current discharged using electromagnetic heating effect, and the super fine metal structure appears around the crack tip for improving the mechanical performance of metal component after crack arrest, and it is reasonable to anticipate that the crack arrest by using electromagnetic heating will be developed to repair the damage and fracture of metal component.