Study On Metal Magnetic Memory Based On Accumulative Fatigue Damnification And Application In Engineering

This subject comes from the national 11th 5-years science and technology plans, and it focus on the core issue which is the characteristics of metal magnetic memory signal in the process of high-cycle fatigue. And this subject study on the characteristics of metal magnetic memory signal and microstructure in the process of static load tension and high-cycle fatigue by the metal magnetic memory testing method, It built important experimental foundation for the application of metal magnetic memory method in engineering.This study involves two key issues: First, the changes law of metal magnetic memory signal which changes with the degree of plastic deformation in the process of static load tension,the relationship between the macroscopical magnetic memory signal and the changes of microstructure. Another problem is that the changes law of metal magnetic memory signal with fatigue cycle and micro-defects in the process of high-cycle fatigue, as well as the relationship between the macroscopical magnetic memory signal and the micro-defects. At the present time, the study on the mechanism of metal magnetic memory technology,the law of metal magnetic memory signal in the process of fatigue as well as corresponding relation between macroscopical magnetic memory signal and microstructure is far from perfect. For these two issues, this article has done two aspects experiments of static load tension and high-cycle fatigue.This paper focuses on metal magnetic memory characteristics in the process of high-cycle fatigue and static load tensile, and finally study the relationship between the changes of metal magnetic memory signal of material and the process of high-cycle fatigue or static load tensile from macro and micro levels. In order to study the characteristics of metal magnetic memory signal and microstructure, this paper has done the experiments of different types sample of different materials. The results showed that :①With the changes of metallic material specimen's deformation, the intensity of magnetic field on the surface of metal material specimen changes. The changes of magnetic field intensity has nothing to do with the outside environment magnetic field, It has no relation with repeated loading.②When the material defect which caused by stress concentration, the intensity of magnetic field (Hp) occurred concave changes, and the derivative of magnetic field intensity (dHp/dx) show a larger increase. There are different threshold limit value of derivative about different metal materials.③The results about macroscopical magnetic memory signal and microstructure in the process of high-cycle fatigue showed that: when the dHp/dx come up to the limit value state ,the microstructure on the surface of specimen is natural, While once the state overstep the limit value state, if only a short-time (about 3000~4000 fatigue cycle), the dHp/dx suddenly increase, a large number of microstructure are embossed, and there are obvious dislocations on the boundary of microstructure. This result show that the metal magnetic memory technology has the special effect on testing stress concentration of material and early diagnosis.④The fact that whether the specimen is destructive or not has no relation with dHp/dx, and it has nothing with zero-point about magnetic field intensity(Hp=0).⑤The material whether it has welding structure or not does no effect on the distribution of magnetic field intensity.In order to study the practicality of metal magnetic memory method in engineering, a number of metal magnetic evaluation had been done through the metal magnetic memory method based on the laboratory studies. The oil tanks in the refineries plant of Yanshan petrochemical and the boiler in Zhuhai power plant had been tested thought metal magnetic memory method, then a large mounts of data obtained, After the analysis of these data, the practicality and reasonable feasibility of metal magnetic memory method in engineering had been verified.In this paper, the results of research is further evidence of magnetic memory method for early evaluation of the fatigue defects, this study lead to a concept which is limit derivative value based on a large number of experiments, this study provide an important experimental basis for the application of magnetic memory method in practical engineering and the development of"magnetic memory method on pressure equipment".