Research Of Q235 Steel Stress Concentration Based On Metal Magnetic Memory Testing Technology

The stress concentration are always common concern issues to engineering. If components have stress concentration, it would reduce it's bearing capacity, what's worse,stress concentration may make the running load components fracture suddenly, this may lead to catastrophic accidents. So, the best solution is to real-time monitor the components in the working, discovering the stress concentration and early damage in time, reducing the incidence of sudden accidents. Although the traditional nondestructive testing technology has been widely used in the engineering, they are mainly better used for defecting existing defects,it's can't used for those early damage by stress concentration and so on. The emergence of metal magnetic memory testing technology, make it possible to make early diagnosis for the ferromagnetic components. This technology is the use of the magnetic field environment, determining the damage location and damage degree of components due to the surface leakage magnetic field change caused by stress concentration. Because the technology development time is shorter and not very mature,also have more influence factors in the process of testing, this technology just as a preliminary test methods for judging the stress concentration position of ferromagnetic component at present, and also need to use other detection methods to re-inspection the components and can't provide quantitative results. At present, in magnetic memory testing technology, the commonly used magnetic parameters is leakage magnetic field of normal component and it's gradient in the length direction .In most experimental study, it's mainly testing some measuring line on the surface of specimens and studying the magnetic memory signal changing, determining the stress concentration position by a zero curve of normal magnetic memory signal. But some experiment show that through this method to determine the stress concentration of the specimens is not very accurate. Aiming at this question, In this paper, first of all, testing tensile specimens of different diameter center hole by magnetic memory testing technology,study on the change of normal magnetic memory signal on the line near the center small hole of the test specimen surface, and make a mechanical simulation, analysis of the relationship between magnetic memory signal and stress concentration;secondly testing the center hole and two semicircles specimens by magnetic memory testing technology respectively, proposing the method of using normal magnetic flux leakage signals gradient of two directions to judge the stress concentration of tensile specimens, the main contents and conclusions including:(1)Testing a series of different diameter of center hole tensile specimens by magnetic memory testing technology, observing the change of normal magnetic memory signals, and making a mechanical simulation,getting specimen under different tensile load,there are the same stress concentration coefficients on different locations but magnetic memory signal passing zero have different phenomenons.It is concluded that the method of according to magnetic memory signal passing zero position determining the stress concentration position is inappropriate.(2)In the elastic stage, using the demarcation mesh method for the surface of center hole specimens, testing the magnetic memory signals of grid point on the surface under different tensile load, putting forward to the method of using the normal magnetic signals gradient on length and width two directions of detection plane to judge stress concentration position. In addition, simulating mechanics of the center hole specimen in it's elastic stage by COMSOL, comparing the stress distribution chart with the normal magnetic memory signals gradient nephogram, founding that stress is proportional to the gradient of magnetic memory signal,that is the stress concentration location of the loaded specimen can be determined by the gradient in two directions of the magnetic memory signal .(3)Testing the magnetic memory signal of two semicircles specimen tensile specimens,It's experimental method is the same as the method of center hole sample exactly, further validation, according to the method of the gradient in length and width two direction of the magnetic memory signal to judge the stress concentration of specimen is feasible.