MMM Characteristic Study Of Different Strain States

Metal magnetic memory(MMM) technology not only assess the quality and safety measurement of mechanical equipment, but also can predict the early structural damage. With the improving of the social production and living standard, the railway, transportation and oil pipelines are more and more close to the people’s life and the safety requirements are also related to the safety of people’s lives and property, but many safety accidents still happens during process of production and construction such as broken rails, boiler explosions, pipeline leakage. So the scientific personnel must deeply study the MMM testing for equipment detection during the crack generation, expansion until fracture. Different strain stage models are set to determine quantitatively the state of the stress tip for components, then the necessary preventive measures are taken to ensure the safety of people’s lives and property.In order to study the different strain states, which are the crack initiation, steady propagation and unstable propagation, the standard three point bending experiments are operated to find the law of the MMM signal. In the meantime, the fracture mechanics characteristics(KIC 、 COD) of the experiments is calculated. The two values which are obtained before are shown the consistency during the critical state. The model is established by the MMM and fracture mechanics characteristic parameters. In this way, the MMM technology can test the crack extension instead of the fracture mechanics method during the actual detection process The experiment results show the orthogonal vector synthesis gradient Gvs increase dramatically when the crack is in the critical cracking state, which are two times the value before the critical state. The cracking characteristic is obvious, which are truly reflect the critical characteristic of the crack opening displacement δc. The Gvs is also increase obviously during the steady to instability extension of crack, which are twice than the value before the critical state. The instability characteristics can truly represent the critical characteristic of the crack instability extension. The mathematical model of the MMM signal and fracture mechanics is established quantitatively firstly, which shows the consistency in the aspect of the critical characteristic.The cracking displacement and the critical displacement of the instability extension is obtained by using the convenient MMM technology, which avoids the tedious calculation process of the fracture mechanics. A new way is provided to determine the cracking critical state and instability extension by the MMM characteristic in engineering.