Ferromagnetic Material Stress Testing Technology Research Based On The Coercivity

Ferromagnetic materials have excellent mechanical properties, it is one of the most widely used material in various fields of industry. In the process of manufacture and using, the ferromagnetic material components inevitably will be affected by a variety of stress. When the stress concentration reaches a certain degree, the artifacts will appear local deformation and even develop into macroscopic defects, these will lead the artifacts being distorted, thin and even ruptured. Oil and gas pipelines are usually laid underground or the lake, its working environment is extremely complex and the wall is under tremendous pressure. If the pipes have crack, there will easily be pipe burst accident, oil and gas leaking, widespread environmental pollution, threated people’s life and property and suffered huge economic losses of the country. Therefore, conducting the early evaluation of pipeline, making out the detecting the stress concentration area, finding the problem as soon as possible and eliminating hidden danger in time, have great significance to ensure the safety of oil and gas pipeline operation.This paper from the micro perspective, further studied the crystal structure of ferromagnetic materials, atomic magnetic moment, the magnetic domain structure, the mechanism of magnetization and other magnetization mechanism and discussed the mechanism of residual stress and the influence of stress on magnetic properties. And based on hysteresis loop of ferromagnetic materials detection mechanism, designed hysteresis loop test system, using the system can measure the coercive force of material. By measuring the coercive force of materials under different stress, analyze the impact of stress on the coercivity. The system used U type probe as a sensor, the sensor can be used in the detection of the coercive force of the plate and the tube. It used the excitation coil to magnetization of the magnetic circuit and used the detecting coil to testing the magnetization intensity of the magnetic circuit. Designed the signal generating circuit, power amplifier, arithmetic circuit and sampling circuit. In the experiment, this system can measure the hysteresis loop and coercivity of the magnetic circuit quickly and accurately.In the experimental process, using the hysteresis loop-coercive force detection system, testing the steel and iron which is under the action of the different stress, collecting the hysteresis loop of waveform and coercivity of the calculated value. The experimental results show that under the action of tensile stress in ferromagnetic materials coercive force value is being smaller and under compressive stress, the coercive force values is being smaller too.