Study On Measurement Technique Of Stress Measurement System On Coercive Force For Ferromagnetic Materials

With the extensive use of pipeline transportation, the ensuing network security issues deserve attention. Petroleum and natural gas pipelines are usually made of low carbon steel. With the accumulation of time, the service pipeline will inevitably appear fatigue failure, and fatigue failure parts usually appear in the stress concentration area. Oil and gas pipeline damage, fracture will lead to oil and gas leakage, and serious explosion will can occur. Therefore, it is an important method to avoid the occurrence of the accident by studying the stress detection method of the pipeline and forming a perfect stress concentration area measurement system. The magnetic parameters of the ferromagnetic materials will be affected by the stress, the coercive force and stress have a certain relation and the measurement is not affected by outside influences.So the stress can be measured indirectly by coercive force, and the stress concentration region detection is of great significance.In this paper, we mainly study the magnetic properties of ferromagnetic materials, the principle of magnetization, magnetic effect and a series of theories. In order to verify the feasibility of indirect measurement of stress by coercive force, the influence of stress on the coercivity of ferromagnetic materials was studied. The coercive force is derived from the irreversible magnetization process of the domain wall of the material, but the existence of stress can hinder the irreversible magnetization process, thus affecting the coercivity of ferromagnetic materials. The experiment was carried out with the U type probe. The multi chip U type silicon steel sheet is formed by the superposition of the probe, and a certain number of turns of the winding excitation coil and induction coil. Then the probe is placed on workpiece to be measured, and the probe and the air gap are tested to form a closed loop. The probe and the test piece are passed into a certain waveform or a certain frequency of the excitation signal, then the probe and the test piece is magnetized. In the closed loop, with the change of the magnetic flux, induction coil in the induction electromotive force generated. The excitation end is connected with a sampling resistor, and collect electrical signal that proportional to the magnetic field strength, and put this signal access 1 channels of oscilloscope. The induction terminal access integral circuit, and collect electrical signal that proportional to the magnetic induction intensity, and put this signal access 2 channels of oscilloscope. With the change of the excitation signal, the two signal output ends of the oscilloscope form a hysteresis loop. On the hysteresis loop, coercive force is that the magnetic field intensity corresponding to the magnetic induction intensity is zero.In the experiment, the sine wave ratio, triangular wave and square wave are chosen as the excitation signal to measure. When the excitation signal is 40 Hz square wave, the measurement effect is better. The hysteresis loops were measured at different external force and different thickness. The experimental results show that the coercivity is smaller with the stress of ferromagnetic materials larger, and the thickness has no effect on the coercivity of the material..