Study Of Stress Non-conatct Detection And Its Experimental Based On Magnetoelastic Effect

In a series of methods testing the stress of ferromagnetic materials, the techniqueof magnetic stress measurement can offset the defects existent in the commonmethods of testing the stress, and realize the fast, efficient and non-contact stressmeasurement. Based on the magnetoelastic effect, this paper centers on the techniqueof magnetic stress measurement, and makes a research of the sensors to magneticallymeasuring the stress and its detecting system.The magnetoelastic effect refers to the phenomenon that under the force ofexternal loads on ferromagnetic materials, the internal magnetic properties likepermeability change. According to the magnetoelastic effect and Faraday’s law ofelectromagnetic induction, when the measured materials are affected by externalforces, the sensors of magnetic stress measurement can transform the changes in theinternal magnetic properties of measured materials into the changes in the outputvoltage of the measurement coils of the sensors, thus reaching the aim of testing thestress. This paper mainly makes relevant researches in terms of the following aspects:Firstly, according to the basic principles of ferromagnetic, starting from themagnetostrictive effect of ferromagnetic materials and its inverse effect, namely, themagnetoelastic effect, this paper expounds basic theories relevant to the magneticstress measurement. In this part, the paper mainly analyzes the microcosmicmechanism of forming the magnetic domain structure of ferromagnetic materials andthe magnetization process of ferromagnetic materials when affected by externalmagnetic fields and the magnetization mechanism. Then the thesis studies theinfluence of the stress on ferromagnetic materials magnetization and provides thetheoretical basis for magnetically measuring the stress.Secondly, this paper designs the stress measurement system based on the sensorsto magnetic stress measurement and introduces every part in this detecting system. Inthis part, the author mainly theoretically compares the performances of the magneticstress measurement sensors with different probe structures and finally chooses thestress sensor with E-shaped probe of three poles as the object of study. Afterascertaining such parameters as the material of the probe, the geometric dimension,the number of exciting coils and the intensity of exciting currents, by analyzing themagnetic circuits of the sensors and using the electromagnetic principle, the paper deduces the basic equation of the output voltage of the sensors when the testedmaterials are affected by the static stress and dynamic stress.Finally, this paper designs testing programs and conducts the experimentalstudies of exciting current, frequency and air gap of the sensors when the measuredpieces are stretched and contracted and gets the suitable current intensity ofexcitation, size of frequency,distance of non-contact detectionand other parameterswhen the sensors are working. Then based on this, through the calibration test of thesensor, its static characteristic parameters are obtained.