UTILIZING MAGNETOELASTIC EFFECT TO MONITOR THE STRESS IN THE STEEL TRUSS STRUCTURES

Dorota Jackiewicz – Roman Szewczyk – Adam Bieńkowski

   This paper presents possibility of magnetoelastic effect applying to monitor the stress in the streel truss structures. The in-vestigation was performed on the truss made of 13CrMo4-5 steel. The three central truss members were wound with the mag-netizing and sensing windings, and they form a triangular, closed magnetic circuit. Thus, the magnetic circuit is formed and closed by the truss construction itself, and there is no need to design or include in the construction any additional sensing ele-ments. For the measurement of the magnetoelastic properties, special measurement stand was developed. It consists of the me-chanical part for applying force to the steel truss, and thus stresses in the samples. The second part is the magnetic characteris-tics measurement system. During the magnetoelastic measurements, three member samples were installed into the truss. The truss was put under the mechanical load. The experimental results of measurements of the magnetic characteristics stress de-pendence of the sample magnetic circuit are very interesting. The stress dependence of the shape of magnetic hysteresis B(H) loops can be observed for different amplitude values of magnetizing field H_m. Under the influence of external force, value of the flux density B decrease. The magnetoelastic B_m(F)H_m characteristics for the sample magnetic circuit can be fit with the second degree polynomial. In presented case high agreement between the measurement results and curve fit was achieved, as shown by the coefficient of determination R² equal to 0,998. Knowing this characteristic, it is possible to calculate the force acting upon the truss on the basis of the magnetic induction measurement. When the force is known, one can calculate the tensile and com-pressive stresses in the magnetic circuit elements, namely the steel truss members. With the knowledge of the mechanical prop-erties of steel we are able to determine whether the internal stresses in the truss are a threat to the structure.

Keywords: magnetoelastic effect, steel truss constructions, non-destructive stress evaluation

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