Conversion Theory of Magnetic Anisotropy Sensor and Measurement of Residual Stress Distribution in Punched Steel Sheet

Abstract

A magnetic anisotropy sensor (MAS) is a probe-type sensor capable of non-contact, non-destructive measurement of stress in ferromagnetic materials. The output voltage of the MAS is induced by a directional difference of relative permeabilities caused by the inverse magnetostrictive effect.
It is often necessary that the internal stress distribution in the direction of depth should be clarified. By changing the MAS exciting frequency, it is possible to searching for the different depth stress. This paper proposes a method for measuring the stress distribution in the direction of depth. Furthermore, this paper shows that the stress distributions in the measurement surface and opposing surface can be estimated from the MAS output.
In this paper we discuss the followings:
(1) By developing a stress-electric conversion theory of the MAS, it is clarified that the output voltage is proportional to the principal stress differences.
(2) Using punched thin steel sheet as a specimen, by changing the exciting frequency, the measurements from one side makes it possible to estimate the stress in the opposite surface.
(3) Conversion of the principal stress differences to relative permeabilities reveals that tensile stress remains in the upper surface, and compressive stress exists in the lower surface.