Hidekazu Nishizawa

Effect of stress on the law of approach to saturation magnetization in carbon steels

In high fields where the magnetization is approaching saturation, the resolved magnetic polarization I can be expressed by a power series of the inverse of external field H as: I=I/sub s/-b/H/sup 2/-c/H/sup 3/ . . ., or alternatively in terms of the reversible permeability mu /sub rev/=1+(2b/H/sup 3/+3c/H/sup 4/+ . . .)/ mu /sub 0/ where I/sub s/ is the spontaneous magnetic polarization and b, c, are constants. These equations express the law of approach to saturation magnetization. The coefficient b for a cubic crystal has been deduced as b=0.0762/I/sub s/(K+1.5( lambda /sub 100/- lambda /sub 111/) sigma )/sup 2/, where sigma is the applied stress and others are magnetic constants. The values of reversible permeability mu /sub rev/ under biasing field H were measured for carbon steels with applied stresses. The results showed that the square root of 2b changed linearly with the applied stress, The values of magnetic constant K and lambda /sub 100/ - lambda /sub 111/ were calculated, They agreed with the standard values, but were affected by chemical composition and heat treatment of materials, especially in lambda /sub 100/- lambda /sub 111/. >

Biaxial stress measurement using a magnetic probe based on the law of approach to saturation magnetization

Abstract This paper is concerned with the development of a magnetic technique for nondestructive evaluation of stress in carbon steels. The method proposed is based on the linear dependence on the applied stress of a parameter determined from the law of approach to saturation magnetization. Biaxial stresses in a cruciform specimen are measured by using the proposed method with a magnetic probe. The experiment has shown that the magnetic parameter varies linearly with the principal stresses, σ 1 and σ 2 , such that m 1 = A + B (σ 1 − 0.5σ 2 ) , where m 1 is the magnetic parameter in the direction of σ 1 , and A and B are constants. This indicates that the principal stresses can be determined directly from the measured values in the principal directions. The formula is further extended to the case in which the measuring direction is not the principal direction of the biaxial stress state.