This paper presents a new method to evaluate magnetostriction of a silicon steel sheet as an eigen value of 2-dimensional strain tensor. Conventional way to measure the property was to measure the strain only by the direction of magnetic flux density vector, although the directions of flux density and strain are not the same. This paper presents a method to evaluate the strain of all-around-horizontal direction using 2-dimensional strain tensor, its eigenvalue and eigenvector, and a method to measure the strain with 3-axis strain gage to calculate strain tensor. Measured results indicate that NO sheet expands by the same direction as magnetic flux density vector, although GO sheet expands to the transverse direction with no relation to the direction of magnetic flux density vector. Then an angle difference between the magnetic flux density vector and the direction of maximum magnetostriction is observed in GO material.
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