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

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, σ₁ and σ₂, such that m₁ = A + B (σ₁ - 0.5σ₂), where m₁ is the magnetic parameter in the direction of σ₁, 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.