ABSTRACT
A magnetic anisotropy sensor is used for nondestructive measurement of stress on surfaces of a ferromagnetic material, such as steel. The sensor is built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of a ferromagnetic material is measured in a nondestructive manner, which then can be translated into the absolute values of stresses existing on the surface of the material. Proper treatment of boundary conditions allows determination of stress tensor completely on surfaces of H-beam flanges, for example. This technique was applied to measure stresses of H-beams, used as tunnel support structures, to confirm expected measurement accuracy. The results show that this method could be one of the promising technologies for non-destructive stress measurement for safe construction and probably maintenance of rock structures.
