Stress measurement in ferromagnetic articles

摘要

Apparatus for measuring stress in ferromagnetic materials 16 comprises an electromagnet formed by a U-shaped core 26 having two spaced poles 28, a magnetic sensor 32 arranged between the poles to detect magnetic flux density perpendicular to the direction of the free space magnetic field between the poles and a second magnetic sensor arranged to sense the reluctance of the part of the magnetic circuit between the poles. In use, the probe is rotated while placed adjacent to the surface of the material under test, the electromagnet being energised with an alternating current, measurements being taken from the magnetic sensors for a plurality of different orientations of the probe with respect to the material. The directions of the principal stress axes and values of the principal stresses are determined from the measurements.