Flaw imaging in ferrous and nonferrous materials using magneto-o

Details Flaw imaging in ferrous and nonferrous materials using magneto-o Flaw imaging in ferrous and nonferrous materials using magneto-o

1983-07-05

1986-11-25

Strecker, Gerard R.

Electricity: measuring and testing

Magnetic

With means to create magnetic field to test material

324213, 324238, 350377, 356237, G01N 2782, G01N 2121, G02F 109

Patent

active

046251677

ABSTRACT:
A method for the direct visualization of surface and near surface cracks, voids, flaws, discontinuities, etc. in materials is disclosed. The detection of flaws or the like is accomplished by the visualization of the static and/or dynamic magnetic fields, either ambient or induced, associated with various flaws in a target material. A magnetic garnet epitaxial film is deposited on a non-magnetic substrate. In one embodiment, a reflective coating or material is provided adjacent to the epitaxial film, and the substrate with its associated layers is placed over the target material. A magnetic field is then applied to the target material and substrate. Polarized light is directed onto the through the substrate and associated epitaxial layer, and is reflected by the reflective coating such that the polarized light passes back out of the substrate. The existing magnetization within the epitaxial film interacts with nearby magnetic fields associated with near surface flaws in the target material, such that the domain structure of the epitaxial film is altered. The altered domain structure induces a rotation of the plane of polarization of the incident projected light. When viewed through a polarizing material, the rotation of the reflected light renders the magnetic field variations associated with the flaws directly visible. Accordingly, surface and near surface flaws are optically detected. An alternate embodiment is disclosed which utilizes a transmission geometry.

REFERENCES:
patent: 3443214 (1969-05-01), Meservey
patent: 3564924 (1971-02-01), De Sorbo
patent: 3594064 (1971-07-01), Bierlein
patent: 3650601 (1972-03-01), Bierlein
patent: 3893023 (1975-07-01), Otala
patent: 4064453 (1977-12-01), Haas et al.

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