초록 ▼

Apparatus for the detection of cracks or other defects near the surface of a conducting engineering material of interest includes a magnetic probe having two sites which in operation act as magnetic poles on the same side of the probe such that an external magnetic field extends between them princip

Apparatus for the detection of cracks or other defects near the surface of a conducting engineering material of interest includes a magnetic probe having two sites which in operation act as magnetic poles on the same side of the probe such that an external magnetic field extends between them principally in a region adjacent to that one side of the probe, means for rotating the probe about an axis spaced from the mid-point between the two sites, whereby when the probe is adjacent to the surface of an engineering material of interest occupying the region with the axis substantially perpendicular to the surface the magnetic field is able to penetrate the surface and rotate beneath it about the axis causing energy associated with the magnetic field to be dissipated in the material, and means for detecting a change caused by a defect in the material, to the dissipated energy.

대표청구항 ▼

Apparatus for the detection of cracks near the surface of a workpiece and adjacent to a fastener hole therein comprising: a magnetic probe including a magnetic core having a coil mounted thereon, the core having two arms forming magnetic poles and a link portion between them, said coil being mounted

Apparatus for the detection of cracks near the surface of a workpiece and adjacent to a fastener hole therein comprising: a magnetic probe including a magnetic core having a coil mounted thereon, the core having two arms forming magnetic poles and a link portion between them, said coil being mounted on a first one of said arms, said arms and said link portion having a cross-sectional thickness perpendicular to its axis which is small compared to the spacing between said arms, whereby in operation with the surface of the workpiece adjacent to said poles a magnetic field extends between said poles and penetrates said workpiece, said magnetic field being concentrated in the region of both of said poles, the lateral spread of said magnetic field being restricted by the cross-sectional thickness of said arms and said line portion to a width which is small compared to the spacing between said poles; a rotational stepping drive arrangement for rotating said probe in a stepwise manner about an axis of rotation substantially parallel to said arms and displaced from said first arm which axis may in use be made coincident with the axis of said fastener hole, whereby said first arm and said coil are rotationally stepped about said axis of rotation; means for energizing said coil; detection circuit means for generating at the end of each step of said stepped rotation a first signal representative of the energy of said magnetic field dissipated in said workpiece by detecting the energy supplied to said coil; reference signal generator means for generating a second signal representative of the energy dissipated in the defect free regions of said workpiece; comparator means for comparing said first and second signals and for providing a third signal representing any difference between said first and second signals; an analog-to-digital converter for digitizing said third signal, a digital store for storing said third signal in digital form while said probe is rotating; and a display, having an input from said store, for displaying a graphical plot of the variation of said third signal with the rotational position of said probe.