The Boeing Company

Iver G Hendrickson

Karl A Hansen

Disclosed is an eddy current inspection system for nondestructive detection of subsurface flaws in regions of multilayer conductive structure that surround a fastener which joins the conductive layers. The eddy currents are induced by an aperiodic drive current having a relatively long rise time and a relatively last fall time that is supplied to a drive coil and a pick-up coil that is mounted with the drive coil supplies a signal representative of the induced eddy currents. Compensation is provided for variation in lift-off (spacing between the surface of the structure being inspected and the surface of the drive coil and pick-up) by utilizing parametric relationships relative to the maximum amplitude of inspection signals supplied when subsurface flaws exist and inspection signals supplied when lift-off is present. Because similar parametric relationships exist relative to other system characteristics that affect the electromagnetic environment of the inspection media, compensation can also be provided for variation in the height of fasteners (protrusion), fastener edge margin, and gaps or spacing between the successive conductive layers of the multilayer structure. By utilizing a microprocessor or other sequential digital signal processing apparatus, values that define the parametric relationships utilized in compensating for any particular system characteristic can be stored in memory for the inspection of a relatively large number of structural configurations.

Eddy current flow detection including compensation for system variables

Nondestructive evaluation of conductive materials is disclosed wherein a magnetic field having a relatively slow rise time and a relatively fast fall time induces eddy currents in the conductive material being tested and subsurface flaws such as internal cracks or other discontinuities are detected by monitoring the magnetic field produced by the eddy currents. The magnetic field is generated by sequentially discharging two capacitor banks through a coil with the currents supplied by the capacitor banks being of opposite polarity and the first capacitive discharge exhibiting a time constant that is substantially longer than the second capacitive discharge. The initial, slowly rising portion of the magnetic field establishes magnetic flux that extends to substantial depths within the conductive material and the fast fall time of the magnetic field causes eddy currents of substantial magnitude to circulate within the region of the conductive material being examined. Flaws within the material cause perturbations in the eddy currents and induce current variations in a pickup coil during a time interval occurring shortly after the magnetic field begins to collapse. Detection equipment, connected for receiving the signal supplied by the pickup coil, monitors the amplitude of the pickup coil signal and, in some situations, its relationship in time relative to the rapid collapse of the magnetic field to determine the presence and location of a flaw.

Apparatus and method for eddy current detection of subsurface

An electromagnetic force (EMF) machine with a universal portable power supply is disclosed. The universal portable power supply energizes either a multiple turn flux concentrator or a single turn flux concentrator. The flux concentrators produce magnetic fields that create an outward tension force adapted to perform non-destructive bond tests (tension proof loading) and/or dent removal operations on panels or the like. The power supply includes a slow current pulse subsystem; a fast current pulse subsystem; slow and fast crowbars; and, a firing control. The firing control controls the production of pulses by the slow and a fast current pulse subsystems, and, the operation of the slow and fast crowbars. The slow pulse subsystem, via the flux concentrator, slowly creates a magnetic field that penetrates the panel; the fast pulse subsystem, via the flux concentrator, rapidly decreases the magnetic field, whereby a negative field gradient is produced across the panel. The negative field gradient exerts the outward tension force on the panel. Further, a set of control switches control the magnitude of the current produced by the slow current pulse subsystem; and, determine the flux concentrator to which the slow and fast pulses are to be applied. Finally, a charging circuit controls the charge level of capacitor banks forming part of the slow and fast current pulse subsystems such that a predetermined ratio exists between the pulses produced by the slow and fast current pulse subsystems.

Electromagnetic force machine with universal portable power supply

An apparatus and method of electromagnetically pulling dents from conductive material. A coil is formed to direct an effective electromagnetic coupling to a limited area between the coil and a dented part. A nonconductive mold placed between the coil and part has openings to overlie the dent. The coil is first energized with a slowly rising current then is energized with a fast pulsing countercurrent to generate a strong pulling electromagnetic coupling.

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Seattle, WA, United States of America

Iver G Hendrickson