Electricity: measuring and testing – Magnetic – Calibration
Reexamination Certificate
2002-02-05
2004-02-24
Barlow, John (Department: 2863)
Electricity: measuring and testing
Magnetic
Calibration
C324S219000
Reexamination Certificate
active
06696830
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates generally to the inspection of structures by employing non-destructive techniques and, more particularly, to a method and an inspection standard for eddy current inspections.
The safety and structural integrity of aircraft is a concern to manufacturers as well as consumers. As the average age of aircraft in service grows, reliable and accurate inspections of aircraft components become increasingly important. For example, non-destructive inspections may be the only means available to identify deteriorating areas of an exterior surface of the aircraft and associated surface fastener openings. Furthermore, it is common to detect cracks or other defects located below the aircraft surface using non-destructive methods.
Eddy current inspection is a commonly used non-destructive inspection means used to detect discontinuities or flaws in the surfaces of various components, including aircraft engine components and aircraft skin surfaces. Generally, eddy current inspection is based on the principle of electromagnetic induction. In at least one known method, a drive coil is used to induce eddy currents within a conductive material that is being inspected. Secondary magnetic fields that may result from the eddy currents are detected by a sense coil which generates signals that are subsequently processed for the purpose of detecting flaws.
Eddy current testing for flaws in materials is typically done by mechanically scanning a single probe in at least two dimensions. For example, U.S. Pat. No. 5,345,514, entitled “An Improved Method for Inspecting Components Having Complex Geometric Shapes” and assigned to The General Electric Company describes methods for interpreting eddy current image data acquired by a single probe, particularly in the context of inspecting a high pressure turbine (HPT) disk dovetail slot. Such inspection instruments are capable of detecting cracks and other deformations in a workpiece by measuring the eddy current induced in the workpiece.
The term eddy current, as generally understood in the art and as used herein, refers to a current created or induced in a material by an applied varying magnetic field, or by moving the material in a magnetic field. Suitable electronics for acquiring data from an eddy current inspection are disclosed in U.S. Pat. No. 5,182,513, entitled “Method and Apparatus for a Multi-Channel Multi-Frequency Data Acquisition System for Nondestructive Eddy Current Inspection Testing” and assigned to The General Electric Company.
At least some known systems for performing eddy current inspections include a master or standard component (hereinafter “standard”) which is believed to be structurally sound. The standard has an eddy current signature which is determined by performing an eddy current inspection of the standard. An eddy current inspection of a component to be inspected (suspect component) is performed to obtain an eddy current signature of the suspect component, and, the signatures are compared to determine whether the suspect component is structurally sound. Standards are especially useful in field inspections where process drift and differing environments may generate erroneous results when using a pre-calibrated scanning electronics. Therefore, in field inspections, it is sometimes useful to calibrate the scanning electronics using an eddy current signature of a standard as a reference. The standard is typically an actual component that is fabricated from the same material as the suspect component. Accordingly, when the suspect component is expensive and/or heavy, the standard is typically also expensive and/or heavy which may result in additional expenses and/or difficulty in handling.
SUMMARY OF INVENTION
In one aspect, a method for inspecting a metallic component is provided. The method comprises providing an inspection standard having a body shaped substantially similar to a body of the metallic component, wherein the inspection standard body is fabricated from a non-metallic material. The method also comprises inspecting the metallic component with an eddy current probe with reference to the inspection standard.
In another aspect, an inspection standard is provided. The inspection standard comprises a body fabricated from a non-metallic material and having at least one surface. A plurality of grooves extends across the outer surface and inner surface. The inspection standard also comprises a conductor positioned within each of the
In a further aspect, an inspection device comprises an inspection standard having a non-metallic body and an inspection device comprising a probe, wherein the probe is in close proximity to the inspection standard.
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Casarcia Dominick A.
Ingram Douglas E.
McKnight William S.
Armstrong Teasdale LLP
General Electric Company
Herkamp Nathan
Le Toan M
Reeser, II Robert B.
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