File:Animation Controle Non Destructif Courants Français: Schéma d’un contrôle non destructif par courants de Foucault. Download scientific diagram| Principe du CND par courants de Foucault from publication: Design of eddy current microsensor arrays and signals inversion for . Job postings: Spécialiste CND – Ingénieur d’application Ultrason et Courants de Foucault (6 mois) at Olympus NDT Canada, Québec, Québec.

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While conductivity and permeability are properties of the test material that are outside of the operator’s control, the test frequency, coil type, and coil size can be chosen based on test requirements.

In courans cases, eddy current and ultrasonic testing are used together as complementary techniques, with eddy current having an advantage for quick surface testing and ultrasonics having better depth penetration.

Conductivity Testing – Eddy current testing’s ability to measure conductivity can be used to identify and sort ferrous and nonferrous alloys, and to verify heat treatment. Sliding probes – Also used in testing aircraft fastener holes, offering higher scan rates than donut probes. The horizontal line is the lift off in which the probe has been “nulled” balanced on the aluminum part and when it is lifted in the air, the signal moves directly to the left.

The phenomenon of eddy currents was discovered by French physicist Leon Foucault inand for this reason eddy chd are sometimes called Foucault currents.

Contrôle par courants de Foucault

Once the parameters are set, they should not be changed during foucaulf inspection. Low frequency probes can be used to locate corrosion on second and third layers of metal that cannot be inspected ultrasonically.

The top line shows the signal on aluminum without any coating. In thickness measurement foucalt the reference standards would consist of various samples of know thickness. Donut probes – Designed to inspect aircraft fastener holes with fasteners in place.

Eddy current testing is now a widely used and well-understood inspection technique for flaw detection as well as for thickness and conductivity measurements.

By Tom Nelligan and Cynthia Calderwood Magnetism, the underlying principle behind electric motors and generators, relays and stereo speakers, is also the force that enables an important category of NDT tools called eddy current instruments. At the same time, eddy current testing is limited to materials that conduct electricity and thus cannot be used on plastics. The operator observes the response from the reference standards and then compares the indications from test pieces to these reference patterns to categorize parts.


Another common test involves measurement of nonconductive coatings like paint over metals. Types of probes Eddy current instruments can perform a wide variety of tests depending on the type of probe being used, and careful probe selection will help optimize performance.

Variations in the plot correspond to variations in the test piece. Surface Inspection – Surface cracks in machined parts and metal stock can be readily identified with eddy current. Both cracking and thickness variations can be detected. In addition to finding cracks, eddy current can also be used vnd check metal hardness and conductivity in applications where those properties are of interest, and to measure thin layers of nonconductive coatings like paint on metal parts.

The top curve represents a 0. Some inspections involve sweeping through multiple frequencies to optimize results, or inspection with fucault probes to obtain the best resolution and penetration required to detect all possible flaws.

This in turn affects the foucaupt of electrons in the coil by varying the electrical impedance of the coil. Pencil probes – Smaller diameter probes housing coils built for foucaklt frequencies for high resolution of near surface flaws. Some of the most common are listed below. Thus, variations in the conductivity of the test material, its magnetic permeability, the frequency of the AC pulses driving the coil, and coil geometry will all have an effect on test sensitivity, resolution, and penetration.

Optimisation particulaire par métamodèle appliquée au CND par courants de Foucault

This example was a 0. Eddy current density is highest near the surface of the part, so that is the region of highest test resolution. Inanother breakthrough was foucualt when another English scientist, David Hughes, demonstrated how the properties of a coil change when placed in contact with metals of different conductivity and permeability. This measurement is most commonly used to determine the conductivity of a material but it will also provide the thickness of a coating which is considered the “Liftoff” from the material or how far the probe is above the surface of the conductive material.


For example, the display below shows a setup for inspection for surface cracks in aluminum.

There have been many recent developments in eddy current testing, leading to improved performance and the development of new applications. This measurement uses a special conductivity probe that displays the below screen instead of the standard impedance screen shown above. To create this image, the display position had foucalut be changed between each measurement in order to display a separation between each signal. In addition to crack detection in metal sheets and tubing, eddy current can be used for certain metal thickness measurements such as identifying corrosion under aircraft skin, to measure conductivity and monitor the effects of heat treatment, and to determine the thickness of nonconductive coatings over conductive substrates.

ID probes – Used for inspection of heat exchangers and similar metal tubing from the inside, available in a variety chd sizes. Bolt hole probes – Designed to inspect the inside of a bolt hole. Eddy current testing is widely used in the aerospace industry and in other manufacturing and service environments that require inspection of thin metal for potential safety-related or quality-related problems.

In a given test, resolution will be determined by the probe type while detection capability will be controlled by material and equipment characteristics.


Impedance plane displays While some older eddy current instruments used simple analog meter displays, the standard format now is an impedance plane plot that graphs coil resistance on the x-axis versus inductive reactance on the y-axis.

ECA can permit use of simpler fixturing, and can also simplify inspection of complex shapes through custom probes built to fit the profile of the test piece. Bolt Hole Inspection – Cracking inside bolt holes can be detected using bolt hole probes, often with automated rotary scanners.

Menu More Pour nous joindre. Eddy current testing began largely as a result of the English scientist Michael Faraday’s discovery of electromagnetic induction in Variations in permeability of a material generate noise that can limit flaw resolution because of greater background variations.

This inspection is done with a pencil probe.