Thermographic test method and testing device for carrying out the test method

• US 9,194,831 B2
• Filed: 04/07/2011
• Issued: 11/24/2015
• Est. Priority Date: 04/08/2010
• Status: Active Grant

• Current Assignee: Institut Dr. Foerster GmbH & Co. KG
• Original Assignee: Institut Dr. Foerster GmbH & Co. KG
• Inventors: Traxler, Gerhard, Palfinger, Werner
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): COTEY, PHILIP L
• Application Number:
  US13/639,354
• Publication Number:
  US 20130077650A1
• Time in Patent Office: 1,692 Days
• Field of Search: 374/5
• US Class Current: 1/1
• CPC Class Codes: G01N 25/72 Investigating presence of flaws
• CPC Class Codes: G06T 2207/10048 Infrared image
• CPC Class Codes: G06T 2207/30136 Metal
• CPC Class Codes: G06T 7/0004 Industrial image inspection

Abstract

A thermographic test method locally resolves detection and identification of defects near the surface in a test object. A surface area of the test object is heated up. A series of thermographic images following one after another at a time interval is recorded within a heat propagation phase, each image representing a local temperature distribution in a surface region of the test object recorded by the image. Positionally correctly assigned temperature profiles are determined from the images, each positionally correctly assigned temperature profile being assigned to the same measuring region of the test object surface. Variations over time of temperature values are determined from the temperature profiles for a large number of measuring positions of the measuring region. These variations are evaluated on the basis of at least one evaluation criterion indicative of the heat flow in the measuring region.

Claims

1. A thermographic test method for locally resolving detection and identification of defects near a surface in a test object, the method comprising the acts of:

heating up a portion of the test object such that a thermal disequilibrium occurs between defective regions, affected by defects, and material of the test object that is free from defects, a defect-free surrounding area of a defective region not being heated up or heated up less intensely than the defective region, the surrounding area being located laterally with respect to the surface of the test object;

recording a series of thermographic images one after another at a time interval within a heat propagation phase, which heat propagation phase begins when a lateral heat flow with respect to the surface of the test object from the locally heated-up defective region laterally into a surrounding area of the defective region manifests itself, each thermographic image representing a local temperature distribution in a surface region of the test object that is recorded by the thermographic image;

determining positionally correctly assigned temperature profiles from the thermographic images, a temperature profile being a locally resolving profile, wherein different locations within the temperature profile are respectively assigned values of a measured variable representing the temperature at the respective location, and each positionally correctly assigned temperature profile being assigned to a same measuring region of the surface of the test object;

determining variations over time of temperature values from the temperature profiles for a large number of measuring positions of the measuring region that are recorded by the temperature profiles; and

evaluating the variations over time based on at least one evaluation criterion indicative of the lateral heat flow in the measuring region.

2. The thermographic test method as claimed in claim 1, wherein, in the act of evaluating, at least one local maximum of the temperature values within the temperature profiles is sought.

3. The thermographic test method as claimed in claim 2, wherein, in the act of evaluating, a variation over time of an amplitude of temperature values in the region of the local maximum is evaluated.

4. The thermographic test method as claimed in claim 3, wherein, in the act of evaluating, a heat concentration value in the region of a local maximum of the temperature values within the temperature profiles is determined and a variation over time of the heat volume concentration value is evaluated.

5. The thermographic test method as claimed in claim 2, wherein, in the act of evaluating, a heat concentration value in the region of a local maximum of the temperature values within the temperature profiles is determined and a variation over time of the heat volume concentration value is evaluated.

6. The thermographic test method as claimed in claim 1, wherein, in the act of evaluating, at least three positionally correctly assigned temperature profiles are evaluated together.

7. The thermographic test method as claimed in claim 6, wherein between four and twenty positionally correctly assigned temperature profiles are evaluated together.

8. The thermographic test method as claimed in claim 4, wherein between four and twenty positionally correctly assigned temperature profiles are evaluated together.

9. The thermographic test method as claimed in claim 1, wherein, for testing an elongated test object, a relative movement is produced between the elongated test object and a recording device for recording the thermographic images in a direction of movement extending substantially parallel to a longitudinal direction of the elongated test object such that surface regions recorded by the thermographic images are offset with respect to one another in the direction of movement, the surface regions of the thermographic images recorded directly one after another overlapping in an overlapping region.

10. The thermographic test method as claimed in claim 9, wherein the recording device remains stationary and the elongated test object is moved relative to the recording device.

11. The thermographic test method as claimed in claim 10, further comprising the acts of:

analyzing a first thermographic image, recorded at a first point in time, of a series of thermographic images for the identification of at least a first picked-out image detail, which picked-out image detail contains a surface detail with a defect-like anomaly;

automatically finding a second image detail, corresponding to the first image detail, in a second thermographic image, recorded at a later, second point in time at a time interval from the first thermographic image; and

evaluating thermographic data of the first image detail and the second image detail together, wherein a local maximum of the temperature values within the temperature profiles is sought if defect-like anomalies are identified.

12. The thermographic test method as claimed in claim 9, further comprising the acts of:

analyzing a first thermographic image, recorded at a first point in time, of a series of thermographic images for the identification of at least a first picked-out image detail, which picked-out image detail contains a surface detail with a defect-like anomaly;

automatically finding a second image detail, corresponding to the first image detail, in a second thermographic image, recorded at a later, second point in time at a time interval from the first thermographic image; and

evaluating thermographic data of the first image detail and the second image detail together, wherein a local maximum of the temperature values within the temperature profiles is sought if defect-like anomalies are identified.

13. The thermographic test method as claimed in claim 11, wherein for the automatic finding, an expected position of the surface detail containing the defect-like anomaly in the second thermographic image is determined based on a relative speed between the elongated test object and the recording device, the direction of movement and the time that has passed between the first point in time and the second point in time;

and

wherein the relative speed is measured.

14. The thermographic test method as claimed in claim 12, wherein for the automatic finding, an expected position of the surface detail containing the defect-like anomaly in the second thermographic image is determined based on a relative speed between the elongated test object and the recording device, the direction of movement and the time that has passed between the first point in time and the second point in time;

and

wherein the relative speed is measured.

15. A thermographic testing device for locally resolving detection and identification of defects near a surface in a test object, the thermographic testing device comprising:

a heating device operatively configured to heat up a portion of the test object such that a thermal disequilibrium occurs between defective regions, affected by defects, and material of the test object that is free from defects, wherein a defect-free surrounding area of a defective region is not heated up or heated up less intensely than the defective region;

at least one recording device operatively configured to record a series of at least two thermographic images one after another at a time interval;

an evaluating device operatively configured to evaluate thermographic data of the at least two thermographic images; and

wherein the testing device is operatively configured to carrying out the method as claimed in claim 1.