Method and device for detecting damage in materials or objects

• US 20040134280A1
• Filed: 10/01/2003
• Published: 07/15/2004
• Est. Priority Date: 04/02/2001
• Status: Active Grant

• Current Assignee: Impresonic AB
• Original Assignee: Impresonic AB
• Inventors: Sutin, Alexander, Johnson, Paul A., Hedberg, Claes
• Granted Patent: US 6,880,379 B2
• Time in Patent Office: Days
• US Class Current: 73/579
• CPC Class Codes: G01N 19/08 Detecting presence of flaws or irregularities
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 29/045 by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks measuring resonant frequency G01H13/00; measuring strength properties by application of mechanical stress G01N3/00
• CPC Class Codes: G01N 29/2412 using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 3/30 by applying a single impulsive force, e.g. by falling weight

Abstract

In a method of detecting damage in materials or objects (4) the material or object is physically influenced to produce a physical change of the material or object inducing transient slow dynamics in case of damages in the material or object. Slow dynamics induced material elastic modulus changes are detected as indication of damages of the material or object. In a device for non-destructive detection of damage in materials or objects (4), an impact source (16) is provided to impact the material or object to physically influence the material or object to produce a physical change of the material or object inducing transient slow dynamics in case of damages in the material or object. A detector (2,8,10,12,14,6) is provided to detect by said slow dynamics induced material elastic modulus changes as indications of damages of the material or object.

Claims

1. A method of detecting damage in materials or objects, wherein the material or object is physically influenced to produce a physical change of the material or object in case of damages therein, characterized in that the material or object is influenced to induce transient slow dynamics in case of damage in the material or object and in that slow dynamics induced material elastic modulus changes are detected by applying a probe signal to the material or object, sweeping the frequency of the probe signal at least twice, before and after physically influencing the material or object, to determine at least one eigenmode of the material or object, and sensing the probe signal in the material or object while physically influencing it, and analysing said sensed signal to determine a transient frequency displacement of the eigenmode as an indication of a material modulus change resulting from a damage in the material or object.

2. The method according to claim 1, characterized in that to physically influence the material or object it is impacted by application of an electromagnetic impulse to it.

3. The method according to claim 1, characterized in that to physically influence the material or object it is impacted by application of a continuous electromagnetic wave to it.

4. The method according to claim 1, characterized in that to physically influence the material or object it is impacted mechanically.

5. The method according to claim 4, characterized in that the material or object is impacted by a change in an applied load.

6. The method according to claim 5, characterized in that the material or object is hit by a mechanical hammer.

7. The method according to claim 1, characterized in that to physically influence the material or object it is impacted by a change of temperature.

8. The method according to claim 1, characterized in that to physically influence the material or object it is impacted by a change of the ambient pressure.

9. The method according to claim 8, characterized in that to physically influence the material or object it is air impacted by an air gun providing an acoustic impulse.

10. The method according to any one of the claims 1-9, characterized by after determining eigenmodes of the material or object, supplying to the material or object a probe signal of at least one tone of a single frequency chosen to be situated in a selected point on a resonance peak corresponding to a selected one of said determined eigenmodes, sensing said probe signal in the material or object while physically influencing the material or object, and analysing the effect of said physical influence on said sensed probe signal to detect said changes in the material or object elastic modulus.

11. The method according to claim 10, characterized in that said selected point is chosen to be positioned on one flank of said eigenmode resonance peak.

12. The method according to claim 11, characterized in that said selected point is chosen to be located on or near the inflection point of said flank.

13. The method according to any one of the claims 10-12, characterized in that in order to determine said eigenmodes said signal frequency is swept over a predetermined frequency interval and a time-averaged response from the material or object is measured.

14. The method according to any one of the claims 10-13, characterized in that said electromagnetic wave to impact the material or object is a large amplitude signal with a broad frequency band signal of, preferably 10-1000 times, larger amplitude than the probe signal.

15. The method according to any one of the claims 10-13, characterized in that said electromagnetic wave to impact the material or object is a large amplitude signal of a single frequency tone.

16. The method according to claim 14 or 15, characterized in that the frequency of the probe signal is considerably higher than frequencies of said large amplitude signal.

17. The method according to any one of the claims 1-16, characterized in that said probe signal is continuously supplied with constant amplitude.

18. The method according to any one of the claims 15-17, characterized in that said probe signal and said large amplitude signal are acoustic signals.

19. The method according to any one of the preceding claims, characterized in that a plurality of single tone probe signals are supplied to the material or object said signals having single tone frequencies chosen to be situated on different flanks of resonance peaks corresponding to selected ones of said determined eigenmodes, and in that the effect of said physical influence on said plurality of probe signals are monitored for the detection of damages.

20. The method according to any one of the preceding claims for use on a production or manufacturing line, characterized in that changes in the monitored material or object elastic modulus are compared to predetermined baseline information to determine pass or fail status for the material or object.

21. A device for non-destructive detection of damage in materials or objects, comprising an impact source provided to impact the material or object to physically influence the material or object to produce a physical change of the material or object characterized in that said impact source is adapted to produce a physical change of the material or object to induce transient slow dynamics in case of damage therein in that a probe signal source is provided to supply a probe signal to the material or object, in that sweeping means are provided to sweep the probe signal frequency at least twice, before and after physically influencing the material or object, to determine at least one eigenmode of the material or object, in that sensing means are provided to sense the probe signal in the material or object while physically influencing it, and in that analysing means are provided to determine a transient frequency displacement of the eigenmode as an indication of a material elastic modulus change resulting from a damage in the material or object.

22. The device according to claim 21, characterized in that said impact source comprises a signal generator adapted to impact the material or object with a continuous or pulsed electromagnetic wave for physically influencing the material or object.

23. The device according to claim 21, characterized in that said impact source comprises an air gun adapted to impact the material or object by an acoustic impulse for physically influencing it.

24. The device according to any one of the claims 21-23, characterized by a first signal generator for supplying a first signal to the material or object, a control means to control said first signal generator to sweep the frequency of said first signal over a predetermined frequency interval, a determining means to determine eigenmodes of the material or object when sweeping the frequency of the supplied first signal, a second signal generator for supplying a probe signal of at least one single tone frequency to the material or object, said frequency being chosen to be situated in a selected point on a resonance peak corresponding to a selected one of said eigenmodes, a sensing means to sense said probe signal in the material or object while physically influencing the material or object, and analysing means to analyse the effect of said physical influence on said sensed probe signal for detecting changes in said material or object elastic modulus.

25. The device according to claim 24, characterized in that said selected point is positioned on one flank of said eigenmode resonance peak.

26. The device according to claim 24 or 25, characterized in that a computer is provided to form said control means.

27. The device according to any one of the claims 24-26, characterized in that said second signal generator is adapted to supply an acoustic probe signal.

28. The device according to any one of the claims 24-27, characterized in that said second signal generator is connected to an acoustic signal source, such as a piezoelectric transducer, to be contacted with the material or object for supply of the probe signal.

29. The device according to any one of claims 24-27, characterized in that said second signal generator is connected to a non-contact wave source, such as a speaker for contactless supply of the probe signal to the material or object.

30. The device according to any one of claims 24-29, characterized in that said second signal generator is adapted to supply a probe signal having a plurality of single tone frequencies.

31. The device according to any one of claims 24-30, characterized in that said first and second signal generators are one and the same signal generator.

32. The device according to any one of claims 21-31, characterized in that said impact source comprises a laser impulse source.

33. The device according to any one of the claims 21-32, characterized in that said analysing means comprises a data acquisition means for receiving and analysing sensed signals from the materiel or object.

34. The device according to claim 33, characterized in that said data acquisition system comprises a digitising means.

35. The device according to any one of claims 33 or 34, characterized in that at least one vibration sensor is provided to contact the material or object to deliver said sensed signal to said data acquisition system.