AIR COUPLED ULTRASONIC CONTACTLESS METHOD FOR NON-DESTRUCTIVE DETERMINATION OF DEFECTS IN LAMINATED STRUCTURES

• US 20140216158A1
• Filed: 08/09/2012
• Published: 08/07/2014
• Est. Priority Date: 08/17/2011
• Status: Abandoned Application

• Current Assignee: EMPA, Eidgenoessische Materialpruefungs- Und Forschungsanstalt
• Original Assignee: Jurg Neuenschwander, Sergio Jose Sanabria Martin
• Inventors: Sanabria Martin, Sergio Jos, Neuenschwander, Jrg, Sennhauser, Urs
• Application Number:
  US14/238,895
• Publication Number:
  US 20140216158A1
• Time in Patent Office: Days
• US Class Current: 73/588
• CPC Class Codes: G01N 2291/0231 Composite or layered materials
• CPC Class Codes: G01N 2291/0238 Wood
• CPC Class Codes: G01N 2291/0289 Internal structure, e.g. defects, grain size, texture
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 29/06 Visualisation of the interior, e.g. acoustic microscopy medical or veterinary diagnosis using sonic waves A61B8/00; representation of acoustic wave distribution G01H3/125, G01H9/002; short-range imaging systems using reflection of acoustic waves G01S15/8906
• CPC Class Codes: G01N 29/069 Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
• CPC Class Codes: G01N 33/46 Wood

Abstract

There is an air coupled ultrasonic contactless method and an installation for non-destructive determination of defects in laminated structures with a width (W) and a multiplicity of n lamellas with intermediate N−1 bonding plants (B), whereas at least one transmitter (T) in a fixed transmitter distance (WTS) radiates ultrasound beams at multiple positions and at least one receiver (R) in a sensor distance (WSR) is receiving re-radiated ultrasound beams at multiple positions relative to the laminated structure (S). The method images the position and geometry of for example lamination defects and allows for inspection of laminated structure (S) of arbitrary height (H) and length (L), and an individual assessment of specific bonding planes (e.g. B1, B2, B3), as well in situations with constrained access to the faces of the sample parallel to the bonding planes.

Claims

1. Air coupled ultrasonic contactless method for non-destructive determination of defects in a laminated structure (S) with a width (W) and a multiplicity of n lamellas with intermediate n−

1 bonding planes (Bi), wherein at least one transmitter (T) in a fixed transmitter distance (WTS) radiates ultrasound incident sound fields (IF) at multiple positions and at least one receiver (R) in a sensor distance (WSR) is receiving re-radiated ultrasound fields (RRF, RSF) at multiple positions relative to the laminated structure (S), comprising the steps of;

coupling the incident sound field (IF) of an ultrasound beam from an active area of the at least one transmitter (T) through a lateral face (FN1) after passing a gas medium (A) in a fixed transmitter distance (WTS) into the laminated structure (S),

whereas the normal of the lateral face (FN1) is at least essentially perpendicular to the normals of the bonding planes (Bi),

whereas the ultrasound incident sound field (IF) is tilted with an inclination angle θ

_I from 0°

to 20°

from the normal of the lateral face (FN1),

receiving re-radiated refracted and/or scattered sound fields (RRF, RSF) with the at least one receiver (R) in the sensor distance (WSR) after propagation of the ultrasound beam through the width (W) of the laminated structure (S) within a reduced portion of the total height (H) and length (L) of the laminated structure (S) after passing a re-radiated lateral face (FN2) and a gas medium (A), before;

ultrasound wave signatures are extracted by subsequent low-noise electrical signal amplification, filtering, analogue to digital conversion and signal processing of ultrasound datasets, before;

generation and representation of ultrasound images (UI) of the gluing state of each bonding plane is performed, such that defects are determined independently from the total height (H) and length (L) of the laminated structure (S) and defects are determined without access to the long side faces (FP1, FP2, . . . ) of the laminated structure (S).

2. Air coupled ultrasonic contactless method according to claim 1, wherein the lateral face (FN1) and the re-radiated lateral face (FN2) are two different opposing faces of the laminated structure (S).

3. Air coupled ultrasonic contactless method according to claim 1, wherein the incident sound field (IF) comprising a center excitation frequency (f) is chosen to achieve a smaller wavelength in the laminated structure (S) than a mean lamella height (HL).

4. Air coupled ultrasonic contactless method according to claim 3, wherein the fixed transmitter distance (WTS) satisfies WTS>

0.5r² c_A<sup>−

1</sup> f, where f is the center excitation frequency of the ultrasound incident sound field (IF), c_A is the sound velocity in air and r is the radius of the active area of the transducer (T).

5. Air coupled ultrasonic contactless method according to claim 1, wherein the inclination angle θ

_I is calculated by

6. Air coupled ultrasonic contactless method according to claim 1, wherein the separation between the intersection of the normal of the at least one transmitter (T) with the lateral face (FN1) and the Intersection of the normal of the at least one receiver (R) with the re-radiated lateral face (FN2) is estimated by

7. Air-coupled ultrasonic contactless method according to claim 5, wherein Δ

H is a multiple of lamella height (HL).

8. Air coupled ultrasonic contactless method according to claim 1, wherein the incident sound field (IF) is a pulse with center frequency (f).

9. Air coupled ultrasonic contactless method according to claim 8, wherein the sensor distance (WSR) between the receiver transducer (R) and re-radiated lateral face (FN2) is adjusted before the coupling of the incident sound field (IF) to the length of the analyzed time window (T_R) matching WSR>

0.5c_AT_R, where (c_A) is the sound velocity in air.

10. Air coupled ultrasonic contactless method according to claim 1, wherein measured ultrasound datasets are represented as a multiplicity of time vs. amplitude waveforms, and ultrasound images (UI) are generated by determining for each waveform amplitude and phase within analyzed time window (T_R).

11. Air coupled ultrasonic contactless method according to claim 1, wherein a multiplicity of transmitter (T) and/or a multiplicity of receiver (R) forming arrays are used.

12. Air coupled ultrasonic contactless method according to claim 1, wherein the at least one transmitter (T) is scanned at least parallel to the lateral face (FN1) and/or the at least one receiver (R) is scanned at least parallel to the re-radiated lateral face (FN2) with a scanning system unit (SU) as a fix unit.

13. Air coupled ultrasonic contactless method according to claim 10, wherein the scanning system unit (SU) is implemented either mechanically, with multiple axes scanner or robotic arms or is implemented electronically, with array phasing technology.

14. Air coupled ultrasonic contactless method according to claim 10, wherein the at least one transmitter (T) and the at least one receiver (R) are scanned synchronized to each other in Y and Z directions.

15. Air coupled ultrasonic contactless method according to claim 1, wherein the laminated structure (S) is moved relative to the at least one transmitter (T) and/or the at least one receiver (R).

16. Air coupled ultrasonic contactless method according to claim 1, wherein the at least one transmitter (T) and the at least one receiver (R) are adjusted relative to each other in such a way, that the normals of active areas of transducer (T, R) faces are parallel to each other.

17. Air coupled ultrasonic contactless method according to claim 1, wherein the at least one transmitter (T) and the at least one receiver (R) are adjusted relative to each other in such a way, that the normals of active areas of transducer (T, R) faces are angled including an angle of (180°

−

2*inclination angle θ

_I).

18. Air coupled ultrasonic contactless method according to claim 1, wherein the at least one transmitter (T) and the at least one receiver (R) are adjusted relative to each other in such a way, that the normals of active areas of transducer (T, R) faces are angled including an angle of 2*inclination angle θ

_I.

19. Air coupled ultrasonic contactless method according to claim 1, wherein transmitter (T) and/or receiver (R) with active areas possessing radii (r) of the active areas in the order of half of the mean lamella height (HL) are chosen.

20. Air coupled ultrasonic contactless method according to claim 1, wherein directive, omnidirectional, focused or planar transducers (T, R) are chosen.

21. Air coupled ultrasonic contactless method according to claim 20, wherein single or multi element ultrasound transducers (T, R) are used.

22. Air coupled ultrasonic contactless method according to claim 1, wherein measurement parameters as transmitter distance (WTS), sensor distance (WSR), separation between the intersection of the normal of the transmitter and the lateral face (FN1) and the intersection of the normal of the receiver (R) with the re-radiated lateral face (FN2), inclination angle θ

_I and excitation frequency f are estimated by simulation and computation of a direct ultrasound wave propagation model (DPM) on the basis of a defect free laminated structure, before insonification of the lateral face (FN1) with an incident sound field (IF).

23. Air coupled ultrasonic contactless method according to claim 1, wherein after a measurement, measured ultrasound images (UI) or ultrasound datasets are interpreted by inverting the data with an inverse ultrasound wave propagation model (IPM) and associating the results with defect positions, types and geometries within the laminated structure (S).

24. Air coupled ultrasonic contactless method according to claim 22, wherein the direct ultrasound wave propagation model (DPM) incorporates:

a) synthesis of ultrasound beam in the vicinity of coupling lateral faces (FN1, FN2) by decomposition of transducer near field in elementary point excitations,

b) computation of coupling and wave propagation phenomena within laminated structure (S) in a defined discretization domain,

c) projection of the re-radiated sound field to specific receiver (R) positions,

d) incorporation of transfer functions associated to the at least one transducer (T) and/or electric equipment, and

e) selection of wave paths with specific orientation and polarization.

25. Air coupled ultrasonic contactless method according to claim 23, wherein the inverse ultrasound wave propagation model (IPM) incorporates:

a) measurement and/or simulation of re-radiated sound fields for calibration sample (S_C) in at least a receiver plane (Σ

R) parallel to the re-radiated lateral face FN2,

b) measurement of re-radiated sound fields for an equivalent sample (S) with undetermined defects,

c) calculation of difference re-radiated sound field by comparison of re-radiated sound fields measured obtained in a) and b),

d) mirroring with respect to time axis and signal processing of the difference re-radiated sound field,

e) computation of coupling through lateral face FN2 and wave propagation of processed difference re-radiated sound field within calibration laminated structure (S_C) in a defined discretization domain, and

f) interpretation of sound field computed within the discretization domain by extraction of wave signatures as wave convergences with subsequent signal processing and associating the results with defect positions, types and geometries within the laminated structure (S).

26. Air coupled ultrasonic contactless method according to claim 22, wherein for repeated measurements of the same laminated structure (S) the optimized parameters determined by measurement and successive simulation, are later used for further measurements.

27. Air coupled ultrasonic contactless method according to claim 1, wherein after repeated measurements of the same laminated structure (S), for which the same or different measurement parameters are used, measured ultrasound images (UI) or ultrasound datasets are interpreted by identifying differences and/or similarities in repeated measurements and associating the results with defect positions, types and geometries within the laminated structure (S).

28. Air coupled ultrasonic contactless method according to claim 1, wherein the laminated structures (S) are comprising wood and/or wood composites, and the laminated structures (S) are inspected in a production line or in situ at a construction site.

29. An installation for performing an air coupled ultrasonic contactless method for non-destructive determination of defects in a laminated structure (S) having a width (W) between opposing lateral faces (FN1, FN2) and having a multiplicity of n lamellas with intermediate n−

1 bonding planes (Bi), the installation comprising;

at least one transmitter (T) disposed relative to the laminated structure (S) at a fixed transmitter distance (WTS) for radiating ultrasound incident sound fields (IF) at multiple positions for rendering the lateral faces (FN1, FN2) insonified,

at least one receiver (R) disposed at a sensor distance (WSR) for receiving re-radiated ultrasound fields (RRF, RSF) at multiple positions relative to the laminated structure (S),

a transducer fixture attached to the at least one transmitter (T) and/or the at least one receiver (R), the transducer fixture comprising a targeting device, positioning means and pivoting means, wherein the targeting device, which includes a first line laser (7.10) and a second line laser (7.11), which are disposed for generation of a reference point-in a contactless way in the form of a light cross (7.14) on the insonified lateral faces (FN1, FN2) of the laminated structure (S) for simplified transducer positioning with respect to the lateral faces (FN1, FN2) and bonding planes (Bi).

30. (canceled)