Composite Inspection

• US 20170176393A1
• Filed: 03/15/2016
• Published: 06/22/2017
• Est. Priority Date: 12/21/2015
• Status: Active Grant

• Current Assignee: The Boeing Co., University of Washington
• Original Assignee: The Boeing Co., University of Washington
• Inventors: Kennedy, James C., Motzer, William P., Gordon, III, Clarence Lavere, Bingham, Jill Paisley, Stewart, Alan F., Brady, Steven Kenneth, O'Donnell, Matthew, Pelivanov, Ivan, Georgeson, Gary Ernest, Kollgaard, Jeffrey Reyner
• Granted Patent: US 10,345,267 B2
• Time in Patent Office: Days
• CPC Class Codes: B64F 5/60 Testing or inspecting aircraft components or systems
• CPC Class Codes: G01N 2021/1706 in solids
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/015 Attenuation, scattering
• CPC Class Codes: G01N 2291/0231 Composite or layered materials
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/2694 Wings or other aircraft parts
• CPC Class Codes: G01N 29/043 in the interior, e.g. by shear waves
• CPC Class Codes: G01N 29/0645 Display representation or displayed parameters, e.g. A-, B- or C-Scan
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• 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 29/343 pulse waves, e.g. particular sequence of pulses, bursts
• 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 29/4454 Signal recognition, e.g. specific values or portions, signal events, signatures
• CPC Class Codes: G01N 29/449 Statistical methods not provided for in G01N29/4409, e.g. averaging, smoothing and interpolation
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01N 29/50 using auto-correlation techniques or cross-correlation techniques

Abstract

A method of detecting material changes in a composite structure is presented. A pulsed laser beam is directed towards the composite structure comprised of a number of composite materials. Wide-band ultrasonic signals are formed in the composite structure when radiation of the pulsed laser beam is absorbed by the composite structure. The wide-band ultrasonic signals are detected to form data. The data comprises a number of ultrasonic A-scans. The data is processed to identify a plurality of frequency measurements for each of the number of ultrasonic A-scans. A frequency image is displayed using the plurality of frequency measurements. The material changes are represented in the frequency image.

Claims

1. A method of detecting material changes in a composite structure, the method comprising:

directing a pulsed laser beam towards the composite structure comprised of a number of composite materials, wherein wide-band ultrasonic signals are formed in the composite structure when radiation of the pulsed laser beam is absorbed by the composite structure;

detecting the wide-band ultrasonic signals to form data, wherein the data comprises a number of ultrasonic A-scans;

processing the data to identify a plurality of frequency measurements for each of the number of ultrasonic A-scans; and

displaying a frequency image using the plurality of frequency measurements, wherein the material changes are represented in the frequency image.

2. The method of claim 1, wherein processing the data comprises:

applying a moving window to each of the number of ultrasonic A-scans; and

determining at least one of a mean frequency or a maximum frequency within the moving window.

3. The method of claim 2, wherein the moving window has a Gaussian shape.

4. The method of claim 1 further comprising:

determining whether undesirable conditions are present in the composite structure by analyzing the frequency image, wherein the undesirable conditions include the material changes.

5. The method of claim 1, wherein the plurality of frequency measurements are selected from at least one of mean frequencies or maximum frequencies.

6. The method of claim 1, wherein processing the data comprises:

determining a maximum frequency of a windowed signal of an A-scan of the number of ultrasonic A-scans using the equation S_n=Σ

_k=1^p a_k*S<sub>n−

k</sub>, where p is a quantity of coefficients and S_n is an A-scan signal at sample point n.

7. The method of claim 1, wherein processing the data to identify the plurality of frequency measurements comprises:

determining a mean frequency of a windowed signal of an ultrasonic A-scan of the number of ultrasonic A-scans using an autocorrelation function of a complex, analytic representation of the windowed signal of the ultrasonic A-Scan, {circumflex over (R)}(t), according to at least one of equation

8. The method of claim 1, wherein the wide-band ultrasonic signals are detected using a point-like optical detector.

9. A method comprising:

directing a pulsed laser beam towards a composite structure comprised of a plurality of layers, wherein a number of wide-band ultrasonic signals are formed in the composite structure when radiation of the pulsed laser beam is absorbed by the composite structure;

detecting the wide-band ultrasonic signals to form data, wherein the data comprises a plurality of ultrasonic A-scans for the composite structure;

applying a moving window to each of the plurality of ultrasonic A-scans to form windowed signals;

determining a frequency measurement within the windowed signals for each of the plurality of ultrasonic A-scans;

removing spectral components of a structure signal from an A-scan spectrum of each of the plurality of ultrasonic A-scans using the frequency measurement; and

performing an interpolation on the A-scan spectrum of the each of the plurality of ultrasonic A-scans after removing the spectral components of the structure signal to form interpolated A-scan spectrum data.

10. The method of claim 9 further comprising:

Fourier transforming each of the plurality of ultrasonic A-scans to form the A-scan spectrum of each of the plurality of ultrasonic A-scans; and

performing an inverse Fourier transformation on the interpolated A-scan spectrum data to form a plurality of structureless ultrasonic A-scans.

11. The method of claim 10 further comprising:

filtering a structureless B-scan image formed from the plurality of structureless ultrasonic A-scans.

12. The method of claim 11, wherein filtering the structureless B-scan image comprises using a low-pass filter on the structureless B-scan image.

13. The method of claim 9, wherein the frequency measurement is selected from a mean frequency or a maximum frequency.

14. The method of claim 13, wherein the mean frequency is determined using an autocorrelation function of a complex, analytic representation of a windowed signal of an ultrasonic A-Scan, R(t), according to at least one of the equation

15. The method of claim 13, wherein the maximum frequency is determined using equation S_n=Σ

_k=1^p a_k*S<sub>n−

k</sub>, where p is a quantity of coefficients and S_n is an A-scan signal at sample point n.

16. A method comprising:

obtaining data for a composite structure using a laser ultrasound inspection system;

determining a width and a frequency of spectral components of a structure signal in the data;

removing the spectral components of the structure signal from the data in a frequency domain;

performing an interpolation routine to fill in a region of an A-scan spectrum left empty by removing the spectral components of the structure signal to form interpolated data; and

performing an inverse Fourier transformation on the interpolated data to form a processed A-scan with the structure signal removed.

17. The method of claim 16 further comprising:

filtering the processed A-scan to form filtered data; and

displaying the filtered data in a structureless B-scan image.

18. The method of claim 16, wherein the frequency of the spectral components of the structure signal is estimated using equation S_n=σ

_k=1^p a_k*S<sub>n−

k</sub>, where p is a quantity of coefficients and S_n is an A-scan signal at sample point n.

19. The method of claim 16, wherein the frequency of the spectral components of the structure signal is estimated using an autocorrelation function of a complex, analytic representation of a windowed signal of an ultrasonic A-Scan, {circumflex over (R)}(t), according to at least one of equation

20. The method of claim 16, wherein the width of the spectral components associated with the structure signal is the mean frequency ±

two times the width of the structural signal spectrum in the frequency domain.

21. The method of claim 20, wherein the width of the structural signal spectrum in the frequency domain is estimated using an autocorrelation function of a complex, analytic representation of the windowed signal of an ultrasonic A-Scan, {circumflex over (R)}(t), and wherein for an N-point sampled version of the A-Scan,