Integration of Digital Image Correlation with Acoustic Emission

• US 20150035950A1
• Filed: 10/17/2014
• Published: 02/05/2015
• Est. Priority Date: 04/18/2012
• Status: Active Grant

• Current Assignee: Drexel University
• Original Assignee: Drexel University
• Inventors: Kontsos, Antonios, Bartoli, Ivan, Vanniamparambil, Prashanth Abraham
• Granted Patent: US 10,488,368 B2
• Time in Patent Office: Days
• US Class Current: 348/47
• CPC Class Codes: G01M 5/0066 by exciting or detecting vibration or acceleration vibration testing of structures G01M7/00
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection
• CPC Class Codes: G01N 21/8803 Visual inspection measuring projectors G01B9/08
• CPC Class Codes: G01N 2291/0232 Glass, ceramics, concrete or stone
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 29/14 using acoustic emission techniques echo of particles G01N29/046; measuring mechanical vibrations or acoustic waves in solids in general G01H1/00
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 2207/30108 Industrial image inspection
• CPC Class Codes: G06T 7/0008 checking presence/absence
• CPC Class Codes: H04N 13/246 Calibration of cameras

Abstract

An inventive approach is disclosed to integrate Digital Image Correlation (DIC) with the Acoustic Emission method that may be used for structural health monitoring and assessment of critical structural components in civil, mechanical, and aerospace industries. The inventive approach relies on passively recording acoustic emission across the specimen being tested and activating the DIC cameras automatically to measure deformation on the specimen'"'"'s surface. The resulting acousto-optic system can be used to determine damage initiation, progressive damage development, identify critical regions and make lifetime predictions of the tested specimen.

Claims

1. A nondestructive method of determining the structural integrity of a specimen as a load is applied to the specimen, the method comprising the steps of:

attaching at least one acoustic sensor to the specimen;

applying a contrasting pattern on the surface of the specimen;

calibrating a pair of stereoscopic cameras at the contrasting pattern;

passively recording acoustic stress waves propagating in the specimen in an Acoustic Emission (AE) system electronically coupled to the at least one acoustic sensor;

triggering operation of the cameras by the AE system;

measuring deformation in the specimen based on load-induced movement of the contrasting pattern in a Digital Image Correlation (DIC) system, the DIC system being electronically coupled to the cameras; and

correlating acoustic stress waves and strain data to determine the structural health of the specimen.

2. The method according to claim 1, further comprising, after calibrating the cameras at the contrasting pattern, applying a load to the specimen.

3. The method according to claim 2, wherein the load applying step comprises attaching the specimen to a load applying test stand.

4. The method according to claim 3, wherein the at least one acoustic sensor and the cameras are electrically connected to the test stand.

5. The method according to claim 4, wherein a digital output is sent from the AE system to the DIC system.

6. The method according to claim 5, further comprising triggering the DIC cameras based on an input signal received from the AE system.

7. The method according to claim 6, wherein the correlating step comprises measuring deformation in the specimen synchronized with the applied load and acoustic activity.

8. The method according claim 7, wherein the correlating step comprises computing a life fraction of the specimen by using synchronized DIC and AE data.

9. The method according to claim 1, wherein the at least one acoustic sensor comprises a plurality of acoustic sensors.

10. A method of determining the structural integrity of a specimen as a load is applied to the specimen, the method comprising the steps of:

attaching at least one acoustic sensor to the specimen;

determining a contrasting pattern on the surface of the specimen;

aiming two cameras at the contrasting pattern;

determining strain in the specimen based on load-induced movement of the contrasting pattern;

passively recording acoustic stress waves propagating in the specimen; and

correlating acoustic stress waves and strain data to determine structural health of the specimen.

11. The method according to claim 10, wherein the step of determining the contrast pattern comprises applying a speckle pattern.

12. The method according to claim 10, further comprising, after aiming the two cameras at the contrasting pattern, applying a load to the specimen.

13. The method according to claim 12, wherein the load applying step comprises attaching the specimen to a load applying test stand.

14. The method according to claim 13, wherein the at least one acoustic sensor and the two cameras are electrically connected to the test stand.

15. The method according to claim 14, wherein the test stand varies the applied load based on electronic information transmitted to the test stand during the strain measurement step.

16. The method according to claim 10, wherein the acoustic sensor attaching step comprises attaching the at least one acoustic sensor to the specimen before the load has been applied to the specimen.

17. The method according to claim 16, wherein the correlating step comprises measuring strain in the specimen as a function of applied load and acoustic activity.

18. The method according claim 10, wherein the correlating step comprises measuring a life fraction of the specimen versus the energy density value.

19. The method according to claim 10, wherein the correlating step further comprises measuring the life fraction of the specimen versus cumulative acoustic energy.

20. The method according to claim 10, wherein the correlating step comprises measuring a life fraction of the specimen versus the residual stiffness of the specimen.