DETECTING DAMAGE IN METAL STRUCTURES WITH STRUCTURAL HEALTH MONITORING SYSTEMS

• US 20080255778A1
• Filed: 04/14/2008
• Published: 10/16/2008
• Est. Priority Date: 04/16/2007
• Status: Active Grant

• Current Assignee: Acellent Technologies, Inc.
• Original Assignee: Acellent Technologies, Inc.
• Inventors: Chang, Fu-Kuo, Beard, Shawn J., Li, Irene, Liu, Bao
• Granted Patent: US 7,908,095 B2
• Time in Patent Office: Days
• US Class Current: 702/35
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 2291/106 one or more transducer arrays
• CPC Class Codes: G01N 29/041 on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
• CPC Class Codes: G01N 29/36 Detecting the response signal , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G01N 29/4463 Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering

Abstract

A method useful in structural health monitoring (SHM) systems for detecting damages in metal structures includes extracting the zero-order symmetric and anti-symmetric mode signal components from each of a plurality of current sensor signals of an array of transducers mounted on the structure, matching the extracted signal components with corresponding signal components of a plurality of baseline sensor signals previously detected in the structure, computing respective indices I_S0 and I_A0 for each of the matched extracted current and baseline signal components based on respective signal energies thereof, and determining the presence of a damage in the structure if either of the indices I_S0 and I_A0 of a plurality of neighboring sensor paths of the structure is greater than a selected threshold value.

Claims

1. A method for detecting damages in a metal structure, the method comprising:

determining featured signal windows of selected signal components for each of a plurality of sensor signals of an array of transducers mounted on the structure;

extracting selected signal components from each of a plurality of current sensor signals of the transducer array using the featured signal windows;

matching the extracted signal components with corresponding signal components of a plurality of baseline sensor signals previously detected in the structure with the transducer array;

computing respective indices I_S0 and I_A0 for each of the matched extracted current and baseline signal components based on the respective signal energies thereof; and

,

determining the presence of a damage in the structure if either of the indices I_S0 and I_A0 of at least a specified number of neighboring sensor paths of the structure is greater than selected threshold values of I_S0 and I_A0.

2. The method of claim 1, wherein the selected signal components comprise the respective first arrival wave packets of the zero-order symmetric and anti-symmetric modes S0 and A0 of the signals and the respective scattering wave packets corresponding thereto.

3. The method of claim 1, wherein the determining of the featured signal windows comprises:

selecting a set of sensor signals having the same frequency and about the same path length;

locally shifting the signals to align their respective phases;

computing the average of the signals, the envelope of the average, and the local maxima of the envelope;

finding the time locations of the first two local maxima respectively corresponding to the zero-order symmetric and anti-symmetric modes that are greater than a selected threshold;

computing the group velocities corresponding to the two modes using their local maximum locations in time and the average path length of the paths of the selected signals;

determining the propagation time of the respective first arrival wave packet of each mode of other signals outside the selected set of signals using the computed group velocity of each mode and the path lengths;

determining the featured signal windows; and

,

extracting the first arrival wave packet of each mode for all the signals and the scattering wave packets respectively corresponding thereto.

4. The method of claim 1, wherein the indices I_S0 and I_A0 are respectively determined according to the equations:

5. The method of claim 1, further comprising:

computing local energy difference functions I(t) of the selected components of the S0 and A0 modes of each of the current and baseline sensor signals; and

,

determining the location of the damage in the structure with a diagnostic imaging method using the computed local energy difference functions of the signal components.

6. The method of claim 5, wherein the computing of the local energy difference functions I(t) of the selected components comprises:

applying a moving window function g(t) to each of the respective selected components of each of the current and baseline signals; and

,

computing the respective local energies E_c and E_b of each of the selected components of each of the current and baseline signals.

7. The method of claim 6, wherein the moving window function g(t) comprises a Gaussian function having the same length as an actuation signal used to produce the current sensor signals.

8. The method of claim 6, wherein the respective selected components of the current signals are denoted by x_c(t) and the selected component of the baseline signal is denoted by x_b(t), and wherein the computing of the respective local energies E_c and E_b of each of the selected components comprises evaluating the equations:

E_c=∫

{x_c(t)g(t)}²dt and E_b=∫

{x_b(t)g(t)}²dt

for each of the current and baseline signals.

9. The method of claim 8, wherein the computing of the local energy difference function I(t) of the respective selected components of the signals comprises evaluating the equation:

10. A method for extracting the respective first arrivals of the zero-order symmetric and anti-symmetric modes and the respective scattering wave packets corresponding thereto from a plurality of sensor output signals of a structural health monitoring (SHM) system, the method comprising:

selecting a set of sensor signals having the same frequency and about the same path length;

locally shifting the signals to align their respective phases;

computing the average of the signals, the envelope of the average, and the local maxima of the envelope;

finding the time locations of the first two local maxima respectively corresponding to the zero-order symmetric and anti-symmetric modes that are greater than a selected threshold;

computing the group velocities corresponding to the two modes using their local maximum locations in time and the average path length of the paths of the selected signals;

determining the propagation time of the respective first arrival wave packet of each mode of other signals outside the selected set of signals using the computed group velocity of each mode and the path lengths;

determining the featured signal windows; and

,

extracting the first arrival wave packet of each mode and the scattering wave packets respectively corresponding thereto for all of the signals.

11. An apparatus for detecting damages in a metal structure, comprising:

means for extracting respective first arrivals of zero-order symmetric and anti-symmetric modes and scattering wave packets respectively corresponding thereto from each of a plurality of current sensor signals of an array of transducers mounted on the structure;

means for matching the extracted signal components with corresponding signal components of a plurality of baseline sensor signals;

means for computing respective indices I_S0 and I_A0 for each of the matched extracted and baseline signal components based on the respective energies thereof; and

,

means for determining whether either of the indices I_S0 and I_A0 of at least a specified number of neighboring sensor paths of the structure is greater than a given threshold value.

12. The apparatus of claim 11, further comprising means for determining the location of the damage in the structure.

13. The apparatus of claim 12, further comprising means for displaying a visual image of the location of the damage.