Identifying structural defect geometric features from acoustic emission waveforms

1. A method for identifying features of a fatigue crack, comprising:

analyzing emission waves from a fatigue crack;

applying external excitation to the fatigue crack;

capturing at least one echo emanating from the fatigue crack caused by the external excitation;

generating at least one secondary emission wave that emanates from the fatigue crack;

analyzing amplitude and frequency of the at least one secondary emission wave; and

establishing an initial fatigue crack fingerprint for the fatigue crack and comparing the initial fatigue crack fingerprint to a subsequent fatigue crack fingerprint to analyze fatigue crack progression.

2. The method of claim 1 , further comprising identifying at least one geometric feature of the fatigue crack from analysis of the at least one secondary emission wave.

3. The method of 2 , further comprising identifying fatigue crack length and crack tip locations as part of the at least one geometric feature.

4. The method of 2 , wherein frequency dependent patterns in polar plots identify the at least one geometric feature of the fatigue crack.

5. The method of claim 1 , further comprising establishing a library of signal signatures paired with fatigue crack geometries.

6. The method of claim 5 , wherein modeling and scanning laser vibrometry are used in association with time signal analysis are used to establish the library of signal signatures.

7. Creating a library of acoustic emission waveforms linked to crack geometric features comprising:

generating structural vibrations in a test material;

generating excitation signals and applying same to the test material;

collecting first acoustic emission signals generated by the test material;

measuring surface vibration and displacement in the test material;

obtaining a frequency response of the test material to the excitation signals;

extracting surface relative displacement to determine multiple candidate frequencies for acoustic wave detection;

exciting the test material with at least one candidate frequency and collecting at least one second acoustic emission signals from the test material;

analyzing the at least one second acoustic emission signal to extract at least one signal signature associated with fatigue crack geometric features; and

forming a library of features wherein the at least one signal signature is associated with fatigue crack geometric features; and

establishing an initial fatigue crack fingerprint for the fatigue crack geometric features and comparing the initial fatigue crack fingerprint to a subsequent fatigue crack fingerprint to analyze fatigue crack progression.

8. The method of claim 7 , wherein the structural vibrations are generated by internal and external excitation sources.

9. The method of claim 8 , wherein the internal excitation is provided by piezoelectric wafer active sensors.

10. The method of claim of 8 , wherein the external excitation is created by a mechanical shaker.

11. The method of claim 7 , further comprising identifying at least one geometric feature of a fatigue crack from analysis of the at least one second acoustic emission.

12. The method of claim 11 , further comprising identifying fatigue crack length and fatigue crack tip locations as part of the at least one geometric feature of the fatigue crack.

13. The method of claim 12 , wherein frequency dependent patterns in polar plots identify geometric features of the fatigue crack.

14. A method for ensuring structural integrity comprising:

receiving acoustic emissions from a structure;

analyzing the acoustic emissions to determine if structural faults exist in the structure; and

wherein when at least one structural fault exists, establishing an initial structural fault fingerprint for the structural fault and comparing the initial structural fault fingerprint to a subsequent structural fault fingerprint to analyze structural fault progression.

15. The method of claim 14 , wherein analyzing the acoustic emissions compares structural vibration resonance frequencies and mode shapes.

16. The method of claim 14 wherein, for structural faults found within the structure, a stress field is created.

17. The method of claim 16 wherein the structural fault is a fatigue crack.

18. The method of claim 17 , further comprising analyzing the stress field around a fatigue crack tip to calculate resonance frequencies related to fatigue crack opening.

19. The method of claim 17 , wherein at least one geometric feature of the fatigue crack located within the structure is revealed by the analysis of the stress field.