System, method, and apparatus for wireless non-powered stress history and fatigue monitoring of a structure

• US 20070107530A1
• Filed: 11/14/2005
• Published: 05/17/2007
• Est. Priority Date: 11/14/2005
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Anderson, Todd
• Granted Patent: US 7,377,179 B2
• Time in Patent Office: Days
• US Class Current: 73/808
• CPC Class Codes: G01N 2203/0073 Fatigue
• CPC Class Codes: G01N 2203/0244 Tests performed "in situ" or after "in situ" use
• CPC Class Codes: G01N 2203/0623 using piezoelectric gauges
• CPC Class Codes: G01N 2203/0664 using witness specimens
• CPC Class Codes: G01N 3/56 Investigating resistance to wear or abrasion

Abstract

A wireless, non-powered fatigue monitoring sensor uses a piezoelectric element that is attached to the surface of or embedded within a structure to be monitored. When subjected to stress over time, the material properties of the element change reliably and permanently. These properties are used to determine the fatigue history of the structure. The monitoring device requires no power for monitoring and is nondestructively queried to determine the stress history using wireless means such as radio frequency technology.

Claims

1. An apparatus for analyzing stress, comprising:

an element adapted to be mounted to a structure, the element having a material property that degrades over time due to stress cycling of the structure during service operation of the structure;

a sensor coupled to the element for detecting a condition of the property of the element, and neither the sensor nor the element have a source of power; and

a detector for providing wireless power to and wirelessly communicating with the sensor to detect the condition of the property of the element and adapted to ascertain a level of fatigue and prediction of residual life of the structure, the detector being non-invasive, non-destructive, and remote relative to the element and the sensor.

2. An apparatus according to claim 1, wherein the element comprises a piezoelectric element and the material property of the element is selected from the group consisting of impedance, admittance, piezo strain coefficients, piezo coupling, and complex portions of the impedance or admittance.

3. An apparatus according to claim 1, wherein the sensor is inductively powered by the detector and uses radio frequency to communicate with the sensor.

4. An apparatus according to claim 1, wherein the sensor comprises an impedance analyzer that scans a frequency range with respect to the element, an antenna for enhancing communication with the detector, and a microprocessor for controlling the sensor.

5. An apparatus according to claim 1, wherein the structure forms a portion of a component and the element is mounted inside the component such that the element is physically inaccessible from an exterior of the component.

6. An apparatus according to claim 1, wherein the element comprises a form selected from the group consisting of a thin film, a sheet, a beam, and a rod, and wherein a means of mounting the element to the structure is selected from the group consisting of bonding the element to the structure and embedding the element in the structure.

7. An apparatus according to claim 1, wherein the element comprises a plurality of elements, each of which has a different physical property than other ones of the elements to increase a fidelity and sensitivity to fatigue cycle prediction of the structure.

8. An apparatus according to claim 7, wherein a first fixture is secured to the structure, a second fixture is mounted to the structure, spaced apart from the first fixture and displaceable relative to the first fixture, and the plurality of elements extend between the first and second fixtures, and the physical property is length.

9. An apparatus according to claim 7, wherein one of the plurality of elements is sensitive to low stresses, and another one of the plurality of elements is sensitive to high stresses.

10. A system for analyzing structural stress, comprising:

a structure;

an element mounted to the structure, the element having a material property that degrades over time due to stress cycling of the structure during service operation of the structure;

a sensor coupled to the element for detecting a condition of the material property of the element, and neither the sensor nor the element have a source of power; and

a detector for providing wireless power to and wirelessly communicating with the sensor to detect the condition of the material property of the element and thereby ascertain a level of fatigue and prediction of residual life of the structure, the detector being non-invasive, non-destructive, and remote relative to the element and the sensor.

11. A system according to claim 10, wherein the element comprises a piezoelectric element and the material property of the element is selected from the group consisting of impedance, admittance, piezo strain coefficients, piezo coupling, and complex portions of the impedance or admittance, and wherein the sensor is inductively powered by the detector and uses radio frequency to communicate with the sensor.

12. A system according to claim 10, wherein the sensor comprises an impedance analyzer that scans a frequency range with respect to the element, an antenna for enhancing communication with the detector, and a microprocessor for controlling the sensor.

13. A system according to claim 10, wherein the structure forms a portion of a component and the element is mounted inside the component such that the element is physically inaccessible from an exterior of the component.

14. A system according to claim 10, wherein the element comprises a form selected from the group consisting of a thin film, a sheet, a beam, and a rod, and wherein a means of mounting the element to the structure is selected from the group consisting of bonding the element to the structure and embedding the element in the structure.

15. A system according to claim 10, wherein the element comprises a plurality of elements, each of which has a different physical property than other ones of the elements to increase a fidelity and sensitivity to fatigue cycle prediction of the structure.

16. A system according to claim 15, wherein a first fixture is secured to the structure, a second fixture is mounted to the structure, spaced apart from the first fixture and displaceable relative to the first fixture, and the plurality of elements extend between the first and second fixtures, and the physical property is length.

17. A system according to claim 15, wherein one of the plurality of elements is sensitive to low stresses, and another one of the plurality of elements is sensitive to high stresses.

18. A method of monitoring structural stress, comprising:

(a) mounting a device to a structure;

(b) querying the device for a baseline condition of the device;

(c) saving the baseline condition;

(d) placing the structure in service such that the structure and device experience stress cycles;

(e) querying the device after a period of service;

(f) determining whether the device and, therefore, the structure have an acceptable fatigue history;

(g) continuing service of the structure if the fatigue history is acceptable; and

(h) discontinuing service of the structure if the fatigue history is unacceptable.

19. A method according to claim 18, wherein step (a) comprises bonding the device to a surface of the structure or embedding the device inside the structure.

20. A method according to claim 18, further comprising performing steps (b) and (e) wirelessly, non-intrusively, non-destructively, and remotely.

21. A method according to claim 18, wherein the device does not have a power source and steps (b) and (e) comprise providing wireless power to the device from an external source.

22. A method according to claim 18, wherein step (h) comprises repairing or rebuilding the structure.

23. A method according to claim 18, wherein step (d) comprises degrading a material property of the device over time due to stress cycling of the structure during service of the structure.

24. A method according to claim 18, further comprising providing the device with a piezoelectric element and monitoring a material property of the piezoelectric element.

25. A method according to claim 18, further comprising inductively powering the device and using radio frequency to communicate with the device.

26. A method according to claim 18, further comprising increasing a fidelity and sensitivity to fatigue cycle prediction of the structure via different physical properties of the device.