Diagnostic layer and methods for detecting structural integrity of composite and metallic materials

• US 6,370,964 B1
• Filed: 11/23/1999
• Issued: 04/16/2002
• Est. Priority Date: 11/23/1998
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Chang, Fu-Kuo, Lin, Mark
• Primary Examiner(s): NOORI, MAX H
• Application Number:
  US09/447,480
• Time in Patent Office: 875 Days
• Field of Search: 737/60, 737/63, 737/67, 737/72, 738/55, 738/620.41, 738/620.46
• US Class Current: 73/862.046
• CPC Class Codes: G01B 5/30 for measuring the deformation in a solid, e.g. mechanical strain gauge
• CPC Class Codes: G01H 11/08 using piezoelectric devices
• CPC Class Codes: G01L 1/146 for measuring force distributions, e.g. using force arrays G01L1/148 takes precedence
• CPC Class Codes: G01M 5/0016 of aircraft wings or blades
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection
• CPC Class Codes: G01N 2291/0231 Composite or layered materials
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 2291/106 one or more transducer arrays
• CPC Class Codes: G01N 29/045 by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks measuring resonant frequency G01H13/00; measuring strength properties by application of mechanical stress G01N3/00
• CPC Class Codes: G01N 29/2475 Embedded probes, i.e. probes incorporated in objects to be inspected
• CPC Class Codes: G01N 29/2481 Wireless probes, e.g. with transponders or radio links

Abstract

A diagnostic layer having a network of actuators and sensors may be incorporated into or on the surface of composite, metallic, and laminated materials for monitoring the structural health of the material. The diagnostic layer is adapted for detecting and measuring changes in the condition of the material, e.g., the site and extent of damage in the material. In a preferred embodiment, piezoelectric devices are embedded in the diagnostic layer in a network, and serve as actuators and sensors. Signals emitted from the sensors in response to physical deformation, either by an impact or as a result of stress waves generated by the actuators, are diagnostic of the current condition of the diagnostic layer. The diagnostic layer is also adapted to monitor the curing process of a composite material and accurately determine when curing is complete. Methods for monitoring changes in conditions of a material are also disclosed.

Claims

1. A diagnostic layer for detecting a structural condition of a material, said diagnostic layer comprising:

a thin and flexible dielectric substrate having embedded therein;

a network of actuators/sensors spatially distributed such that at least two actuators/sensors detect a propagating stress wave generated by at least one other actuators/sensors, wherein said actuators/sensors capable of generating electrical signals representative of a structural condition of said material;

a plurality of conductive elements electrically interconnecting said actuators/sensors; and

an output lead electrically connected to said conductive elements.

2. The diagnostic layer of claim 1, wherein said actuators/sensors are spatially distributed such that each of said actuators/sensors detects propagating stress waves generated by at least two other actuators/sensors.

3. The diagnostic layer of claim 1, wherein said actuators/sensors are piezoelectric sensors and generate said electrical signals in response to physical deformations of said piezoelectric sensors.

23. The diagnostic layer of claim 3, wherein said interconnected actuators/sensors are piezoceramic sensors.

4. A diagnostic system for detecting a structural condition of a material, said diagnostic system comprising:

a diagnostic layer comprising;

a thin and flexible dielectric substrate having embedded therein;

a network of actuators/sensors spatially distributed such that at least two actuators/sensors detect a propagating stress wave generated by at least one other actuators/sensors;

a plurality of conductive elements electrically interconnecting said actuators/sensors; and

an output lead electrically connected to said conductive elements;

a signal receiving means electrically coupled to said output lead for receiving said output signals from said actuators/sensors; and

an interfacing means in electrical communication with said signal receiving means, said interfacing means comprising a processing means for processing said output signals and generating data representing said structural condition of said material.

5. The diagnostic system of claim 4, further comprising a signal generating means electrically connected to said output lead for providing an input signal to said at least one other actuators/sensors.

6. The diagnostic system of claim 5, wherein said signal generating means is electrically connected to said interfacing means, said interfacing means further comprises a control means for controlling said input signal to said at least one other actuators/sensors.

7. The diagnostic system of claim 5, further comprising a network of actuators/sensors spatially distributed such that each of said actuators/sensors detects propagating stress waves generated by at least two other actuators/sensors.

8. The diagnostic system of claim 4, wherein said actuators/sensors are piezoelectric sensors and generate said output signals in response to physical deformations of said piezoelectric sensors.

9. The diagnostic system of claim 4, wherein said signal receiving means is electrically coupled to said output lead by wireless means.

10. The diagnostic system of claim 4, wherein said interfacing means further comprises a memory means for storing data from said signal receiving means.

11. The diagnostic system of claim 4 wherein said structural condition comprises a location and a size of structural damage in said diagnostic layer.

12. The diagnostic system of claim 4 wherein said structural condition comprises a location and a force of an impact to said diagnostic layer.

13. The diagnostic system of claim 4 wherein said structural condition comprises progression of curing.

14. A method for detecting a change in a structural condition of a material, said method comprising the steps of:

a) providing said material a diagnostic layer, said diagnostic layer comprising;

a thin and flexible dielectric substrate having embedded therein;

a network of actuators/sensors spatially distributed such that at least two actuators/sensors detect a propagating stress wave generated by at least one other actuators/sensors;

a plurality of conductive elements electrically interconnecting said actuators/sensors; and

an output lead electrically connected to said conductive elements;

b) transmitting a first input signal to said at least one other actuators/sensors through said output lead;

c) receiving a first set of output signals from said at least two actuators/sensors in response to said first input signal;

d) subsequently transmitting a second input signal to said at least one other actuators/sensors through said output lead;

e) receiving a second set of output signals from said at least two actuators/sensors in response to said second input signal; and

f) analyzing said first set of output signals and said second set of output signals to determine a difference between said first set of output signals and said second set of output signals, wherein said difference represents said change in said structural condition.

15. The method of claim 14, wherein step (f) further comprises generating a first set of data from said first set of output signals and generating a second set of data from said second set of output signals, wherein set first set of data represents a first structural condition of said material and said second set of data represents a second structural condition of said material.

16. The method of claim 14 wherein said change in said structural condition comprises a location and a size of damage in said diagnostic layer.

17. The method of claim 14 wherein said change in said structural condition comprises progression of curing.

18. The method of claim 14, further comprising the steps of:

a) subsequently transmitting an n^th input signal to said at least one other actuators/sensors through said output lead;

b) receiving an n^th set of output signals from said at least two actuators/sensors in response to said n^th input signal; and

c) analyzing said n^th set of output signals and a prior set of output signals to determine a difference between said n^th set of output signals and said prior set of output signals, wherein said difference represents a further change in said structural condition of said material; and

d) repeating steps (a), (b), and (c) for a predetermined time.

19. The method of claim 14, further comprising the step of, before step (a), bonding said diagnostic layer to an external surface of said material.

20. A method for detecting a physical deformation of a material having a diagnostic layer, said diagnostic layer comprising a network of interconnected actuators/sensors spatially distributed on a thin and flexible dielectric substrate and electrically connected to an output lead by a plurality of conductive elements, at least two of said actuators/sensors capable of detecting a structural condition in a region of said material, said method comprising the steps of:

a) receiving a signal from at least one actuators/sensors of said network, wherein said signal represents a physical deformation of said at least one actuators/sensors of said network; and

b) processing said signal to generate data representing said physical deformation of said material.

21. The method of claim 20 wherein said sensors are piezoelectric sensors.

22. The method of claim 20 wherein said physical deformation of said material comprises an impact on said material and said data comprise a force and a location of said impact.

24. A diagnostic layer for detecting a structural condition of a material, said diagnostic layer comprising:

a thin and flexible dielectric substrate having embedded therein;

a network of actuators/sensors spatially distributed on said substrate, said actuators/sensors capable of generating electrical signals representative of a structural condition of said material, wherein at least two actuators/sensors detect a structural condition in a region of said material;

a plurality of conductive elements electrically interconnecting said actuators/sensors; and

an output lead electrically connected to said conductive elements.

25. The diagnostic layer of claim 24, wherein said actuators/sensors are piezoelectric sensors and generate said electrical signals in response to physical deformations of said piezoelectric sensors.

26. The diagnostic layer of claim 25, wherein said actuators/sensors are piezoceramic sensors.