Heath monitoring method and apparatus for composite materials

• US 20070166831A1
• Filed: 08/23/2006
• Published: 07/19/2007
• Est. Priority Date: 02/23/2005
• Status: Active Grant

• Current Assignee: Kenneth Watkins, Shelby Morris
• Original Assignee: Kenneth Watkins, Shelby Morris
• Inventors: Watkins, Kenneth, Morris, Shelby
• Granted Patent: US 7,924,031 B2
• Time in Patent Office: Days
• US Class Current: 436/149
• CPC Class Codes: G01N 27/20 Investigating the presence of flaws

Abstract

An in-situ method for monitoring the heath of a composite component (103) utilizes a condition sensor (101) made of electrically conductive particles (109) dispersed in a polymeric matrix (111). The sensor is bonded or otherwise formed on the matrix surface of the composite material. Age-related shrinkage of the sensor matrix results in a decrease in the resistivity of the condition sensor. Correlation of measured sensor resistivity with data from aged specimens allows indirect determination of mechanical properties and remaining age of the composite component.

Claims

1. A method for monitoring the health of a composite structure comprising a composite structural matrix and a reinforcement fiber, the method comprising the steps of:

disposing a condition sensor in communication with said composite structural matrix of said composite structure, said condition sensor comprising a conductive composite portion comprising a polymeric sensor matrix and a selected quantity of conductive particles sufficient to adjust an electrical resistivity of said conductive composite portion to a preselected value between an upper percolation threshold and a lower percolation threshold and correlatable to a second electrical resistivity from a previously degraded sample of a test condition sensor;

measuring a first electrical property of said condition sensor; and

equating said first electrical property to said heath of said composite structure whereby said heath comprises chemical aging of said composite structure.

2. The method for monitoring the health of a composite structure of claim 1 wherein said electrical property is a resistance of said condition sensor.

3. The method for monitoring the health of a composite structure of claim 1 wherein said composite structural matrix comprises a first polymer and said sensor matrix comprises said first polymer.

4. The method for monitoring the health of a composite structure of claim 1 wherein said conductive particles comprise carbon.

5. The method for monitoring the health of a composite structure of claim 4 wherein said conductive particles comprise carbon black particles.

6. The method for monitoring the health of a composite structure of claim 4 wherein said conductive particles comprise carbon nanotubes.

7. The method for monitoring the health of a composite structure of claim 1 wherein said conductive particles comprise metallic particles.

8. The method for monitoring the health of a composite structure of claim 1 wherein said condition sensor is physically disposed on a first portion of said composite structural matrix.

9. The method for monitoring the health of a composite structure of claim 8 wherein said first portion of said composite structural matrix is disposed between a web of said reinforcement fiber and a surface of said composite structure.

10. The method for monitoring the health of a composite structure of claim 8 wherein said condition sensor is bonded to said first portion of said composite structural matrix.

11. The method for monitoring the health of a composite structure of claim 10 wherein said condition sensor is bonded to said first portion of said composite structural matrix by said polymeric sensor matrix.

12. The method for monitoring the health of a composite structure of claim 11 wherein said selected quantity of conductive particles provides a resistivity of said condition sensor less than a resistivity of said composite matrix.

13. The method for monitoring the health of a composite structure of claim 1 comprising an electrical insulative material disposed between said condition sensor and said composite structural matrix and wherein said selected quantity of conductive particles is selected wherein a resistivity of said condition sensor comprises a resistivity less than said insulative material.

14. The method for monitoring the health of a composite structure of claim 2 wherein said equating said electrical property with said heath of said composite material comprises equating an increase in said resistivity of said condition sensor with mechanical damage of said composite structural matrix of said composite structure.

15. The method for monitoring the health of a composite structure of claim 2 wherein said condition sensor comprises an electrode for measuring said resistance of said condition sensor.

16. The method for monitoring the health of a composite structure of claim 2 wherein said condition sensor is disposed on an outside surface portion of said composite structure and said resistivity is measured by electrode contact with an outside surface portion of said condition sensor.

17. The method for monitoring the health of a composite structure of claim 14 wherein time domain analysis is used to distinguish chemical aging and mechanical damage of said composite structure.

18. The method for monitoring the health of a composite structure of claim 15 wherein a plurality of electrodes are disposed on a membrane bonded to said condition sensor.

19. A composite component configured for condition monitoring, the component comprising:

a composite structural matrix;

a reinforcing fiber; and

a condition sensor attached to said composite component comprising a conductive composite portion comprising a polymeric sensor matrix and a selected quantity of conductive particles sufficient to adjust an electrical resistivity of said conductive composite portion to a preselected value between an upper percolation threshold and a lower percolation threshold and correlatable to a second electrical resistivity from a previously degraded sample of a test condition sensor.

20. The composite component of claim 20 wherein said sensor matrix comprises a polymeric component of said composite structural matrix.

21. The composite component of claim 20 wherein said condition sensor is disposed on a surface of said composite component.

22. The composite component of claim 21 comprising a polymeric interface layer between said condition sensor and said composite structural matrix wherein said interface layer comprises a resistivity higher than a resistivity of said composite matrix.

23. The composite component of claim 21 wherein said condition sensor is bonded to said surface of said composite component.

24. The composite component of claim 21 comprising an electrode disposed on said condition sensor.