Structural life monitoring system

• US 5,816,530 A
• Filed: 10/09/1996
• Issued: 10/06/1998
• Est. Priority Date: 10/09/1996
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Grube, Kenneth Peter
• Primary Examiner(s): Barefoot, Galen L.
• Application Number:
  US08/728,680
• Time in Patent Office: 727 Days
• Field of Search: 244/1 R, 244/129.1, 73/760, 73/762, 73/763, 73/767, 73/788, 73/789, 73/791, 73/799, 73/802, 73/808, 364/149, 364/150, 364/506, 364/508, 340/665
• US Class Current: 244/1.00R
• CPC Class Codes: B64D 47/00 Equipment not otherwise provided for
• CPC Class Codes: G01B 5/30 for measuring the deformation in a solid, e.g. mechanical strain gauge

Abstract

A method for measuring growth and magnitude of structural damage in a structure such as an airframe, as reflected by growth of a crack therein, by securing to a structural portion thereof at least one ligament assembly whose properties replicate such damage. The ligament assembly has a metallic load test coupon having a loading response substantially identical to a loading response of the structural portion and an artificial flaw simulating a metallurgical crack. The crack has a growth rate magnitude substantially identical to a magnitude of structural damage of the structural portion as such damage occurs. A crack growth measurement gage is in alignment with the crack of the test coupon and in communication with a recorder unit to record crack growth, and crack growth is compared to correlated structural damage of the structural portion as associated with such growth. The recorder unit preferably includes a data processor capable of comparing crack growth recorded by the recorder unit, correlating this growth to structural damage, reporting the structural damage as a viewable output correlated to the crack growth, and accruing crack-growth data. The method is particularly, but not limitedly, applicable for monitoring structural damage as it occurs to aging aircraft.

Claims

1. A method for monitoring growth and magnitude of structural damage of a structural portion of a structure as reflected by growth of a crack therein, the method comprising:

a) simulating structural damage present in the structural portion with a load test coupon secured to the structural portion, said load test coupon having a loading response substantially identical to a loading response of the structural portion and a crack substantially equivalent to structural damage already present in the structural portion, said crack in the load test coupon having a growth rate magnitude substantially identical to a magnitude of structural damage of the structural portion as said damage occurs and having in alignment therewith a crack growth measurement gage;

b) recording growth of the crack of the test coupon with a recorder unit in communication with the crack growth measurement gage; and

c) comparing crack growth recorded by the recorder unit to correlated structural damage of the structural portion associated with such crack growth.

2. A method as claimed in claim 1 wherein the structural portion to which the load test coupon is secured is a portion of an airframe of an aircraft.

3. A method as claimed in claim 2 wherein the recorder unit has in addition a data processor capable of comparing crack growth recorded by the recorder unit, correlating said growth to structural damage, reporting the structural damage as a viewable output correlated to the crack growth, and accruing crack-growth data.

4. A method as claimed in claim 3 wherein the data processor is capable of predicting a next immediate increment of crack growth based on accrued crack-growth data.

5. A method as claimed in claim 4 wherein the structural portion is a structurally critical area.

6. A method as claimed in claim 5 wherein the structurally critical area is a main spar beam of a wing lower surface near its attachment to a fuselage.

7. A method as claimed in claim 1 wherein the recorder unit has in addition a data processor capable of comparing crack growth recorded by the recorder unit, correlating said growth to structural damage, reporting the structural damage as a viewable output correlated to the crack growth, and accruing crack-growth data.

8. A method as claimed in claim 1 wherein the data processor is capable of predicting a next immediate increment of crack growth based on accrued crack-growth data.

9. A method as claimed in claim 1 wherein the structural portion is a structurally critical area.

10. A method for monitoring growth and magnitude of structural damage of a structural portion of a structure as reflected by growth of a crack therein, the method comprising:

a) simulating structural damage present in the structural portion with two load test coupons secured to the structural portion such that the load test coupons are either in a generally parallel relationship with the structural portion therebetween or in a side by side relationship, each of said load test coupons having a loading response substantially identical to a loading response of the structural portion and a crack substantially equivalent to structural damage already present in the structural portion, said crack in the load test coupon having a growth rate magnitude substantially identical to a magnitude of structural damage of the structural portion as said damage occurs and having in alignment therewith a crack growth measurement gage;

b) recording growth of each crack of each test coupon with a recorder unit in communication with the crack growth measurement gage; and

c) comparing crack growth of each test coupon recorded by the recorder unit to correlated structural damage of the structural portion associated with such crack growth.

11. A method as claimed in claim 10 wherein the structural portion to which the load test coupon is secured is a portion of an airframe of an aircraft.

12. A method as claimed in claim 11 wherein crack growths from both test coupons are averaged to correlate structural damage of the structural portion.

13. A method as claimed in claim 12 wherein the recorder unit has in addition a data processor capable of comparing crack growth recorded by the recorder unit, correlating said growth to structural damage, reporting the structural damage as a viewable output correlated to the crack growth, and accruing crack-growth data.

14. A method as claimed in claim 13 wherein the data processor is capable of predicting a next immediate increment of crack growth based on accrued crack-growth data.

15. A method as claimed in claim 14 wherein the structural portion is a structurally critical area.

16. A method as claimed in claim 15 wherein the structurally critical area is a main spar beam of a wing lower surface near attachment to a fuselage.

17. A method as claimed in claim 10 wherein the recorder unit has in addition a data processor capable of comparing crack growth recorded by the recorder unit, correlating said growth to structural damage, reporting the structural damage as a viewable output correlated to the crack growth, and accruing crack-growth data.

18. A method as claimed in claim 10 wherein the data processor is capable of predicting a next immediate increment of crack growth based on accrued crack-growth data.

19. A method as claimed in claim 10 wherein the structural portion is a structurally critical area.

20. A structural damage monitoring system for monitoring growth and magnitude of structural damage of a structural portion of a structure as reflected by growth of a crack therein, the system comprising:

a) a ligament assembly securable to the structural portion, the ligament assembly comprising;

i) a metallic load test coupon having a loading response substantially identical to a loading response of the structural portion and an artificial flaw simulating a metallurgical crack substantially equivalent to structural damage already present in the structural portion, said crack having a growth rate magnitude substantially identical to a magnitude of structural damage of the structural portion as said damage occurs; and

ii) a crack growth measurement gage in alignment with the crack of the test coupon;

b) a recorder unit in communication with the crack growth measurement gage for recording growth of the crack of the test coupon; and

c) a data processor capable of comparing crack growth recorded by the recorder unit, correlating said growth to structural damage, and reporting the structural damage as a viewable output correlated to the crack growth.

21. A structural damage monitoring system as claimed in claim 20 wherein the data processor is capable of accruing crack-growth data.

22. A structural damage monitoring system as claimed in claim 21 wherein the data processor is capable of predicting a next immediate increment of crack growth based on accrued crack-growth data.

23. A structural damage monitoring system for monitoring growth and magnitude of structural damage of a structural portion of a structure as reflected by growth of a crack therein, the system comprising:

a) two ligament assemblies securable to the structural portion either in a generally parallel relationship with the structural portion therebetween or in a side by side relationship, each ligament assembly comprising

i) a metallic load test coupon having a loading response substantially identical to a loading response of the structural portion and an artificial flaw simulating a metallurgical crack substantially equivalent to structural damage already present in the structural portion, said crack having a growth rate magnitude substantially identical to a magnitude of structural damage of the structural portion as said damage occurs; and

ii) a crack growth measurement gage in alignment with the crack of the test coupon;

b) a recorder unit in communication with the crack growth measurement gage for recording growth of the crack of the test coupon; and

c) a data processor capable of comparing crack growth recorded by the recorder unit, correlating said growth to structural damage, and reporting the structural damage as a viewable output correlated to the crack growth.

24. A structural damage monitoring system as claimed in claim 23 wherein the data processor is capable of accruing crack-growth data.

25. A structural damage monitoring system as claimed in claim 24 wherein the data processor is capable of predicting a next immediate increment of crack growth based on accrued crack-growth data.