System and method for measuring stress at an interface

• US 6,776,049 B2
• Filed: 12/07/2001
• Issued: 08/17/2004
• Est. Priority Date: 12/07/2001
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Alliant Techsystems Incorporated (Northrop Grumman Corporation)
• Inventors: Everton, Randy L., Johnson, Mont A.
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): ALLEN, ANDRE J
• Application Number:
  US10/016,479
• Publication Number:
  US 20030106379A1
• Time in Patent Office: 984 Days
• Field of Search: 738/49, 738/52, 738/53, 738/54, 738/46, 738/12, 738/41, 738/47, 738/15, 737/60
• US Class Current: 73/841
• CPC Class Codes: F02K 9/34 Casings; Combustion chambers; Liners thereof
• CPC Class Codes: F02K 9/346 Liners, e.g. inhibitors
• CPC Class Codes: F02K 9/38 Safety devices, e.g. to prevent accidental ignition
• CPC Class Codes: G01G 3/125 wherein the weighing element is an optical member
• CPC Class Codes: G01L 1/242 the material being an optical fibre
• CPC Class Codes: G01L 1/26 Auxiliary measures taken, or devices used, in connection with the measurement of force, e.g. for preventing influence of transverse components of force, for preventing overload

Abstract

A stress sensor is provided that is suited for measurement of stress between adjacent mated bodies, such as at an interface. The stress sensor permits measurement of stress, preferably a shear component of the stress substantially exclusive of the normal component. A system including the stress sensor and a method of measuring stress, especially the shear component of stress, using the sensor are also provided.

Claims

1. A stress sensor, comprising:

a sensor body comprising a first wall and a second wall coupled to one another, the first wall and the second wall each having a respective portion opposing one another, the opposing portion of the first wall and the opposing portion of the second wall extending parallel to one another and spaced apart from one another along a y-axis that is perpendicular to a central x-axis, the central x-axis extending parallel to and equidistant from the opposing portions of the first and second walls, wherein the sensor body is resiliently deformable in response to a physical stress having a shear component and optionally a normal component for permitting movement of the first wall relative to the second wall along a direction parallel to the central x-axis in response to the shear component and for permitting movement of the first wall relative to the second wall along a direction parallel to the y-axis in response to the optional normal component; and

a sensing device comprising first and second sensor elements each extending between the opposing portions of the first and second walls for outputting sensor measurement signals representative of the physical stress and from which the shear component of the physical stress can be determined, the first sensor element having a first longitudinal axis intersecting the central x-axis at a first oblique angle α and

the second sensor element having a second longitudinal axis intersecting the central x-axis at a second oblique angle −

α

.

2. The stress sensor of claim 1, wherein the sensor body comprises aluminum.

3. The stress sensor of claim 1, wherein the sensor body consists essentially of aluminum.

4. The stress sensor of claim 1, wherein the sensor body further comprises third and fourth walls spaced apart from and opposing one another and each extending in a respective plane parallel to the y-axis, the third and fourth walls coupling the first and second walls to one another to provide a block with a quadrangular cross-section.

5. The stress sensor of claim 4, wherein the quadrangular cross-section is rectangular.

6. The stress sensor of claim 5, wherein the rectangular cross section has a length-to-height ratio of about 4 to 1.

7. The stress sensor of claim 4, wherein the sensor body has a chamber with a periphery bounded by at least the first, second, third, and fourth walls.

8. The stress sensor of claim 4, wherein:

the block has first and second pairs of diagonally opposed corners;

the first sensor element comprises a first strain gauge having opposite ends respectively connected proximate to the first pair of diagonally opposed corners of the block to extend diagonally across the block; and

the second sensor element comprises a second strain gauge having opposite ends respectively connected proximate to the second pair of diagonally opposed corners of the block to extend diagonally across the block and cross the first sensor element.

9. The stress sensor of claim 1, wherein the first and second sensor elements comprise first and second strain gauges, respectively.

10. The stress sensor of claim 1, wherein the first and second sensor elements comprise first and second optical strain gauges, respectively.

11. The stress sensor of claim 10, wherein:

the first and second optical strain gauges each have a respective longitudinal axis;

the first and second optical strain gauges are both arranged to undergo equal compression or extension along the longitudinal axes thereof representative of the normal component of the physical stress; and

the first optical strain gauge is arranged to undergo compression along the longitudinal axis thereof and the second optical strain gauge is arranged to undergo extension along the longitudinal axis thereof of equal magnitude representative of the shear component of the physical stress.

12. The stress sensor of claim 11, wherein the first and second optical strain gauges are symmetrical to each other across the central x-axis.

13. The stress sensor of claim 10, wherein the first and second optical strain gauges undergo a corresponding deformation in response to a physical parameter to alter an optical characteristic of light signals being transmitted therethrough or reflected therein.

14. The stress sensor of claim 1, wherein the stress sensor measures the shear component of the physical stress substantially exclusive of the optional normal component of the physical stress.

15. The stress sensor of claim 1, further comprising a sensor measurement signal output device for outputting the sensor measurement signals from the sensing device.

16. The stress sensor of claim 15, wherein the sensor measurement signal output device comprises an optical-to-electrical converter.

17. The stress sensor of claim 16, wherein the sensor measurement signal output device further comprises a light source.

18. A system for measuring a stress at an interface, the system comprising:

a first body;

a second body mated to the first body at the interface;

a stress sensor situated at the interface, the stress sensor comprising;

a sensor body comprising a first wall coupled to the first body and a second wall coupled to the second body, the first wall and second wall each having a respective portion opposing one another, the opposing portion of the first wall and the opposing portion of the second wall extending parallel to a central x-axis and spaced apart from one another along a y-axis that is perpendicular to the central x-axis, the central x-axis extending parallel to and equidistant from the opposing portions of the first and second walls, wherein the sensor body is resiliently deformable in response to a physical stress having a shear component and optionally a normal component for permitting movement of the first wall relative to the second wall along a direction parallel to the central x-axis in response to the shear component of the physical stress and for permitting movement of the first wall relative to the second wall along a direction parallel to the y-axis in response to the optional normal component of the physical stress;

a sensing device comprising first and second sensor elements each extending between the opposing portions of the first and second walls for outputting sensor measurement signals representative of the physical stress and from which the shear component is determined substantially exclusive of the normal component, the first sensor element having a first longitudinal axis intersecting the central x-axis at a first oblique angle α and

the second sensor element having a second longitudinal axis intersecting the central x-axis at a second oblique angle −

α

; and

a sensor measurement signal output device for outputting the sensor measurement signals from the sensing device; and

a data-receiving device operatively coupled to the sensor measurement signal output device for receiving the sensor measurement signals and determining the shear component of the physical stress substantially exclusive of the optional normal component of the physical stress.

19. The system of claim 18, further comprising a plurality of the stress sensors.

20. The system of claim 18, wherein the first and second sensor elements comprise first and second strain gauges, respectively.

21. The system of claim 18, wherein the first and second sensor elements comprise first and second optical strain gauges, respectively.

22. The system claim 21, wherein:

the first and second optical strain gauges each have a respective longitudinal axis;

the first and second optical strain gauges are both arranged to undergo equal compression or extension along the longitudinal axes thereof representative of the normal component of the physical stress; and

the first optical strain gauge is arranged to undergo compression along the longitudinal axis thereof and the second optical strain gauge is arranged to undergo extension along the longitudinal axis thereof of equal magnitude representative of the shear component of the physical stress.

23. The system of claim 22, wherein the first and second optical strain gauges are symmetrical to each other across the central x-axis.

24. The system of claim 18, wherein the data-receiving device comprises a data processor.

25. The system of claim 18, wherein the data-receiving device comprises a data display.

26. The system of claim 18, wherein the first body comprises a casing member or insulation layer of a rocket motor.

27. The system of claim 26, wherein the second body comprises a solid propellant of the rocket motor.

28. The system of claim 27, wherein the stress sensor is embedded in a liner of the rocket motor, the liner bonding the solid propellant to the casing member or the insulation layer.

29. A method for measuring shear stress at an interface between first and second mated bodies, the method comprising:

disposing a stress sensor at the interface between the first and second mated bodies, the stress sensor comprising;

a sensor body comprising a first wall coupled to the first mated body and a second wall coupled to the second mated body, the first wall and second wall each having a respective portion opposing one another, the opposing portion of the first wall and the opposing portion of the second wall extending parallel to a central x-axis and spaced apart from one another along a y-axis that is perpendicular to the central x-axis, the central x-axis extending parallel to and equidistant from the opposing portions of the first and second walls, wherein the sensor body is resiliently deformable in response to a physical stress having a shear component and optionally a normal response for permitting movement of the first wall relative to the second wall along a direction parallel to the central x-axis in response to the shear component and for permitting movement of the first wall relative to the second wall along a direction parallel to the y-axis in response to the optional normal component;

a sensing device comprising first and second strain gauges each having opposite ends respectively connected to the opposing portions of the first and second walls to extend the first and second strain gauges between the first and second walls, the first strain gauge intersecting the central x-axis at a first oblique angle α and

the second strain gauge intersecting the central x-axis by a second oblique angle −

α

; and

a sensor measurement signal output device; and

sensing physical stress applied to the sensor body and outputting sensor measurement signals representative of the physical stress.

30. The method of claim 29, further comprising communicating the sensor measurement signals to a data-receiving device and determining the shear component of the physical stress.

31. The method of claim 29, further comprising communicating the sensor measurement signals to a data-receiving device and determining the shear component of the physical stress substantially exclusive of the optional normal component of the physical stress.

32. The method of claim 29, further comprising disposing a plurality of stress sensors at the interface between the first and second mated bodies.

33. The method of claim 29, wherein the first and second strain gauges comprise first and second optical strain gauges, respectively.

34. The method of claim 33, wherein:

the first and second optical strain gauges each have a respective longitudinal axis;

the first and second optical strain gauges are both arranged to undergo equal compression or extension along the longitudinal axes thereof representative of the normal component of the physical stress; and

the first optical strain gauge is arranged to undergo compression along the longitudinal axis thereof and the second optical strain gauge is arranged to undergo extension along the longitudinal axis thereof of equal magnitude representative of the shear component of the physical stress.

35. The method of claim 34, wherein the first and second optical strain gauges are symmetrical to each other across the central x-axis.

36. The method of claim 29, wherein communicating the sensor measurement signals to the data-receiving device comprises communicating the sensor measurement signals to a data processor.

37. The method of claim 29, wherein communicating the sensor measurement signals to the data-receiving device comprises communicating the sensor measurement signals to a data display.

38. The method of claim 29, wherein the first mated body comprises a casing member or insulation layer of a rocket motor.

39. The method of claim 38, wherein the second mated body comprises a solid propellant of the rocket motor.

40. The method of claim 39, wherein disposing a stress sensor at the interface between the first and second mated bodies comprises embedding the stress sensor is embedded in a liner of the rocket motor, the liner bonding the solid propellant to the casing member or the insulation layer.