STRAIN INDICATOR AND METHOD

• US 3,850,133 A
• Filed: 11/29/1972
• Issued: 11/26/1974
• Est. Priority Date: 11/29/1972
• Status: Expired due to Term

• Current Assignee: RBS Industries, Inc.
• Original Assignee: Robert Carol Johnson
• Inventors: Johnson, Robert Carol
• Primary Examiner(s): Capozi, Louis J.
• Application Number:
  US05/310,445
• Time in Patent Office: 727 Days
• Field of Search: 116/114R,70,DIG.24 73/1,85.5,88,88E,88F 85/62,1R
• US Class Current: 116/212
• CPC Class Codes: F16B 31/02 for indicating the attainment of a particular tensile load or limiting tensile load apparatus for, or method of, determining value of torque or twisting moment for tightening a nut or other member similarly stressed G01L5/24
• CPC Class Codes: F16B 31/025 with a gauge pin in a longitudinal bore in the body of the bolt
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
• CPC Class Codes: G01L 5/24 for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
• CPC Class Codes: Y10S 116/34 Tension indicating

Abstract

A strain indicator of the type wherein a change in length of a strain member produces a change in color of a visual indicator. An indicator member and a light-absorbing indicator fluid are sealed in a capsule member that also includes a window. The capsule is fastened to the strain member. A change in length of the strain member causes the indicator member to become separated from the window with the result that light-absorbing indicator fluid is caused to flow between the indicator member and the window. The method of the invention comprises method steps of manufacturing subassemblies of the strain indicator as well as the method steps leading to complete assembly of the indicator.

Claims

1. An indicator comprising in combination:

a first member, a second member fastened to said first member and having a first end and a second end, a fluid holding member having a window, said second member being located entirely outside of said fluid holding member, said fluid holding member fastened to said first member adjacent said second end of said second member, a light-absorbing indicator fluid in said fluid holding member, an indicator member disposed in said fluid, said indicator member including an indicator area disposed substantially adjacent said window, means maintaining said indicator area in close proximity to said window with said first member in an unstressed condition, means operable to move said indicator member in response to movement of said second member, whereby;

upon a change of length of said first member as a result of a stressed condition in said first member said second member and said indicator member are caused to move and said indicator fluid is caused to flow between said indicator area and said window thus giving a visual indication of a change in length of said first member.

2. An indicator comprising in combination:

a first member, a second member fastened to said first member, a fluid holding member having a window and a contact wall, said fluid holding member fastened to said first member in contact with said second member at said contact wall, a light-absorbing indicator fluid in said fluid holding member, an indicator member disposed in said fluid, said indicator member including an indicator area disposed substantially adjacent said window, means to bias said indicator member into close proximity to said window with said first member in an unstressed condition;

means operable to move said indicator member in response to movement of said second member upon a change in length of said first member, whereby;

upon placement of a strain in said first member said indicator fluid is caused to flow between said indicator area and said window thus giving a visual indication of a strain condition in said first member.

3. The invention of claim 2 in which said second member is a ferrous material and said second recited means comprises a magnetic force at said indicator member.

4. The invention of claim 3 in which said magnetic force is defined by a magnet attached to said indicator member.

5. The invention of claim 2 in which said first recited means comprises a compressive force operatively exerted on said indicator member by said second member.

6. The invention of claim 5 in which said contact wall is resilient and said compressive force is exerted on said contact wall by said second member and, in turn, said contact wall exerts a compressive force on said indicator member.

7. The invention of claim 2 in which a dead space is provided within said indicator member to compensate for changes in volume of said light-absorbing indicator fluid within said fluid holding member.

8. The invention of claim 2 in which said fluid holding member is defined by a capsule having a side wall, a bottom wall defining said contact wall, and a window.

9. The invention of claim 8 in which said side wall is fastened to said first member with said bottom wall in contact with said second member.

10. The invention of claim 8 in which said side wall and said bottom wall define a generally cup shaped element closed by said window.

11. The invention of claim 2 in which said indicator member is defined by a generally cup shaped element having a side wall and an upper wall with said indicator area defined at said upper wall.

12. The invention of claim 11 in which said cup shaped element defining said indicator member is closed by a magnet.

13. The invention of claim 12 in which said cup shaped element defining said indicator member and said magnet define a dead space.

14. The invention of claim 13 in which an annular groove is defined in said indicator member.

15. The invention of claim 2 in which said second member is a pin having a free end in contact with said contact wall.

16. The invention of claim 15 in which said free end is defined by a spherical surface.