STRAIN INDICATOR AND METHOD

• US 3,799,108 A
• Filed: 12/13/1971
• Issued: 03/26/1974
• Est. Priority Date: 12/13/1971
• Status: Expired due to Term

• Current Assignee: RBS Industries, Inc.
• Original Assignee: Jack E. Mosow
• Inventors: Mosow, Jack E.
• Primary Examiner(s): Capozi, Louis J.
• Application Number:
  US05/207,260
• Time in Patent Office: 834 Days
• Field of Search: 116/114,DIG.34 73/88F,88E,1,85.5 85/62 340/373
• US Class Current: 411/13
• 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 area and a light-absorbing indicator fluid are encapsulated in a member that also includes a window. The capsule is fastened to the strain member with an adhesive. A change in length of the strain member causes the indicator area to become separated from the window with the result that light-absorbing indicator fluid is caused to flow between the indicator area 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 optical stress-strain indicator comprising in combination:

a first member subject to stress-strain and having a bore extending into said member from an external surface thereof;

an elongated second member having a first end and an exposed shank portion, said elongated second member being disposed in said bore substantially concentric therewith with said first end secured to said first member at an interior portion thereof;

a fluid holding member having a side wall portion, a window, and an indicator element disposed within said fluid holding member, said indicator element including an indicator area adjacent said window;

light-absorbing indicator fluid in said fluid holding member;

said fluid holding member being secured to said first member at said side wall portion and within said bore and substantially concentric therewith with said window substantially adjacent said external surface of said first member so as to be visible;

said indicator fluid substantially filling said fluid holding member while remaining out of contact with said first member and said exposed shank portion of said elongated second member;

means for operatively interconnEcting said exposed shank portion of said elongated second member and said indicator element, whereby;

upon application of stress to said first member with a resulting change of length of said first member, said elongated second member is caused to move axially thereby causing said indicator element to move simultaneously in the same direction with the result that said indicator area is caused to move from said window and indicator fluid is caused to flow between said indicator area and said window.

2. The invention of claim 1 in which said elongated second member is provided with a second end which is received in said fluid holding member, said second end defining said indicator element.

3. The invention of claim 2 in which said fluid holding member is defined as a capsule having at least one side wall, and outer wall including said window and an inner wall through which said elongated second member extends.

4. The invention of claim 1 in which said side wall portion is surrounded by a complementary wall of said first member whereby an axial adjustment of said fluid holding member may be made with respect to said first member prior to fastening of the members.

5. An optical stress-strain indicator comprising in combination:

a first member subject to stress-strain and having a head and a bore extending from said head into said member;

a pin member received within said bore substantially concentric therewith and having a first end and a second end and an exposed shank portion therebetween, said first end being secured to said first member at an interior portion thereof;

a counterbore in said first member opening through said head and concentric with said bore;

a fluid holding member having a side wall portion and a window;

said fluid holding member being secured to the wall defining said counterbore at said side wall portion and substantially concentric therewith with said window substantially adjacent said head so as to be visible;

said second end of said pin received in said fluid holding member;

sealing means between said pin and said fluid holding member;

a light-absorbing indicator fluid in said fluid holding member and substantially filling said fluid holding member while remaining out of contact with said first member and said exposed shank portion of said pin member;

an indicator area at said second end of said pin disposed adjacent said window, whereby;

upon application of stress to said first member there is accomlished a change in length of said first member with the result that said pin member is caused to move axially thereby causing said second end to move simultaneously in the same direction with the consequence that said indicator area moves from said window and indicator fluid is caused to flow between said indicator area and said window.

6. The invention of claim 5 in which said first member is a threaded bolt.

7. The invention of claim 5 in which said first end of said pin is fastened to said first member by means of an adhesive.

8. The invention of claim 5 in which said fluid holding member is defined by at least one side wall, an outer wall including said window and an inner wall, said side wall being fastened to said first member.

9. The invention of claim 8 in which said inner wall is defined by a sealing member engaging said side wall and the exterior surface of said pin.

10. The invention of claim 9 in which said sealing member is a stepped seal having one portion in compression between said side wall and said pin.

11. The invention of claim 9 in which said sealing member engages a shoulder defined on said pin.

12. The invention of claim 5 in which said fluid holding member is fastened to said first member by means of an adhesive.

13. An optical stress-strain indicator comprising in combination:

a first member subject to stress-strain and having a bore extending into said member from an external surface thereof;

a second member disposed in said bore suBstantially concentric therewith and having a first end secured to said first member at an interior portion thereof and an exposed shank portion;

a fluid holding member having a side wall portion, a window, and an indicator element disposed within said fluid holding member, said indicator element including an indicator area;

light-absorbing indicator fluid in said fluid holding member;

said light-absorbing indicator fluid substantially filling said fluid holding member while remaining out of contact with said first member and said exposed shank portion of said second member;

said fluid holding member being disposed substantially within said bore and substantially concentric therewith with said window visible from the exterior of said first member;

said side wall portion being substantially surrounded by a generally complementary wall portion of said first member there being provided means to adjust the axial position of said fluid holding member relative to said first member prior to the securing of these members together;

means for operatively interconnecting said exposed shank portion of said second member and said indicator element;

said fluid holding member being secured to said first member with said indicator area disposed substantially adjacent said window, whereby;

upon application of stress to said first member there is accomplished a change in length of said first member with the result that said second member is caused to move axially thereby causing said indicator element to move simultaneously in the same direction with the result that said indicator area is caused to move from said window and indicator fluid is caused to flow between said indicator area and said window.