Strain indicator

• US 4,002,139 A
• Filed: 02/05/1976
• Issued: 01/11/1977
• Est. Priority Date: 08/05/1974
• Status: Expired due to Term

• Current Assignee: RBS Industries, Inc.
• Original Assignee: William J. Payne
• Inventors: Payne, William J.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Corr, Denis E.
• Application Number:
  US05/655,495
• Time in Patent Office: 341 Days
• Field of Search: 116/114 R, 116/DIG. 34, 73/88 F, 73/88 E, 73/88 A, 85/62, 85/1 R, 85/1 T
• US Class Current: 116/212
• CPC Class Codes: G01B 5/30 for measuring the deformation in a solid, e.g. mechanical strain gauge
• 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.

Claims

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

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

a second member received within said first member and having a first end and a second end, said first end being secured to said first member;

a fluid holding member having a window, said fluid holding member being secured to said first member with said window substantially adjacent said head so as to be visible;

light-absorbing indicator fluid within said fluid holding member;

a first indicator area in said fluid holding member disposed substantially adjacent said window;

a second indicator area in said fluid holding member disposed substantially adjacent said window and substantially coplanar with said first indicator area;

means independently operatively connecting said first indicator area and said second indicator area to said second end of said second member such that;

a. as said first member undergoes an elastic change in length said second end of said second member is caused to move with respect to said window with the result that said first indicator area and said second indicator area become separated from said window an equal distance with the consequence that said fluid is caused to flow between said window and said first and second indicator areas;

b. as said first member undergoes a further change in length exceeding the elastic limit of said first member, said first indicator area and said second indicator area move relative to each other and assume a non-coplanar relationship.

2. The invention of claim 1 in which said first indicator area is defined by a planar surface of said second end of said second member received within said fluid holding member.

3. The invention of claim 2 in which said second indicator area is defined by a planar surface of a generally annular member received about said second end of said second member.

4. The invention of claim 1 in which said first indicator area is maintained in coplanar relationship with said second indicator area in a non-stress condition of said first member, by means of releasable locking means.

5. The invention of claim 4 in which said first indicator area is defined by a planar surface of said second end of said second member and said second indicator area is defined by a planar surface of an annular member received about said second end of said second member and said releasable locking means is defined by a pressfit relationship of said annular member with said second end of said second member.

6. The invention of claim 5 in which said releasable locking means is actuated by the engagement of said annular member with a stop shoulder defined at the interior of said fluid holding member.

7. The invention of claim 6 in which said internal stop shoulder is defined by a generally annular ring secured to the internal wall of said fluid holding member.

8. The invention of claim 7 in which a predetermined clearance space is defined between said stop shoulder and said annular member which clearance face defines the elastic limit of the material from which said first member is fabricated.

9. The invention of claim 5 in which said releasable locking means is defined by complementary tapered surfaces defined by said annular member and said second member and said releasable locking means is actuated by engagement of said annular member with an internal stop shoulder of said fluid holding member.

10. The invention of claim 9 in which internal bias means is provided at said fluid holding member to move said annular member into engagement with said window at such time as said annular member is released from said second member.

11. The invention of claim 10 in which said internal bias means is defined by an elastomeric member disposed in a state of compression between said annular member and a shoulder of said second member.

12. The invention of claim 1 in which bias means is provided at said fluid holding member to bias said first and second indicator areas into said window with said first member in a non-stressed condition.

13. The invention of claim 12 in which said second member is provided with a shoulder and said bias means is defined by an elastomeric member disposed in a state of compression against said shoulder.

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

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

a second member received within said first member;

a fluid holding member having a window, said fluid holding member being secured to said first member with said window substantially adjacent said head so as to be visible;

light-absorbing indicator fluid within said fluid holding member;

a first indicator area in said fluid holding member disposed substantially adjacent said window;

a second indicator area in said fluid holding member disposed substantially adjacent said window and substantially coplanar with said first indicator area;

bias means maintaining said first indicator area and said second indicator area in contact with the internal surface of said window with said indicator in a non-stress condition;

means independently operatively connecting said first indicator area and said second indicator area to said second member such that;

a. as said first member undergoes an elastic change in length said second member is caused to move with respect to said window with the result that said first indicator area and said second indicator area become separated from said window an equal distance with the consequence that said fluid is caused to flow between said window and said first and second indicator areas;

b. as said first member undergoes a further change in length exceeding the elastic limit of said first member, said first indicator area and said second indicator area move relative to each other and assume a non-coplanar relationship.

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

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

a second member received within said first member;

a fluid holding member having a window, said fluid holding member being secured to said first member with said window substantially adjacent said head so as to be visible;

light-absorbing indicator fluid within said fluid holding member;

a first indicator area in said fluid holding member;

a second indicator area in said fluid holding member;

means operatively connecting said first indicator area and said second indicator area to said second member;

means providing for the equal movement of said first indicator area and said second indicator area as said first member undergoes an elastic change in length;

means providing for the movement of one of said indicator areas relative to the other of said indicator areas as said first member undergoes a change in length exceeding the elastic limit of said first member.

16. The invention of claim 15 in which said first indicator area and said second indicator area are disposed in substantially a coplanar relationship with said stress-strain indicator in a non-stress condition.

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

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

a second member extending from said first member;

a fluid holding member having a window, said fluid holding member being secured to said first member with said window substantially adjacent said head so as to be visible;

18. light-absorbing indicator fluid within said fluid holding member;

a first indicator area in said fluid holding member;

a second indicator area in said fluid holding member;

means independently operatively connecting said first indicator area and said second indicator area to said second member;

means providing for the movement of at least one of said indicator areas as said first member undergoes an elastic change in length;

means providing for the movement of one of said indicator areas relative to the other of said indicator areas as said first member undergoes a change in length exceeding the elastic limit of said first member.