TENSION INDICATING FASTENER

• US 3,823,639 A
• Filed: 11/24/1972
• Issued: 07/16/1974
• Est. Priority Date: 11/24/1972
• Status: Expired due to Term

• Current Assignee: Theodore Liber
• Original Assignee: Theodore Liber
• Inventors: Liber, Theodore
• Primary Examiner(s): Parsons, Jr., Marion
• Application Number:
  US05/309,053
• Time in Patent Office: 599 Days
• Field of Search: 85/1T,61,62 73/88A,88F
• US Class Current: 411/14
• CPC Class Codes: F16B 31/025 with a gauge pin in a longitudinal bore in the body of the bolt
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01L 1/241 by photoelastic stress analysis

Abstract

Fasteners such as mine bolts are provided with tension indicators to directly read tension in the shank of the bolt. The preferred tension indicators comprise an elongated pin disposed in a bore formed in the bolt and connected at the bottom of the bore to the bolt shank to be tensioned thereby. The tension indicator further comprises a cross bar attached to the other end of the pin and extending laterally into engagement with another portion of the bolt, such as the head of the bolt, to be bent upon tensioning of the pin. Preferably, a photoelastic member is attached to the cross bar and bending stresses in the cross bar are manifested in the photoelastic member in the form of photoelastic fringes for reading by a reflection polariscope.

Claims

1. A tension indicator for indicating the tension in a shank of a bolt comprising an elongaged pin having means at one end for connection to a bolt shank, an elongated cross bar integral with and joined directly to said pin at the other end of said pin, an end support on at least one end of said cross bar for engagement with another portion of said bolt and for holding said cross bar free of said bolt for bending by said pin, and a stress indicating means mounted on said cross bar for visually manifesting the bending stress created in the cross bar during tensioning of said pin by said bolt shank.

2. A bolt tension indicator in accordance with claim 1 in which said pin is joined substantially centrally of said cross bar, and end supports are provided on opposite ends of said cross bar causing said cross bar to deflect centrally thereof between opposite end supports with tensioning of said pin.

3. A bolt tension indicator in accordance with claim 1 in which said end support comprises a depending flange integral with said cross bar and said means at one end of said pin is threaded for threading engagement into a portion of said bolt.

4. A bolt tension indicator in accordance with claim 1 in which said end support is at one end of said cross bar and in which said cross bar is attached at its other end to said pin.

5. A tension indicator for indicating the tension in the shank of a bolt having a bore therein and a support platform in a depression in said head of the bolt, said bolt tension indicator comprising:

an elongated pin having a predetermined cross section for loosely fitting within the bore, a thread on one end of said pin for threading into the bolt shank for tensioning the pin with tensioning of the shank of the bolt, an elongated cross bar integrally joined directly with and to said pin at the other end of the pin and extending laterally from said pin, at least one end support on said cross bar depending from said cross bar to engage the support platform in the bolt and space the cross bar from said bolt head for facilitating bending of said cross bar by said pin, and a photoelastic strip fastened to the upper side of said cross bar for manifesting in the form of photoelastic fringes the bending stresses created in the cross bar during tensioning of said pin by said bolt shank.

6. In the combination of a bolt and a tenSion indicator, the bolt having a bolt head and a shank with a central bore therein, said pin being loosely fitted within said bore and having an inner end fastened to said bolt shank to be tensioned thereby, the improvement comprising:

a support platform formed in said bolt head, a cross bar integral with said pin and extending laterally therefrom into engagement with said support platform for bending by said pin and stress indicating means on said cross bar for visually manifesting the bending stresses created in the cross bar during the bending thereof by said pin.

7. The combination in accordance with claim 6 in which said cross bar has a length about or less than the diameter of the shank of said bolt to reduce the effects of any bending of said bolt head on said photoelastic member.

8. A combination in accordance with claim 7 in which said bolt head is formed with a depression therein, said support platform in a flat planar surface in the lower portion of said depression, and at least one end support is formed on said cross bar for resting on said support platform and spacing said cross bar from the remainder of said bolt head.

9. The combination in accordance with claim 8 in which said depression is pyramidal in shape, said cross bar extends generally across said opening in said shank and said pin is joined centrally to said cross bar to deflect the center portion thereof.

10. The combination in accordance with claim 9 in which said cross bar has a length substantially equal to or less than the diameter of said shank.

11. The combination in accordance with claim 8 in which the top of said cross bar is below the top surface of said bolt head and is thereby in a protected space.

12. In the combination of a bolt and tension indicator in which the bolt has a head and a shank with a bore therein, and in which the indicator comprises a pin having an inner end fastened to the bolt and extending longitudinally in said bore the improvement comprising:

a support platform formed in said bolt head, a threaded end on said indicator pin for fastening to said bolt shank, a cross bar integral with said pin and extending substantially normal thereto for bending with tension in said pin, a depending end support on said cross bar for engaging said bolt head in a depression in said bolt head, and means including a photoelastic member on said cross bar for manifesting in the form of photoelastic fringes bending stresses created in the cross bar during tensioning of said pin and said bolt shank.