Fastener incorporating ultrasonic transducer

• US 4,294,122 A
• Filed: 07/12/1979
• Issued: 10/13/1981
• Est. Priority Date: 07/12/1979
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: General Dynamics Corporation
• Inventors: Couchman, James C.
• Primary Examiner(s): Ciarlante, Anthony V.
• Application Number:
  US06/057,059
• Time in Patent Office: 824 Days
• Field of Search: 73/761, 73/629, 73/597, 116/DIG. 34, 310/336
• US Class Current: 73/761
• CPC Class Codes: B25B 23/14 Arrangement of torque limiters or torque indicators in wrenches or screwdrivers couplings for transmitting rotation or clutches F16D; devices for measuring torque per se G01L
• CPC Class Codes: F16B 2031/022 using an ultrasonic transducer
• CPC Class Codes: G01L 5/246 using acoustic waves
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 2291/2691 Bolts, screws, heads
• CPC Class Codes: G01N 29/24 Probes transducers for acoustic waves B06B, G10K; for measuring G01H

Abstract

A threaded bolt having an opening in either its head or its opposite end with an ultrasonic transducer fixedly secured therein for use in obtaining preload measurements as well as other measurements for quality control inspection or for monitoring purposes.

Claims

1. A fastener for fastening together structural members comprising:

a shank having a head at one end and threads formed at the other end,

a shallow opening formed in one end of said fastener and having a maximum depth from said one end of said fastener which is substantially less than the length of said fastener, and

an acoustic transducer located in said opening and permanently secured therein with said transducer being acoustically coupled to said fastener,

the entire portion of said fastener between said opening and the end of said fastener opposite said opening being formed of solid metal throughout.

2. The fastener of claim 1, wherein:

said opening is formed in said head and has a depth less than the length of said head as measured along the longitudinal axis of said fastener.

3. The fastener of claim 1, wherein:

said opening is formed in said other end of said shank.

4. The fastener of claim 1, wherein:

said transducer comprises a disc shaped member secured in said opening such that its thin plane is substantially perpendicular to the axis of said shank.

5. The fastener of claims 1, 2, 3, or 4, wherein:

said fastener is formed of metal,

said transducer has electrodes formed at opposite ends thereof,

one of said electrodes being in electrical contact with said fastener,

20. The fastener of claims 1, 14 or 16 wherein:

said fastener is intended for use on aircraft or on spacecraft.

23. The fastener of claims 1, 14 or 16 wherein:

said transducer is located in said opening such that it may be used for pulse-echo measurements wherein when said transducer is pulsed, a transducer signal is generated which travels from said transducer through said fastener to said end of said fastener opposite said opening and back to said transducer at least once,

the distance between said transducer and said end of said fastener opposite said opening being equal to a major portion of the length of said fastener such that when said signal is generated, it will travel through the entire gripping length of said fastener, including the portion of said shank next to said head, when traveling between said transducer and said end of said fastener opposite said opening.

24. The fastener of claim 23, wherein:

said opening is formed in said head only.

6. A method of attaching two members together with a threaded fastener comprising the steps of:

attaching said two members together with a threaded fastener having an acoustic transducer permanently attached to one end thereof,

while said fastener is being torqued in place, employing said transducer to obtain measurements indicative of stress on said fastener,

continuing to torque said fastener in place until a desired preload stress value is obtained, and

leaving said transducer permanently attached to said fastener after said two members are attached together with said fastener.

7. The method of claim 6 comprising the steps of:

at a later date employing said transducer to make subsequent measurements.

8. The method of claim 7 wherein said subsequent measurements comprise:

monitoring for flaws or cracks in said fastener.

9. The method of claim 8 wherein said subsequent measurements are obtained by:

actuating said transducer to produce an acoustic pulse, and

detecting for pulses reflected from the other end of said fastener.

10. The method of claim 8 wherein said subsequent measurements are obtained by:

actuating said transducer to produce an acoustic pulse, and

detecting for pulses reflected from surfaces other than from said other end of said fastener.

11. The method of claim 8 wherein said subsequent measurements are obtained by:

detecting for acoustic pulses in said fastener.

12. The method of claim 7 wherein said subsequent measurements comprise:

monitoring for acoustic emissions produced by said fastener or by surrounding structure.

13. The method of claim 6 wherein said measurements are obtained by:

actuating said transducer to produce an acoustic pulse, and

detecting for pulses reflected from the other end of said fastener.

14. A fastener for fastening together structural members, comprising:

a shank having a head at one end and threads formed at the other end,

an opening formed in one end only of said fastener,

said opening being defined by side wall structure extending from said one end only of said fastener to a substantially flat surface substantially parallel to the end of said fastener opposite said opening,

the maximum distance between said one end only of said fastener and said surface of said opening being substantially less than the length of said fastener, and

an acoustic transducer located in said opening and permanently secured therein with said transducer being acoustically coupled to said fastener,

the entire portion of said fastener between said opening and said end of said fastener opposite said opening being of solid metal throughout.

15. The fastener of claim 14 wherein:

said substantially flat surface of said opening is substantially perpendicular to the longitudinal axis of said fastener,

said transducer has substantially flat opposite ends which are substantially parallel to said substantially flat surface of said opening and to said end of said fastener opposite said opening.

18. The fastener of claims 14, 16, 17, or 15, wherein:

said acoustic transducer is formed of a piezoelectric material.

21. The fastener of claims 14 or 16, wherein:

said fastener is intended for use on aircraft or on spacecraft,

said opening is formed in said head,

said one end only of said fastener being the end of said head,

said maximum distance between said end of said head and said surface of said opening being less than the length of said head as measured along the longitudinal axis of said fastener,

said shank being of solid metal throughout its length.

16. A fastener for fastening together structural members, comprising:

a shank having a head at one end and threads formed at the other end,

an opening formed in one end only of said fastener,

said opening being defined by side wall structure extending from said one end only of said fastener to a surface which forms the end of said opening in said fastener,

the maximum distance between said one end only of said fastener and said surface of said opening being substantially less than the length of said fastener, and

an acoustic transducer located in said opening and permanently secured therein with said transducer being acoustically coupled to said fastener,

said transducer having substantially flat opposite ends which are substantially perpendicular to the longitudinal axis of said shank

the entire portion of said fastener between said opening and the end of said fastener opposite said opening being of solid metal throughout.

17. The fastener of claim 16, wherein:

said substantially flat opposite ends of said transducer are substantially parallel to said end of said fastener opposite said opening.

19. The fastener of claims 16 or 17 wherein:

one of said ends of said acoustic transducer is acoustically coupled to said surface of said opening.

22. A fastener, comprising:

a shank having a head at one end and threads formed at the other end,

a shallow opening formed in one end only of said fastener,

an acoustic transducer located in said opening and permanently secured therein with said transducer being acoustically coupled to said fastener,

said fastener being formed of metal with the portion of said fastener between said opening and the end of said fastener opposite said opening being of solid metal throughout.

25. A fastener, comprising:

a shank having a head at one end and threads formed at the other end,

an opening formed in said head from the end of said fastener coinciding with the end of said head,

said opening being defined by side wall structure extending from said end of said fastener coinciding with the end of said head to a surface which forms the end of said opening in said fastener,

the maximum distance between said end of said fastener coinciding with the end of said head and said surface of said opening being less than the length of said head as measured along the longitudinal axis of said fastener,

an acoustic transducer located entirely in said opening and permanently secured therein,

said fastener being formed of metal with the portion of said fastener between said opening and the end of said fastener opposite said opening being of solid metal throughout,

said acoustic transducer being acoustically coupled to said surface of said opening,

said acoustic transducer having two electrodes,

one of said electrodes being electrically coupled to said fastener,

the other of said electrodes being located to be electrically connectible to a utilization device.

26. A method of attaching two members together with a metal fastener of the type comprising a shank having a head at one end and threads formed at the other end with a shallow opening formed in one end of said fastener, and an acoustic transducer located in said opening and permanently secured therein, the portion of said fastener between said opening and the end of said fastener opposite said opening being of solid metal throughout, said method comprising the steps of:

attaching said two members together with said fastener,

while said fastener is being torqued in place, pulsing said transducer to generate transducer signals to obtain measurements indicative of stress on said fastener,

continuing to torque said fastener in place until a desired preload stress value is obtained, and

leaving said transducer permanently secured in said opening of said fastener after said two members are attached together with said fastener.

27. A fastener, comprising:

a shank having a head at one end and threads formed at the other end,

a shallow opening formed in one end only of said fastener,

an acoustic transducer located in said opening and permanently secured therein with said transducer being acoustically coupled to said fastener,

said transducer being located in said opening such that it may be used for pulse-echo measurements wherein said transducer is pulsed, a transducer signal is generated which travels from said transducer through said fastener to the end of said fastener opposite said opening and back to said transducer at least once,

the distance between said transducer and said end of said fastener opposite said opening being equal to a major portion of the length of said fastener such that when said signal is generated, it will travel through the entire gripping length of said fastener, including the portion of said shank next to said head, when traveling between said transducer and said end of said fastener opposite said opening,

said fastener being formed of metal with the portion of said fastener between said opening and said end of said fastener opposite said opening being of solid metal throughout.

28. A fastener, comprising:

a shank having a head at one end and threads formed at the other end,

a shallow opening formed in one end only of said fastener,

an acoustic transducer located in said opening and permanently secured therein with said transducer being acoustically coupled to said fastener,

said transducer being located in said opening such that it may be used for pulse-echo measurements wherein when said transducer is pulsed, a transducer signal is generated which travels from said transduer through said fastener to the end of said fastener opposite said opening and back to said transducer at least once,

said fastener being formed of metal with the portion of said fastener between said opening and said end of said fastener opposite said opening being of solid metal throughout.

29. The fastener of claim 37, wherein:

said opening is formed in said head only.