Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Threaded fastener stress
Patent
1993-06-28
1995-02-14
Noland, Tom
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Threaded fastener stress
G01L 114, F16B 3102
Patent
active
053884639
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the indication of a load to which a member is subjected. The invention has been devised primarily for use in fasteners or other members which are to be subjected to a predetermined load and the invention is useful during initial loading of the member and subsequently for checking that the required lead has been maintained.
2. Description of the Related Art
In GB 2212284 A., there is disclosed a hollow bolt containing first and second carriers, each carrying a respective electrically conductive element. When the bolt is subjected to a first load, these elements are in mutual contact. When the bolt is subjected to a second load, the conductive elements are out of mutual contact. This change in the condition of the device is detected electrically. To facilitate this, the first electrical contact extends through the first carrier to a face thereof exposed at an end of tile bolt. The second carrier provides an electrically conductive path between the second element and the bolt. To ascertain whether the elements are in mutual contact, electrically conductive probes are applied to an end of the bolt and an exposed end of the first element, these probes being connected in an electrical circuit which includes a source of electrical power and a lamp or other signalling device.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a more reliable indication of load than can be achieved by the known arrangement under certain conditions.
According to the present invention, there is provided a device comprising a hollow member, an inductor and first and second electrically conductive elements which are anchored to or freed with respect to respective portions of the member, which portions undergo relative movement when the member is stressed, wherein, when the member is subjected to a first load, the elements are in mutual electrically conductive contact at a position inside the hollow member and, when the member is subjected to a second load, the elements are out of mutual electrically conductive contact and wherein the inductor is connected electrically between said elements so that a closed circuit including the inductor exists when the elements are in mutual contact.
The presence or absence of the closed circuit can be checked, using inductive coupling between testing apparatus and the inductor of the device embodying the invention. It is therefore unnecessary to establish an electrically conductive relation between test apparatus and the device.
BRIEF DESCRIPTION OF THE DRAWINGS
An example of a fastener embodying fie present invention will now be described, with reference to the accompanying drawing, which shows the fastener partly in cross section.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The particular fastener illustrated in the accompanying drawing is a bolt 10 having a male screw thread 11 and a head 12. The bolt is hollow. In the particular example illustrated, a blind bore extends into the bolt from an end face thereof presented by fie head 12. The bore is preferably coaxial with the thread 11 and extends substantially beyond the head 12.
There is disposed inside the bolt a first electrically conductive element 13 carried by a carrier 14. The carrier also is disposed at least partly inside the bolt. However, at least one face 15 of the carrier is exposed at the outside of the bolt. The carrier 14 is fixed with respect to the bolt 10. In the example illustrated, the carrier and fie bolt have respective cooperating screw threads and fie carrier is restrained against turning relative to the bolt, for example by means of an adhesive on the threads. Also in the example illustrated, the electrically conductive element 13 is fled with respect to the carrier 14.
A second electrically conductive element 16 is also disposed inside the bolt. This element occupies an inner portion of the bore formed in fie bolt and is urged by a spring 17 onto a seat at the blind end of the bore. The spring 17 acts bet
REFERENCES:
patent: Re30183 (1980-01-01), Popenoe
McCall Eric S.
Noland Tom
RotaBolt Limited
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