Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Threaded fastener stress
Patent
1992-01-17
1994-03-08
Raevis, Robert
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Threaded fastener stress
F16B 3102
Patent
active
052917894
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to devices for indicating the 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 load has been maintained.
SUMMARY OF THE INVENTION
According to the first aspect of the invention, there is provided a member having first and second electrically conductive elements which are anchored to or fixed with respect to respective portions of the member. which portions underto relative movement when the member is stressed, wherein, when the member is subjected to a first load, the conductive elements are in electrical contact or other first electrical relation with each other and wherein, when the member is subjected to a second load, the elements are out of electrical contact or otherwise out of the first electrical relation with each other.
At least one of the electrically conductive elements may be an integral part of the member. The other conductive element is preferably adjustable relative to the member during preparation of the member for use.
In the preferred member, the first electrically conductive element is fixed, during preparation of the member, with respect to a first portion of the member and is electrically insulated from the member, there is provided a carrier for the second electrically conductive element, the carrier is fixed with respect to a second portion of the member and retaining means is provided for limiting movement of the second element relative to its carrier so that the second element is anchored to the second portion of the member.
During use of the member, the electrical conductive elements are used to provide an electrical signal when the load to which the member is subjected rises above or falls below a predetermined level. The member may be stressed in tension or in compression during use.
The invention also provides a load indicator for providing a signal representing the load to which a member is subjected or for providing a signal when the member is subjected to a predetermined load, the indicator comprising first and second electrically conductive elements, respective carriers for the elements and means for maintaining the carriers in respective positions which are fixed with respect to respective portions of the member.
The electrically conductive elements are preferably arranged to be in electrically conductive contact with each other when the member is subjected to the first load and to be out of electrically conductive contact with each other when the member is subjected to the second load. Making and breaking of electrical contact between the element provides a signal indicating attainment of a predetermined load. If a continuously variable signal is required to represent any load to which the member is subjected within a predetermined range of loads, then the change in the capacitance between the electrically conductive elements are arranged to remain out of contact with each other through the load range within which indication is required. The elements may contact each other at one limit of this range.
It is known to provide mechanical indicating means for indicating when the tension in a fastener exceeds a predetermined value. One form of mechanical indicating means which has been proposed for use in a bolt is a rod which extends along a bore formed in the main body of the bolt from one end thereof. The rod is anchored to the main body at an inner end of the bore and carries a crosspiece which lies outside the bore. When the fastener is unstressed, the crosspiece projects from the main body. As the fastener is tightened, the main body is stressed and the crosspiece enters a transverse groove formed in the end face of the main body. When the stress in the main body exceeds a predetermined value, the crosspiece lies entirely within the groove and does not project from the main body. This form o
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Raevis Robert
RotaBolt Limited
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