The Ultrabend bolt is a specially designed bolt instrumented with strain gauges (see figure) that are connected into twin Wheatstone-bridge circuits. The geometric arrangement of the strain gauges is such that by suitable electrical switching of the Wheatstone-bridge circuits, these circuits can be made to either (1) suppress responses to bending and torsional stresses while putting out signals indicative of axial preload or (2) suppress responses to axial and torsional stresses while putting out signals indicative of the magnitude and direction of the bending moment in the bolt. Switching between these two measurement modes is accomplished by use of field-effect transistors controlled by a logic circuit.

Pairs of Strain Gauges located at 90° intervals are connected into Wheatstone-bridge circuits so as to respond to either bending or axial preload in the bolt.

The strain gauges are positioned and oriented orthogonally about the cylindrical axis of the bolt. In the bending-measurement mode, the root sum square of the outputs from the Wheatstone bridges is proportional to the magnitude of the bending moment in the bolt. At the same time, the arctangent of the ratio between the bridge outputs is the angle between the plane of bending and one of the radial coordinate axes defined by the positions of the strain gauges.

This work was done by Douglas E. Smith, Peter D. Totman, Randy L. Everton, Paul A. St. Jean, Marvin D. Bunderson, Mark R. Egget, and Randy Borgstrom of ATK Thiokol Propulsion, Inc., for Marshall Space Flight Center.

Title to this invention has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457(f)} to ATK Thiokol Propulsion, Inc. Inquiries concerning licenses for its commercial development should be addressed to

Thiokol Propulsion Patent Office
(435) 863-3511

Refer to MFS-31609, volume and number of this NASA Tech Briefs issue, and the page number.

NASA Tech Briefs Magazine

This article first appeared in the January, 2002 issue of NASA Tech Briefs Magazine.

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