Project Title:

Direct Measurement of Bolt Tension Utilizing Magnetostriction

04.15-0540
NAS9-18331
Direct Measurement of Bolt Tension Utilizing
	Magnetostriction
Satcon Technology Corporation
	12 Emily Street
	Cambridge, MA 02139-4507
		James H. Goldie
(617-661-0540)

Abstract:

	A new method for measuring bolt tension directly exploits the relationship between
stress and magnetic flux density in magnetostrictive materials. A conventional washer
is either replaced or supplemented by a washer made from a magnetostrictive alloy.
A wrench modified to include a Hall-effect probe and a permanent magnet is utilized
to monitor the change in magnetic flux due to compression of the washer. This represents
an improvement over current techniques in that the compressive force on the washer
is a direct measure of the tension in the bolt. Consequently, calibration to account
for bolt parameters such as length, stressed length, diameter, velocity of sound,
tensile stiffness, and surface characteristics is not necessary. The objective of
Phase I is to determine the feasibility of this approach and to develop a optimal
configuration. The anticipated result is a bolt tension measurement technique which
is easy to use, accurate, and applicable to all joint configurations and bolt types
and that does not require bolt preparation or calibration on an individual basis.

Potential Commercial Application:

Potential Commercial Applications: The result would be applicable to all equipment
containing critical or remote bolt joints, such as aircraft and undersea vehicles.
In addition, there are important applications in automated assembly and robotics.