Shown above is the small contacts from the strain gauges to the wires.
We used this specific type of strain gauges to sense all directions of torsional strain.
The device was clamped, and weights were applied to both ends to induce torsional stress within the shaft.
The data was personally collected and analysed graphically to find a line of best fit. That equation was use to calculate the torque that was being applied to the bolt.
The picture above is the connection from the strain gauges to the Wheatstone bridge circuit that read the electrical resistance in the circuit. With that electrical resistance we could find the strain occurring in the shaft.
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Strain Gauge Torque Wrench

A project for my Strength of Materials class in which we were challenged to design and assemble a device that can be used to measure stress while utilizing strain gauges. My team and I created a torque wrench that sensed torsional stain in a 6061 aluminum shaft. I personally helped install and wire the strain gauges, machined the necessary parts, and created a calibration curve to properly measure over 120 in-lbs.less.

James Hertzel
Product Design Engineer Rochester, NY