This document provides instructions for using strain gauges to measure torsion on a specimen. It describes how strain gauges work by changing electrical resistance when stretched or compressed. It explains how to connect strain gauges in a Wheatstone bridge configuration to accurately measure small resistance changes. The document outlines the test procedure, which involves applying known weights to a torsion test specimen instrumented with strain gauges and measuring the resulting stresses to calculate the specimen's shear modulus.

2. How to Torsion on Strain
Gauge
Submitted To:
Ali Raza
By: Salman Jailani , Umar Farooq

3. Strain Gauge
1. Electrical sensor (transducer) that measures strains.
2. Its electrical resistance changes when an external force
stretches or compresses it
3. Change in resistance is directly proportional to
displacement (strain)
4. Small sheet of metal foil cut in zigzag pattern, only a few
micron thick
5. Normally mounted on a backing sheet

4. Strain Gauge
User should:
• prepare the surface bond the gauge properly
• use the gauge in the right direction

5. Wheatstone Bridge
• R1 and R4:
• Opposite arms
• R1 and R2:
• Adjacent arms

6. Strain Gauge
Half Bridge Connection 1 (OppositeArms)
• Identical strain values With the same sign: Bothe tensile
Both compression.

7. Strain Gauge
Half Bridge Connection 2 (AdjacentArms)
Identical strain
values With
opposite sign:
One tensile and
one
compression

8. Strain Display Device
• Set:
Configuration number (N),
Gauge Factor;
• And, zero before loading.

9. Strain Display Device
Half bridge
• Fit inactive arms
with dummy plugs
• Config. = 2

10. Strain Display Device
•Full bridge:

11. Torsion Test Device
Main frame
Torsion test
specimen
(bar) with
installed
strain gauges
Loading arm,
hanger and
weights
Strain
displa
y

12. The load distance is
constant 15 cm

13. Test Procedure
• Using vernier caliper, measure the diameter of the
specimen
• Calculate J (torsional stiffness)
• Using a same weight, find the colors (gauges) with same
sign (which two are copressive and which two are
tensile)
• Setup the full bridge connection
• Try 100g, 300g, 400g, 500g, and 750g weights, read the
strain from strain display and calculate the stress for
each one
• Plot the five points and compute the shear modulus, G,
using a best-fit straight line

14. Thank You