**Introduction**

Torsion test is carried out to determine the shear modulus of structural materials, such as steel and aluminum. Shear modulus is a material property that is useful in calculating the compliance of structural materials in torsion, provided that they follow Hooke’s law; that is, that the angle of twist is proportional to the applied torque.

**Objective(s) of the Experiment**

Torsion test is conducted on steel in other to determine the shear modulus of the material.

**Equipments Needed**

- A torsion testing machine.
- Twist meter for measuring angles of twist
- A steel rule and Vernier Caliper or micrometer
- Grips to hold the ends of the specimen in the jaws of the testing machine

**Procedures**

- Measure the diameter of the specimen using the vernier caliper at about three places on the specimen and take the average
- Place the specimen in the torsion testing machine with careful alignment and apply torque
- Make simultaneous measurements of torque and angle of twist, and record the data.
- Maintain the speed of testing high enough to make creep negligible.

**Results and Calculations**

- Gauge length of specimen = ________
- Diameter of specimen =_________
- Calculate Polar Moment of Inertia = J =
**p**d^{4}/32 = _______ - Calculate the maximum shear stress (tmax) and shear strain (
**g**) using the formulas **t**_{max}= Tr/J**g**=**Q**r/L- Where
- T = Torque
- R = radius
- J = polar moment of inertia of the specimen about its center
**Q**= angle of twist in radians- L = gauge length.
- Plot a graph of shear stress versus shear strain, as shown in the Figure below.
- Determine the shear modulus G as the slope of the straight portion of the shear stress versus strain relation. That is, G =
**t**_{max}/**g**

**Conclusion**

The following precautions should be taken during the test:

- Measure the dimensions of the specimen carefully.
- Measure the Angle of twist accurately for the corresponding value of Torque.

References

- Bhagwant University. “Torsion Test on Mild Steel Rod”
- Mamlouk, M.S. And Zaniewski J.P. (2011). ‘Materials For Civil and Construction Engineers’