# Mechanical Engineering Test Questions

Lab 5. TORSION TESTING: Finding G

Like Bending, Torsion is an important type of loading that can produce critical stresses in engineering applications. Under torsion, SHEAR stresses are produced. The stiffness under shear stress is called the MODULUS OF RIGIDITY G.(MPa) It is also called Shear Modulus. In this laboratory, we will determine the Modulus of Rigidity of the metal rod, and verify that the angle of deflection corresponds to what we would predict from equations. You must do your working in Excel.

1. Prepare a report, describing the purpose of the experiment, the equipment and setup used and the results obtained.

2. Using the following equations, calculate the shear strain and shear stress for each increment. Tabulate the stress and strain values. Rod Diameter = .................... +/- .................. mm Load (kg) > Weight (N) > radius > Torque (Nm)

Angle of twist > radians. (To convert degrees to radians: Radians = Degrees * /180 Shear Stress & Shear Strain (These are needed for you graph)

3. Using the vertical axis for shear stress and horizontal axis for shear strain, plot stress -strain diagram.

4. Determine the shear modulus (G) from the slope of the straight line.

5. Compare your result with the published value of the shear modulus. Calculate the % error using the error analysis rules. Make sure you include all the possible sources of error (apart from silly mistakes like mis-reading. These errors should be discovered and eliminated)

Torsion Theory

Shear Strain:

s = r / L

Shear Stress:

s = T r /J

Angle of Twist:

= TL/(JG)

s = Shear strain (radians)

s = Shear Stress (MPa)

= Angle of twist (radians)

L = Gage length (mm)

r = Radius (mm)

G = Shear Modulus (MPa)

T = Torque (Nm)

J = Polar Moment of Inertia (mm4)

Where J is the Polar Second Moment of Area, which is used when under torsion. For a cylinder...

For...

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