Torsion Test on Steel

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 = pd⁴/32 = _______
Calculate the maximum shear stress (tmax) and shear strain (g) using the formulas
t_max = Tr/J
g = Qr/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