To perform torsional test on steel bars and determine modulus of rigidity.

OBJECT: TO PERFORM A TORSIONAL TEST ON A STEEL BAR AND DETERMINE THE MODULUS OF RIGIDITY

APPARATUS:

•  Steel Bars
•  Torsion Testing Machine
•  Vernier Calliper and Tape

THEORY:

1. TORSION
2. TORQUE
3. MODULUS OF RIGIDITY
4. SHEAR STRESS
5. SHEAR STRAIN

METHODOLOGY:

OBSERVATIONS:

• Diameter of steel bar = ____________________ mm
• Length of Steel Bar = _____________________ mm
• Rotations of Angle = _______________________
• Angle Theta = ____________________________Radians
• Torque = __________________________________ N/mm

CALCULATIONS:

SHEAR STRESS OF SOLID BAR

𝑆𝑠 = 16 (16 𝑇⁄𝜋 𝐷𝑜3)

SHEAR STRAIN OF SOLID BAR

𝛾 = 𝐴𝜃/𝐿

MODULUS OF RIGIDITY

𝐺 = 𝑆𝑠/𝛾

DRAW THE FIGURE OF STEEL BAR SAMPLE

RESULTS:

Ss _______________________

𝜸 ________________________

G ________________________

AIM: To conduct torsion test on mild steel specimen to find modulus of rigidity or to find angle of twist of the materials.

APPARATUS:

1. A torsion test machine along with angle of twist measuring attachment.

1. Standard specimen of mild steel or cast iron.
   
2. Steel rule.
   
3. Vernnier caliper or a micrometer.
   

DIAGRAM:

THEORY:

For transmitting power through a rotating shaft it is necessary to apply a turning force. The force is applied tangentially and in the plane of transverse cross section. The torque or twisting moment may be calculated by multiplying two opposite turning moments. It is said to be in pure torsion and it will exhibit the tendency of shearing off at every cross section which is perpendicular to the longitudinal axis.

𝑇 / 𝐼_𝑝 = 𝐶𝜃 / L = 𝜏 / 𝑅

T= maximum twisting torque (N mm)

𝐼𝑝= Polar moment of inertia (mm⁴)

τ = shear stress 𝑁/𝑚𝑚2

C = modulus of rigidity 𝑁/𝑚𝑚2

Θ = angle of twist in radians

L = length of shaft under torsion (mm)

PROCEDURE:

1. Select the suitable grips to suit the size of the specimen and clamp it in the machine by Adjusting sliding jaw.
   
2. Measure the diameter at about the three places and take average value.
   
3. Choose the appropriate loading range depending upon specimen.
   
4. Set the maximum load pointer to zero
   
5. Carry out straining by rotating the hand wheel or by switching on the motor.
   
6. Load the members in suitable increments, observe and record strain reading.
   
7. Continue till failure of the specimen.
   
8. Calculate the modulus of rigidity C by using the torsion equation.
   
9. Plot the torque–twist graph (T vs θ)
   

OBSERVATIONS:

Gauge length L =

Polar moment of inertia 𝐼𝑝 =

Modulus of rigidity C = 𝑇𝐿 / 𝐼𝑝𝜃

RESULT:

The modulus of rigidity of the given test specimen material is

VIVA-QUESTIONS:

1. What is torque?
   
2. What is torsion equation?
   
3. What is flexural rigidity?
   
4. Define Section modulus.
   
5. What is modulus of rigidity?
   

APPLICATIONS:

1. Structural members
   
2. Power transmission of shafts
   
3. Mixer