TORSION TESTING MACHINE

AIM OF THE EXPERIMEN T : Determination of modulus of rigidity ,torsional yield strength and modulus of fracture of a mild steel specimen.

APPARATUS REQUIRED :

1.Torsion testing m/c

2. Inside & out side caliper

3. Scale

4. Micrometer

5. Specimen

THEORY : In factories , a turning force is always applied to transmit energy by rotation .This turning force is applied either to the rim of the pulley , keyed to the shaft or to any other suitable point at some distances from the axis is to the shaft . The product of this turning force and the distance between the point of application of the force and the axis of the shaft is known as torque , turning moment or twisting moment.The shaft is said to be subjected to torsion .Due to this torque ,every cross section of the shaft is subjected to some shear stress.This shear stress is also equal to the modulus of rupture. Now the torsion formulae is given by

Where T=The maximum twisting moment

Fs=Modulus of fracture

r =Original outer radius of test pieces

θ =Angle of twist

L =Parallel length of test pieces

C =modulus of rigidity.

DESCRIPTION OF THE MACHINE : The torsion testing m/c consists of two end holders one of which the torque is applied , the other is connected to the torque arm by means of which the torque on the specimen is measured . The torque akgrm is connected to the indicating dial through intermediate levers housed in the cabinet.The total arrangement in the cabinet is known as pendulum dynamometer. The levers of pendulum dynamometer are so arranged that ,theindicator moves in clock wise direction irrespective of the direction of torsion in the specimen . The chart range (60,000kgcm or 20,000kgcm) selected by means of a hand lever at the front of the m/c , identical faceplates provided with

attachment holes and tenon slots are fitted to the straining spindle and torque arm spindle . The angular moments of the spindle and holder is indicated on a large proctactor and vernier, which records the deflection .

PRCEDURE :Select the suitable grips or specimen holder to suit the specimen and clamp it in the m/c.Measure its diameter at three places and take its mean value.Choose the capacity and adjust the range.Change the lever .Set live pointe and proctactor to zero . Carry out straining by rotating the hand wheel in either direction .Load the m/c .Observe the reading .Plot T vs θ graph .The highest point on the T –θ curve corresondance to torque for ultimate yield strength .

OBSERVATION :

CALCULATION:

Breaking torque =

Torque-twist diagram

PRECAUTION :

1. Error should be avoided in taking reading T & θ2. Test pieces should be free from tool marks.3. The rate of angle of twist should be kept low at tha beginning .