Torsion test 2

torsion test

1. Department: Mechanical Engineering Class: B.Tech. III – Semester Course: U18ME308 MECHANICS OF SOLIDS LAB Lecture – 02 Topic to be covered : After completion of this lecture, the student will be able to, Find the torsional Rigidity of given material by conducting Torsion Test

2. IMPACT test

3. Objective: To determine the Rigidity Modulus of the given circular shaft. Torsion Test APPARATUS : Torsion Testing machine, Vernier Calliperse , and scale . The torsion testing machine is used to measure the torque applied and the angle turned in a torsion test. The specimen can be clamped in the correct position at a specified place provided on the machine. The torque is applied by rotating a handle. The torque applied and corresponding angle turned can be read on the dials provided on the machine.

4. THEORY : If the angles of twist given to the specimen and the corresponding torques are known a graph may be drawn between the variation of the torque (T) and the angles of twist (Ф). The graph is a straight line. From the graph, angle of twist for any desired value of torque is noted. The substituting the value of T and Ф in the expression Ф= and the rigidity modulus, of the material can be obtained. G = The rigidity modulus (G) of the material is given by = …………………… ..(1) Where, G = rigidity modulus in N/mm 2 T = Torque produed in N-mm Ф = angle of twist in radians L = effective gauge length of the specimen in mm J = Polar moment of Inertia of the circular cross-section = d = diameter of the circular shaft

5. Procedure Initial adjustments: Before testing, adjust the pendulum weight to suit the capacity of the test piece. To obtain accurate results suitable capacity range for the specimen should be selected with the aid of the following table Adjust corresponding range on the dial of torsion testing machine with the adjusting knob. The diameter of circular shaft (d) is measured in mm. The polar moment of Inertia (J) is calculated in mm4. The length of the specimen (L) is measured in mm. The specimen is placed on the machine and is gripped properly (already fixed). The gear is adjusted so that, the dial gauge which is used to measure torque is set to zero. The circular disc which is used to measure the amount of twist is adjusted to zero. Sl.No . Capacity Method of increasing capacity 1 400 Pendulum + A counter weight 2 1000 Pendulum + A + B 3 2000 Pendulum + A + B + C + D

6. Procedure The gear is rotated in clock wise so that the amount of twist produced in the shaft is 2 . The amount of torque produced is measured through the dial gauge in form of divisions. Repeat the test for every 2 increment up to 10 of twist and measure the torque. Then the gear is rotated in opposite direction such that the twist is decreased from 10 to 0 and the corresponding torque is measured. The torque (T) is calculated in N-mm and the corresponding twist (Ф) is calculated in radians. A graph is drawn between the variation of the torque (T) in N-mm on Y-axis and the angle of twist (Ф) on X-axis. From the graph, the slope of the line in N-mm/radians is noted. Substitute the ratio in N-mm/radians in equation (1) to obtain the rigidity modulus (G).

7. Observations OBSERVATIONS: Length of the circular shaft (L) = mm Diameter of the circular shaft (d) Lease count of vernier calipers(L.C.) = mm Sl.No Main Scale Reading(MSR) (mm) Vernier Coincidence (VC) V.C. x L.C. (mm) Total MSR+(VCxLC) (mm) 1 2 3 Average Diameter of circular shaft (d) = mm

8. During Test: Lease count of dial gauge of torsion testing machine (L.C) 1 division = kg-cm Sl. No. Angle turned at right end in degrees Ф 1 Dial gauge readings (No. of divisions) Angle turned at right end in degrees Ф 2 = (mean/30) Angle of twist Ф = (Ф 1 - Ф 2 ) Torque = Mean x L.C Increasing Decreasing Mean Ф in degrees Ф in radians Torque (kg-cm) Torque (N-mm)

9. Length of the circular shaft (L) = mm The polar moment of Inertia (J) = mm 4 . From Graph, the ratio = N-mm/radians CALCULATIONS: The rigidity modulus of the material is given by G = = = N/mm 2 RESULT: The Rigidity Modulus of the given specimen G = N/mm 2

10. Outcomes of the Lecture You will be able to, Determine the Torsional Rigidity of given material by conducting Torsion Test