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EXPERIMENT 4
TORSION TEST
1. OBJECTIVES:
1.1 To understand the concept of mechanical properties of solid materials 1.2 To construct the shear stress-strain diagram based on Torsion Testing Machine data 1.3 To understand the material behavior under torsion mode 1.4 To understand how to determine: (a) Shear Modulus (b) Proportional limit (c) Ultimate stress (d) Maximum elastic displacement (e) Maximum shear stress
2. INTRODUCTION
Many products and components are subjected to torsional forces during their operation. Products such as shaft, switches, fasteners, and automotive steering columns are just a few devices subject to such torsional stresses. By testing these products in torsion, manufacturers are able to simulate real life service conditions, check product quality, verify designs, and ensure proper manufacturing techniques.
A torsion test can be conducted on most materials to determine the torsional properties of the material. These properties are modulus of elasticity in shear, yield shear strength, ultimate shear strength, and modulus of rupture in shear and ductility
The torsion test generates the "torque versus angle" diagram that looks very similar to a "stress versus strain" curve in a tensile test. They are not the same however they are analogous to properties that can be determined during a tensile test
3. EQUIPMENT & MATERIALS
3.1 Equipment Torsion Tester Machine
3.2 Materials Aluminum & Mild Steel
Fig. 1 Torsion test machine
3. TORSION TEST
The most notable test that demonstrates the effects of shearing forces and resulting stresses is the torsion test of a solid circular bar or rod. As a matter of fact, this test generates a state of pure shear stress in the torsional loaded rod. Such a test is used to ascertain all the major shear properties of metal materials, i.e., the ultimate shear stress, the yield shear stress and the modulus of rigidity or shear modulus.
Figure 1
The applied torque ( T ) as shown in Figure 1 , to the specimen and resulting deformation (angle of twist,) are measured during the torsion test. These results are converted to shear stress ( ) and shear strain( ) by the following respective equations:
J
Tc
4. PROCEDURE
The setup procedure is given as follow:
4.1 Loosen the four screws on the movable steel plate. Move the movable steel plate to behind. 4.2 Select the desired test specimen and identify the material. Record it into a Table
4.3 Measure diameter of the test specimen using appropriate tools. Repeat the measurement few times and take the average reading. 4.4 Draw, with a pencil or marker, a line on the straight section of the specimen so that the line is 90 mm. This will be the gage length, Lo. 4.5 Fix the hexagonal sockets to both sides of the torque shafts. 4.6 Insert the test specimen to the one of the hexagonal socket. Follow the instruction given by Teaching Engineer. 4.7 Push the movable steel plate so that the test specimen can be inserted into the second hexagonal socket. If the test specimen could not fit into the second socket, slowly turn the motor shaft adjustor until the specimen is inserted to the socket. 4.8 Tighten the four screws provided. 4.9 Switch ON the MCB/ELCB and the ON/OFF switch on the control box. 4.10 Tare the torque meter and the counter to zero reading. Make sure the maximum and minimum torque reading is tare as well. 4.11 Press the ‘RUN’ soft button on the frequency inverter. Slowly increase the frequency and keep an eye on the torque reading. 4.12 For every 0.5 Nm of torque increment, record downs the value on dial indicator. Repeat this step until maximum torque reached (where the torque value no longer increases). 4.13 Once the maximum torque reached or plastic region reached, press the stop soft button on the frequency inverter. 4.14 Repeat procedure for each specimen. 4.15 Turn main switch ‘OFF’.
5. ANALYSIS
5.1. Make a table giving the specimen, the original dimensions and the final dimensions. This will be Table 1. 5.2. Construct a shear stress-shear strain curve from the torque-angle curve i. First, make copies of your torque-angle curve data and insert it on Table 2. ii. Next, construct the torque-angle curves by utilizing spreadsheet software and name it as Fig. 1. The torque is on the y-axis and angle is on the x-axis. The unit of torque and angle are N.m and deg, respectively. iii. For each point, compute the shear stress and angle. Use radian (rad) as the unit for shear strain and MPa as the unit for shear stress. Insert the result on Table 3 iv. Plot the data points of shear stress vs. shear strain and draw a smooth curve through them and name it as Fig. 2
5.3. Using the Fig. 2 make the following calculations (and on the graphs, show how you made those calculations) i. The shear modulus. ii. Proportional limit iii. Ultimate stress iv. Maximum elastic displacement (in elastic region) v. Maximum shear stress (in elastic region) 5.4. Make another table that is Table 4 and insert the results properly.
Name : ______________________________ Date : ______________
Matrix No : ______________________________
Fig. 1
Fig. 1 Torque vs. Angle
TABLE 3
No
Torque ( N.m )
Angle (deg )
Shear Stress ( MPa )
Shear Strain ( rad )
1
2
3
…
end
Name : ______________________________ Date : ______________
Matrix No : ______________________________
Fig. 2
Fig. 2(a) Shear Stress vs. Shear Strain
Name : ______________________________ Date : ______________
Matrix No : ______________________________
6. QUESTIONS
Answer all the questions
6.1 Using your own word, what do you understand about Torsion?
6.2. Give three examples where torsion are applied?
Name : ______________________________ Date : ______________
Matrix No : ______________________________
7. DISCUSSION
( Include a discussion on the result noting trends in measured data, and comparing measurements with theoretical predictions when
possible. Include the physical interpretation of the results and graphs, the reasons on deviations of your findings from expected results, your recommendations on further experimentation for verifying your results, and your findings.)
- Briefly summarize the key results of this experiment
- Explain the significance of your finding in this experiment
- Explain any unusual difficulties or problems which may have led to poor results
- Offer suggestions for how the experimental procedure or design could be improved in Torsion test
- Compare your experimental values with theoretical values given
REFERENCES
R.C. Hibbeler. (2005). SI 2th.ed. Mechanics of Materials. Prentice Hall James M. Gere. (2004). 6th^ ed. Mechanics of Materials. Thomson. David W. A. Rees.(2000) .Mechanics of Solids and Structures Imperial College Press. Instron Homepage, www.instron.com
APPENDIX
Shear Modulus of Elasticity Tangent or secant modulus of elasticity of a material subjected to shear loading. Alternate terms are modulus of rigidity and modulus of elasticity in shear. Also, shear modulus of elasticity usually is equal to Torsional Modulus of Elasticity. A method for determining shear modulus of elasticity of structural materials by means of a twisting test is given in ASTM E-143. A method for determining shear modulus of structural adhesives is given in ASTM E-229.
Torsional Modulus of Elasticity Modulus of Elasticity of material subjected to twist loading. It is approximately equal to shear modulus and also is called modulus of rigidity.
Torsional Strength Measure of the ability of a material to withstand a twisting load. It is the Ultimate strength of a material subjected to torsional loading, and is the maximum torsional stress that a material sustains before rupture. Alternate terms are modulus of rupture and shear strength.
