lab. 1 - pure torsion - 2015 sem. 2
DESCRIPTION
Faculty of Science, Engineering and TechnologyMEE20004 - STRUCTURAL MECHANICSTRANSCRIPT
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Faculty of Science, Engineering and Technology
MEE20004 - STRUCTURAL MECHANICS
LAB. 1 - PURE TORSION - 2015 Sem. 2
By writing my name below, I declare this is an individual assignment and no part of this submission
has been copied from any other student's work or from any other source except where due
acknowledgment is explicitly made in the text, nor has any part been written for me by another
person. Refer to Unit of Study Outline for Plagiarism guidelines.
STUDENT NAME & No: Shehan Fernando (7664613)
Lab. Date & Time: 17/8/2015 from 11.30 to 1.30
Demonstrator: Dr. Jinghan LU
INTRODUCTION :
The aim of this Laboratory is to compare experimental measurements and theoretical calculations
relating to Pure Torsion of circular test specimens. Angle of Twist, Φ, is measured using a
Protractor Scale on a STR6 TORSION TESTING Machine – see Fig. 1 below and Fig. 2 on page 3.
PROCEDURE : [ DEMONSTRATOR : - Ensure Φ is < 00 before tightening chuck jaws .]
STUDENT NOTES :
(i) Measure rod test specimen diameter using Vernier, at three typical locations and record
average value of rod diameter (why average?).
(ii) Slide in test specimen, rotate Chuck Jaws in opposite directions and tighten both Jaws
with key. Check effective length tested, L= 500 mm. Zero Protractor Scale then zero
Force display.
(iii) Rotate test specimen end using Thumbwheel, determine Torque from Digital Force
Display [Moment Arm = 50 mm]. Measure Angular Deflection or Twist, Φ.
Fig. 1 - STR6 TORSION TESTING Machine.
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A. Solid Steel Rod Measure up
test specimen :
Rotate rod end until noted Torque achieved , record corresponding Angular Deflection, Φ.
Force
(Newtons)
Applied
Torque,T (Nm)
Observed Ang.
Defl’n, φ (deg.)
Calc’d Ang. Defl’n,
φ (deg.)
Error۞
(%)
0 0 0 0 0
1 0.05 2.5 1.9 24
2 0.1 4.75 3.8 20
3 0.15 7 5.7 18.57
4 0.20 9 7.6 15.5
5 0.25 11 9.5 13.6
B. Solid Brass Rod Measure up
test specimen :
Rotate rod end until noted Torque achieved , record corresponding Angular Deflection, Φ.
Force
(Newtons)
Applied
Torque,T (Nm)
Observed Ang.
Defl’n, φ (deg.)
Calc’d Ang. Defl’n,
φ (deg.)
Error۞
(%)
0 0 0 0 0
1 0.05 5 3.91 21.8
2 0.1 9.5 7.85 17.4
3 0.15 14 11.14 20.4
4 0.20 18 15.66 13
5 0.25 21.5 19.57 8.9
Measured Diameter (mm) Average Diameter (mm)
3.14 3.11 3.14 3.13
Measured Diameter (mm) Average Diameter (mm)
3.13 3.13 3.18 3.15
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C . Hollow Brass Tube
Measure up
test specimen :
Rotate rod end until noted Torque achieved, record corresponding Angular Deflection, Φ.
Force
(Newtons)
Applied
Torque,T (Nm)
Observed Ang.
Defl’n, φ (deg.)
Calc’d Ang. Defl’n,
φ (deg.)
Error۞
(%)
0 0 0 0 0
1 0.05 4.5 4.3 4.2
2 0.1 9 8.6 4.3
3 0.15 13.5 12.9 4.4
4 0.20 18 17.2 4.4
5 0.25 22 21.5 2.3
LABORATORY REPORT :
Measured Diameter (mm) Average Diameter (mm)
3.16 3.16 3.2 3.17
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(i) Discussion:
The error percentage in our results did not go over 25%, meaning that the experiment was
close to perfect, however the experimental data and theoretical data of the hallow brass
alloy had only very small error percentage. the variations between the theoretical and
experimental data possibly could be due to human error such as calculation error, reading
errors, even machine errors. We also have to factor in the fact that all three rods have
different material properties one being steel rod and other two being brass with a hallow
rod, due to that they have different yield pints and elastic modulus also it seems that they
have been used in previous experiments as a result mechanical and structural properties of
the rods may have changed slightly.
(ii) Conclusion:
Overall I believe it was a successful experiment; there were only small variations between
the calculated and experimental data. I believe the objective of the experiment has been
achieved was able to relationship between angle twist and torque. To my understanding I
enjoyed the experiment and it was a straightforward experiment and I don’t believe much
improvements can be done to close the gap between experimental and theoretical data.
(iii) Sample Calculations:
To calculate therotical data:
Example from table 1:
=1.900φ
DATA : Brass : G = 38 GPa; Steel : G = 80 GPa.
THEORY : Refer to Beer et. al. - Mechanics of Materials –Global Ed. 6E – Chapter 3.
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Fig. 2 - STR6 TORSION TESTING Machine.