LAB. 1 - PURE TORSION - 2015 Sem. 2

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 –  Machine  – see Fig. 1 below and Fig. 2 on page 3.

PROCEDURE :

[

DEMONSTRATOR  :  : - Ensure Φ is < 0

0

before  tightening chuck jaws . ]

STUDENT NOTES :

(i) Measure rod test specimen diameter using using Vernier, at three typical locations and record average value of rod diameter ( why average?). 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, Twist , Φ.

Fig. 1 - STR6 TORSION TESTING Machine. 1 of 5

A. Solid Steel Rod Measure up test specimen :

Measured Diameter (mm) 3.11 3.14 3.14

Average Diameter (mm) 3.13

Rotate rod end until noted Torque achieved , record corresponding Angular Deflection, Φ. Force Applied Observed Ang. Calc’d Ang. Defl’n, Error (Newtons) Torque,T (Nm) Defl’n, φ (deg.) φ (deg.) (%) 0 0 0 0 0 1 2 3 4 5

B. Solid Brass Rod Measure up test specimen :

0.05 0.1 0.15 0.20 0.25

2.5 4.75 7 9 11

Measured Diameter (mm) 3.13 3.18 3.13

1.9 3.8 5.7 7.6 9.5

24 20 18.57 15.5 13.6

Average Diameter (mm) 3.15

Rotate rod end until noted Torque achieved , record corresponding Angular Deflecti on, Φ. Force Applied Observed Ang. Calc’d Ang. Defl’n, Error (Newtons) Torque,T (Nm) Defl’n, φ (deg.) φ (deg.) (%) 0 0 0 0 0 1 5 3.91 21.8 0.05 2 9.5 7.85 17.4 0.1 3 14 11.14 20.4 0.15 4 18 15.66 13 0.20 5 21.5 19.57 8.9 0.25

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C . Hollow Brass Tube Measure up test specimen :

Measured Diameter (mm) 3.16 3.16 3.2

Average Diameter (mm) 3.17

Rotate rod end until noted Torque achieved, record corresponding Angular Deflection, Φ. Force Applied Observed Ang. Calc’d Ang. Defl’n, Error (Newtons) Torque,T (Nm) Defl’n, φ (deg.) φ (deg.) (%) 0 0 0 0 0 4.5 4.3 4.2 1 0.05 9 8.6 4.3 2 0.1 13.5 12.9 4.4 3 0.15 18 17.2 4.4 4 0.20 22 21.5 2.3 5 0.25

LABORATORY REPORT : 3 of 5

(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. - M echani cs of

M ater ial s – Global

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Ed. 6E –  Chapter 3.

Fig. 2 - STR6 TORSION TESTING Machine.

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