DEPARTMENT OF MECHANICAL ENGINEERING
LABORATORY HANDOUT
COURSE STRENGTH OF MATERIALS- MENG222
Semester: Spring 2007-2008
Lab. No: 1
Name of Exp: Torsion Test
Instructor: Assoc. Lec. Cafer Kizilors
Assistant: Gülşah Taşel
Submitted by: …………………………………………………
Student No: ……………………………………………………
Date: …………………………………………………………..
------
EVALUATION
PROCEDURERESULTS & GRAPHS
DISCUSSION
REPORT PRESENTATION
OVERALL MARK
Name and signature (of evaluator):…………………………………………
OBJECT:
To carry out a torsion test to destruction in order to determine the following for a specimen.
a) The modulus of rigidity.
b) The shear stress at the limit of proportionality.
c) The general characteristics of the torque ,angle of twist relationship.
APPARATUS:
Tecquipment Torsion Testing Machine and Torsiometer ,steel rule and micrometer
.
Standard torsion specimen for use with the torsion testing machine and torsiometer
THEORY:
From the general torsion theory for a circular specimen.
Where,
T = Applied Torque ……………………………………… Nm or lbf in
J = Polar second moment of area………………………… or
G = Modulus of rigidity …………………………………. or
= Angle if twist (over length L)……………………….. radians
= Shear stress at radius ‘r’…………………………… or
r = radius…………………………………………………. mm or in
EXPERIMENTAL PROCEDURE ( In instruction form)
1) Measure the overall length and test diameter of the specimen.
2) Draw a line down the length of the degree of the section of the specimen with a pencil this serves as a visual aid to the degree of twist being put on the specimen during loading.
3) Mount the specimen firmly in the Torsion Testing Machine as indicated in the operating instructions—see later.
If the Torsimeter is to be used the fixing procedure should be carried out as prescribed.
For each increment of strain record the following :
a) angle of twist of the specimen () in degrees.
b) Applied torque……………..(T)
c) Angle of twist over the 50 millimeter or 2.00 inch gauge length in radians, as recorded by the dial gauge indicator………..( ) in radians.
d) When the elastic limit has been passed continue to test to destruction with ever increasing increments of strain, recording for each strain increment,
i) Angle of twist in degrees.
ii) Applied torque.
NOTE: In some tests it may be found unnecessary to use the Torsiometer after the elastic limithas been reached. The Torsiometer, if this is the case, can be removed from the specimen and readings of twist taken direct from the machine scales. To remove the Torsiometer unclamp the two cap screws securing it to the specimen and slip each end clamp of the Torsiometer off the specimen. The end clamps have been slotted for this purpose. It is not possible to remove the center cylindrical spacer of the Torsimeter as this would involve disturbing the end fixing of the specimen ,i.e. releasing it from the chuck, and this SHOULD NOT BE DONE UNDER ANY CIRCUMSTANCES DURING TEST.
RESULTS:
Initial diameter of specimen………………………..
Final diameter of specimen…………………………
Gauge length of specimen………………………….
Initial overall length of specimen………………….
Final overall length of specimen…………………..
SUGGESTED INCREMENTS OF STRAIN
To ensure that an adequate number of values are obtained from the test ,particularly during the elastic region of strain, the following is recommended:
OPERATING INSTRUCTIONS FOR THE TORSION TESTING MACHINE AND TORSIOMETER
(In instruction form)
1) Allow the spring balance to hang free of the torque arm and zero the balance by adjusting the small knurled screw at the top right hand of the balance.
2) Slide balance along the supporting framework until the two engraved lines, one on the horizontal cross member of the frame and the other on the balance assembly block which is sliding along this member, coincide.
3) Slid the hook of the balance under the knife edge on the torque arm with the hook hanging free at its lowest position.
4) Clamp the specimen in to the jaws of the Torsion Machine and fit the Torsiometer on to the specimen a full account of this is found earlier in the bulletin under the mean heading “Use and Operation of the Torsiometer”.
It is essential when using the Torsion Machine to make sure that the whole length of the hexagonal ends of the specimen are contained fully within the chuck jaws. Also when the straining head, specimen and Torsiometer are pushed along the bed so that the end of the specimen enters the headstock chuck, enter the specimen in to the chuck until the light compression spring behind the headstock chuck just beings to compress.
5) when the specimen has been firmly fixed in position clamp the straining head to the bed.
6) Turn the handle on the straining head until the torque arm is in the horizontal as shown by the spirit level.
7) Turn the spring balance hand wheel to raise the balance until the hook on the balance is just contacting the knife edge on the torque arm. This will be seen by movement of the spirit level bubble.
Care should be exercised to carry out this operation so that the torque arm and spring balance are ‘zeroed’
Both balance hand wheel and straining head hand wheel may have to be adjusted together to obtain this condition.
8) Zero the fine and course angular displacement dials on the input and output shafts of the straining head. A knurled nut is provided behind each dial to lock the dial in position.
9) Zero the revolution counter-by turning clockwise .
10) Adjusting the arm on the Torsiometer so that it just contacts the dial gauge plunger. A knurled nut is provided for this purpose and a full description is found under the main heading “Use and Operation of Torsiometer” earlier in this bulletin.
11) Zero the dial gauge indicator by rotating the dial.
12) The apparatus is now ready for use and the test specimen can be loaded, in the desired increments, by turning the handle on the straining head until the specimen has been rotated the requisite number of degrees as shown on the fine angular displacement on the machine. BEFORE TAKING TORQUE AND DIAL GAUGE REDAINGS BRING THE TORQUE ARM BACK INTO HORIZONTAL BY TURNING THE BALANCE HNDWHEEL.
13) When testing the more elastic materials the Torsiometer dial needs to be reset periodically to zero due to the limitation on the plunger travel. See “use and Operation of the Torsiometer”.
NOTE ON THE CONTENT OF THE LABORATORY REPORT
Once again the content of the report will depend largerly on the type of test carried out and the detailed investigation required, but for a test similar to that described above the following suggestion are offered:
Include in the report a dimensioned drawing of the specimen .
Using the tabulated results,
a) Plot a graph of applied Torque ‘T’ against angle of twist as a base for the elastic region. Use the slope of this graph to determine the value of the modulus of rigidity. Also from this graph determine the torque, and then calculate the shear stress at the limit of proportionality.
b) Plot a graph of applied torque against angle of twist of the specimen as a base, for the complete test to destruction.
DISCUSSION OF RESULTS
1. State and comment upon the values obtained from the test .
2. Comment upon the overall result obtained from the test.
3. Comment upon the apparatus an procedure.
4. Discuss the errors involved in determining the modules rigidity using the angle of twist from the machine dial, and compare the result obtained with the value found by using the Torsiometer.
Tabulate the results as follows:
ELASTIC REGION:
Angle of Twist(degrees) / Applied Torque
T
Nm(or) ibf in / Angle of twist
0.001
radians
NON-ELASTIC REGION:
Angle of Twist(degrees) / Applied Torque
T
Nm(or) ibf in / İf the Torsiometer is used during the non-elastic range then record the dial gauge reading in this column as before for the Elastic Range.
1