Operational Manual - DCU

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SECTION 5 EXPERIMENTATION r r The fonn of Laboratory Sheets and Reports quite obviously will depend very much on the individual lecturer and the type of experiment being carried out; however for the more elementary work the following example serve as a guide for the student operator. Notes on Laboratory Sheets Using a Torsion Test to Destruction as an example, the following is a suggested layout for a laboratory sheet. Object To carry out a torsion test to destruction in order to determine 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 Torsion Testing Machine and Torsiometer, steel rule and micrometer. Theory From the general torsion theory for a circular specimen: T Ge 't - = =- J where: I r T= Applied torque Nm or lbfin J = Polar second moment of area mm or in G = Modulus of rigidity N/mm2 of Ibf/in2 e = Angle of twist (over length) radians I = Gauge length mm or in t = Shear stress at radius r N/mm2 or 1 bf/in2 r = Radius mm or in Experimental Procedure I. Measure the overall length and diameter of the test section of the specimen. 2. Draw a line down the length of the test 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 finnly in the Torsion Testing Machine. For each increment of strain record the following: (a) Angle of twist of the specimen in degrees (b) Applied torque (c) Angle of twist over the 50 mm gauge length in radians, as recorded by the dial gauge indicator (d) When the elastic limit has been passed continue to test to destruction with ever increasing increments of strain, recording for each strain increment: ]. Angle of twist in degrees 2. Applied torque Note: In some tests it may be found unnecessary to use the torsiometer after the elastic limit has been reached. If this is the case, the torsiometer can be removed from the specimen and readings of twist can be taken din:ctly from the machine scales. To remove the Torsiom'~ter, unclamp the two cap screws securing it to the specimen and slip each end clamp off the specimen. The end clamps have been slotted for this purpose. It is not possible to remove the centre cylindrical spacer of the Torsiometer as this would involve disturbing the end fixing of the specimen, i.e. releasing it from the chuck. This should be done under any circumstances during test. Results Initial diameter of specinen Final diameter of soedmen Gauge length ~ specinen Initial overall length of spec"men Final overall length of specimen Tabulate the results under pressure headings for the elastic and non-elastic regions. 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: Notes on the Content of the Laboratory Report As in the case of the Laboratory Sheet the content of the report will depend largely on the type of test carrie
TQ Torsion Testing Machine Items to be Included Include in the report a dimensioned drawing of the specimen. Using the tabulated results plot a graph of applied torque, T, against angle of twist a as a base for the elastic region. Use the slope of this graph to determine the value of the modules of rigidity. Also from this graph determine the torque, and then calculate the shear stress at the limit of proportionality. 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 and procedures. 4. Discuss the errors involved in determining the modulus of rigidity using the angle of twist from the machine dial, and compare the results obtained with the value found by using the Torsiometer.
Page 1 and 2: @ TQ Education and Training Ltd 200
Page 3 and 4: ~ m I,. r '1:- ~- The 8Ml Torsion T
Page 5 and 6: SECTION 2 ASSEMBLY The apparatus is
Page 7: ~ arm / I. SECTION 4 USE OF THE TOR
Page 11 and 12: APPENDIX A TORSION TEST SPECIMEN ~
Page 13: Ta Torsion Testing Machine [ r: 2.

Operational Manual - DCU

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