To study the UTM and perform the tensile test.
APPARATUS :- A UTM, mild steel specimen, vernier caliper/micrometer, dial gauge & graph paper.
THEORY :- Various m/c and structure components are subjected to tensile loading in numerous application. For safe design of these components, there ultimate tensile strength and ductility one to be determine before actual use. Tensile test can be conducted on UTM.
A material when subjected to a tensile load resists the applied load by developing internal resisting force. These resistances come due to atomic bonding between atoms of the material. The resisting force for unit normal cross-section area is known as stress.
The value of stress in material goes on increasing with an increase in applied tensile load, but it has a certain maximum (finite) limit too. The minimum stress, at which a material fails, is called ultimate tensile strength.
The end of elastic limit is indicated by the yield point (load). This can be sen during experiment as explained later in procedure with increase in loading beyond elastic limit original cross-section area (Ao) goes on decreasing and finally reduces to its minimum value when the specimen breaks.
ABOUT OF UTM & ITS SPECIFICATIONS :-
The tensile test is conducted on UTM. It is hydraulically operates a pump, oil in oil sump, load dial indicator and central buttons. The left has upper, middle and lower cross heads i.e; specimen grips (or jaws). Idle cross head can be moved up and down for adjustment. The pipes connecting the lift and right parts are oil pipes through which the pumped oil under pressure flows on left parts to more the cross-heads.
SPECIFICATIONS :-
1. Load capacity = 0-40000 kgf.
2. Least count = 8kgf.
3. Overall dimn. =
4. Power supply = 440V
PROCEDURE :-
1. The load pointer is set at zero by adjusting the initial setting knob.
2. The dial gauge is fixed and the specimen for measuring elongation of small amounts.
3. Measuring the diameter of the test piece by vernier caliper at least at three places and determine the mean value also mark the gauge length.
4. Now the specimen is gripped between upper and middle cross head jaws of the m/c.
5. Set the automatic graph recording system.
6. Start the m/c and take the reading.
7. The specimen is loaded gradually and the elongation is noted until the specimen breaks.
OBSEVATION :-
(I) Initial diameter of specimen d1 =—–
(II) Initial gauge length of specimen L1 =—-
(III) Initial cross-section area of specimen A1 = —-
(IV) Load of yield point Ft. =—-
(V) Ultimate load after specimen breaking F =—-
(VI) Final length after specimen breaking L2 =—–
(VII) Dia. Of specimen at breaking place d2 =——
(VIII) Cross section area at breaking place A2 = —-
CALCULATION :-
(i) Ultimate tensile strength =
(ii) Percentage elongation % =
(iii) Modulus of elasticity E =
(iv) Yield stress =
(v) % reduction in area =
PRECAUTIONS :-
1. The specimen should be prepared in proper dimensions.
2. The specimen should be properly to get between the jaws.
3. Take reading carefully.
4. After breaking specimen stop to m/c.
RESULT :-
CONCLUSION :-
VIVA-QUESTIONS :-
· Which steel have you tested ? what is its carbon content ?
· What general information are obtained from tensile test regarding the properties of a material ?
· Which stress have you calculated : nominal stress or true stress ?
· What kind of fracture has occurred in the tensile specimen and why ?
· Which is the most ductile metal ?How much is its elongation ?