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ME 218: SOLID
MECHANICS LABORATORY
IMPA IMP A CT T EST ON METAL SPECIMEN EXPERIMENT NO.2(A) NO.2(A)
BATCH: A8 07010042-07010046
I M PA PA C T T E S T O N M E T A L SPECIMEN EXPERIMENT NO.2(A)
AIM
To study the impact resistance of metals using Impact testing machine of the Charpy type. EQUIPMENT AND TOOLS
THE FOLLOWING HAVE BEEN USED: 1.
Impact testing machine.
2.
scale.
3.
Standard charpy specimens.
4.
Furnace and thermocouple. thermocouple.
5.
Liquid nitrogen. THOERY
Impact strength is defined as the resistance of the materials to shock. The impact testing is to find out the energy absorbed by a specimen when brought to fracture by hammer blow and gives a quality of the material, particularly its brittleness. Highly brittle materials have low impact strength. Heat treatment of metals has found to lower impact considerably. Temperature also influences impact strength of the materials. The area under the stress strain curve in a static tensile test is measure of the energy absorbed per unit volume of the material, called the modules of toughness. This is also a measure of the impact strength of the material. The impact load can be applied in many ways. Allowing a standard mass to fall on the specimen from progressively increasing heights until fracture occurs tests rails and framed structural members. For Laboratory Charpy and Izod impact tests are used. Both the tests employ beam type of specimen. Charpy test the specimen is supported as a simply supported beam and in Izod test a cantilever type of beam support. These notched specimens are fractured with a standard blow from a pendulum hammer and energy absorbed is measured. In addition to these beam type of specimen there are also Tension and shear or torsion specimen, which can be used with special type of testing machines. In any event, the distribution of stress throughout the impact test specimen is not known and the test results are therefore mainly comparative, even though they have some correlation with the fracture toughness.
2
PROCEDURE
The following procedure has been followed:
Note down the dimensions of the specimen and find the working area of the specimen at the place of notch.
With no specimen on the anvil raise the pendulum to an initial reading R1 in the dial and release it.
Note the reading R2 of the dummy pointer on the dial. The difference is the energy loss due to friction.
Now place the specimen accurately in position on the anvil.
Raise the pendulum to the same initial height and release. The pendulum swings to the other side rupturing the specimen.
Note the reading R3 on the dummy pointer on the dial.
Tabulate the readings.
OBSERVATIONS
Dimensions Dimensions of material: Length of side without considering notch= 10mm Length of side considering notch=8.5mm Area under impact=10x8.5mm2 Aluminium test piece did not break in the impact test at room temperature. M.S test pieces broke in all impact tests.
3
Material
Voltage(mV)
Aluminium
Temperature (°C)
0
Frictional Loss(in Joules) 27
Area of specimen(in mm2) 1.4194
Energy of rupture(in Joules)
Impact strength (in Joule/m2) 5 ) 42.078 4.783X(10
10X8.5
M.S.
0
27
1.4194
10X8.5
14.568
1.547X(10 5 )
M.S.
1.2
30
1.4194
10X8.5
35.714
4.035X(10 5 )
M.S.
3.7
86
1.4194
10X8.5
56.419
6.471X(10 5 )
M.S.
-3.0
-90
1.4194
10X8.5
2.77598
0.160X(10 5 )
M.S.
-2.5
-78
1.4194
10X8.5
5.5919
0.491X(10 5 )
Temperature vs Impact Energy 86, 647100
700000 600000 500000
30, 403500
400000 300000 27, 154700
200000 -78, 49100 -90, 16000
100000 0
-100
-80
-60
-40
-20
0
20
Impact Energy
4
40
60
80
100
NOTE
M.S. stands for Mild Steel. Area of specimen excludes the area of the notch, i.e. the working area of the specimen (Notch is 1.5 mm deep).
CONCLUSION
Impact Energy of M.S decreases with temperature. This indicates material becomes more brittle as temperature decreases. Aluminum is more ductile and hence has higher impact energy than M.S at room temperature.
PRECAUTIONS
1. Keep away from the machine during the impact test. 2. The test piece has to be carefully kept so that area of impact is minimized. 3. When the pendulum hammer is loaded at maximum position position make sure that it is latched.
