CHARPY IMPACT TEST

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Aim:-Determination of the energy absorbed and impact strength of given specimen using Charpy impact testing machine.
Need and scope of the experiment:-

The necessity for impact tests has arisen due to the failure of materials used in high speed machinery under repeated forces of impulsive character, even when such material has shown satisfactory strength and deformation in a static tensile test. Various forms of impact test has been devised, of which Izod impact test is the only one to try to determine the imperfections in material likely to fracture by "shock".

Although the Izod impact test has long been used as the standard form of test for checking the brittleness of metals, the need has arisen for test at elevated and subzero temperatures. For this purpose the CHARPY IMPACT test is more convenient. The specimen need not be , clamped and it can be quickly positioned without significant change of temperature.

The standard shape of the test' specimen is as shown in fig, which is being tested in bending with a standard notch in this Charpy test. Under this test, the notch on the specimen sets up stress concentrations, which ensures that fracture, does occur.

Equipments:-

1. Charpy impact testing machine
2. Charpy specimen of lOmm x 10mm. square cross section and 55min length, with a V -notch 45⁰ angle, 2mm deep and 0.25 mm root radius along the middle of the length according to ASTM E23, For a U -notch specimen, the dimensions are 5mm deep, 2mm width and lmm root radius according to ASTM E23. The specimen is kept as a simply supported beam in horizontal position and loaded behind the notch by the impact of a heavy swinging pendulum. The angle of drop of pendulum is 140⁰. The impact velocity is approximately 5.3465m/sec. The specimen bends and fractures at high strain rate.
   

Procedure:-

1. Without the specimen in the machine, swing the pendulum to ensure free movement.
2. Lift the pendulum and lock it at 140⁰.
3. Place the Charpy test specimen as shown in fig.
4. Select the test and its parameter given in the digital indicator.
5. Remove the lock nut and engage the lever.
6. Pendulum will strike the specimen and result will display in digital indicator.

Observations:-
Charpy value or Impact Strength
= ^{Energy absorbed N-m}⁄_{Cross section area at nortch $mm^2$} Result:-
Energy required to fracture the Specimen U = ____________ J
Charpy value = _________ $\frac{Nm}{mm^2}$