To determine impact strength of materials
AIM: - To determine impact strength of materials
OBJECTIVE: -To Determine the impact strength of materials by Izod and Charpy impact test
APPARATUS: - Impact testing machine, specimens of size 75 mm X 10mm X 10mm and 10 mm x 10 mm X 55mm
DIAGRAM:-For Izode test
THEORY:-
An impact test signifies toughness of material that is ability of material to absorb energy during plastic deformation. Static tension tests of unnotched specimens do not always reveal the susceptibility of a metal to brittle fracture. This important factor is determined by impact test. Toughness takes into account both the strength and ductility of the material. Several engineering materials have to withstand impact or suddenly applied loads while in service. Impact strengths are generally lower as compared to strengths achieved under slowly applied loads. Of all types of impact tests, the notch bar tests are most extensively used. Therefore, the impact test measures the energy necessary to fracture a standard notch bar by applying an impulse load. The test measures the notch toughness of material under shock loading. Values obtained from these tests are not of much utility to design problems directly and are highly arbitrary. Still it is important to note that it provides a good way of comparing toughness of various materials or toughness of the same material under different condition. This test can also be used to assess the ductile brittle transition temperature of the material occurring due to lowering of temperature.
PROCEDURE:-
(a) lzod test
1. With the striking hammer (pendulum) in safe test position, firmly hold the steel specimen in impact testing machine’s vice in such a way that the notch face the hammer and is half inside and half above the top surface of the vice.
2. Bring the striking hammer to its top most striking position unless it is already there, and lock it at that position.
3. Bring indicator of the machine to zero, or follow the instructions of the operating manual supplied with the machine.
4. Release the hammer. It will fall due to gravity and break the specimen through its momentum, the total energy is not absorbed by the specimen. Then it continues to swing. At its topmost height after breaking the specimen, the indicator stops moving, while the pendulum falls back. Note the indicator at that topmost final position.
5. Again bring back the hammer to its ideal position and back
( b) Charpy Test
1. With the striking hammer (pendulum) in safe test position, firmly hold the steel specimen in impact testing machine’s vice in such a way that the notch face the hammer and is half inside and half above the top surface of the vice.
2. Bring the striking hammer to its top most striking position unless it is already there, and lock it at that position.
3. Bring indicator of the machine to zero, or follow the instructions of the operating manual supplied with the machine.
4. Release the hammer. It will fall due to gravity and break the specimen through its momentum, the total energy is not absorbed by the specimen. Then it continues to swing. At its topmost height after breaking the specimen, the indicator stops moving, while the pendulum falls back. Note the indicator at that topmost final position.
5. The specimen is placed on supports or anvil so that the blow of hammer is opposite to the notch.
OBESERVATION:- (a) Izode Test / Charpy Test
1. Impact value of - Mild Steel ------------N-m
2. Impact value of - Brass------------N-m
3. Impact value of - Aluminum ------------N-m
RESULT:-
i. The energy absorbed for Mild Steel is found out to be….. . Joules.
ii. The energy absorbed for Brass is found out to be ….. Joules.
iii. . The energy absorbed for Aluminum is found out to
be…… Joules
PRECAUTION:-
1. Measure the dimensions of the specimen carefully.
2. Hold the specimen firmly.
3. Note down readings carefully.
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