EXPERIMENT
OBJECTIVE:
To determine the impact strength of steel by CHARPY TEST.
APPARATUS REQUIRED:
- Impact testing machine.
- Steel specimen.
THEORY:
An impact test signifies the 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. The 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 load while in service. Impact strengths are generally lower as compared to strengths achieved under slowly applied load. Of all types of impact test, the notched 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 conditions. This test can also be used to assess the ductile brittle transition temperature of the material occurring due to lowering of temperature.
PROCEDURE:
- For conducting Charpy test, a proper striker is to be fitted firmly to the bottom of the hammer with the help of the clamming piece.
- Bring the striking hammer to its top most striking position unless it is already there, and lock it at that position.
- Firmly held the steel specimen in impact testing machine vice in such a way that it is simply supported and the notch is opposite to the hammer.
- Bring indicator of the machine to zero, or follow the instructions of the operating manual supplied with the machine.
- After ascertaining that there is no person in the range of swinging pendulum, release the pendulum to smash the specimen.
- The hammer will fall due to gravity and break the specimen through its momentum. If 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 reading at the topmost final position and note indicated value.
- Remove the broken specimen by loosening the clamping screw.
The notch impact strength depends largely on the shape of the specimen and the notch. the values determined with other specimens therefore may not be compared with each other.
OBSERVATIONS:
Energy absorbed = Impact value = ….. N-m
OBSERVATION TABLE:
|
S. No. |
AREA OF CROSS-SECTION OF SPECIMEN (A) |
IMPACT ENERGY (K) |
IMPACT STRENGTH (I) |
PRECAUTIONS:
- Measure the dimensions of the specimen carefully.
- Hold the specimen firmly.
- Locate the specimen in such a way that the hammer. Strikes it at the middle.
- Note down readings carefully.
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