IZOD IMPACT TEST
The Izod impact test is a standardized test used to measure the impact resistance of a material, particularly plastics. It determines the amount of energy required to break a specimen under a high-speed pendulum impact.
Here's how the Izod impact test typically works:
Specimen Preparation: A rectangular-shaped specimen is cut from the material to be tested. The specimen has a notch machined into one side, which serves as the point of impact.Test Setup: The specimen is clamped vertically in a specially designed Izod impact test machine. The machine consists of a swinging pendulum with a striker at the end, positioned at a specific height above the specimen.
Pendulum Release: The pendulum is released, and it swings down, striking the notched side of the specimen. The impact causes the specimen to fracture.
Measurement: The machine measures the energy absorbed by the specimen during fracture. This energy is referred to as the Izod impact strength and is typically reported in joules (J).
Repeat Testing: Multiple specimens are tested to obtain an average value and ensure the reliability of the results.
The Izod impact test helps assess a material's toughness and its ability to withstand sudden impact or shock loading. It is widely used in quality control, material selection, and product development in various industries, including automotive, aerospace, construction, and manufacturing.
It's worth noting that there are other impact tests, such as the Charpy impact test, which is similar to the Izod test but involves a different specimen configuration and testing setup. Both tests serve the purpose of evaluating the impact resistance of materials, but they may yield slightly different results.
Aim:- To find the impact resistance of mild steel and cast iron.
Apparatus used:- Impact Testing Machine
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| Impact Testing Machine |
Theory
Impact test signifies toughness of material that is the ability of material to absorb energy during plastic deformation.Toughness takes into account both the strength and ductility of the material.There are two distinct type of toughness mechanism and in this case it is appropriate to consider notch as a very high local stress concentration.
The first type of mechanism occurs in ductile material. This is because very high stresses at the end of the notch produce local yielding of the material and local plastic flow at the crack tip. This has a action of blunting the sharp tip of the notch and hence reduces the stress concentration effect.
The second mechanism occurs in fibers, wood materials etc which have a weak interface. Local tensile stress developed at the front of a propagated crack opens up the interface and produces a crack sink i.e., blunts the crack by effectively increasing the radius of the crack tip. The stress-concentration at the notch increases with decreasing notch radius.
Impact testing machine consists of a pendulum suspended from a short shaft that rotates in ball bearing and swings midway between two rigid upright stands supported on a rigid base near the bottom of which are the specimen supports anvils. The knife-edge or striking edge is slightly rounded. The pendulum can be raised to any desired height and rested at that position. It is supported in the starting position by a catch and can be released by a trigger. The mechanism is so designed that the pendulum is not disturbed when the catch is released.
Impact strengths are generally lower as compared to strengths achieved under slowly applied loads. Indian standard method of izod impact test consists of breaking the specimen by one blow from a swinging hammer under specified condition, a notched test piece is gripped vertically with the bottom of the notch in the same plane as the upper face of the grips.The-blow is struck at a fixed position on the face having the notch. When a striker impacts the specimen, the specimen will absorb energy till it yields. At this point the specimen will begin to undergo plastic deformation at the notch. The specimen continues to absorb energy and work harden at the plastic zone, when the specimen can absorb no more energy fracture takes place.
Procedure:-
1. With the striking hammer ( pendulum) in safe position, hold the specimen in impact testing machine’s vice in such a way that the notch face the hammer and 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 it 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 top most 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 idle position and back.
Total loss of energy during transit of hammer Et= 49 J
Energy for failure of Specimen = Et- Ef= 45 J
Observation:-
Initial energy of the hammer = 164 J
Average loss of energy due to friction Ef = 4 J
Total loss of energy Et during transit of hammer = 49 J
Energy for failure of specimen = Et- Ef = 45 J
Average energy for failure of specimen = 45.33 J
Results :- The energy absorbed for mild steel is found out to be 45.33 J.