To test the resistance of the material towards an impact load
Charpy Testing machine, a rod of mild steel and a rod of carbonate steel.
The Charpy impact test is one of the impact-testing that is used to determine the resistance towards a sudden load or impact. Impacted specimens with small fracture or with a very little plastic deformation is said to be in a brittle manner whereas fracture of a metal after extensive plastic deformation is said to be in a ductile manner. Brittle fracture looks clear, shinny with surfaces while ductile fracture looks grayish and fibrous.
1) A Charpy V-notch specimen is placed across parallel jaws in the impact-testing machine
2) The pointer is being set up to it’s maximum value (300 J)
3) The hammer is released from the initial height downward towards the sample
4) Observations and the energy absorbed is recorded and tabulated.
5) Step 1-3 is repeated for another type of metal
Energy Absorbed (Joule)
Mild Steel Carbon Steel
From the results obtain from the experiment, we can see that the specimen fracture differently. The mild steel fracture but did not broke completely and some part of the steel still attached therefore it is said to be in the ductile manner. The carbon steel is said to be in brittle manner although it is harder. The carbon specimen broke completely into 2 parts and the broken surfaces looks smoother than the mild steel.
Carbon steel has lower ductility compared to the mild steel but the carbon steel is more brittle than the mild steel. This is because carbon steel has high percentage of carbon in it (percentage of carbon in mild steel is less than 0.2%) that lower the ability to absorb energy when sudden load is given.
From the way both specimen cracks and the ‘grayish and fibrous’ broken surfaces of the mild steel shows that it undergoes plastic deformation and in the ductile manner. The carbon steel experience less plastic deformation and the surfaces looks smoother and shinny.
Ductile fracture is better because of the following reasons:
a) More energy needed in the ductile fracture because it is a tough material
b) Brittle fracture happens quickly without warning while the ductile fracture took a longer time before the whole process to happen
From the Charpy impact test, carbon steel undergoes brittle fracture while the mild steel undergoes ductile fracture. More energy is absorbed by mild steel shows that it is more suitable to be use in the structural construction that expose to high load for example: car body.