Title:

The Charpy impact test

Objective:

To test the resistance of the material towards an impact load

Apparatus:

Charpy Testing machine, a rod of mild steel and a rod of carbonate steel.

Introduction:

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.

Figure 1

40 mm

10 mm triangle

30°

Hammer0.25mm rad

2 mm

45°

Procedure:

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

Results:

Steel Energy Absorbed (Joule)Mild steel 299.0

Carbon steel 21.0

Mild Steel Carbon Steel

Discussion:

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

Conclusion:

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.

References:

a) Foundation of Material Science and Engineering – 4th edition, William F. Smith and Javad Hashemi