Table of Contents
The Charpy test is used to determine the resistance capacity of metal (steel) specimens against the sudden impact of a pendulum that swung from a certain height.
The Charpy impact is also known as the Charpy V-notch test because the specimen used in this test is cut at a certain depth in a ‘V’ shape.
1. What does the Charpy Impact Test Measure?
The Charpy impact test is performed to measure the required amount of energy to break a metal piece by the force of pendulum weight.
2. Importance of Charpy Test
The primary purpose of performing this experiment is to discover whether the material is brittle or ductile.
Materials that break without plastic deformation (no energy absorption) are known as brittle materials.
Material breaks with large plastic deformation (little energy absorption) are known as ductile material.
It is a way of measuring the toughness of materials and the quantity of energy absorption during their fracture.
3. Apparatus Required
The apparatus required is as follows:
a. The specification of the test specimen and methodology has been mentioned in IS code 1757.
b. Charpy Machine-a heavyweight would be attached to the pendulum swing machine.
c. Metal Specimen as Per IS standard.
4. Test procedure of Charpy Test
a. Specimen Preparation
The size of the sample should be 55mm x 10mmx 10mm and should have a depth of 2mm at notch at the center.
a. Lift the pendulum to its starting position. Then you have to check whether the test machine has been adjusted correctly.
b. Initially, the Charpy machine has to be calibrated. To do this turn the dial gauge to the en value (highest value measurement) and release the pendulum without placing the specimen. The needle now goes to the starting value 0. Hence the Charpy machine is ready for the test.
c. Now place the test specimen on the machine at the correct position by using the centering device.
d. Then turn the dial gauge indicator needle downwards at the end value and release the pendulum.
e. Now the pendulum swings down and cuts the specimen.
f. Due to the energy absorption by the specimen, the pendulum does not attain the full height on the other side.
g. Using the dial gauge, we can measure the amount of energy absorbed by the specimen (in terms of Joules or Nm). Note clown the value from the dial gauge.
b. Test formula
The amount of energy absorbed by the test specimen to break is called Knotch impact energy.
Knotch impact energy = mgH-mgh
Where,
m= Mass of Pendulum
H= Height of pendulum starting point.
g= Gravity
h=Height of pendulums from the first reversal point
c. Lab report
The test has to be applied to a minimum of three specimens from the same batch.
| Specimen | Impact energy in Joules |
| Sample 1 | |
| Sample 2 | |
| Sample 3 |
The test is conducted to calculate whether the material is brittle or ductile. The brittle material absorbs less dose of energy, and ductile material absorbs large amounts of energy.
5. Factors Affecting Charpy Energy
The factors affecting Charpy impact energy are as follows:
a. Yield Strength
High-yield strength metal will absorb less impact energy
b. Notch
The shape and depth of the notch should be made accurately. The improper notch will show the error value of energy absorption
c. Temperature
The test should be executed at 23ºC +/- 5ºC. Higher temperature affects the ductility
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