Guide to Charpy V-Notch Impact Tests
November 3, 2021 | Categorised in: Steel 101
Charpy impact testing is a critical part of planning and analyzing potential building materials for a structure or other project, as well as the quality control process. It can determine whether you’re able to use a certain component or type of part based on the purpose and design of the final build, but what is the actual test?
What is a Charpy impact test?
Charpy impact test, or v-notch test, is an evaluation of a material’s strength and performance under impact conditions. It involves a pendulum with a pointed hammer on the end swinging and hitting a bar of steel to determine the impact toughness (which is a function of its brittleness) of the metal specimen.
This is accomplished by setting the pendulum’s potential energy at a specified starting value. Once released, the hammer swings down and through the steel specimen and pauses at the height of its arc before swinging back. By measuring the potential energy at that pause and subtracting it from the potential energy before release, you can calculate how much energy the specimen absorbed or removed from the hammer’s swing, and therefore the toughness of the material.
Why is it important?
So why does it matter how much energy a small piece of steel can absorb from a swinging hammer? It’s a crucial test for analyzing the toughness of a material, and therefore important for ascertaining whether it can do a job or not. If you’re constructing the steel frame of a new building, you want to make sure the type of steel you’re using is strong enough to withstand the expected loads and environment.
Charpy test steps
1. Notch test specimens
The standard size of a specimen for Charpy impact testing is 10 mm × 10 mm × 55 mm. A 2mm deep notch with an angle of 45° and a tip radius of 0.25mm is then machined into one face of the bar. These specifications have a very tight tolerance because the shape and size of the notch can have a significant effect on the results of the test.
In addition, five specimens are usually produced and tested (often at a specified cold temperature), with an average of the middle three values being used as the calculated toughness of the material. There are other sizes (and a U-shaped notch) that may be used depending on the situation (such as 10 mm × 7.5 mm × 55 mm or 10 mm × 6.7 mm × 55 mm), but the standard dimensions cited above are usually what’s used.
2. Calibrate pendulum
Now that you have your steel specimens, it’s time to set the pendulum up for the test. This will vary depending on your Charpy testing equipment but often involves ensuring that the drag indicator reaches 0 when a test swing is done without a specimen.
3. Set pendulum
Once the hammer is calibrated, you need to raise it and lock it in place at the starting position. Double-check that the dial to record the height of the swing (and therefore the potential energy at that position) has also been reset and will record the measurements for this test.
4. Place specimen
Next, place the specimen horizontally in the anvil at the lower part of the machine with the notch facing away from the direction that the pendulum comes from. Line up the notch with the center of the channel that the hammer swings through (usually with a centering device on the machine).
If the specimens are being cooled for this test, this process needs to be done with time as a consideration. Removing them from the cold environment, placing them, and releasing the pendulum should take less than five seconds for each repetition of the test.
5. Release pendulum
By pulling a lever or switch, the pendulum is released and swings downward and hits the specimen at the bottom. Usually, the halves (or single deformed piece) of the steel will be thrown across the room or away from the machine so make sure you remember to pick them up afterward.
6. Record energy absorbed
Because the steel specimen will absorb a portion of the energy that the pendulum’s swing started with, it won’t reach the same height on the other side of the swing. Depending on your testing machine it will either record this on a dial or a digital screen, which you will then take note of and calculate the absorbed energy with. Some Charpy testers will calculate the energy absorbed for you on the dial or display that measures the height of the swing.
Steps 3 through 6 are then repeated for the other specimens before averaging the measured energy absorbed to come to a final result.
Ensure the toughness of your steel today
We understand the importance of Charpy testing and other services that are key to getting your project finished on time and with the highest quality materials. Always ensure your steel is strong and high-quality with Service Steel, providing fast, reliable, and excellent service for over 50 years. Request a quote for Charpy impact testing today.