In extreme cold weather or sudden impact, we often find that certain plastic and metal parts have unexpectedly snapped. Sometimes it’s the quality, but most of the time, it’s the design. And we must say that by no means is that a safer design. The sudden snap just exposes exactly how much shock the material can handle before it breaks. This is quite important for applications where plastics and steel are used outdoors, in cold storage, or in high-speed environments like packaging lines, car frames, natural gas pipes, etc. Many plastic parts, like containers, casings, or components, may look durable but can unexpectedly crack under fast impact or low temperatures. This test helps identify whether a plastic will bend, flex, or break under real-world stress.
What Exactly Is the Charpy Impact Test?
Also known as the Charpy V-notch test, the Charpy impact test is a standardised high-strain-rate test. It determines how much energy a material can absorb during fracture. The amount of absorbed energy is the measurement of the material's notch toughness.
This test is especially important for steel-like steel that may become brittle at low temperatures. And it’s also important for plastic parts that can crack under the same conditions. It tells us if a material will bend or break in critical or high-stakes situations.
Inside the Machine: How the Charpy Impact Tester Works
Based on the principle of the pendulum method, the Charpy impact test machine uses a heavy swinging pendulum to strike a notched sample. The machine measures the energy absorbed during the break and gives an instant toughness reading. This Charpy impact test includes 2 tests:
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Izod—horizontal impact on a vertically clamped specimen
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Charpy—vertical impact on the horizontally placed specimen
Key parts of the Charpy impact test machine
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A notched specimen holder
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A calibrated swinging pendulum
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A digital or analogue energy scale
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Safety guards for impact testing
When the pendulum strikes, the machine records the absorbed energy, giving a clear indication of the plastic’s toughness. The higher the energy absorbed, the tougher the material.
What Is the Charpy Impact Test Procedure?
To get accurate and repeatable results, the Charpy impact test procedure for plastics follows these key steps:
Sample Preparation
- Whether you are opting for plastic or metal, preparing the ideal samples or specimens is a must. Depending on the material, the standard size varies. For plastic, it’s 80mm x 10 mm x 4 mm, and for metal, mostly 10 x 10 x 55 mm is used. Now cut the specimens according to the given size. If following ASTM D 6110 then specimen dimension has to be 127 mmm x 12.7 mm x 3 mm
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Add a V-notch or U-notch at the centre of the sample using a notching machine.
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This notch will act as a stress point, helping the crack start consistently during impact.
Conditioning the Sample
Now, place the sample in a conditioning chamber to simulate real-use temperatures. If you want to determine the ductile-to-brittle transition temperature (DBTT), pre-conditioning is a must. DBTT means cooling or heating the specimens to the target temperature, whether very cold or very hot, and maintaining that condition for a set time in a controlled environment.
Mount and Test
Before proceeding with the test, check the calibration and pendulum’s original height and weight. These should be correct, and the energy scale has to be accurate.
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Set the notched sample horizontally in the Charpy impact tester.
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Align it properly with the pendulum.
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Release the pendulum. It strikes the sample and breaks it.
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Read the energy absorbed from the machine display.
Analyse the Charpy Impact Test Results for Plastics & Steel
1. Plastics
After the impact, the joule rating shows the strength of the plastic. If the number is high, the plastic handled the blow well; if it’s low, it likely cracked or snapped easily. Depending on the application, you can choose the plastic. Flexible plastic, in general, is great for packaging, containers, or bumpers. However, plastics that absorb little energy usually aren’t the best choice for anything that requires durability, like car parts, outdoor equipment, or sturdy packaging.
2. Steel
The Charpy impact test results for steel are critical to evaluate its toughness, especially in low-temperature or sudden loads. The energy absorbed during the test shows how resistant the steel is to breaking. Low values suggest it could fracture suddenly, especially in the cold.
Engineers often plot the results on a graph of absorbed energy vs. temperature to identify the DBTT. The DBTT shifts steel from toughness to brittleness. To select the right steel for applications like bridges, car frames, storage tanks, and arctic pipelines, this data is a must.
What Is the Charpy Impact Test Formula?
The Charpy impact test formula is:
Energy Absorbed (J) = Initial potential energy of pendulum – Remaining energy after impact
This value measures the toughness of the material, be it plastic or steel.
What are the Benefits of using a Charpy impact tester?
There are multiple benefits to using this tester, especially during quality purchases.
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Accurate measurement of toughness
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Predicts real-world performance
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Flexible material selection based on requirement and grade. Engineers can choose plastics that stay flexible in the cold or steels that remain tough under high stress.
- Saves cost in the long run
- Improves product safety while following compliance
FAQ
What is the difference between the Charpy Impact Test and ESCR?
The Charpy Impact Test measures the toughness of materials like plastic and steel in harsh conditions, such as extreme weather or sudden impact. ESCR, on the other hand, tests the resistance of plastics to cracking. Especially if the plastic goods are exposed to chemicals, UV, or stress over time.
Can the Charpy Impact Test Machine Compare Recycled vs. Virgin Plastic?
Yes, the Charpy impact test machine can compare the virgin and recycled plastics. Recycled plastics have lower impact strength due to multiple usages. This test helps to find out whether the recycled material meets performance standards or not. If yes, then you can go for recycled plastics; otherwise, the virgin counterpart should be chosen. Also, there are different qualities in both types, and applying this test may help you in determining the best one.
Can the Charpy Impact Machine Test The Types of Steel?
Yes, similar to plastics, steel can also be tested. You can compare the impact strength of mild steel vs. high-strength steel or welded vs. base metal. This test highlights changes in toughness due to impurities, alloying, or thermal cycling.
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