Charpy Impact Test： Definition, History, Importance, How to Calculate, and Procedures

2. Qualitative Results

Qualitative data is non-numerical observational data. In the Charpy impact test, this refers to the observation of the fracture surface of the sample. For example, a brittle sample will have a flat fracture surface, whereas a ductile failure will typically have a rough surface with increased deformation. However, it becomes difficult to accurately state the nature of the failure when both failure modes are present in the sample, which is often the case. In these situations, the amount of surface area related to the ductile and brittle failure is measured.

What Is the Charpy Impact Test Used For?

The Charpy impact test is used to determine several properties such as the impact energy of a sample, whether or not a material exhibits ductile or brittle behavior, and at which temperature a material transitions between ductile and brittle failure modes.

What Does the Charpy Impact Test Measure?

The Charpy impact test measures the amount of energy required to rupture a sample in joules (J). This is done by measuring the potential energy before and after the pendulum has struck the sample. This value must be divided by the cross-sectional area at the notch to get the impact energy in J/m2. 

What Are the Factors Affecting Charpy Impact Test?

The Charpy impact test can be affected by several factors; four of the most important are listed below:

1. Yield Strength

In general, as a material's yield strength increases, its impact energy will decrease. In other words, materials with higher yield strength will generally have lower toughness. Materials that can plastically deform before ultimate failure are considered to be tougher.

2. Notch

The V-notch specimen is used when the material is brittle and a U-notch specimen is used when the material is ductile. The U-notch specimen has a higher stress concentration factor than the V-notch specimen. It should be noted that these notches must be precisely the same to get accurate results that can be compared with past tests. 

3. Temperature

The Charpy impact tests are typically performed at 23 °C. However, higher and lower temperatures are used to plot a curve representing a material’s ductile to brittle transition behavior. Higher temperatures will increase impact strength.

4. Fracture Mechanism

There are two fracture mechanisms, namely cleavage, which is common in brittle materials, and microvoid coalescence, which is more common for ductile materials. Materials that fracture via the cleavage fracture mechanism will have lower impact energy than those that fail via microvoid coalescence. 

Is Charpy Impact Test Important in 3D Printing?

Yes, performing Charpy impact tests on 3D printed samples can help engineers determine the impact strength of various 3D printing materials, especially considering that some technologies print parts with anisotropic properties. Testing samples with different print geometries can help engineers understand how to optimize their designs for impact strength. For more information, see our guide on Everything You Need to Know About 3D Printing.

What Is the Charpy Impact Test Result in High-Strength Material?

A high tensile strength material like tungsten has a comparatively low impact strength as it is highly brittle. 

What Is the Charpy Impact Test Result in Low-Strength Material?

Low tensile strength materials like low carbon steel will generally have higher toughness as they can absorb more energy without fracturing and are more ductile.

What Is the Difference Between Charpy Impact Test and IZOD Impact Strength Test?

The key difference between the Charpy impact test and the IZOD impact test is how the sample is secured. For the Charpy test, the sample is supported on two sides and the pendulum strokes the middle of the sample. In the IZOD test, the sample is supported on only one side, i.e., in a cantilever configuration, and the pendulum strikes it on the opposite side. 

Summary

This article presented the Charpy impact test, explained what it is, and discussed its importance and how to calculate it. To learn more about the Charpy impact test, contact a Xometry representative.

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