Charpy Impact Tester vs Izod Impact Tester: What is Difference

Impact testing is a critical testing approach in material science to assess how much force a material can withstand. More specifically, it measures how much energy a material can absorb before it deforms or fractures completely. Some of the more common devices used in impact testing are the Charpy impact tester and the Izod impact tester.

While both of these devices are used to measure the impact resistance of materials, they differ in terms of sample placement and testing configuration. Recognizing the differences will help to choose the best impact testing method for application purposes.  

What is a Charpy Tester? 

A Charpy Impact Tester is used for measuring the amount of impact energy absorbed by a material when it fractures. A notched specimen is placed in a horizontal orientation and supported at both ends. The specimen is then struck behind the notch with a swinging hammer.

The test is designed to model a short-duration impact similar to a short-duration hit or collision. The material absorbs energy when the notched specimen breaks, and the test indicates the material's toughness, which is the material's ability to absorb energy from a short-duration impulse. The best example will be using a pendulum with a specific mass and length, where the pendulum is raised to a specific height and dropped onto the notched specimen. 

The formula for the Charpy Tester is:

E=mgh(h0​−hf​)

Here, E = Energy absorbed by the specimen (in joules)

m = Mass of the pendulum (kg)

g = Acceleration due to gravity (9.81 m/s²)

h₀ = Initial height of the pendulum before impact (m)

hf = Final height of the pendulum after breaking the specimen (m)

What is the Izod Tester?

An Izod Tester is a device used to measure the toughness of materials, particularly plastics, under impact. It strikes the sample with a rapid force and records the energy it absorbs when it fractures. In this test, the sample is positioned vertically, and the impact is delivered to the top of the sample, with the notch pointing towards the striker. 

Example: Think of a plastic part in a car bumper. The Izod test hits a sample to see if it can handle small crashes. This helps makers build safer bumpers for drivers. 

The formula for the Izod impact tester is:

Energy Absorbed = Potential Energy (before impact) – Potential Energy (after impact)

Difference Between Izod Tester and Charpy Tester

The Izod and Charpy Testers are both intended to test a material’s strength through the application of an instantaneous force, but the testing methods are different. With the Izod testing method, the sample is positioned vertically and the strike is made at the top of the sample with the notched side facing the striker. With the Charpy testing method, the sample is placed in a horizontal position on two supports, and the strike is made to the sample behind the notched side. The table below identifies the main differences.

Izod Impact Test vs Charpy Impact Test

Feature	Izod Impact Tester	Charpy Impact Tester
Sample Position	The test specimen is mounted vertically, with the notch facing upwards. This setup simulates bending stress on one end.	The specimen is placed horizontally, resting on two supports. This position creates a bending moment across the entire sample.
Notch Direction	The notch faces the striker, meaning the pendulum directly hits the notched side, initiating the fracture.	The notch is on the opposite side of the striker, so the impact causes the material to break through the notch from behind.
Support Type	The specimen is clamped at one end only, resembling a cantilever. This makes it ideal for testing flexible materials.	The specimen is supported at both ends, allowing it to flex at the point of impact, simulating real structural conditions.
Impact Location	The pendulum strikes the top portion of the specimen, just above the notch.	The striker impacts directly behind the notch, forcing the crack to propagate through the weakened section.
Testing Standards	Common standards followed are ASTM D256 and ISO 180, mostly for plastics and polymeric materials.	Standards include ASTM E23 and ISO 148, which are globally recognized for metallic materials.
Primary Applications	Widely used in quality control, research labs, and educational setups for testing plastics and soft materials.	Common in industrial and structural testing, especially in automotive, aerospace, and metal fabrication.
Energy Range	Measures lower energy impacts, making it suitable for materials that absorb less energy like plastics.	Designed for high energy impact testing, capable of breaking tough materials like steel or alloys.
Pendulum Configuration	Uses a lighter pendulum to measure smaller energy absorption accurately.	Utilizes a heavier pendulum to deliver sufficient force for testing rigid, strong materials.
Materials Tested	Ideal for plastics, polymers, composites, and occasionally non-ferrous metals.	Primarily used for metals and alloys, especially those used in structural applications.
Notch Type	Can use both V-notches and U-notches, depending on the material and testing standard.	Typically uses a V-notch, which provides consistent results across metallic specimens.
Fracture Observation	Helps determine whether a material is ductile or brittle under sudden impact.	Evaluates the energy required to fracture and the mode of failure in metals under high-stress impact.
Sample Preparation	Requires minimal preparation, as plastics are easier to cut and mount.	Involves precision machining and measurement, as metals must meet strict dimensional tolerances.
Mounting Method	The sample is clamped vertically in a vise-like holder, with the free end exposed to the striker.	The sample rests freely on two horizontal anvils, ensuring consistent impact at the center.
Ease of Use	Generally easier to operate and more accessible in educational or small-scale lab settings.	Requires robust setup and calibration, typically found in industrial testing environments.
Cost of Equipment	Typically, less expensive due to its simpler design and lower force requirement.	Usually more costly owing to its heavy-duty design and energy calibration systems.

Conclusion: Which is Right for You

The choice between the Izod and Charpy Impact Test is based on your testing needs, material type, and standards for the industry. If you want a quick and cost-effective way to evaluate the impact resistance of flexible materials, then the Izod Impact Test is the best choice due to its vertical sample position and lower energy use.

On the other hand, if you are testing metals or structural parts that will involve higher energy tests and want to meet international specifications, such as ASTM E23, then the Charpy Impact Test is the better choice. With an understanding of the different setups, energy ranges, and what each test is suited for, you can properly evaluate the materials and enhance the quality control of your materials.