5 steps to selecting hammers for your pendulum impact testing machine

15 Mar 2022

5 STEPS TO SELECTING HAMMERS FOR YOUR PENDULUM IMPACT TESTING MACHINE

The hammer is a critical component of a pendulum impact testing machine. There is now a wide range of hammers to choose from, covering a broad energy spectrum. Selecting the correct device is key to ensuring repeatable pendulum hammer impact test results. Here are some key considerations and features to look out for to maximize efficiency, safety and accuracy.

STEP 1: KNOW WHAT YOU ARE TESTING

Understanding a material’s characteristics and requirements is critical. If you have tested the material before, you can back-calculate the required pendulum impact energy based on previous test results.
If you have never tested the material before, look at third-party material specification databases like UL Prospectorand MatWeb. This way, you can access that material’s specification datasheets and identify the appropriate test method and requirements. Instron is always available to provide further guidance and help you identify the correct test method for a specific material.

STEP 2: KNOW YOUR STANDARDS

Once you have identified the correct pendulum hammer impact test method, always refer to the relevant industry standard. ISO 179 and ASTM D6110 cover the Charpy pendulum impact test. ISO 180 and ASTM D256 cover the Izod method.

According to these standards, you must perform pendulum impact tests within the following energy ranges:

ISO 179-1 and ISO 180 - The specimen must absorb between 10% and 80% of the hammer energy.

ISO 179-2 - The specimen must absorb up to 20% of the hammer energy.

ASTM 6110 and ASTM D 256 - The sample must absorb up to 85% of the hammer energy.

STEP 3: SELECT THE CORRECT ENERGY CAPACITY

Now you know all the specifications and standards that apply to the material you need to test. The next step is selecting the correct hammer capacity range.

The latest, high-capacity pendulum impact testing machines can cover a broad energy spectrum. As the absorbed energy can be as low as 10% of the hammer capacity (according to the ISO standards), a 50 J hammer can perform tests across the entire 5-50 J range.
This equipment is generally the preferred choice for highly resistant composites used in automotive and aerospace.
50 J hammers can also test some metals if the specimens are miniaturized.

However, most resins and brittle materials such as ceramic typically require a lower impact energy.

If in doubt, always refer back to the material’s datasheet or seek Instron’s guidance to identify the correct range.

STEP 4: THINK STRUCTURE

The structure of the pendulum impact tester and hammer is an important consideration. Instron’s pendulums come with dedicated energy hammers. Others require you to add/remove weights to reach the desired capacity. The latter tend to be less safe and efficient due to various reasons:

Handling weights can lead to musculoskeletal disorders as well as hand injuries.

Weights may fall and damage the pendulum, which can affect test repeatability.

Having to add/remove weights typically leads to downtime.

When choosing dedicated energy hammers, design is paramount. Bolted models may become loose after repeated testing, which can affect repeatability.

The pendulum frame is another important consideration. Some pendulum models have dedicated frames for different hammer capacities. Every time you switch hammer, you must change the frame too, which can contribute to downtime.

All Instron pendulum testers feature a solid monolithic hammer structure and monolithic cast iron frame. This design can go a long way towards minimizing vibrations, helping maximize test repeatability. Not only that. The test setup process is faster as the frame is compatible with multiple hammers.

STEP 5: GO AUTOMATIC

The latest pendulum impact testing machines from Instron come with automatic hammer verification software to help you maximize accuracy and minimize downtime.

The embedded app features pre-installed test method templates based on the ISO and ASTM standards and automatically recognizes the installed hammer. All you have to do is load the sample and select the desired test method template. After the first test, the software automatically calculates the absorbed energy and compares it to the relevant standard’s specifications. If it fails to comply, the system immediately flags the error up, prompting you to take action and replace the hammer.