Understanding Impact Testing of Polymers

Overview of Impact Testing

Impact testing assesses the durability and toughness of materials, particularly polymers, under sudden loading conditions. This is essential in industries where materials are subjected to shocks or impacts.

Common Methods of Impact Testing

1. Charpy Impact Test

   • Description: Measures the energy absorbed by a material during fracture. A standardized notched specimen is struck by a pendulum hammer.
   • Example: A polycarbonate sample is tested using a Charpy test. The energy absorbed before breaking is recorded, indicating its toughness.

2. Izod Impact Test

   • Description: Similar to the Charpy test, but the specimen is fixed at one end and struck at the opposite end.
   • Example: An acrylonitrile-butadiene-styrene (ABS) sample is tested using the Izod method. The height of the hammer swing before and after the impact provides data on the material’s resilience.

3. Drop Weight Impact Test

   • Description: A weight is dropped from a specific height onto a specimen, simulating real-world impacts.
   • Example: A polyethylene sample is impacted by a drop weight from various heights. The critical height at which the sample fractures is measured to assess its impact strength.

Practical Example: Charpy Impact Test Procedure

Objective: To determine the toughness of a polymer using the Charpy impact test.

Materials Needed:

• Charpy impact testing machine
• Notched polymer specimens (e.g., polycarbonate, nylon)
• Safety goggles
• Data recording sheet

Procedure:

1. Prepare Specimens: Cut polymer samples into the standardized dimensions (typically 10 mm x 10 mm x 55 mm) with a notch in the middle.
2. Set Up Equipment: Place the Charpy machine in a secure location and ensure it is calibrated.

3. Conduct Test:

   • Place the notched specimen horizontally in the testing machine.
   • Release the pendulum hammer from a known height.
   • Record the energy absorbed during fracture.
4. Repeat: Perform the test on multiple specimens to ensure consistency and reliability of results.
5. Analyze Data: Calculate the average energy absorbed to evaluate the toughness of the polymer.

Conclusion

Impact testing is a vital process in materials science, providing insights into the performance of polymers in various applications. By using methods like the Charpy and Izod tests, researchers can make informed decisions about material selection for products that require durability and strength.