Impact Testing

What is Impact Testing?

Impact testing is a method used to determine a material’s toughness and its ability to absorb energy during a collision. Impact testing measures the material’s capacity to withstand sudden forces or impacts. Common impact tests include the Charpy impact testing and Izod impact testing, both of which involve striking a notched sample with a swinging pendulum. Impact testing is a critical technique in materials science and engineering, providing valuable insights into the behavior of materials under dynamic loading conditions. Impact testing helps in evaluating the performance and reliability of materials in applications where they may be subjected to sudden impacts or shocks. 

Why is this Impact Testing important?

Impact testing is essential for several reasons: 

• Material Selection: Impact testing helps in choosing materials that can withstand impact loads in specific applications. By determining the impact toughness of various materials, engineers can select the most appropriate material for applications where impact resistance is crucial. Impact testing ensures that materials will perform reliably under impact loading conditions. 

• Quality Control: Impact testing ensures materials meet required toughness specifications and standards. Consistent and reliable impact testing during production helps manufacturers maintain high-quality standards and avoid defects that could lead to material failure. Regular impact testing is vital for maintaining product quality and performance. 

• Safety Assurance: Impact testing identifies materials that may fail under impact, thus preventing potential failures in critical applications. This is particularly important in industries such as automotive, aerospace, and construction, where material failure could result in catastrophic consequences. Impact testing enhances safety by ensuring that materials can withstand impact loads without failing. 

• Research and Development: Impact testing aids in developing new materials with improved impact resistance. By understanding how materials behave under impact loading, researchers can design and engineer new materials with enhanced toughness and durability. Impact testing is a key tool in the development of advanced materials for demanding applications. 

• Compliance with Standards: Impact testing ensures that materials comply with industry and governmental regulations. Adhering to standardized impact testing methods ensures consistency and comparability of results across different laboratories and applications. Compliance with impact testing standards is essential for regulatory approval and market acceptance of materials and products. 

Concept of the testing (working principle & theory related)

The principle behind impact testing involves measuring the energy absorbed by a material during fracture. Key concepts in impact testing include: 

• Notch Toughness: The ability of a material to resist fracture when a notch is present, simulating flaws or cracks in impact testing. Notch toughness is an important indicator of a material’s ability to withstand stress concentrations and is a critical parameter in impact testing. 

• Energy Absorption: The amount of energy a material can absorb before fracturing, indicating its toughness in impact testing. Higher energy absorption values generally indicate better toughness and impact resistance. Measuring energy absorption is a fundamental aspect of impact testing.
• Pendulum Impact Tester: A device used in impact testing that employs a swinging pendulum to strike a notched sample, measuring the energy absorbed during fracture. Pendulum impact testers are commonly used in Charpy and Izod impact testing and provide a reliable means of assessing material toughness. The design and operation of pendulum impact testers are crucial for accurate impact testing results. 

These standards provide detailed guidelines on sample preparation, test procedures, and data analysis to ensure reliable and reproducible results in impact testing. Compliance with these standards ensures that impact testing is conducted consistently and accurately, providing valuable data for material characterization, quality control, and regulatory compliance. Adhering to standardized methods in impact testing is crucial for achieving reliable and comparable results across different laboratories and applications. 

Testing Tools

• Charpy Impact Tester: Uses a notched sample and measures the energy absorbed when the sample is struck by a pendulum in impact testing. The Charpy impact tester is widely used for evaluating the impact toughness of metallic and polymeric materials. The test setup and sample orientation in Charpy impact testing are standardized for consistency. 

• Izod Impact Tester: Similar to the Charpy tester but with a different sample orientation, measuring the energy absorbed from a vertical strike in impact testing. The Izod impact tester is commonly used for testing the impact resistance of plastics and other materials. The vertical orientation of the sample in Izod impact testing provides a different loading condition compared to Charpy impact testing. 

• Drop Weight Testers: Use a falling weight to strike a sample and measure the energy absorbed in impact testing. Drop weight testers are suitable for evaluating the impact resistance of large or complex samples and are often used in applications where traditional pendulum impact testing is not feasible. The design and operation of drop weight testers are critical for accurate impact testing. 

• Instrumented Impact Testers: Equipped with sensors to measure force, displacement, and energy during the impact in impact testing. Instrumented impact testers provide detailed data on the impact event, allowing for a more comprehensive analysis of material behavior under dynamic loading. The advanced measurement capabilities of instrumented impact testers enhance the accuracy and reliability of impact testing. 

   

How to perform the testing

1. Perform Impact Testing Performing an impact test involves several steps: 

• Sample Preparation: The material specimen is prepared according to specific dimensions and notched at the center for impact testing. Proper sample preparation is essential for obtaining accurate and consistent results in impact testing. The notch in the sample is designed to create a stress concentration, simulating real-world flaws or defects. 

• Mounting the Specimen: The notched sample is placed in the impact tester, either horizontally (Charpy) or vertically (Izod) for impact testing. Correct mounting of the specimen ensures that the impact load is applied accurately and consistently. Proper alignment and positioning of the sample are critical for reliable impact testing results. 

• Setting Up the Test: The pendulum is raised to a predetermined height to ensure a consistent amount of potential energy in impact testing. Setting the pendulum height accurately is crucial for ensuring repeatability and comparability of impact testing results. The potential energy of the pendulum is a key parameter in impact testing. 

• Conducting the Test: The pendulum is released, striking the notched sample. The energy absorbed during fracture is measured in impact testing. The impact event occurs rapidly, and the measurement of absorbed energy is a critical aspect of impact testing. The data collected during the impact event provides valuable insights into the material’s toughness and impact resistance. 

• Analyzing the Data: The energy absorbed is used to calculate the material’s toughness and compare it against standards in impact testing. Data analysis involves interpreting the results and comparing them to established criteria or specifications. Accurate data analysis is essential for making informed decisions based on impact testing results. 

• Reporting Results: The results are compiled into a report, detailing the absorbed energy and any relevant observations in impact testing. The report includes information on the test method, sample preparation, test conditions, and results. Comprehensive reporting in impact testing ensures that the data is accurately recorded and can be used for 
  quality control, material selection, and compliance purposes.  

Standard for the testing

Impact Testing Impact testing adheres to various international standards to ensure consistency and accuracy. Some key standards in impact testing include: 

• ASTM E23: Standard Test Methods for Notched Bar Impact Testing of Metallic Materials in impact testing. This standard provides guidelines for performing Charpy and Izod impact tests on metallic materials, ensuring consistent and reliable results. ASTM E23 is widely used in the evaluation of metallic materials’ impact toughness. 

• ISO 148: Metallic Materials—Charpy Pendulum Impact Test—Part 1: Test Method in impact testing. This international standard specifies the Charpy impact testing method for metallic materials, ensuring uniformity and comparability of results across different laboratories and applications. ISO 148 is a critical standard for Charpy impact testing. 

• ASTM D256: Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics in impact testing. This standard outlines the procedure for conducting Izod impact tests on plastic materials, providing guidelines for sample preparation, test conditions, and data analysis. ASTM D256 is essential for evaluating the impact resistance of plastics. 

• ISO 180: Plastics—Determination of Izod Impact Strength in impact testing. This standard specifies the Izod impact testing method for plastic materials, ensuring consistency and reliability of results. ISO 180 is widely used in the plastics industry for assessing impact resistance. 

• EN 10045: Metallic Materials—Charpy Impact Test—Part 1: Test Method in impact testing. This European standard provides guidelines for performing Charpy impact tests on metallic materials, ensuring accurate and reproducible results. EN 10045 is an important standard for Charpy impact testing in Europe.