Measuring the Impact Strength of Plastics and Applications in Quality Control

Plastic materials can be exposed to sudden mechanical loads during manufacturing, assembly, transportation and use. A component’s response to impact is an important consideration when assessing material selection and production quality. Izod and Charpy tests examine how specimens respond to impact under defined conditions. The results help compare the brittleness and toughness of materials.

The Izod Charpy Digital Impact Testing Machine determines the energy expended when a pendulum strikes a specimen. Its digital measurement and evaluation system makes test results easier to read and record.

The impact is initiated by pressing a control button. Following the test, results are automatically calculated, recorded and displayed, and printouts can be obtained when required. These functions simplify laboratory testing and the management of test records.

Primary Purpose of the Machine

The machine’s primary purpose is to determine the resistance of plastic specimens to sudden impact and to compare materials under defined test conditions.

This assessment can support raw material evaluation, monitoring of variations between production batches and material development. Comparable results require consistent consideration of the test method, specimen preparation and conditioning requirements.

What Are Izod and Charpy Impact Tests?

Izod and Charpy are two methods used to investigate specimen fracture behaviour through pendulum impact. Their principal difference is how the specimen is positioned and supported.

Izod Impact Test

In the Izod test, the specimen is held vertically and clamped at one end. The pendulum strikes the unsupported section. Correct positioning and appropriate clamping are important for test repeatability.

Charpy Impact Test

In the Charpy test, the specimen is positioned horizontally and supported at both ends. The pendulum strikes the central region between the supports, allowing its response to impact-induced bending and fracture to be assessed.

For both methods, the specimen and test configuration are selected according to the applicable standard. Whether notched or unnotched specimens are used depends on the requirements of the selected method.

Importance and Objectives of Impact Testing

Impact testing enables material properties to be monitored during manufacturing and quality control. Significant differences between specimens of the same material can provide a starting point for investigating raw material or processing conditions.

For example, comparing impact results before and after a change in production parameters can help assess how the change affects material behaviour. Test conditions and specimen preparation procedures must remain consistent for this comparison to be meaningful.

An impact result must be interpreted together with the conditions under which it was obtained. Specimen preparation, notch quality and environmental conditioning can influence the measured value. Test reports should therefore include the relevant conditions alongside the numerical results.

Scientific Principles of the Test

In pendulum impact testing, the pendulum possesses potential energy at its starting position. When released, this energy is converted into motion, and the pendulum strikes the specimen.

During impact, part of the energy is expended in deforming the specimen, initiating a crack and propagating the fracture. The movement of broken specimen fragments can also contribute to the measured energy. The result therefore represents an impact characteristic obtained under a defined configuration and set of conditions.

In conventional pendulum systems, energy is evaluated using the difference between the pendulum’s positions before and after impact. Mechanical friction, the condition of the system and any necessary corrections must be considered to obtain reliable measurements.

Impact energy and the reported impact strength must also be distinguished. Energy is expressed in joules, whereas the applicable method may require the result to be divided by a relevant specimen dimension or cross-sectional area. The calculation and reporting units specified by the selected standard must be followed.

Operating the Machine

Testing begins with the selection of the appropriate method. The specimen and test accessories are then prepared for either Izod or Charpy testing.

1. Prepare the specimen. Check the specimen configuration, surface condition and notch characteristics, where applicable, against the requirements of the selected standard.

2. Prepare the test configuration. Use the appropriate pendulum, striker and specimen clamping or support arrangement.

3. Position the specimen. Clamp and align it for Izod testing, or centre it on the supports for Charpy testing.

4. Apply the impact. Once preparation is complete, initiate the impact using the control button in accordance with the machine’s operating instructions.

5. Evaluate the result. View and record the calculated value, and obtain a printout when required.

Including the test method, specimen identification, conditioning details and observed fracture behaviour in the report makes subsequent evaluation easier.

Technical Specifications

Impact velocity defines the dynamic loading condition of the test. The velocity used must be assessed against the requirements of the selected method and machine configuration.

The 150° test angle relates to the pendulum’s initial position. Establishing the correct starting position is a fundamental part of energy evaluation.

The angular display resolution of 0.05° and energy display resolution of 0.01 J indicate the increments in which values are displayed. Measurement accuracy and uncertainty depend on the machine’s mechanical condition, measurement system and calibration results.

Multiple energy units make it easier to present results in the reporting format used by the laboratory or requested by the customer.

Advantages

Technical Advantages

Digital presentation makes test results easier to read. Automatic calculation and recording reduce the manual steps involved in processing results, while the printout function supports the organisation of test records.

The ability to perform Izod and Charpy tests within the same machine provides flexibility to work with different specimen mounting arrangements when the appropriate test accessories are used.

Contribution to Quality Control

Impact tests can be used for incoming material inspection, production monitoring and the assessment of material specifications. Results obtained using the same method support comparisons between production batches and help identify unexpected changes.

Examining fracture behaviour alongside the measured energy helps improve the interpretation of results.

Support for Export and Certification Activities

Records prepared according to the test method requested by a customer provide a common technical basis for communicating material properties. Clearly identifying the standard, test conditions and reporting units facilitates technical evaluation between organisations.

Reports intended for certification or customer acceptance must be prepared in accordance with the laboratory and reporting requirements of the relevant assessment programme.

Applications

Based on the standards’ scope for plastic specimens, potential applications include the following:

Plastic raw material and compound development: Different formulations can be compared in terms of impact behaviour. Test results can help evaluate changes in additives and fillers.

Injection moulding and extrusion: Suitable specimens can be used to monitor how changes in processing conditions affect material behaviour.

Automotive plastics: Testing can support material comparisons and selection studies for plastics used in interior and exterior trim components.

Electrical and electronic products: Results can support the evaluation of plastics used in housings, covers and connecting components.

Construction products and durable consumer goods: Testing can provide data for quality control assessments of materials used in plastic components.

Research and development laboratories: New formulations and production trials can be compared using the same test method and conditions.

Relevant Standards

ASTM D6110

Covers the determination of Charpy impact resistance using notched plastic specimens. The energy expended in breaking the specimen with a pendulum impact is evaluated. Specimen preparation, test conditions and reporting must follow the requirements of this method.

ASTM D256

Covers methods for determining the resistance of plastics to Izod pendulum impact. Specimen clamping, notch characteristics and impact conditions influence the result. The methods are used in material comparisons and quality control.

ISO 179

A series of standards addressing the determination of Charpy impact properties of plastics. It defines test configurations according to the material and specimen type. The methods support assessment of specimen behaviour under specified impact conditions and comparisons between similar materials.

ISO 180

Covers the determination of Izod impact strength of plastics. It defines test conditions according to the material, specimen and notch type. The method is used to investigate specimen brittleness or toughness under specified conditions.

GB/T 1843

A Chinese national standard for determining the Izod impact strength of plastics. It establishes the relevant test framework for evaluating plastic specimens using the Izod method.

GB/T 1043

A Chinese national standard series addressing the determination of Charpy impact properties of plastics. It covers methods for evaluating specimens in a Charpy test configuration.

For each test, specimen preparation, pendulum selection, striker configuration, clamping or support arrangements and calculation procedures must collectively meet the requirements of the selected standard.

Conclusion

The Izod Charpy Digital Impact Testing Machine is a laboratory system used to evaluate the impact behaviour of plastic specimens. Digital result display, automatic calculation, recording and printout functions simplify the management of test data.

Testing performed with properly prepared specimens and method-appropriate accessories provides data for material comparisons, production monitoring and quality control decisions. Consistent test conditions and reporting results together with the applicable standard help ensure that the data can be evaluated effectively.