Plastic Charpy (Simply Supported Beam) Impact Performance Testing: Principles, Standards, and Applic

Plastic Charpy impact performance testing, also known as simply supported beam impact testing, is a fundamental method for evaluating the toughness and impact resistance of plastic materials under dynamic loading conditions. This test measures the energy absorbed by a plastic specimen when fractured by a single swing of a pendulum hammer, providing critical data for material selection, quality control, and product design. This article provides a comprehensive technical overview of plastic Charpy impact testing, covering test principles, specimen requirements, applicable standards such as ISO 179-1, GB/T 1043.1, and ASTM D6110, testing procedures, and typical industrial applications.

Technical Overview

The Charpy impact test, commonly referred to as simply supported beam impact testing in Chinese engineering practice, is one of the most widely used methods for characterizing the impact toughness of plastics. In this test, a rectangular plastic specimen is positioned horizontally on two supporting anvils, forming a simply supported beam configuration. A pendulum hammer mounted on a defined radius arm is released from a fixed height and strikes the specimen at the midpoint of the span, directly opposite the notch in the case of notched specimens. The difference between the initial and final pendulum heights represents the energy absorbed by the specimen during fracture.

The principal result is the Charpy impact strength, expressed in kilojoules per square meter (kJ/m²), calculated by dividing the corrected absorbed energy by the cross-sectional area of the specimen (or the remaining area at the notch root for notched specimens). The test is governed by several major international and national standards, including ISO 179-1 (Plastics – Determination of Charpy impact properties – Part 1: Non-instrumented impact test), ASTM D6110 (Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics), and the Chinese national standard GB/T 1043.1. The test is especially valuable for comparing the brittleness or ductility of different plastic materials, evaluating notch sensitivity, and assessing the influence of temperature, additives, processing conditions, and environmental aging on impact performance.

A key characteristic of the Charpy configuration is that the specimen is not clamped but freely supported, which avoids the influence of clamping pressure on the results and makes the method particularly suitable for rigid thermoplastics, thermosets, and fiber-reinforced composites. Depending on the material behavior, the test can produce complete break, hinged break, partial break, or non-break outcomes, all of which must be documented in the test report.

Testing Samples

Standard Specimen Dimensions

For ISO 179-1 and GB/T 1043.1 testing, the preferred specimen is a rectangular bar measuring 80 mm × 10 mm × 4 mm, supported on a 40 mm span. ASTM D6110 specifies a longer specimen of 127 mm × 12.7 mm × 3.2 mm (or 12.7 mm thickness for rigid materials) supported on a 101.6 mm span. Specimens may be directly injection molded, compression molded, or machined from sheets, pipes, profiles, or finished parts.

Notch Types

Notched specimens are used to evaluate notch sensitivity and crack initiation resistance. ISO 179-1 defines three principal notch geometries:

• Type A notch: V-notch with a radius of 0.25 mm and a remaining width of 8.0 mm, the most commonly used configuration for plastics.
• Type B notch: V-notch with a radius of 1.00 mm, used for materials that are highly sensitive to sharp notches.
• Type C notch: sharp V-notch with a radius of 0.10 mm, applied to materials with very low notch sensitivity.

Unnotched specimens may also be tested for materials that do not break when notched or when the overall material toughness is of interest.

Specimen Orientation

Depending on the material and geometry, specimens may be tested edgewise (the pendulum strikes parallel to the width), flatwise (the pendulum strikes parallel to the thickness), or vertically. The orientation must be clearly indicated in the test report because it can significantly affect the measured impact strength.

Conditioning

Specimens shall be conditioned prior to testing, typically at 23 °C ± 2 °C and 50 % ± 10 % relative humidity for a minimum of 16 hours, unless otherwise specified by the relevant material standard or client requirements.

Testing Items

Accredited third-party laboratories routinely offer the following Charpy impact test items for plastic materials and products:

• Charpy impact strength of notched specimens (kJ/m²) – evaluating crack initiation resistance under impact loading.
• Charpy impact strength of unnotched specimens (kJ/m²) – evaluating the overall toughness of the material.
• Charpy impact testing at elevated or sub-zero temperatures – assessing low-temperature brittleness, typically down to -40 °C or lower for outdoor and cold-climate applications.
• Fracture behavior classification – complete break (C), hinged break (H), partial break (P), or non-break (N).
• Comparative evaluation of notch sensitivity between different notch radii and material grades.
• Instrumented Charpy impact testing – recording force–time or force–deflection curves to separate initiation and propagation energy (ISO 179-2).

Testing Methods

The general testing procedure in accordance with ISO 179-1, GB/T 1043.1, and ASTM D6110 is summarized below:

• Calibration verification: Confirm that the impact tester is level and that the pendulum energy loss due to friction and air resistance is within the tolerance specified by the standard.
• Hammer selection: Choose a pendulum capacity such that the energy absorbed by the specimen is between 10 % and 80 % (or 20 % and 80 % in some standards) of the available energy, ensuring measurement accuracy.
• Specimen measurement: Measure the width and thickness (or remaining ligament thickness for notched specimens) at the notch with a calibrated micrometer to the nearest 0.02 mm.
• Specimen placement: Position the specimen symmetrically on the anvils with the notch facing away from the pendulum strike point, centered within ±0.5 mm of the mid-span.
• Impact execution: Release the pendulum from the raised position and allow it to strike and fracture the specimen in a single swing.
• Energy recording: Record the absorbed energy after correcting for friction and windage losses.
• Calculation: Compute the impact strength as the corrected absorbed energy divided by the cross-sectional area, reported in kJ/m².
• Replication: Test a statistically sufficient number of specimens, typically a minimum of 10, and report the mean, standard deviation, and observed fracture types.

For instrumented Charpy testing per ISO 179-2, the pendulum is equipped with force and displacement sensors, enabling detailed analysis of the force–deflection curve, including peak force, brittle-to-ductile transition behavior, and the partition of total energy into crack initiation and crack propagation components.

Applications

Plastic Charpy impact testing is applied extensively across industries where impact performance under dynamic loading is critical:

• Automotive: Interior trim, bumpers, battery housings, and under-hood components requiring validated toughness across a wide temperature range.
• Pipes and fittings: Impact resistance testing of PVC, PE, PP, and other piping materials in accordance with product standards.
• Construction: Window profiles, door panels, roofing sheets, and insulation materials subjected to mechanical abuse and low-temperature service.
• Packaging: Containers, crates, and pallets where drop and impact durability are essential.
• Electrical and electronics: Housings, enclosures, and insulating parts evaluated alongside flame-retardancy and electrical safety requirements.
• Material development: Screening of new resin formulations, filler and reinforcement effects, recycling content influence, and long-term aging or weathering studies.

Manufacturers rely on Charpy impact data for incoming material inspection, lot release testing, failure analysis, compliance demonstration for regulatory and certification requirements, and optimization of processing parameters such as mold temperature and annealing conditions.

FAQ

What is the difference between Charpy and Izod impact testing?

The fundamental difference lies in the specimen support configuration. In the Charpy test, the specimen is laid horizontally on two anvils as a simply supported beam and struck at the mid-span. In the Izod test, the specimen is clamped vertically as a cantilever beam and struck above the clamp near the free end. The two methods yield different numerical values and are not directly interchangeable. Charpy testing is generally preferred for rigid plastics, whereas Izod testing is common for certain engineering resins and is referenced in standards such as ASTM D256 and ISO 180.

Why are notches machined into the specimens?

The notch acts as a stress concentrator that promotes brittle fracture and ensures reproducible crack initiation at a defined location. Testing notched specimens reveals the material's notch sensitivity, which is essential information because real plastic parts inevitably contain design features such as ribs, holes, weld lines, and sharp corners that behave as stress raisers under impact.

Which factors influence the test results?

Key influencing factors include test temperature, specimen conditioning, notch machining quality, notch radius accuracy, hammer energy selection, specimen orientation, material morphology and processing history, and the presence of moisture in hygroscopic polymers such as polyamide. Strict adherence to standardized specimen preparation and conditioning is therefore essential for comparable results.

What does a non-break or partial-break result mean?

A non-break (N) result indicates that the specimen did not break but only deformed under the available impact energy, which is a strong indication of ductile behavior at the test temperature. In such cases, the standard requires reporting the result as non-break rather than calculating an impact strength value, and testing with unnotched specimens or a different configuration may be recommended to characterize the material adequately.

Which standards should be specified when commissioning a test?

The applicable standard depends on the target market and product specification: ISO 179-1 and GB/T 1043.1 for international and Chinese requirements, and ASTM D6110 for North American requirements. When commissioning testing at accredited third-party laboratories, clients should specify the standard, notch type, specimen orientation, and test temperature to ensure that results fulfill the intended quality-control or certification purpose.