ISO 8256:2023

Overview

ISO 8256:2023 - "Plastics - Determination of tensile‑impact strength" defines two standardized test methods (Method A and Method B) for measuring the tensile‑impact strength of plastics under defined high strain‑rate conditions. The procedures are designed primarily for materials that are too thin or too flexible for conventional impact tests (ISO 179 Charpy series or ISO 180 Izod), and cover testing of moulding compounds as well as specimens cut from finished or semi‑finished products.

Key topics and technical requirements

• Two methods (A and B): Both measure energy absorbed during a single pendulum impact; the specimen is horizontal at fracture. Method A fixes the specimen relative to the frame (crosshead stationary), while Method B carries the specimen with the pendulum (crosshead moves).
• Energy corrections: Test results require corrections for crosshead motion-Method A uses a “toss” correction, Method B a “bounce” correction-to calculate the corrected tensile‑impact energy.
• Specimens and dimensions: Five specimen types are specified; preferred types differ by method (Method A: types 1 & 4; Method B: types 2 & 4). Specimens are tested at original thickness up to 4 mm. Preferred thicknesses: type 1 = 4 mm ± 0.2 mm; type 4 = 3 mm ± 0.2 mm. Above 4 mm, ISO 179 or ISO 180 is recommended.
• Apparatus and verification: Pendulum, striker, crosshead (specified masses), clamps/jaws and precision micrometers are required. Machine verification is referenced to ISO 13802.
• Scope limitations: Results can vary with specimen geometry, preparation, moulding conditions and between methods A and B. ISO 8256 is not intended as a source for component design calculations but is suitable for material characterization, production control and quality control.
• Reporting and statistics: The standard prescribes calculation of tensile‑impact strength (energy per original cross‑section) for notched and unnotched specimens, statistical treatment and significant figures.

Practical applications and users

Who uses ISO 8256:

• Materials engineers assessing brittleness/toughness of thin or flexible plastics
• Quality and production control teams monitoring batch consistency of moulding compounds, sheets, laminates or extruded products
• Test laboratories performing standardized impact characterization for material comparison, specification or supplier qualification
• R&D teams evaluating effects of additives, processing or temperature on high‑rate tensile behaviour

Practical value:

• Enables reproducible comparison of tensile impact behaviour for thin/flexible plastics
• Helps detect changes in toughness due to formulations or processing without relying on design‑level calculations

Related standards

• ISO 179 (Charpy impact properties)
• ISO 180 (Izod impact strength)
• ISO 472 (Plastics vocabulary)
• ISO 13802 (Verification of pendulum impact‑testing machines)
• ISO 291 (Conditioning and testing atmospheres)
• ISO 294 / ISO 293 / ISO 295 (Specimen preparation by injection/ compression moulding)

Keywords: ISO 8256, tensile-impact strength, plastics testing, impact testing, method A, method B, pendulum impact, specimen thickness, quality control, material toughness.