Impact Embrittlement Performance Testing: Brittleness Temperature Determination for Plastics and Ela

Impact embrittlement performance testing determines the brittleness temperature of plastics, rubbers, and elastomers by striking cooled specimens under controlled impact conditions. This article explains the test principle, applicable standards such as ISO 974, ASTM D746, ISO 812, and GB/T 5470, sample requirements, test procedures, and typical industrial applications of impact brittleness testing.

Technical Overview

Impact embrittlement performance testing, commonly referred to as the brittleness temperature test by impact, is a low-temperature mechanical test used to evaluate the cold-resistance behavior of polymeric materials. Many plastics, rubbers, and elastomers that are flexible and ductile at room temperature transition into a brittle state as the temperature decreases. When a cooled specimen is struck at a defined velocity and energy, the material may crack, fissure, or shatter instead of deforming, and this transition point characterizes the low-temperature service limit of the material.

The principal result of the test is the brittleness temperature, typically expressed as the temperature at which 50% of the tested specimens fail by impact, often designated as T50 or Tb. It is important to note that brittleness temperature is an empirical, comparative property rather than a fundamental material constant: it depends on specimen geometry, impact velocity, heat-transfer medium, and thermal history. Nevertheless, it remains one of the most widely used screening and quality-control tests for materials intended for cold-climate service, and it is routinely performed by accredited third-party laboratories for material qualification, incoming inspection, and product certification.

The test apparatus consists of a temperature-controlled bath filled with a heat-transfer medium (commonly silicone oil, ethanol or methanol cooled with dry ice, or liquid-nitrogen-cooled systems), a specimen holder, and a spring- or motor-driven striker with a defined edge radius. Specimens are conditioned at the target temperature for a specified period, typically three minutes, and are then struck within a controlled time interval after removal of the striker release. Failure is defined as any visible crack, fissure, split, or complete fracture of the specimen, inspected under adequate lighting with or without magnification as required by the standard.

Testing Samples

Rigid and Semi-Rigid Plastics

Compression-molded or injection-molded plaques of polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), polystyrene (PS), polymethyl methacrylate (PMMA), and engineering thermoplastics such as polyamide (PA), polycarbonate (PC), and polybutylene terephthalate (PBT) are machined or die-cut into standard specimens. Specimens taken from finished parts may also be evaluated, provided their dimensions fall within the tolerance band of the applicable standard.

Vulcanized and Thermoplastic Rubbers

Elastomeric compounds such as natural rubber (NR), styrene-butadiene rubber (SBR), ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), silicone rubber (VMQ), fluororubber (FKM), and thermoplastic elastomers (TPE/TPV) are tested as vulcanized sheets or cut from finished components such as seals, gaskets, and hoses.

Wire and Cable Materials

Insulation compounds, sheathing compounds, and complete cable constructions are evaluated for cold impact resistance, particularly for outdoor installations, buried cables, and low-temperature environments. Related cold-impact procedures for finished cables are specified in IEC 60811 series methods and UL-based requirements.

Films, Sheets, Coated Fabrics, and Foams

Thin polymeric films, geomembranes, tarpaulins, coated textiles, and flexible foam products may be assessed using specimen geometry and impact parameters adapted to their thickness and flexibility, following the relevant method clauses of the applicable standard.

Testing Items

The following test items are commonly performed under impact embrittlement performance testing:

• Brittleness temperature (T50) determination for plastics — the statistical temperature at which 50% of specimens fail by impact.
• Low-temperature brittleness point of vulcanized or thermoplastic rubber — the lowest temperature at which no specimen exhibits failure, or a statistically determined failure temperature depending on the selected method.
• Pass/fail verification at a specified temperature — a screening test in which a defined number of specimens are impacted at a contractually agreed temperature, commonly used for lot release.
• Comparative brittle-ductile transition assessment across formulations, batches, or processing conditions.
• Failure mode characterization — classification of specimens as cracked, fissured, or completely broken, with statistical treatment of failure rates versus temperature.

Testing Methods

ISO 974 — Plastics: Determination of Brittleness Temperature at Impact

Specimens, typically 6.35 mm in width with thickness close to 1.6 mm to 2.0 mm depending on product type, are clamped in the specimen holder and immersed in the heat-transfer medium. After conditioning at the set temperature, each specimen is struck by the striker traveling at a linear velocity of approximately 1.8 m/s to 2.1 m/s. At least ten specimens are tested at each of several temperatures spanning the failure range, and the temperature corresponding to a 50% failure probability is determined by statistical or graphical analysis. The result is reported as the brittleness temperature, T50, together with the 95% confidence interval.

ASTM D746 — Brittleness Temperature of Plastics and Elastomers by Impact

This method uses chip-shaped specimens, with Type I specimens commonly 6.35 mm wide and approximately 1.9 mm thick, conditioned for about three minutes at the test temperature before impact. A minimum of ten specimens is tested at each of at least four temperatures to bracket the transition region, and the brittleness temperature is calculated from the failure data using probit or graphical interpolation. The method is widely specified in North American supply agreements and material data sheets.

GB/T 5470 — Determination of Brittleness Temperature of Plastics by Impact

The Chinese national standard is technically aligned with the international impact embrittlement procedure and specifies comparable specimen geometry, conditioning requirements, impact velocity, and statistical evaluation of the 50% failure temperature. It is commonly referenced in domestic specifications and acceptance criteria.

ISO 812 and GB/T 15256 — Low-Temperature Brittleness of Rubber

For vulcanized and thermoplastic rubbers, strip specimens (commonly 25 mm to 40 mm long, approximately 6 mm wide, and 2 mm thick) are conditioned at the selected temperature and impacted at a velocity of approximately 2 m/s. Testing may be performed as a pass/fail verification at a specified temperature or as a stepped determination of the brittleness temperature, in which the temperature is progressively lowered until failures appear. The brittleness temperature is reported as the lowest temperature at which the specimens remain free of cracks and breaks, or as a statistically derived value in multi-specimen procedures.

ASTM D2137 — Brittleness Point of Flexible Polymers and Coated Fabrics

This method applies to flexible polymeric materials and coated fabrics, in which specimens are bent and impacted at low temperature and the brittleness point is identified as the lowest temperature at which no specimen cracks or breaks.

Key experimental parameters that must be controlled and reported in all methods include the heat-transfer medium, bath temperature uniformity (typically maintained within ±0.5 °C), conditioning time, impact velocity, striker geometry, specimen thickness, and the number of specimens tested. Because results are sensitive to these variables, interlaboratory comparison is only valid when test conditions are identical.

Applications

Impact embrittlement performance testing supports material selection, design verification, and regulatory compliance across many industries:

• Automotive — cold-climate qualification of weatherstrips, seals, hoses, gaskets, boots, bellows, battery module components, and exterior plastic trim subjected to winter service temperatures.
• Wire and cable — verification of insulation and sheathing compounds for outdoor, underground, and Arctic installations, and support of certifications based on IEC and UL requirements.
• Aerospace and cryogenics — evaluation of seals, gaskets, dampers, and non-metallic components exposed to high-altitude or cryogenic temperature conditions.
• Construction — low-temperature acceptance testing of window and door seals, waterproofing membranes, roofing materials, and plastic pipes and fittings.
• Consumer goods and appliances — assessment of housings, handles, gaskets, and flexible components for winter transport, storage, and use.
• Medical and packaging — screening of flexible packaging films and device components that must withstand cold-chain distribution and sterilization at reduced temperatures.

Manufacturers frequently combine brittleness temperature data with complementary low-temperature tests, such as torsional stiffness (Gehman), low-temperature retraction (TR test), or low-temperature flexibility bending tests, to build a complete picture of cold-weather performance.

FAQ

What is impact embrittlement performance testing?

It is a low-temperature test in which conditioned specimens of plastics, rubbers, or elastomers are struck by a standardized striker, and the temperature at which the material transitions from ductile to brittle failure is determined. The test measures the cold-impact resistance of the material under a defined rate of loading.

What is brittleness temperature (T50)?

Brittleness temperature is the temperature at which 50% of the specimens fail by visible cracking or breakage when impacted under specified conditions. A lower brittleness temperature indicates better resistance to cold embrittlement. For rubber test methods, the reported value may instead be the lowest temperature at which no failures occur.

Which standards govern the test?

ISO 974 and ASTM D746 cover plastics, ISO 812, ASTM D2137, and GB/T 15256 cover vulcanized and thermoplastic rubbers and flexible polymers, and GB/T 5470 is the Chinese national method for plastics. Selection depends on the material type, product specification, and target market.

How many specimens are required?

For statistical T50 determination, at least ten specimens are tested at each of four or more temperatures bracketing the transition region, typically requiring 40 to 100 specimens in total. Pass/fail screening at a single temperature generally requires a smaller defined batch, commonly four to ten specimens as specified by the method or specification.

How is failure defined?

A specimen is considered failed if any crack, fissure, split, hole, or complete fracture is visible on inspection after impact. Small surface marks or deformation without cracking do not constitute failure.

How long does the test take?

A single-temperature screening test can often be completed within a day, including bath stabilization and conditioning. A full multi-temperature brittleness temperature determination with statistical analysis typically requires two to five working days, depending on specimen availability and the number of temperature points needed to bracket the transition.

Can specimens be taken from finished products?

Yes. Specimens may be die-cut or machined from finished articles such as seals, hoses, cable jackets, and molded parts, provided the resulting dimensions meet the tolerances of the applicable standard and the sampling location is agreed with the client or specification.