Impact embrittlement performance testing determines the brittleness temperature of plastics, rubbers, and elastomers, providing essential data on how polymer materials behave under low-temperature impact loading. This guide explains the testing principles, applicable standards such as ASTM D746, ISO 974, and GB/T 5470, specimen requirements, and typical industrial applications. Whether you need routine quality control data or material qualification for cold-climate service, this article outlines what accredited third-party laboratories deliver.
Technical Overview
Impact embrittlement performance testing, commonly known as brittleness temperature or impact brittleness testing, is a standardized method for evaluating how polymeric materials respond to mechanical shock at low temperatures. As the ambient temperature decreases, thermoplastic and elastomeric materials lose molecular chain mobility, causing a transition from ductile, energy-absorbing behavior to brittle, fracture-prone behavior. This transition is critical for products that must survive cold-climate installation, transport, or service conditions.
In a typical test, strip-shaped specimens are immersed in a temperature-controlled liquid bath (for example, silicone oil, methanol, or ethanol cooled by dry ice or mechanical refrigeration). After a defined conditioning period, each specimen is struck once by a pivoting striker or hammer arm accelerated to a controlled velocity of approximately 2 m/s, in accordance with ASTM D746. A specimen is considered to have failed if it exhibits any visible crack, fissure, fracture, or complete breakage. By testing groups of specimens at a series of temperatures, technicians statistically determine the brittleness temperature, defined as the temperature at which 50% of the specimens fail, also called T50.
It should be emphasized that the brittleness temperature is not an intrinsic material constant. Results are influenced by specimen geometry, thickness, impact velocity, conditioning time, and thermal history. The method is therefore most valuable for quality control, batch-to-batch comparison, specification compliance, and ranking candidate materials for low-temperature service.
Testing Samples
Rigid and Semi-Rigid Thermoplastics
Common sample types include polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), ABS, polyoxymethylene (POM), polyamide (PA), polycarbonate (PC), and PMMA. Specimens are typically die-cut from compression-molded or injection-molded sheets, or machined from finished parts, into strips of approximately 20 mm in length, 2.5 mm in width, and about 1.9 mm in thickness, as specified in ASTM D746 and ISO 974.
Vulcanized Rubbers and Thermoplastic Elastomers
Testing is routinely performed on natural rubber (NR), SBR, NBR, EPDM, silicone rubber, fluoroelastomers (FKM), TPU, and other TPE compounds. Standard practice requires that specimens be taken from vulcanized sheets cured under production-representative conditions, since the state of cure strongly affects low-temperature flexibility.
Films, Sheets, and Geomembranes
Flexible packaging films, agricultural films, roofing membranes, and geomembranes can be evaluated either as stacked strips or using adapted procedures for flexible polymers, such as ASTM D2137.
Coated Fabrics and Polymer Coatings
Coated textile substrates and applied coatings are tested to verify that they do not crack or delaminate when flexed or impacted at low service temperatures.
Wire and Cable Compounds
Insulation and sheathing compounds intended for outdoor or low-temperature cable installations are validated using dedicated cold impact procedures described in the IEC 60811 series.
Testing Items
Accredited third-party laboratories typically offer the following test items under impact embrittlement performance testing programs:
- Determination of brittleness temperature (T50) for plastics and elastomers by impact, per ASTM D746, ISO 974, and GB/T 5470
- Determination of brittleness point for flexible polymers and coated fabrics, per ASTM D2137
- Low-temperature brittleness testing of vulcanized or thermoplastic rubber, per ISO 812 and GB/T 15256
- Pass/fail verification at a customer-specified temperature, for example, no failure at −40 °C
- Cold impact testing of cable insulation and sheaths, per IEC 60811-504 and related cable standards such as UL 2556
- Comparative studies of plasticizer content, filler loading, or polymer grade on low-temperature impact resistance
Testing Methods
ASTM D746 / ISO 974 / GB/T 5470 — Impact Brittleness of Plastics
The specimen strip is clamped as a cantilever in the specimen holder and immersed in the heat-transfer medium. After conditioning for a defined period, typically three minutes, the striking arm is released and impacts the specimen at a controlled velocity. Groups of specimens, commonly ten per temperature, are tested at several temperatures spaced at intervals of 2 to 10 °C. The failure fraction at each temperature is recorded, and the brittleness temperature T50 is obtained by graphical or statistical interpolation of the failure probability curve.
ISO 812 / GB/T 15256 — Low-Temperature Brittleness of Rubber (Multi-Specimen Method)
Multiple rubber specimens are conditioned simultaneously at the test temperature and impacted in rapid succession. Testing generally starts at a temperature where all specimens pass and proceeds downward, or from full failure upward, until the brittleness point bracketing the 50% failure condition is identified.
ASTM D2137 — Brittleness Point of Flexible Polymers and Coated Fabrics
This method applies to flexible materials that remain supple at room temperature. Specimens are struck after low-temperature immersion, and the brittleness point is reported as the lowest temperature at which no specimen exhibits cracks or fractures.
IEC 60811-504 — Cold Impact Test for Cables
A defined mass is dropped onto a cable sample conditioned at the specified low temperature, after which the insulation and sheath are examined for cracks. This method is widely used for qualifying cable products for outdoor and cold-region installations.
Data Reduction and Reporting
The final report normally includes the brittleness temperature or brittleness point, the test standard applied, specimen dimensions and preparation method, bath medium, conditioning time, impact velocity, number of specimens tested, and the failure counts at each temperature. For specification purposes, a simple pass/fail statement at the contractual temperature may also be issued.
Applications
Impact embrittlement performance testing supports material selection, product qualification, and incoming inspection across many industries:
- Automotive and electric vehicles: door and window seals, gaskets, hoses, battery module components, and exterior trim exposed to winter service temperatures
- Wire and cable: low-temperature qualification of insulation and jacketing compounds for outdoor, marine, and arctic installations
- Construction: window and curtain-wall gaskets, roofing membranes, expansion joints, and geomembranes
- Oil, gas, and chemical processing: O-rings, seals, and flexible connections in cold environments and cryogenic-adjacent service
- Consumer goods and appliances: outdoor furniture, sporting goods, footwear components, and refrigeration parts
- Aerospace, rail, and defense: elastomeric and polymeric components requiring verified low-temperature survivability
- Research and development: formulation optimization of plasticizers, elastomer blends, and impact modifiers
FAQ
What is the brittleness temperature?
The brittleness temperature is the temperature at which 50% of the tested specimens fail when impacted under specified conditions. Below this temperature, a material has a high probability of cracking or fracturing on impact, while above it the material generally retains ductile behavior.
How many specimens are required for a brittleness temperature determination?
A full statistical determination usually requires between 60 and 120 specimens, because at least eight to ten specimens must be tested at each of several temperatures. A simple pass/fail verification at a single temperature can be completed with far fewer specimens, often ten or fewer.
How does brittleness temperature differ from glass transition temperature (Tg)?
The glass transition temperature is a thermal property measured by techniques such as DSC or DMA, whereas the brittleness temperature is a mechanical, geometry-dependent result obtained under impact loading. The two values are related but not interchangeable, and brittleness temperature is generally more directly relevant to impact failure in service.
Which standard should I specify for my material?
ASTM D746, ISO 974, and GB/T 5470 are broadly equivalent methods for plastics and elastomers. ASTM D2137 is preferred for flexible polymers and coated fabrics, ISO 812 and GB/T 15256 for vulcanized rubber, and IEC 60811-504 for cable insulation and sheaths. Product standards or customer specifications often dictate the required method and acceptance temperature.
What are typical acceptance criteria?
Acceptance limits depend entirely on the application and specification. Common requirements include a brittleness temperature no higher than −25 °C for general outdoor compounds, −40 °C for automotive and cable applications in cold climates, and −55 °C or lower for arctic, aerospace, and defense uses.
How should specimens be prepared and shipped?
Specimens should be die-cut or machined from sheets or finished parts representing production conditions, free of voids, nicks, and surface defects. Conditioning prior to testing is performed in the laboratory; clients should submit sufficient material to allow for specimen preparation and, where required, retesting.
