Impact testing of plastic extruded products is a critical quality control and certification procedure that evaluates the toughness, ductility, and fracture resistance of pipes, profiles, sheets, and films under dynamic loading conditions. By following recognized standards from ISO, ASTM, EN, and GB, manufacturers can verify product durability, optimize material formulations, and satisfy regulatory requirements in construction, automotive, electrical, and packaging industries. This article provides a comprehensive technical guide covering sample types, test items, standardized methods, and practical applications of impact testing for extruded plastic products.
Technical Overview
Plastic extrusion is a continuous manufacturing process in which molten polymer is forced through a die to produce long, uniform cross-sectional products such as pipes, profiles, sheets, films, and tubing. Because these products are frequently exposed to mechanical shock during transportation, installation, and service—for example, a buried water pipe struck by an excavator, a window profile impacted by hail, or a protective conduit subjected to foot traffic—their impact resistance is one of the most important mechanical performance indicators.
Impact testing measures the ability of a material or finished product to absorb energy during rapid deformation and to resist brittle fracture. Compared with slow-speed tensile or flexural testing, impact testing reveals notch sensitivity, low-temperature brittleness, internal defects such as voids and poor fusion lines, and formulation weaknesses related to insufficient impact modifiers or excessive filler content. Common impact failure modes observed in extruded products include brittle fracture, ductile tearing, cracking at notches or weld lines, and whitening or stress-induced deformation.
Impact evaluation of extruded plastic products is typically performed using pendulum-type testers (Charpy and Izod methods), falling-weight (drop dart or drop tup) testers, and tensile impact testers, in accordance with standards published by ISO, ASTM, EN, GB, and UL. Testing may be conducted at room temperature or at reduced temperatures (for example 0 °C or −20 °C) to assess cold-weather performance. Manufacturers, certification bodies, and accredited third-party laboratories rely on these tests for product development, incoming and outgoing inspection, type approval, and failure analysis.
Testing Samples
Impact testing can be performed on specimens cut directly from finished extruded products or on standardized bars molded from the same compound for material qualification. Typical sample categories include:
Extruded Pipes and Tubing
Rigid and flexible pipes made from PVC-U, PVC-C, HDPE, MDPE, PP, PB, ABS, and PVDF, including pressure pipes for water and gas supply, drainage and sewer pipes, electrical conduit, corrugated pipes, and medical or automotive tubing. Ring segments or short pipe lengths are tested as whole components in falling-weight tests, while longitudinal strips machined from the pipe wall may be prepared as bars for pendulum impact testing.
Extruded Profiles
Solid and hollow profiles such as PVC window and door profiles, siding, fencing, railing, skirting, cable trunking and ducting, WPC (wood-plastic composite) decking, and custom industrial profiles. Specimens are cut from the profile wall or web in both the extrusion (machine) direction and the transverse direction, because extrusion can introduce molecular orientation that affects impact behavior.
Sheets, Panels, and Boards
Flat and corrugated sheets of PC, PMMA, PVC, PP, PE, PETG, and PS, including glazing sheets, signage panels, foam boards (PVC foam, PP honeycomb), and thermoforming stock. Discs or rectangular coupons are stamped or machined from the sheet for falling-weight and pendulum testing.
Films and Flexible Products
Thin extruded films and blown films of LDPE, LLDPE, HDPE, PP, and PA used in packaging and agriculture, tested primarily by free-falling dart methods to determine impact resistance and puncture behavior.
Testing Items
Typical impact-related test items for extruded plastic products include:
- Charpy impact strength, notched and unnotched (kJ/m²)
- Izod impact strength, notched and unnotched (kJ/m² or J/m)
- Falling-weight (drop dart / drop tup) impact resistance of pipes, sheets, and profiles, including pass/fail energy and statistical evaluation (H50, mean failure energy)
- Free-falling dart impact resistance of films (gram failure mass, method A or B)
- Tensile impact strength (kJ/m²)
- Low-temperature impact performance (for example at 0 °C, −20 °C, or −40 °C)
- Brittle-to-ductile transition assessment and failure mode classification (brittle, ductile, partial fracture, C-type break)
- Impact retention after thermal aging, UV/weathering exposure, or heat reversion
- Instrumented impact characterization providing force–deflection curves, peak force, and absorbed energy
Testing Methods
Charpy Impact Testing
Charpy testing is performed with a pendulum striker striking a horizontally supported bar specimen, which is fractured under three-point bending. The energy absorbed by the specimen is calculated from the difference between the initial and residual pendulum heights, and the impact strength is expressed as absorbed energy divided by the cross-sectional area (kJ/m²). Governing standards include ISO 179-1, ASTM D6110, and GB/T 1043. Specimens may be unnotched (1eU designation) or notched (1eA, 1A, 1B types) with a standardized notch radius machined into the extruded or milled bar. Charpy testing is widely used for rigid extruded products such as PVC profiles and pipe wall strips, and it clearly distinguishes brittle from ductile fracture behavior.
Izod Impact Testing
Izod testing uses a vertical cantilever specimen clamped at one end, and the pendulum strikes the free end above the notch. Principal standards include ISO 180, ASTM D256, and GB/T 1843. Results are reported in kJ/m² (ISO) or joules per meter / foot-pounds per inch (ASTM). Izod testing is particularly valuable for comparing the notch sensitivity of different compounds, evaluating the effectiveness of impact modifiers such as CPE, acrylic, or MBS in rigid PVC, and quality control of engineering plastics used in extruded technical parts.
Falling-Weight (Drop) Impact Testing
Falling-weight methods evaluate the finished product geometry rather than a machined bar, making them especially representative of real service conditions. A mass with a hemispherical or specified tup is dropped from a controlled height onto the sample, and the result is recorded as pass/fail, failure energy, or impact marks and cracking. For thermoplastic pipes, ISO 3127, ASTM D2444, and GB/T 14152 specify ring segments tested with a striker of defined radius; a staircase (probit) statistical procedure determines the height or mass at which 50 percent of specimens fail (H50). For rigid plastic sheets, ASTM D5628 and GB/T 11548 apply, while GB/T 6112 and related methods cover tubular products. This method directly detects the "impact brittleness" defects that occasionally occur in poorly plasticized or contaminated extruded pipe and profile batches.
Film Dart Impact Testing
For extruded and blown films, free-falling dart methods per ASTM D1709 (method A and B), ISO 7765-1, and GB/T 9639 measure the mass of a dropped dart that causes 50 percent specimen failure. This test reflects film toughness, seal integrity, and resistance to puncture during handling and transport, and it is sensitive to resin grade, draw-down ratio, and gauge uniformity.
Tensile Impact Testing
Tensile impact testing per ISO 8256 and ASTM D1822 measures the energy absorbed when a small dumbbell or rectangular specimen is ruptured by a swinging pendulum in tension. It is applied to materials that are too flexible, too thin, or too brittle to yield meaningful results in bending-type tests, and it complements Charpy data for thin extruded sheet and film materials.
Specimen Conditioning and Test Conditions
All impact tests require standardized conditioning prior to testing, typically 23 °C ± 2 °C and 50 % ± 10 % relative humidity per ISO 291 or ASTM D618, unless a reduced test temperature is specified. Notches must be machined with sharp, standardized cutters to avoid introducing artificial stress raisers. The number of specimens per condition is defined by the relevant standard—commonly at least 10 specimens for pendulum tests and 20 to 30 for statistical staircase evaluation—and test reports must record specimen type, notch geometry, test temperature, absorbed energy values, failure mode classification, and the standard deviation.
Applications
Impact testing of extruded plastic products supports a wide range of industrial needs:
- Building and construction: type testing and factory production control of PVC-U water and drainage pipes, window and door profiles, roofing sheets, and cable trunking against EN, ISO, GB, and UL requirements
- Water and gas infrastructure: qualification of PE and PVC pressure pipes, verification of impact toughness before burial, and assessment of damage tolerance during pipeline installation
- Electrical and cable management: certification of conduit, ducting, and cable protection systems requiring mechanical strength and impact classification
- Automotive and transportation: validation of extruded trim, sill protectors, battery cooling lines, and protective sleeving under low-temperature impact conditions
- Packaging: quality control of films for puncture resistance and drop performance during distribution
- Research and development: screening of impact modifiers, fillers, and recyclate content; optimization of extrusion temperature, cooling, and haul-off speed to minimize residual stress and orientation
- Failure analysis and dispute resolution: laboratory determination of whether field cracking originated from material brittleness, processing defects, or external mechanical abuse
FAQ
Why is impact testing especially important for extruded products?
Extruded products are often installed in demanding environments—buried pipelines, exterior building components, cable routes—where they experience sudden impacts from tools, debris, foot traffic, or handling. Impact testing detects brittleness caused by poor formulation, contamination, insufficient gelation, excessive filler, or unfavorable process conditions before products reach the field, thereby preventing costly failures and safety risks.
What is the difference between Charpy and Izod impact tests?
In Charpy testing the specimen lies horizontally and is supported at both ends, fracturing in three-point bending; in Izod testing the specimen stands vertically, clamped as a cantilever, and is struck above the notch. Charpy suits comparative material screening and is common for pipe and profile wall materials, while Izod is frequently specified for engineering plastics and notch-sensitivity comparisons. The two methods are not interchangeable, and results must always be cited with the method and standard used.
Why are both notched and unnotched results reported?
Unnotched impact strength reflects the overall toughness of the product, whereas notched impact strength reveals notch sensitivity—how sharply the material's resistance drops when a stress concentrator such as a scratch or groove exists. A material can show high unnotched values yet fail badly in the notched test, which indicates a risk of brittle crack propagation in service. Reporting both provides a complete picture of ductility and crack resistance.
Why test at low temperatures?
Many thermoplastics, particularly rigid PVC and polyolefins, undergo a brittle-to-ductile transition as temperature decreases. Products installed outdoors or in cold climates must retain sufficient toughness in winter. Testing at 0 °C, −20 °C, or lower confirms that the impact modifier system and extrusion quality are adequate for the intended service environment, as required by many EN, GB, and ISO product standards.
How are falling-weight pipe impact results evaluated statistically?
Because individual specimens show pass/fail scatter, standards such as ISO 3127 and GB/T 14152 use a staircase procedure in which the drop height or mass is increased after a pass and decreased after a failure. From the resulting sequence, the 50 percent failure height (H50) or impact strength is computed statistically, giving a reproducible measure of the product's true impact capability rather than a single subjective observation.
Can impact testing be performed on complete products instead of cut specimens?
Yes. Falling-weight and drop-tup methods are designed to test whole pipe rings, profile sections, sheet panels, and finished assemblies in their actual geometry. Testing the finished product captures the influence of wall thickness distribution, surface condition, internal stress, and weld or fusion lines, which specimen-level pendulum tests may not reveal. Many certification schemes therefore combine both approaches—material-level pendulum data with component-level drop impact verification—performed by the manufacturer or by accredited third-party laboratories.