Plastic sheet impact strength determination is a fundamental mechanical test that quantifies how well plastic sheets and plates withstand sudden shock loads, brittle fracture, and dynamic impact during processing and real-world service. This guide covers the principal test methods, including Charpy, Izod, instrumented puncture, and falling dart impact, together with the relevant ISO, ASTM, GB, and JIS standards, specimen requirements, testing procedures, and result interpretation. It is intended for manufacturers, quality engineers, and product designers seeking reliable impact performance data from accredited third-party laboratories.
Technical Overview
Impact strength determination measures the energy absorbed by a plastic sheet or plate when it fractures or deforms under a rapidly applied load. Because failures under impact often occur at stress levels far below static design values, this test is one of the most widely used indicators of material toughness, ductility, and notch sensitivity for plastic sheet products.
Sheet and plate materials differ from injection-molded test bars in several important ways. Extrusion, calendering, and pressing introduce molecular orientation, residual stresses, and skin-core structures, so impact behavior can differ significantly between the machine direction (MD) and the transverse direction (TD). A complete evaluation therefore requires specimens cut in both orientations, tested at the as-supplied thickness.
Results are typically expressed as energy absorbed per unit cross-sectional area (kJ/m², used in the ISO system) or per unit specimen width (J/m or ft-lb/in, used in ASTM methods). The principal standards governing plastic sheet impact testing include:
- ISO 179-1 and GB/T 1043.1 for Charpy impact strength determination
- ISO 180 and GB/T 1843 for Izod impact strength determination
- ISO 6603-2 for instrumented puncture impact of rigid plastic sheet
- ISO 7765-1 and GB/T 9639.1 for falling dart impact of thin plastic sheeting
- ISO 8256 and GB/T 13525 for tensile-impact strength
- ASTM D256 (Izod), ASTM D6110 (Charpy), ASTM D3763 (high-speed puncture), ASTM D5420 (Gardner falling dart), and ASTM D1822 (tensile impact)
- JIS K 7110 and JIS K 7111 series for Izod and Charpy impact of plastics
- UL 746A, which references mechanical impact testing in the qualification of polymeric materials for electrical applications
Unless otherwise specified, specimens are conditioned in a standard laboratory atmosphere of 23 °C ± 2 °C and 50 % ± 10 % relative humidity in accordance with ISO 291 or ASTM D618, typically for a minimum of 40 hours before testing.
Testing Samples
Rigid Thermoplastic Sheets
Common sample types include unplasticized PVC (PVC-U), high-impact polystyrene (HIPS), ABS, polypropylene (PP), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMW-PE), and PET or PETG sheets. These materials are frequently tested in both notched and unnotched conditions to characterize notch sensitivity.
Engineering and Optical Sheets
Polycarbonate (PC) and polymethyl methacrylate (PMMA) sheets used for glazing, roofing, and safety applications are routinely evaluated for impact resistance, often at reduced temperatures to confirm cold-weather performance. Semi-crystalline engineering sheets such as polyamide (PA) may also be tested in the dry-as-molded and conditioned states.
Reinforced, Laminated, and Composite Sheets
Fiberglass-reinforced plastic (FRP) panels, SMC and GMT sheets, wood-plastic composites (WPC), aluminum-plastic composite panels, and multilayer laminated sheets can be assessed using pendulum or instrumented puncture methods, provided the failure mode is properly documented.
Specimen Preparation
For Charpy and Izod testing, specimens of nominally 80 mm × 10 mm are cut from the sheet, normally tested at the supplied thickness. Notches, where required, are machined with a fresh milling cutter to produce a type A notch with a radius of 0.25 mm and a residual depth beneath the notch of 8 mm for Charpy or 8 mm equivalent geometry for Izod. For instrumented puncture testing per ISO 6603-2, 60 mm × 60 mm square specimens are clamped over a 40 mm aperture. Edges must be smooth and free of cracks, and at least five specimens per direction and condition are recommended, with ten preferred where scatter is high.
Testing Items
Typical impact determination items for plastic sheets and plates include:
- Charpy impact strength, notched and unnotched (kJ/m²)
- Izod impact strength, notched (J/m or kJ/m²)
- Instrumented puncture impact: peak force, deflection at peak force, energy to peak force, and total puncture energy
- Falling dart impact: mean failure energy at 50 % probability by the staircase method, or pass/fail verification at a specified energy
- Tensile-impact strength (kJ/m²) for thin or highly ductile materials
- Impact strength after thermal aging, UV exposure, or immersion conditioning
- Low-temperature impact performance at specified sub-zero conditions
Testing Methods
Charpy Impact Test
Charpy testing per ISO 179-1, GB/T 1043.1, ASTM D6110, and the JIS K 7111 series is performed with a pendulum impact tester. The specimen rests freely on two anvils with a standardized support span of 62.5 mm for standard geometry, and the pendulum striker strikes the specimen opposite the notch in a three-point bending configuration. Tests can be conducted edgewise or flatwise depending on sheet thickness. The absorbed energy, corrected for friction and windage losses, is divided by the cross-sectional area beneath the notch to yield impact strength in kJ/m².
Izod Impact Test
Izod testing per ISO 180, GB/T 1843, ASTM D256, and the JIS K 7110 series uses a cantilever specimen clamped vertically at one end and struck on the notched face above the clamp. ASTM D256 reports results in J/m (or ft-lb/in) based on specimen width, while ISO 180 reports in kJ/m² based on the cross-section beneath the notch. Because specimen geometry and clamping differ between the systems, direct numerical comparison is not valid.
Instrumented Puncture Impact Test
ISO 6603-2 and the high-speed method of ASTM D3763 are the preferred methods for flat plastic sheet between roughly 1 mm and 4 mm. A polished hemispherical striker of 20 mm diameter penetrates the clamped specimen at a standardized speed of 4.4 m/s (with 1.0 m/s and 0.1 m/s available for rate studies). Load-cell instrumentation records a complete force-deflection curve, allowing determination of peak force, deflection at peak force, energy absorbed to peak force, and total failure energy. The curve shape clearly distinguishes ductile, semi-ductile, and brittle failure behavior, making this method especially valuable for design and specification work.
Falling Dart and Gardner Impact Test
For thin plastic sheeting, ISO 7765-1 and GB/T 9639.1 apply the free-falling dart method with the staircase technique to determine the impact energy at which 50 % of specimens fail. For rigid flat specimens, ASTM D5420 (Gardner-type falling dart) and ASTM D5628 are used either statistically or as a simple pass/fail verification at a specified mass and drop height. Product standards and buyer specifications frequently define minimum dart masses or energies that the sheet must withstand without cracking or piercing.
Tensile-Impact Test
When sheets are too thin or too ductile for valid pendulum bending tests, ISO 8256, GB/T 13525, and ASTM D1822 determine tensile-impact strength. A small dumbbell or rectangular specimen is fractured by a pendulum-mounted cross-member, and the corrected absorbed energy is divided by the initial cross-sectional area.
Procedure Control and Data Treatment
The pendulum capacity must be selected so that the absorbed energy falls within the valid working range, typically 10 % to 80 % of the nominal hammer energy under the ISO system. Each fracture is classified by break type: complete break, hinged break, partial break, or non-break. Non-breaks cannot be averaged as numerical values and must be reported separately. The report should include the standard used, specimen dimensions and thickness, notch type and direction of strike, conditioning, individual values, arithmetic mean, standard deviation, and break classification. Tests at multiple temperatures allow the ductile-to-brittle transition to be located, which is critical for outdoor and cold-chain applications.
Applications
Impact strength data for plastic sheets and plates support a broad range of industries and regulatory requirements:
- Construction and architecture: polycarbonate and PMMA roofing, glazing, canopies, and safety windows requiring verified impact performance
- Transportation: rail and bus interior panels, glazing, luggage racks, and cargo liners subject to impact and vandalism loads
- Machine guarding and safety enclosures where fragment retention after impact is essential
- Signage, displays, lighting diffusers, and sanitary wall cladding
- Electrical equipment housings and enclosures, where UL 746A material qualification programs reference impact behavior
- Packaging and material handling: PP corrugated sheets, trays, and pallet liners
- Cold storage, refrigeration, and outdoor products requiring verified low-temperature toughness
- Quality control for incoming sheet lots, supplier qualification, and failure analysis of cracked or broken panels
FAQ
What is the difference between Charpy and Izod impact testing?
Charpy tests a horizontally supported specimen struck at mid-span in three-point bending, while Izod tests a vertically clamped cantilever specimen struck above the clamp. They also differ in units and notch geometry, so results from the two methods are not interchangeable.
Why are notched specimens used?
The notch creates a controlled stress concentration that promotes brittle fracture and reveals notch sensitivity. Notched and unnotched results together show whether a material loses toughness when scratched or damaged in service.
Which method is best for thin plastic sheets?
For flat sheet between about 1 mm and 4 mm, instrumented puncture impact per ISO 6603-2 is generally preferred because it produces a full force-deflection record. Thin film-like sheeting is usually tested by the falling dart methods of ISO 7765-1 or GB/T 9639.1.
How many specimens are required?
A minimum of five specimens per direction and condition is typical, with ten recommended when scatter is high or when a statistical failure energy is required by the staircase method.
How does temperature affect the results?
Most thermoplastics become markedly more brittle at low temperature. Testing at 23 °C plus one or more sub-zero temperatures identifies the ductile-to-brittle transition relevant to outdoor, refrigerated, and transportation applications.
Can J/m be converted to kJ/m²?
There is no exact universal conversion because ASTM and ISO methods use different specimen dimensions, clamping, and notch details. For a comparable 10 mm wide specimen, dividing a J/m value by ten gives only a rough approximation in kJ/m² and should never replace testing to the specified standard.
Is impact testing destructive?
Yes. Every impact test fractures or permanently deforms the specimen, so sampling plans should account for material consumption and directional variability.
How should a testing provider be selected?
Choose accredited third-party laboratories holding ISO/IEC 17025 accreditation for the specific impact standards required, with documented traceability of impact machines, verified pendulum energy calibration, controlled conditioning facilities, and clear reporting of individual values, break types, and measurement uncertainty.