Impact Performance Testing of Rigid Plastic Sheets: Standards, Methods, and Technical Evaluation

Glass-fiber or other reinforced composite panels used for roofing and wall systems are evaluated with falling weight impact to simulate hail and wind-borne debris, complementing static mechanical tests.

Specimen Geometry and Direction

Pendulum test specimens are typically cut directly from the sheet, commonly 80 mm × 10 mm for ISO Charpy and Izod methods, with the as-received sheet thickness retained for product qualification. Specimens are cut in both the machine (extrusion) direction and the transverse direction whenever anisotropy from processing orientation is suspected, since impact strength can differ significantly between directions.

Testing Items

Depending on the product standard, end-use requirement, and failure mode of interest, the following impact performance items are commonly evaluated for rigid plastic sheets:

• Charpy impact strength, unnotched and notched (kJ/m²)
• Izod impact strength, unnotched and notched (kJ/m² per ISO, ft·lb/in or J/m per ASTM)
• Falling dart / falling weight impact resistance of finished sheet (mean failure energy or pass/fail at specified energy)
• F50 failure energy—the impact energy at which 50% of specimens fail—determined by the staircase method
• Instrumented puncture properties: peak force, displacement at peak force, energy to peak force, and total absorbed energy
• Notch sensitivity, expressed as the ratio of unnotched to notched impact strength
• Directional anisotropy (machine direction versus transverse direction)
• Low-temperature impact strength after conditioning at specified subzero temperatures
• Failure mode classification: brittle fracture, ductile tearing, hinging, or part-through cracking

Testing Methods

Charpy Impact Testing (ISO 179-1 / ASTM D6110 / GB/T 1043.1 / JIS K 7110)

In the Charpy method, a rectangular specimen is mounted horizontally on two anvils with a support span of 62 mm for the standard 80 mm × 10 mm × 4 mm specimen. A pendulum hammer strikes the specimen at mid-span, either directly opposite a machined notch (edgewise) or across the flat face (flatwise), and the absorbed energy is recorded. The impact strength is calculated as absorbed energy divided by the cross-sectional area under the notch or by the specimen width. At least 10 specimens are normally tested, and the pendulum capacity is selected so that the absorbed energy falls between 10% and 80% of the scale range.

Izod Impact Testing (ISO 180 / ASTM D256 / GB/T 1843 / JIS K 7111)

In the Izod method, the specimen is clamped vertically as a cantilever beam and struck by the pendulum on the notched face at a fixed distance above the clamp. ISO methods use the 80 mm × 10 mm × 4 mm specimen and report results in kJ/m², while ASTM methods traditionally use 63.5 mm × 12.7 mm bar specimens and report energy per unit width (J/m or ft·lb/in). Notch geometry (notch tip radius A = 0.25 mm, B = 1.0 mm, C = 0.10 mm in ISO practice) must be strictly controlled because notch radius strongly affects the measured value.

Falling Dart and Falling Weight Impact Testing (GB/T 14153 / ISO 7765-1 / ASTM D5628 / GB/T 9639.1)

Falling mass methods evaluate the finished sheet rather than a machined bar, making them highly representative of real-world service. A dart with a hemispherical head is dropped vertically onto a clamped or supported sheet specimen, and failure is detected visually or electronically. Two evaluation approaches are used: the pass/fail approach at a specified energy for product classification, and the statistical approach (staircase or probit methods) to determine the 50% failure energy. GB/T 14153 specifically addresses rigid plastic sheets, while ISO 7765-1 and GB/T 9639.1 apply to thinner film and sheeting materials. Failure modes—brittle cracking, ductile puncture, or hinging—must be recorded because they carry different engineering significance.

Instrumented Puncture Impact Testing (ISO 6603-2 / ASTM D3763)

Instrumented drop tower testing uses a force transducer behind a hemispherical striker (typically 20 mm diameter per ISO 6603-2) driven through a clamped sheet at high velocity, commonly 4.4 m/s. The force–displacement curve provides a complete energy absorption profile, distinguishing between brittle materials that fail at low force and deflection and ductile materials that absorb energy through membrane stretching. This method is particularly valuable for comparing glazing materials and for detecting subtle embrittlement caused by processing, weathering, or low temperature.

Specimen Conditioning and Test Environment

Unless otherwise specified, specimens are conditioned per ISO 291 or ASTM D618 at 23 ± 2 °C and 50 ± 10% relative humidity, typically for a minimum of 40 hours, and tested in the same atmosphere. For low-temperature qualification, specimens are conditioned in an environmental chamber at the specified temperature (for example, −20 °C or −40 °C) and tested within a defined short time window after removal to prevent warming.

Data Evaluation and Failure Classification

Reported results include individual values, the arithmetic mean, and standard deviation, together with the failure designation: complete brittle break, partial break, hinge break, or ductile puncture. When mixed failure populations occur, additional specimens are tested so that each failure mode can be reported separately. Acceptance limits are defined by the applicable product standard or by agreement between manufacturer and purchaser; identical limits must not be transferred between test methods because geometry, strain rate, and stress states differ.

Applications

Impact performance verification of rigid plastic sheets supports design, certification, and quality assurance across many industries:

• Building and construction: qualification of corrugated roofing, wall cladding, and glazing sheets against hail impact, site handling, and safety requirements
• Transportation: impact resistance of bus, rail, and marine glazing, interior trim panels, and exterior body panels subject to stone-chip and impact loading
• Safety glazing and machine guarding: verification of polycarbonate guards and viewing windows on machinery and equipment
• Signage and display: durability assessment of acrylic and polycarbonate boards used outdoors or in public spaces exposed to vandalism
• Appliances and electronics: incoming inspection and grade comparison of ABS, HIPS, and PVC panel materials
• Chemical and industrial equipment: qualification of FRP, PP, and PVC linings and covers for fabrication and service impact exposure
• Research and development: evaluation of formulation changes, recycling content effects, processing window optimization, and long-term weathering or embrittlement studies
• Regulatory compliance and market access: generation of test reports by accredited third-party laboratories for product certification, customs inspection, and buyer verification

FAQ

What is the difference between Charpy and Izod impact tests?

Charpy testing supports the specimen horizontally on two anvils and strikes it at mid-span, while Izod testing clamps the specimen vertically as a cantilever and strikes it above the clamp. The two methods use different stress distributions and specimen fixturing, so results are not interchangeable even on identical materials.

Why are notched specimens used in pendulum impact testing?

The notch concentrates stress and accelerates crack initiation, allowing brittle tendencies to be detected that would remain hidden in unnotched ductile failure. The ratio of unnotched to notched impact strength quantifies notch sensitivity, a key selection criterion for sheets used in mechanically demanding environments.

How many specimens are required for a valid test?

Pendulum tests normally require at least 10 specimens per condition and direction, while falling dart staircase methods typically require 20 or more drops to establish the F50 energy. Additional specimens are tested when mixed failure modes are observed so that each mode can be evaluated separately.

Can results from different impact methods be compared directly?

No. Charpy, Izod, falling weight, and instrumented puncture methods differ in geometry, clamping, striker velocity, and failure criterion. Numeric conversion between methods is invalid; comparisons must always be made within a single method, specimen geometry, and test condition.

How does temperature affect the impact performance of rigid plastic sheets?

Most thermoplastics become measurably more brittle as temperature decreases, and some undergo a ductile-to-brittle transition well above room temperature. For outdoor, refrigeration, or cold-climate service, low-temperature impact testing is strongly recommended as part of the qualification program.

Which standard should be selected for certification purposes?

The choice depends on the target market and product specification: ISO or EN methods are commonly referenced in Europe and internationally, ASTM methods dominate in North America, and GB methods apply to Chinese regulatory and procurement requirements. Manufacturers and buyers can confirm the applicable method and acceptance limits with accredited third-party laboratories before submitting samples.