Plastic Impact Resistance Testing: Standards, Methods, and Technical Requirements

Plastic impact resistance testing evaluates a material's ability to absorb energy during sudden, high-speed loading, providing critical data on toughness and brittleness for material selection and quality control. This guide covers the principal test methods—including Izod, Charpy, and instrumented falling-weight impact—along with applicable ISO, ASTM, and GB standards, specimen requirements, and typical industrial applications. Whether you are qualifying engineering polymers or validating finished components, understanding these test protocols is essential for ensuring product reliability and safety.

Technical Overview

Impact resistance is one of the most important mechanical properties of plastic materials, describing their capacity to withstand sudden shocks, drops, collisions, and dynamic loads without fracturing. Unlike slow-strain-rate tests such as tensile or flexural testing, impact testing applies a rapid load over milliseconds, which reveals failure behaviors—particularly brittleness—that static tests often fail to detect.

Plastics are viscoelastic materials whose response depends strongly on strain rate, temperature, and stress concentration. A polymer that behaves in a ductile manner under slow loading may fracture in a brittle manner under impact, especially at low temperatures or in the presence of notches, sharp corners, weld lines, or internal defects. Impact testing therefore serves two purposes: characterizing intrinsic material toughness and assessing the notch sensitivity and defect tolerance of molded parts.

Test results are typically expressed as absorbed impact energy per unit cross-sectional area (kJ/m²) for pendulum methods, or as force–displacement curves with peak force and total absorbed energy for instrumented methods. Accredited third-party laboratories routinely perform these tests in accordance with ISO, ASTM, EN, JIS, and GB standards to support material qualification, incoming inspection, and failure analysis.

Testing Samples

Standard Injection-Molded Bars

The most common specimens are rectangular bars of 80 mm × 10 mm × 4 mm, produced by injection molding in accordance with ISO 179-1, ISO 180, and the corresponding GB standards (GB/T 1043 and GB/T 1843). ASTM D256 also permits bars of 63.5 mm × 12.7 mm × 3.2 mm up to 12.7 mm thickness. Specimens may be tested unnotched or notched depending on the required test configuration.

Notched Specimens

Notches are machined into specimens to create a controlled stress concentration. The standard A-type notch has a radius of 0.25 mm and a remaining width of 8 mm; B-type (1.0 mm radius) and C-type (0.10 mm radius) notches are used for specific evaluations. Notched impact strength quantifies a material's resistance to crack propagation from a sharp defect, which is often the limiting factor in real-world service.

Plates, Sheets, and Finished Parts

For falling-weight (dart) and instrumented puncture tests, flat plaques or disks—commonly 60 mm to 100 mm in diameter and 1 mm to 4 mm thick—are clamped and struck by a striker with a hemispherical head. Finished components such as housings, covers, films, and packaging containers may also be tested directly in end-use geometry, often with instrumented systems that record the full force–deflection response.

Specimen Conditioning

Specimens must be conditioned before testing, typically at 23 °C and 50% relative humidity for a minimum of 16 hours, unless otherwise specified. For materials with pronounced temperature sensitivity, additional conditioning at −40 °C, −30 °C, 0 °C, or elevated temperatures may be performed to map the ductile-to-brittle transition. Specimens should be free of voids, sink marks, flash, and machining damage, and at least five (preferably ten) replicate specimens per condition are recommended due to the statistical scatter typical of impact data.

Testing Items

Core test parameters measured in plastic impact testing programs include:

• Charpy impact strength (notched and unnotched), kJ/m²
• Izod impact strength (notched and unnotched), kJ/m² or J/m (ft·lb/in)
• Instrumented falling-weight puncture impact: peak force, energy to peak force, and total absorbed energy
• Free-falling dart impact resistance (F50 failure energy or pass/fail mass), for films and thin sheets
• Tensile impact strength for materials too flexible or thin for pendulum bending tests
• Temperature-dependent impact strength across a defined service range
• Failure mode classification: complete break, hinge break, partial break, or non-break

Testing Methods

Charpy Impact Test (ISO 179-1, ASTM D6110, GB/T 1043)

In the Charpy configuration, the specimen is supported horizontally on two anvils and struck by a pendulum hammer at the middle of the span, opposite the notch. The pendulum is released from a fixed height; the energy absorbed in breaking the specimen is calculated from the difference between the initial and final pendulum heights. The method is suited to rigid thermoplastics, thermosets, and fiber-reinforced compounds, and edgewise (1eU, 1eA), flatwise (1fU), and unnotched configurations are available.

Izod Impact Test (ISO 180, ASTM D256, GB/T 1843)

In the Izod configuration, the specimen is clamped vertically as a cantilever beam and struck by the pendulum above the clamp on the notched side. ASTM D256 is the dominant specification in North America and reports results in J/m or ft·lb/in of notch depth, while ISO 180 reports kJ/m². Careful notch preparation is critical, since notch geometry and cutting quality strongly influence results. Modified procedures address plastics that do not break completely in the standard test.

Instrumented Falling-Weight (Puncture) Impact Test (ISO 6603-2, ASTM D3763)

A striker with a 10 mm or 20 mm hemispherical head is driven vertically into a clamped plate at speeds typically between 1 m/s and 4.4 m/s. Load cells and displacement sensors record the complete force–displacement curve, distinguishing brittle failure (sharp force drop) from ductile failure (gradual load decay after yielding). This method is particularly valuable for automotive interior and exterior components, multi-layer structures, and parts with complex failure sequences.

Free-Falling Dart Test (ISO 7765-1, ASTM D1709)

Designed for plastic films and thin sheets, this method drops a rounded dart from a fixed height onto a clamped specimen. Using the staircase (bracketing) approach, the mass at which 50% of specimens fail (F50) is determined. It is widely applied to packaging films, liners, and geomembranes.

Tensile Impact Test (ISO 8256, ASTM D1822)

For materials that are too thin or too flexible for bending-impact methods, a small dumbbell specimen is ruptured in tension by a swinging pendulum. The absorbed energy per cross-sectional area is reported as tensile impact strength, useful for thin-walled moldings and films.

Applications

Plastic impact resistance testing is applied across virtually every industry that uses polymeric materials:

• Automotive: bumpers, fascias, interior trim, instrument panels, battery housings, and under-hood components requiring validation at subzero temperatures
• Packaging: blow-molded bottles, caps, transport containers, and protective films evaluated by falling-dart methods
• Consumer electronics: housings and enclosures validated against drop and impact loads
• Construction: PVC-U and PE pipes and fittings, window profiles, roofing sheets, and glazing subjected to impact durability requirements
• Household appliances and power tools: external covers, switches, and structural brackets
• Medical devices: instrument handles, IV components, and sterilization-resistant housings
• Material development: ranking of new resins, modified compounds, recycled-content blends, and verification of the toughening effect of elastomers or fillers

FAQ

What is the difference between Izod and Charpy impact tests?

The two methods use the same pendulum principle but different specimen support. In the Charpy test the specimen lies horizontally on two supports and is struck at mid-span; in the Izod test the specimen is clamped vertically as a cantilever and struck near the free end. Results are not interchangeable, so the method must always be specified when reporting data.

Why are some specimens notched?

Notching creates a sharp, controlled stress concentration that promotes brittle fracture and measures resistance to crack propagation. Many ductile plastics do not break completely in unnotched tests, making notched values more discriminating for engineering comparisons. Notch radius and machining quality must be tightly controlled because they strongly affect results.

How does temperature affect impact strength?

Impact strength generally decreases as temperature drops, and many plastics undergo a ductile-to-brittle transition. Testing at low temperatures (for example −40 °C for automotive parts) is essential whenever products will experience cold service environments, because room-temperature data alone may drastically overestimate toughness.

What does it mean when a specimen shows "non-break"?

When a specimen does not break or only partially breaks, the pendulum method reports a minimum impact strength rather than a true fracture value. Instrumented tests or smaller hammer energies are then recommended to obtain quantitative failure data.

How many specimens are required?

Most standards require a minimum of five specimens per condition, but ten or more are commonly tested because impact results show significant statistical scatter. Outliers caused by specimen defects should be investigated rather than simply discarded.

Can finished products be impact tested directly?

Yes. Instrumented falling-weight systems and drop-tower setups can test complete components in their end-use orientation, which is often more representative than testing molded bars. This approach is common for automotive trim, appliance housings, and packaging validation.