Impact Performance Testing of Plastics After Aging: Methods, Standards, and Evaluation

Impact performance testing of plastics after aging evaluates how ultraviolet radiation, heat, and moisture degradation affect the toughness and impact resistance of polymer materials and products. By combining accelerated weathering or thermal aging with standardized Charpy, Izod, or instrumented impact tests, manufacturers can quantify impact strength retention, predict long-term durability, and validate material selection for demanding service environments. This article provides a comprehensive technical overview of the sample types, test items, methods, and applicable ISO, ASTM, and GB standards involved in post-aging impact testing of plastics.

Technical Overview

Plastic materials are inherently susceptible to degradation during service. Exposure to ultraviolet radiation, elevated temperature, oxygen, humidity, and thermal cycling triggers photo-oxidation, chain scission, crosslinking, plasticizer loss, and surface chalking in polymers. These molecular-level changes manifest macroscopically as discoloration, embrittlement, microcrack formation, and a significant reduction in ductility. Because impact loading is one of the most failure-critical conditions for plastic components, the degradation of impact performance after aging is a primary indicator of long-term material durability.

Impact performance testing after aging is a two-stage evaluation: specimens or finished parts are first subjected to controlled artificial aging, such as xenon-arc exposure, fluorescent UV conditioning, or thermal oven aging, and are then tested for impact strength using pendulum or instrumented impact methods. The results are typically expressed as impact strength in kJ/m² and as an impact retention rate, which is the percentage of the original impact strength remaining after a defined aging period. This approach allows engineers to establish ductile-to-brittle transition behavior, define useful service life, and compare stabilizer packages or material formulations on a quantitative basis.

The test framework draws on well-established international and national standards, including ISO 179-1 and ASTM D256 for pendulum impact, ISO 6603-2 and ASTM D3763 for instrumented high-speed puncture impact, ISO 4892 and ASTM G154/G155 for artificial weathering, and the corresponding GB/T standards used in the Chinese national system. Accredited third-party laboratories routinely perform these evaluations for material qualification, product certification, and failure analysis.

Testing Samples

Post-aging impact evaluation can be performed on standard laboratory specimens, material plaques, or finished components. The sample type determines both the applicable test method and the engineering relevance of the data.

Standard Injection-Molded Specimens

The most common sample form is the injection-molded rectangular bar of 80 mm × 10 mm × 4 mm, produced according to ISO 294 or ASTM D638 Type specimen practice. These bars are suitable for direct Charpy and Izod testing and can be notched after molding. Standardized molding conditions are essential because processing history, molecular orientation, and internal stresses strongly influence both aging behavior and impact response.

Machined Specimens from Finished Parts or Plaques

When evaluating an actual product, such as an automotive trim panel, pipe segment, or appliance housing, impact specimens are machined from flat regions of the finished part or from compression-molded plaques. This approach captures the combined effects of the production process, pigment systems, and real-world thickness, though results are specific to the part geometry and should be interpreted accordingly.

Notched Specimens

Notched specimens are used to assess notch sensitivity, which typically increases sharply as polymers degrade. Standard notch geometries include the Type A notch with a 0.25 mm radius and the Type B notch with a 1.0 mm radius per ISO 179-1 and ISO 180. Notches are machined with a dedicated notching cutter, and the notch radius is verified before testing because notch quality directly governs the measured result.

Relevant Material Families

• Polyolefins: PP, HDPE, LDPE, and their filled, talc-reinforced, or impact-modified grades
• Engineering thermoplastics: ABS, PC, PC/ABS blends, PA6, PA66, POM, PBT, and PMMA
• PVC compounds: rigid profiles, pipe grades, and flexible formulations with plasticizer systems
• Thermosets and composites: epoxy, unsaturated polyester, SMC, GMT, and long-fiber-reinforced thermoplastics
• Finished components: bumpers, window profiles, cable sheathing, junction boxes, and outdoor enclosures

Testing Items

Typical test items for post-aging impact evaluation include:

• Charpy impact strength, notched and unnotched, per ISO 179-1, GB/T 1043, or JIS K 7110
• Izod impact strength, notched and unnotched, per ISO 180, ASTM D256, GB/T 1843, or JIS K 7111
• Tensile impact strength per ISO 8256 or ASTM D1822 for thin or highly ductile materials
• Instrumented puncture impact, force–deflection curves, and maximum force per ISO 6603-2 or ASTM D3763
• Low-temperature impact strength at −20 °C, −30 °C, or −40 °C after aging, relevant for outdoor and cold-climate service
• Impact strength retention rate, calculated as aged impact strength divided by unaged impact strength, expressed as a percentage
• Ductile-to-brittle failure mode determination and brittle fraction analysis on specimen fracture surfaces
• Multi-point aging time-series testing to establish degradation kinetics curves

Testing Methods

The complete test sequence consists of conditioning, artificial aging, post-aging reconditioning, impact testing, and data evaluation. Each stage is governed by defined parameters to ensure reproducibility.

Stage 1: Artificial Aging

Aging conditions are selected to simulate the intended service environment. Common accelerated aging methods include:

• Xenon-arc weathering per ISO 4892-2 or ASTM G155, with daylight filters, controlled irradiance, water spray cycles, and black standard temperatures of 55–65 °C, representing full-spectrum outdoor exposure
• Fluorescent UV lamp conditioning per ISO 4892-3 or ASTM G154, using UVA-340 lamps for outdoor simulation and UVB-313 lamps for severe screening tests
• Thermal oven aging per ISO 188 or ASTM D573 at temperatures such as 85 °C, 100 °C, or 120 °C for long-duration heat exposure assessment
• Damp heat aging at 85 °C and 85% relative humidity for electrical and electronic applications
• Natural outdoor exposure per ISO 877 as a benchmark for correlating accelerated results with real climate data

Stage 2: Post-Aging Conditioning

After aging, specimens are conditioned in a standard atmosphere of 23 °C ± 2 °C and 50% ± 10% relative humidity per ISO 291 or ASTM D618 for a minimum of 16 hours, unless the specified procedure requires testing in the as-aged state. This step stabilizes moisture content and specimen temperature before impact measurement.

Stage 3: Pendulum Impact Testing

Charpy testing per ISO 179-1 or GB/T 1043 subjects a horizontally supported specimen to a single pendulum strike at mid-span, while Izod testing per ISO 180, ASTM D256, or GB/T 1843 strikes a vertically clamped, notched cantilever specimen. The hammer energy is selected so that specimen fracture consumes between 10% and 80% of the available energy, as required by the standards. Impact strength is calculated in kJ/m² from absorbed energy divided by the specimen cross-sectional area or residual cross-section under the notch. A minimum of five, and preferably ten, specimens per condition are tested, and results are reported with the observed failure mode as completely brittle, ductile, or mixed.

Stage 4: Instrumented Impact Testing

For a more detailed failure characterization, instrumented falling-dart or high-speed puncture tests per ISO 6603-2 or ASTM D3763 record the full force–deflection response at impact speeds of several meters per second. This yields maximum force, deflection at maximum force, and total energy to failure, which distinguishes between a loss of stiffness, a loss of ductility, or both, in the aged material.

Stage 5: Data Evaluation

Impact strength retention is calculated and plotted against aging duration or total radiant exposure. Degradation curves are fitted to determine the exposure level at which impact retention falls below a defined threshold, for example 50% retention, which is frequently used as a durability criterion in material specifications. Statistical analysis of replicate data and correlation with complementary measurements such as tensile properties, carbonyl index, and yellowing index strengthen the conclusions.

Applications

Post-aging impact testing supports material qualification and product reliability across many industries:

• Automotive: validating bumper fascias, body cladding, exterior mirror housings, and interior trim for impact performance after simulated sunlight and heat exposure over the vehicle design life
• Building and construction: demonstrating long-term impact resistance of PVC window profiles, roofing sheets, drainage pipes, fencing, and glazing polycarbonate panels after UV and thermal aging
• Electrical and electronics: confirming the retained mechanical integrity of enclosures, junction boxes, connector bodies, and cable sheathing after heat aging, supporting long-term property programs aligned with the UL 746B framework
• Renewable energy: evaluating photovoltaic junction boxes, backsheets, and mounting components after combined UV, heat, and humidity exposure
• Packaging and consumer goods: verifying drop and impact resistance of aged containers, crates, garden tools, and outdoor furniture
• Agriculture: assessing the retained toughness of greenhouse films, irrigation fittings, and mulch materials after seasonal weathering
• Failure analysis: comparing impact retention of failed field parts against unaged references to diagnose degradation-related breakage

FAQ

Why is impact testing performed after aging instead of on new material only?

New plastics frequently show excellent toughness, but degradation processes such as photo-oxidation and thermal embrittlement act over time. Testing impact performance after controlled aging reveals how much of the original toughness the material retains, which is the property that actually determines whether a component survives real service conditions. Unaged impact data alone cannot predict premature brittle fracture in the field.

How do I choose between xenon-arc, UV fluorescent, and thermal aging?

Xenon-arc weathering per ISO 4892-2 or ASTM G155 best simulates full-spectrum outdoor sunlight and is preferred for exterior applications. Fluorescent UV conditioning per ISO 4892-3 or ASTM G154 is economical and emphasizes the UV portion of the spectrum, making it suitable for screening. Thermal oven aging per ISO 188 or ASTM D573 is used when the dominant degradation driver is sustained heat rather than light, such as in engine compartments or electrical enclosures. Many specifications require a combination of methods.

What is the difference between notched and unnotched impact testing?

Unnotched tests measure the overall impact energy absorption of the material and are sensitive to bulk degradation. Notched tests concentrate stress at a machined notch and measure resistance to crack propagation, which is highly sensitive to embrittlement and notch sensitivity changes caused by aging. Running both conditions provides the most complete picture of degradation.

What impact retention level is generally considered acceptable?

Acceptance criteria depend on the application and the applicable product standard, but many automotive and construction specifications require impact strength retention of at least 50% after a defined aging exposure, together with no shift from ductile to fully brittle failure at the service temperature. The specific requirement should always be confirmed against the relevant material or product specification.

How long does accelerated aging need to run?

Aging duration is defined either as a fixed time in the specification or as a total radiant exposure in kJ/m² at a reference wavelength, commonly 340 nm. Typical programs range from several hundred to several thousand hours, often arranged as a time series with intermediate measurement points so that a degradation curve and extrapolated service life can be established rather than a single pass/fail value.

Can finished products be tested directly instead of standard bars?

Yes. Finished parts can be evaluated by machining specimens from flat areas, by instrumented dart impact on the actual component, or by product-level drop and impact tests after aging. Product-level testing validates the real geometry, thickness, color, and processing effects, while standard bar testing provides data comparable with material datasheets and standards. A combined approach is recommended for critical applications.