Weathering resistance testing evaluates how non-metallic automotive materials—such as plastics, elastomers, coatings, textiles, and adhesives—withstand long-term exposure to ultraviolet radiation, heat, and moisture. By replicating years of outdoor and in-cabin aging in a laboratory setting under internationally recognized standards such as ISO 4892 and ASTM G155, accredited third-party laboratories help vehicle manufacturers and tier suppliers predict long-term durability, prevent premature discoloration and cracking, and validate compliance with OEM material specifications. This article explains the sample types, test items, exposure methods, evaluation procedures, and typical applications of weathering resistance testing for automotive non-metallic parts.
Technical Overview
Weathering resistance testing, also known as artificial accelerated weathering or light-exposure aging, is a laboratory technique that reproduces and intensifies the environmental stresses acting on automotive non-metallic materials: ultraviolet (UV) radiation, elevated temperature, humidity, condensation, and water spray. Unlike metals, polymeric materials are vulnerable to photo-oxidative degradation, in which UV photons initiate chain scission and free-radical oxidation reactions that permanently alter the chemical structure, appearance, and mechanical performance of the material.
In a vehicle, non-metallic components face two distinct aging environments. Exterior parts are exposed to the full solar spectrum, rain, and large temperature swings, while interior parts behind glazing experience filtered UV, sustained high cabin temperatures that can exceed 90 °C in summer, and volatile condensation effects such as window fogging. Accelerated weathering instruments simulate both scenarios in a controlled, repeatable manner, compressing several years of field exposure into weeks or months of testing.
Typical degradation phenomena investigated in weathering tests include:
- Fading, yellowing, and color shift of pigmented polymers and textiles
- Gloss loss, chalking, and haze formation on painted and transparent surfaces
- Surface cracking, micro-checking, blistering, and embrittlement
- Loss of tensile strength, elongation, and impact resistance
- Dimensional change, warpage, and delamination of multi-layer structures
- Fogging and volatile condensation on interior glass surfaces
Test procedures are governed by standards published by ISO, ASTM, EN, JIS, and GB, along with vehicle-OEM-specific technical requirements. Accredited third-party laboratories perform these tests to support material qualification, design validation, supplier comparison, root-cause analysis of field failures, and regulatory or export compliance programs.
Testing Samples
Weathering tests can be performed on standard material plaques, injection-molded or extruded specimens, coated panels, fabric swatches, or finished production parts. The main categories of non-metallic automotive samples include:
Interior Plastic Components
Polypropylene (PP), acrylonitrile butadiene styrene (ABS), polycarbonate/ABS blends (PC/ABS), polyvinyl chloride (PVC), and polyurethane (PU) skins used for instrument panels, door trim panels, center consoles, pillar trims, air-vent louvers, switch bezels, and decorative inserts. These materials are typically evaluated for colorfastness, gloss retention, fogging, and thermal-light stability behind window glass.
Exterior Plastic Components
Thermoplastic polyolefins (TPO), PP with elastomer modifiers, polyamide (PA), polybutylene terephthalate (PBT), acrylonitrile styrene acrylate (ASA), and polyurethane reaction-injection-molded parts used for bumper fascias, radiator grilles, exterior mirror housings, body-side moldings, wheel-arch claddings, spoilers, and license-plate brackets. These samples face the harshest full-spectrum solar exposure.
Elastomeric Seals and Rubber Parts
EPDM door and window seals, glass-run channels, TPV and TPE soft-touch surfaces, rubber grommets, wiper components, and hose materials. Testing focuses on compression-set behavior, surface cracking, hardening, and retention of elastic properties after light and heat exposure.
Coatings and Painted Surfaces
Automotive topcoats, clear coats, basecoats, primer systems, black-out trims, wheel coatings, and refinish paints applied to steel, aluminum, or plastic substrates. Weathering tests assess gloss retention, color stability, chalking resistance, adhesion, and resistance to water spotting and etching.
Soft Trim Materials
Woven and knitted seat fabrics, synthetic leather, genuine leather, headliner fabrics, and carpet fibers. These materials are evaluated for colorfastness to light, abrasion after aging, strength retention, and plasticizer volatility.
Transparent Optical Components
Polycarbonate and polymethyl methacrylate (PMMA) headlamp and rear-lamp lenses, light guides, interior display covers, and instrument-cluster windows. Key evaluation parameters include yellowing index, haze, light transmittance, and optical distortion.
Adhesives, Sealants, and Tapes
Structural adhesives, direct-glazing polyurethane sealants, acrylic foam tapes, and pressure-sensitive attachment systems, which are tested for bond-strength retention and cohesive integrity after UV and moisture exposure.
Testing Items
Depending on the material type, the part location on the vehicle, and the applicable OEM specification, weathering test programs typically include the following evaluation items:
- Color difference (ΔE) before and after exposure, measured instrumentally per ASTM D2244 or ISO 7724
- Greyscale rating for color change and staining per ISO 105-A02 and ISO 105-A03
- Gloss retention at specified geometries (20°, 60°, 85°) per ASTM D523 or ISO 2813
- Visual defect assessment: cracking, crazing, blistering, chalking, flaking, and staining
- Tensile strength and elongation retention per ISO 527 or ASTM D638
- Flexural strength and modulus retention per ISO 178 or ASTM D790
- Impact strength retention (Izod/Charpy) per ISO 179, ISO 180, or ASTM D256
- Hardness change (Shore A/D, ball indentation) per ISO 868 or ASTM D2240
- Haze and luminous transmittance change for transparent parts per ASTM D1003 or ISO 13468
- Yellowing index per ASTM E313
- Fogging characteristics (reflectimetric and gravimetric) per ISO 6452 or relevant DIN-equivalent OEM methods
- Adhesion strength of coatings and bonds after exposure (cross-cut, pull-off, peel)
- Mass change and dimensional stability after hygrothermal cycling
Acceptance criteria are defined by the responsible OEM and commonly specify, for example, a maximum ΔE of 2–3 after a defined radiant exposure, a greyscale rating of 3–4 or better, gloss retention above a defined percentage, and no visible cracking under specified magnification.
Testing Methods
Weathering methods fall into two families: laboratory accelerated exposure using artificial light sources, and natural outdoor exposure at benchmark climates. Selection depends on the material, the intended service environment, and the governing specification.
Xenon Arc Lamp Exposure
Xenon arc weathering, performed per ISO 4892-2, ASTM G155, ISO 11341 for coatings, or the equivalent GB/T 16422.2 and GB/T 1865 standards, is the most widely used method for automotive materials because a filtered xenon lamp closely reproduces the full solar spectrum, including visible and infrared energy. Typical exterior cycles combine a long light phase with a shorter water-spray phase, for example 102 minutes of light followed by 18 minutes of front-side spray, at a black-standard temperature of 63–65 °C or higher and controlled relative humidity. Interior simulations use daylight-filtered or window-glass-filtered radiation with dry, dark, and humidity phases to reproduce cabin conditions. Radiant exposure is monitored and reported in kJ/m² or MJ/m², commonly at 340 nm, per ISO 9370.
Fluorescent UV Condensation Exposure
Fluorescent UV testing per ISO 4892-3, ASTM G154, or the equivalent GB/T 16422.3 emphasizes the UV portion of sunlight, which drives most polymer degradation. UVA-340 lamps provide the closest match to the solar UV cut-off, while UVA-351 lamps simulate sunlight filtered through window glass for interior applications. A typical cycle alternates 4 hours of UV light at 60 °C with 4 hours of condensation at 50 °C. This method is economical, highly reproducible, and particularly effective for screening coatings, adhesives, and sealants.
Carbon Arc Lamp Exposure
Carbon arc exposure per ISO 4892-4, including open-flame and sunshine-type carbon arc, remains referenced in some legacy Japanese-market specifications under JIS D 0205 and certain OEM standards. Although modern xenon and UV systems have largely replaced it, carbon arc testing is still performed for program continuity and comparative databases.
Natural Outdoor Exposure
Direct outdoor weathering per ISO 877 and ASTM G7 mounts samples on racks facing the equator at a defined tilt angle in benchmark climates—typically a humid subtropical site for moisture-driven degradation and a hot arid desert site for UV and heat-driven degradation. Materials for vehicle interiors are tested behind glass per ASTM G24 to simulate sunlight passing through windshields and windows. Outdoor exposure provides the reference data used to establish acceleration factors for laboratory methods, with radiant dose documented in MJ/m² and test durations often spanning 12 to 60 months.
Post-Exposure Evaluation
After exposure, specimens are reconditioned in a standard atmosphere per ISO 291 or ISO 187 before evaluation, because many properties drift during the recovery period. Changes in color, gloss, and appearance are quantified per ISO 4582, which standardizes the reporting of property variations after exposure. Mechanical tests, optical measurements, and visual ratings are then compared against unexposed control specimens retained under dark, ambient storage.
Applications
Weathering resistance testing is applied across the entire vehicle development cycle, from material selection to production quality control, and covers all major vehicle subsystems:
- Interior systems: instrument panels, door trim, headliners, seats, steering wheels, shifter knobs, and switchgear, validated against cabin solar-heat loading and fogging requirements
- Exterior systems: bumper fascias, grilles, mirror housings, body moldings, trim badges, wheel covers, and running boards, validated for full-spectrum outdoor durability
- Lighting systems: headlamp and rear-lamp lenses, reflectors, bezels, and light guides, assessed for yellowing, haze, and optical performance retention
- Sealing systems: door and glass-run seals, trunk seals, and glazing sealants, assessed for crack resistance and compression-set retention
- Electrified vehicle components: charging-port covers, high-voltage cable jacketing and connector housings, battery-module plastics, and insulation films, which must combine weathering durability with electrical safety over a 10–15 year service life
- Coatings and finishes: OEM paint systems, wheel finishes, decorative metallized and piano-black trims, and protective films, evaluated for gloss, etch, and scratch appearance retention
- Failure analysis and benchmarking: comparing incumbent and candidate materials, validating supplier or formulation changes, and supporting warranty and field-failure investigations
By integrating weathering data with thermal aging, humidity cycling, and chemical-resistance testing, manufacturers can build a complete durability profile and confidently warrant the appearance and function of non-metallic parts over the full vehicle life.
FAQ
What is the difference between xenon arc and fluorescent UV weathering?
Xenon arc testing reproduces the full solar spectrum, including visible and infrared radiation, and is therefore preferred for color evaluation, finished-part qualification, and correlation with outdoor exposure. Fluorescent UV testing concentrates on the ultraviolet band and uses condensation rather than spray for wetting, making it faster and more economical for screening polymer formulations and coatings. Many test programs use both methods complementarily.
How does accelerated laboratory exposure correlate with real-world service life?
Correlation depends on the material, the light source, the cycle, and the reference climate. Laboratory xenon exposure is quantified by radiant dose, and experienced laboratories establish acceleration factors by comparing aged properties with panels exposed at natural benchmark sites. A common engineering approach equates a defined radiant exposure in kJ/m² at 340 nm with a corresponding period of outdoor or behind-glass exposure, but no universal conversion factor exists, so correlation must be validated per material family.
What samples and quantities are required for testing?
Flat plaques or panels of approximately 50 × 100 mm to 75 × 150 mm are preferred for exposure and subsequent color and gloss measurement, while mechanical testing requires separately exposed tensile or impact bars cut or molded to standard dimensions. A minimum of three exposed specimens plus unexposed reference specimens is recommended, and finished parts can often be sectioned or mounted directly in the exposure chamber.
Which standards apply to interior versus exterior automotive materials?
Exterior materials are typically tested with daylight-filtered xenon exposure and water spray per ISO 4892-2 or ASTM G155. Interior materials are tested behind-glass using window-glass filters, longer light phases, higher black-panel temperatures, and dry or humidity-controlled dark phases, frequently combined with fogging evaluation per ISO 6452. The governing OEM specification ultimately defines the exact cycle, temperature, irradiance, and acceptance limits.
How long does a weathering test take?
Durations are specified either as total radiant exposure or elapsed hours. Typical automotive programs range from several hundred to more than three thousand hours of xenon exposure, corresponding to roughly one to six months of continuous chamber operation, while fluorescent UV screening cycles may run shorter. Outdoor benchmark exposure typically requires one to five years depending on the specification target.
What does a typical test report include?
A professional report documents the exposure standard, light source and filters, irradiance level, chamber temperature, black-panel or black-standard temperature, relative humidity, wet/dry cycle structure, total radiant exposure, specimen identification, and all measured changes in color, gloss, appearance, and mechanical properties, together with photographs and pass/fail conclusions against the specified acceptance criteria.