Navistar CEMS GT-31 Accelerated Wear of Non-Metallic Materials

Developed by Navistar (now International Motors), a manufacturer of commercial trucks, buses, and engines, as part of its corporate engineering materials specifications (CEMS), the standard, "Navistar CEMS GT-31 Accelerated Weathering of Non-Metallic Materials," describes test methods for evaluating the durability and accelerated aging of non-metallic materials (e.g., polymers, coatings, plastics, textiles, and composites) used in automotive and heavy-duty vehicle applications under environmental conditions such as ultraviolet (UV) light, heat, humidity, and atmospheric pollutants. This standard ensures that materials can withstand environmental degradation from UV exposure, humidity, and thermal cycling without significant loss of performance, appearance, or mechanical properties.

This standard evaluates the durability, performance and appearance of a material against prolonged outdoor exposure over a compressed time period, typically for applications in industries such as automotive, construction, aerospace and consumer goods.

The primary objective of this standard is to predict material durability by simulating long-term outdoor exposure in a controlled laboratory environment, accelerating the effects of sunlight, humidity, and temperature. This standard is critical for components such as interior trim, exterior panels, gaskets, and paints exposed to harsh conditions.

This standard applies to non-metallic materials. It refers to xenon arc or similar UV exposure devices to simulate natural weathering. The latest update to this standard was published under Navistar MPAPS-GT-31, a material, part, and process specification (MPAPS), and is still active.

This standard specifies accelerated weathering using equipment such as the Weather-Ometer (xenon arc lamp system) that simulates solar radiation. The key elements are:

• Light source: Xenon arc lamp with filters to simulate full-spectrum sunlight (UV, visible, IR). Typical values: Borosilicate or quartz internal/external filters for automotive-grade exposure.
• Irradiance level: Controlled dose of UV energy to accelerate aging. Typical values: 0,35–0,55 W/m at 340 nm² (common in automotive standards).
• Test duration: Varies depending on material and specification, acceptance test for UV resistance. Typical values: 100-1.000 hours (e.g. up to 700 hours in relevant studies for impact-resistant mixtures).
• Cycle: Alternating light/dark phases with water spray to simulate rain and condensation. Typical values: light phase 102 min, dark phase 18 min, water spray 12 min, temperature during light approximately 60-70 degrees.
• Evaluation criteria: Post-exposure checks for physical, mechanical, and aesthetic changes. Typical values: color change no more than 2-3 units, gloss retention greater than 80 percent, tensile/impact strength retention greater than 90 percent, no cracking, chalking, or delamination.
• Pass/fail: Defined in the material's specific MPAPS specification (for example, the MPAPS D-7116 standard for injection-molded interior trim). Typical values: Materials must meet or exceed threshold values ​​after specified hours.

Testing generally follows ASTM G155 Standard Practice for Operating a Xenon Arc Lamp for Exposure to Materials or ISO 4892-2 Plastics - Methods for Exposure to Laboratory Light Sources for Procedural Compliance. All materials tested must also meet MPAPS B-50 for essential properties such as flammability and chemical resistance.

The Navistar CEMS GT-31 standard is similar to SAE J1960 or ASTM D2565 for automotive plastics. Accelerated wear helps reduce real-world exposure time (e.g., 1.000 hours in the Florida sun is approximately 2-5 years).

Accelerated decomposition is carried out using special equipment that mimics natural conditions at an intensified level:

• Xenon arc decomposition (e.g. according to ASTM G155 or ISO 4892-2 standards):
  • Xenon arc lamps are used to simulate full-spectrum sunlight (UV, visible, infrared).
  • Typical settings: 0,35–0,55 W/m at 340 nm², light cycles (e.g. 102 min) and dark/wet phases (e.g. 18 min with water spray).
  • It is common for automotive and aerospace applications because it accurately mimics sunlight.
• Fluorescent UV Test (e.g. ASTM G154):
  • Fluorescent UV lamps are used to focus UV wavelengths.
  • Less expensive but less accurate for full-spectrum simulation, used for certain polymer tests.
• Carbon arc (older, less common): Used in some older standards.
• Environmental chambers: Combine UV, heat and humidity with precise control.

Major areas of use for this standard include:

• Automotive use: Validates interior/exterior non-metallic materials for Navistar vehicles (e.g., international trucks). Referenced in the MPAPS D-7116 standard for cladding materials.
• Research links: Studies on recycled polycarbonate blends (e.g., with ABS/HIPS) use similar protocols and show approximately 10-20 percent strength loss after 700 hours.
• Alternatives: For xenon-free methods, the ASTM G154 standard can be used, but xenon is preferred for full-spectrum accuracy.

The Navistar CEMS GT-31 standard is considered important for the following reasons:

• Cost and time savings: Real-world exposure testing takes years, whereas accelerated weathering tests provide results in weeks, aiding material selection and product development.
• Reliability: Ensures components meet performance standards in harsh environments, reducing warranty claims or failures.
• Regulatory compliance: Meets industry requirements (e.g. automotive, aerospace) for safety and durability.

Our organization, with its competent and experienced team, has been understanding the needs of its customers for years, providing them with the advanced testing services they need, and assisting them in the establishment, implementation, and improvement of management systems. In this context, we also provide testing services in accordance with the Navistar CEMS GT-31 Accelerated Corrosion of Non-Metallic Materials standard.