GMW 16526 Water Absorption Test Method for Automotive Materials

The “GMW 16526 Water Absorption Test Method for Automotive Materials” standard, developed by General Motors Worldwide (GMW), is an engineering standard that specifies a method for determining the water absorption properties of materials used in automotive applications. This standard is primarily designed for materials and components where moisture absorption may affect dimensional stability, mechanical properties, durability, or functional performance.

Many automotive materials are exposed to humid environments, condensation, rainwater, washing processes, or systems containing coolant and water throughout their lifespan. Some materials absorb moisture, which can lead to swelling, reduced strength, changes in stiffness, or dimensional changes.

The GMW 16526 standard provides a standardized procedure for measuring how much water a material absorbs under controlled conditions. This allows engineers and suppliers to consistently compare materials and verify compliance with General Motors material requirements.

The main objectives of this standard are:

• Measuring the amount of water a material absorbs.
• To assess dimensional stability after exposure to water.
• To evaluate potential changes in mechanical properties.
• Comparing the moisture resistance of different materials.
• To verify compliance with General Motors material specifications.
• To support material selection and verification processes.

This standard applies generally to materials whose water absorption properties are relevant to automotive performance and includes the following:

• thermoplastics
• Thermoset plastics
• Elastomers and rubber materials
• Composite materials
• Certain porous or fiber-reinforced materials
• Components made from moisture-sensitive materials.

The measured water absorption value can be used during material qualification, product development, and supplier verification.

According to the GMW 16526 standard, test specimens are, in principle, conditioned and weighed before exposure to water. The specimens are then immersed or exposed to water for a specified period under controlled environmental conditions. After exposure, the specimens are weighed and evaluated again. The increase in mass is used to determine the amount of water absorbed by the material. Additional measurements may be taken to assess dimensional changes or property degradation.

The described test method generally follows these steps:

• Sample preparation: Test samples are prepared according to material or component requirements. Surfaces must be clean and free of contamination.
• Drying and conditioning: Samples are dried or conditioned until a stable starting mass is obtained. This step minimizes the effect of previously absorbed atmospheric moisture.
• Initial weighing: Each sample is weighed using a balance with appropriate resolution, and the dry mass is recorded.
• Water exposure: Samples are immersed in water for the temperature and duration specified in the standard or the relevant General Motors material specification.
• Surface drying: After removal from the water, excess water is removed from the sample surface without removing the water that has penetrated into the material.
• Final weighing: Samples are weighed again immediately after the surface drying process.
• Calculation: The percentage increase in mass is calculated and reported.

Typically, test equipment includes the following:

• Analytical or precision balance: Accurate mass measurement.
• Water bath or immersion tank: Controlled water exposure.
• Temperature control system: Maintains the specified test temperature.
• Conditioning chamber or oven: Drying and pre-conditioning
• Absorbent, lint-free cloth: Removes surface water.

Moisture absorption can significantly affect the performance of automotive materials. Excessive water absorption can lead to:

• Inflation or size changes
• Reduced mechanical strength
• Loss of firmness
• Separation of composite structures
• Corrosion of adjacent components
• Surface defects and appearance problems
• Durability decreased over time.

Using the GMW 16526 standard, engineers can identify materials that maintain their properties when exposed to moisture and ensure reliable vehicle performance throughout the product lifecycle.

This standard is applicable to a variety of automotive materials, including:

• thermoplastics
• Thermoset plastics
• Elastomers and rubber compounds
• foams
• Composite materials
• Interior furnishing materials
• Lower body components
• Adhesive systems
• Sealing materials

These materials are commonly found in vehicle interiors, exteriors, engine compartments, and sealing applications.

Depending on the material specification, the following properties can be evaluated:

• Water absorption by the face
• weight change
• Thickness variation
• Length and width variation
• Surface condition
• Visual appearance
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• Preservation of mechanical properties.

The results are compared against the acceptance criteria specified in the relevant General Motors material specification.

In the automotive industry, the GMW 16526 standard is frequently used in the following situations:

• Materials development: Engineers use testing to compare candidate materials and optimize formulations.
• Supplier qualification: Suppliers demonstrate that their materials meet General Motors' moisture resistance requirements.
• Product validation: Components are tested to ensure their long-term durability under exposure to environmental influences.
• Quality control: Manufacturers may conduct periodic tests to verify production consistency.

A test report prepared according to the GMW 16526 standard normally includes the following:

• Material description
• Supplier and material class
• Sample dimensions or description
• Number of samples tested
• Conditioning method
• Immersion conditions
• Initial mass
• Final mass
• Individual water absorption values
• Average water absorption
• Any deviation from the stated procedure

Water absorption is an important material property because moisture can significantly affect the behavior of many automotive polymers and composites. For example,

• Polyamides (nylons) can absorb significant amounts of moisture, which alters their stiffness and dimensions.
• Fiber-reinforced plastics may experience a decrease in interfacial strength after exposure to moisture.
• Elastomers can swell when exposed to water.
• Electrical components made from moisture-sensitive materials may experience a decrease in insulation performance.

By using this testing method, suppliers can consistently assess these effects across different materials and production locations.

The GMW 16526 standard is generally used as a material characterization test rather than a full durability test. The results can be used as a reference in other material specifications that define the maximum allowable water absorption values ​​for specific material families or applications.

In short, it provides a consistent method for comparing moisture absorption and verifying material performance.

In conclusion, the GMW 16526 standard establishes a controlled and repeatable method for measuring water absorption in automotive materials. The test is valuable because moisture absorption can affect dimensional stability, mechanical performance, electrical properties, and long-term durability. By standardizing sample preparation, water exposure, weighing, and calculation procedures, this standard enables General Motors and its suppliers to make reliable comparisons between materials and ensure that moisture-sensitive materials meet the requirements of their intended automotive applications.

This standard contributes to the durability, quality, and long-term reliability of modern automotive components by controlling moisture-related risks such as swelling, deterioration, and performance loss.

GMW 16526 standard is often used in conjunction with other material and environmental testing standards that evaluate the following aspects:

• heat aging
• Chemical resistance
• moisture resistance
• Thermal cycle
• mechanical performance
• Weather resistance

Together, these tests provide a comprehensive assessment of the material's suitability for automotive applications.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the GMW 16526 standard.