GMW 14145 Automotive Seat Material Seam Strength Test

The “GMW 14145 Automotive Seat Material Seam Strength Test” standard, developed by General Motors Worldwide (GMW), includes a test procedure used to determine the strength of seams in automotive seat materials. This standard evaluates the tensile force required to break a seam prepared under specified conditions. It primarily applies to upholstery materials used in vehicle seats, including textiles, leather, and plastic roll materials.

Seam strength is a crucial property in automotive seats because seat covers are subjected to repeated loading, stretching, friction, passenger movement, and environmental conditions throughout the vehicle's lifespan. A seam that is significantly weaker than the surrounding material can become a point of failure, even if the upholstery itself possesses sufficient strength.

The basic concept in the GMW 14145 standard is simple: a sample containing a prepared weld is subjected to tensile load until the weld fractures. The force required to cause the fracture is then used to characterize the strength of the weld.

This standard defines seam strength as the tensile force required to break a seam prepared under standardized conditions. This approach allows General Motors and its suppliers to assess whether a particular floor covering structure can withstand the mechanical stresses expected during vehicle use.

The GMW 14145 standard is designed for seat materials, specifically the following upholstery materials:

• Textile fabrics
• Automotive leather
• Plastic roll materials
• Other materials used in seat cover making

This procedure is more concerned with the performance of the welded structure than the tensile strength of the seamless material. This distinction is important because a material may have good tensile properties while its welded portion performs poorly.

Automotive seat covers are subjected to significant mechanical stresses. These stresses can occur in the following situations:

• Passenger entry and exit
• Repeated sitting and standing
• Seat adjustment
• Passenger movement
• Folding or bending of seat components
• Prolonged vibration
• Installation of the flooring
• Seat structure and interaction with foam.

The seam is often a mechanically sensitive area because it creates holes and alters the path of the load within the material. If the seam is not strong enough, various problems can arise:

• Stitch dehiscence: The stitches may open under load.
• Material tearing near the seam: The substrate may be damaged around the seam.
• Loss of upholstery appearance: The cover may loosen or deform.
• Progressive damage: A minor stitch failure can develop into a larger tear.
• Reduced durability: The seating system may not maintain its intended performance over its lifespan.

Therefore, the GMW 14145 standard provides an important quality control tool for seat cover manufacturing.

The basic principle is a tensile test on a prepared seam. Generally, this test method follows these steps:

• Sample preparation: Test samples are prepared from the seat material with the required stitching structure. The stitching should represent the actual structure being evaluated, including the relevant material and stitching characteristics.
• Conditioning: Samples are prepared and conditioned according to the requirements of the relevant procedure to ensure that test results are obtained under controlled and repeatable conditions.
• Tensile loading: The specimen is mounted on a tensile testing machine. The machine applies a controlled tensile force to the specimen to transfer the load along the seam.
• Seam fracture: The force continues to increase until the seam or related material fractures. The maximum force associated with failure is recorded as the resulting seam strength.
• Evaluation: The measured force is compared to the relevant material or component specification.

Therefore, the test provides a quantitative indication of whether the suture structure is sufficiently strong.

The exact sample dimensions, seam configuration, conditioning requirements, machine settings, loading speed, number of samples, and acceptance criteria are specified in the GMW 14145 standard.

The primary result is the force required to cause the seam to rupture. A higher measured seam strength value generally indicates a stronger seam structure, but the result should always be interpreted according to the material type, seam design, failure mode, and applicable General Motors requirements. The test can also provide useful information about how the sample failed. For example, failure might include:

• Stitching failure
• Thread breakage
• The stitches coming undone
• Material tearing
• Defect adjacent to the seam.
• Separation related to suture structure.

The failure mode can be as important as the numerical strength because it helps engineers determine whether the problem stems from the stitching process, thread, material, or structural design.

The following factors affect seam strength:

• Material properties: The strength, elongation, thickness, and structure of the flooring material affect how loads are transferred to the seam.
• Yarn characteristics: The strength, structure, material, and compatibility of the yarn with the upholstery fabric can significantly affect sewing performance.
• Seam type: Seam type, seam density, and seam shape affect the distribution of load along the seam.
• Needle holes: Sewing creates holes in the material. Excessive needle hole creation can form a weakened area and encourage tearing.
• Stitch tension: Incorrect sewing machine tension can affect both the appearance of the stitches and mechanical performance.
• Seam allowance: The amount of material around the seam line can affect tear resistance.
• Material processing: Coatings, laminations, embossing, finishing applications, and other manufacturing processes can alter the strength of the material around the seam.

In conclusion, seam strength should be considered not merely as a property of the flooring material itself, but as a systems property of the material and seam structure.

For automotive manufacturers, seats are a component with a high rate of use. Seat covers must maintain both their functional integrity and appearance throughout repeated use. The GMW 14145 standard contributes to this goal by providing a controlled method for evaluating one of the most important mechanical properties of stitched upholstery.

This test can be used in the following situations:

• Materials development
• Supplier qualification
• Product verification
• Production part approval
• Process improvement
• Quality control
• Troubleshooting
• Comparative material evaluation

For automotive upholstery suppliers, compliance with the GMW 14145 standard helps demonstrate that seat materials and stitching constructions can meet General Motors' mechanical performance requirements. Suppliers must check the following variables:

• Material batch
• Yarn type
• Stitch type
• Stitch density
• Sewing machine settings
• Needle selection
• Suture structure
• Conditioning
• Test equipment calibration
• Sample preparation

Good control of these variables increases repeatability and reduces the risk of producing seemingly acceptable material that performs poorly after stitching.

In short, tests conforming to the GMW 14145 standard focus on the following characteristics:

• Wear resistance
• Color fastness
• Resistance to chemicals
• Elasticity resistance
• Tensile properties
• Tear strength
• Flammability
• Environmental aging
• UV/light exposure
• Stain and cleaning resistance.
• Stitch strength

In conclusion, the GMW 14145 standard is important because stitching is a critical part of automotive seat cover construction. Even a material with good inherent strength can fail prematurely if the stitching structure is inadequate. This standard supports material selection, stitching process optimization, supplier qualification, quality control, and automotive seat durability by providing a standardized method for measuring stitching strength.

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 14145 standard.