BMW AA-0551 Bending Stiffness (accredited)

Our test laboratory performs testing according to BMW AA-0551 for determining bending force using the 2-point procedure as an accredited test method. The BMW work instruction provides a reproducible method for assessing the bending stiffness of flexible sheet materials and is based on the beam method according to DIN 53121.

The test records the force exerted by a material on a measuring beam when bent to a specified angle. The bending force allows the stiffness and flexibility of different materials and material constructions to be compared.

Applications

The test is primarily intended for flexible materials used in automotive interiors. AA-0551 specifies test conditions for upholstery fabrics, leather, artificial leather and piping, carpet raw materials, carpets with heavy layers, floor mats and reversible mats, as well as ski bag materials.

Bending behaviour is relevant, for example, when assessing haptics, drapability, processing behaviour and the ability of interior materials to conform to component geometries. Different material formulations, coatings, layer constructions and production batches can be compared in terms of their bending behaviour.

Testing according to AA-0551

The specimens are conditioned before testing and are taken in defined directions depending on the material. Leather specimens are taken parallel and perpendicular to the backbone, while roll materials are tested in the machine and cross directions. For textiles, the specimens are taken straight with respect to the yarn direction where possible.

The specimen is clamped in a rotatable holder. As the holder rotates, the specimen is bent against a measuring beam and the resulting force is recorded. The test parameters are selected according to the applicable technical delivery specification, customer requirements or the material-specific conditions defined in AA-0551.

Depending on the material, the visible or coated side is tested both under compression and under extension. The results for the two bending directions are evaluated separately. The maximum bending force is used as a principal test parameter.

Related tests

A closely related automotive method is VDA 230-209 – Determination of bending properties of leather, plastic roll goods and textiles for automobiles, which FILK also offers as an accredited test method.

For leather, FILK also offers DIN EN ISO 14087 – Determination of bending force. AA-0551 is explicitly based on the beam method of DIN 53121 – Determination of bending stiffness by the beam method.

For plastic films and coated textile fabrics, FILK additionally offers DIN 53350 – Determination of bending stiffness according to the Ohlsen method.