The “BMW TL 9 192 340 Determination of total elongation (static elongation) and permanent elongation” standard, developed by BMW, a leading German multinational company in the automotive sector, describes a test method designed for luggage nets made of polypropylene (PP) material used in vehicle interior upholstery, particularly in the luggage compartment. This is a mechanical properties test that evaluates the total elongation (total stress or elongation under load or before failure) of the net material or the assembled net structure.
Determining total elongation (static elongation or elongation at fracture/rupture) and permanent elongation (plastic elongation after fracture) measurements is extremely important in materials science and engineering, especially during tensile testing of metals and other materials. These measurements provide crucial information about a material's ductility, formability, safety margins, and overall mechanical behavior under load.
Total elongation is the total increase in length measured at the moment of fracture (or just before the load drops significantly) of the specimen. This includes:
Permanent elongation (post-fracture elongation or plastic elongation) is the permanent (irrecoverable) increase in length after fracture, once the elastic portion has slightly returned. It is measured by piecing together the fractured fragments and comparing them to the original length. It fully represents the plastic deformation the material has undergone.
In practice, total elongation = elastic strain at fracture + permanent (plastic) elongation. The elastic portion is usually small (0,1-0,5 percent for most metals), so the two values are generally close, but permanent elongation is a more accurate indicator of true ductility.
These measurements are considered important for the following reasons:
According to the BMW TL 9 192 340 standard, luggage nets must withstand dynamic loads (e.g., during braking, acceleration, or cargo impacts) without causing excessive stretching that could lead to dangerous shifting of goods or failure of the net. Total elongation measures how much the net can stretch under tensile force, ensuring it remains effective while providing controlled flexibility for energy absorption.
During testing, a sample strip or section of the mesh is clamped in a tensile testing machine. Force is applied at a constant rate until a specific load, fracture, or maximum elongation is reached. The total elongation is calculated as the percentage increase in length from the original measurement length. This can be at fracture (elongation at break) or under a specific preload/load (e.g., elastic/total recoverable + permanent deformation).
Polypropylene meshes are designed to be lightweight, chemically resistant, and durable. Specifications define minimum/maximum limits for total elongation (e.g., to prevent excessive sagging or brittle failure under load). Excessive elongation can reduce holding effectiveness, while too little elongation can make them prone to tearing.
This method generally refers to other BMW tests, such as tensile strength, tear resistance, UV aging, flammability according to the FMVSS 302 standard, abrasion, and so on. Elongation is a fundamental mechanical criterion for approval.
This standard is a supplier quality and testing requirement. The entire procedure, pass/fail criteria (limits), sample preparation, test speed, conditioning (temperature and humidity) and any fixtures (e.g. for hook attachment points) are described in detail in the relevant standards, which are only accessible through BMW's supplier portal.
Section § 3.3.3 of this standard describes the requirements and detailed procedure for determining the total elongation test on polypropylene (PP) luggage nets. Determining the total elongation combines elastic and permanent deformation or measures the total elongation under specific load conditions (e.g., total elongation at a defined force level before fracture or including the non-recoverable portion). This method involves a standardized tensile/stress test on net samples (e.g., strips cut from the net or full connection points) using a constant elongation rate on a universal testing machine. Preconditioning of the samples is required prior to testing. Test speed (e.g., 100 mm/min or similar, usually referring to the ISO 13934-1 standard for textiles or adapted for nets) is used. Load levels are e.g., 50 N, 100 N, or elongation to breaking point. Pass/stay criteria include minimum total elongation (to ensure energy absorption/flexibility) and maximum elongation (to prevent excessive sagging under load). Special handles or hooks are used to simulate attachment points in a vehicle trunk.
Unlike pure elastic elongation (which is recoverable), total elongation involves permanent deformation/shape change. This is critical for safety nets that need to not stretch too much (risk of puncture under load) but also not be too rigid (risk of tearing).
The BMW TL 9 192 340 § 3.3.3 standard ensures that the luggage net meets BMW's safety and durability standards for interior trim components (preventing loose items from becoming flying objects in the event of accidents or sudden maneuvers).
This standard is based on the “DIN 53360 Testing of artificial leather and similar sheet materials - Determination of total elongation (static elongation) and irreversible elongation” standard, which is now deprecated.
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 BMW TL 9 192 340 standard.
To get an appointment, to get more detailed information or to request an evaluation, you can ask us to fill in our form and reach you.
