Definition
Elongation at break is one of the important indicators of the mechanical properties of a material, which describes the incremental percentage of the length of the gauge part of the material relative to the original gauge before tensile fracture. This parameter intuitively reflects the ductility or toughness of a material under stress, i.e., the ability of the material to withstand plastic deformation before breaking. Elongation at break is an indispensable evaluation criterion in the quality control and R&D of polymer materials, textiles, sheet metal, rubber products and packaging materials in many industrial fields.
Measurement principle
Measurement of elongation at break is based on uniaxial tensile testing. The standardized specimen is mounted in the upper and lower fixtures of the material testing machine to apply axial tension at a constant rate. During the test, the force sensor records the change in tensile force, while the extensometer or optical measurement system synchronously and accurately monitors the elongation of the gauge segment of the specimen. When the specimen breaks, the final gauge length is recorded. Elongation at break (ε) is calculated by the following formula:
ε = [(L - L₀) / L₀] × 100%
where L₀ represents the original gauge length of the specimen, and L represents the gauge length when the specimen breaks. This principle ensures that the measurement results can quantitatively characterize the deformation limit of the material under tensile conditions.
Measurement method
The measurement of elongation at break follows strict standardized procedures. First, the specimen is cut or prepared according to the specific material type (e.g., plastic, rubber, metal foil, textile, etc.) to meet the standard size. Common reference standards include ISO 527, ASTM D638 (plastics), ISO 37, ASTM D412 (rubber), and ISO 13934-1 (textiles). Testing is typically performed in a laboratory environment with controlled temperature and humidity. After clamping the specimen, select the stretching speed that is appropriate for the material's properties. The whole testing process is automatically completed by the material testing machine until the specimen breaks, and the system directly calculates and outputs the elongation at break. Method standardization is the basis for ensuring data comparability and reproducibility.
Influencing factors
The elongation at break of a material is influenced by a variety of internal and external factors. The internal factors mainly include the chemical composition, molecular chain structure, crystallinity, molecular weight and distribution of the material itself, as well as the orientation and internal stress formed during the production process. For example, the pliability of polymer chains is often associated with higher elongation at break. External factors include test conditions such as tensile rate, ambient temperature and humidity. Higher tensile rates tend to result in low measured elongation at break. In addition, the preparation process, geometry, and presence of chips or defects can also have a significant impact on the measurement results. Understanding these factors is crucial for correctly interpreting data and optimizing material properties.
Applications
The evaluation of elongation at break is widely used in a variety of non-medical industries and research and development fields. In the plastics and film industry, it is used to evaluate the impact and tear resistance of packaging materials. In the rubber products industry, it is a key measure of the resilience and durability of products such as seals, tires, conveyor belts, and more. In the textile industry, elongation at break directly impacts the comfort, conform, and durability of fabrics. In the fields of composite materials, coatings, metal foils, wire and cable insulation sheaths, this parameter is also the core basis for product design, quality acceptance and failure analysis. It provides engineers with important information to predict how well a material will withstand deformation in real-world use.
Instrument selection considerations
When choosing an instrument to measure elongation at break, consider a combination of factors. The force range and accuracy of the instrument should match the strength range of the material to be measured. High-resolution displacement or strain measurement devices, such as contact extensometers or video extensometers, are essential for accurately capturing deformations. The test software must support relevant international, national or industry standards and automatically calculate the required parameters. The fixture must be designed to ensure that the specimen does not slip during testing and does not break prematurely at the grip. For some materials, an environmental chamber may be a necessary accessory to enable testing at specific temperatures and humidity. In addition, the reliability, ease of use, maintenance costs, and technical support capabilities of the equipment should also be included in the evaluation. Proper selection helps to obtain reliable, repeatable test data.