A tensile testing machine, or universal material testing machine, is a device that evaluates the mechanical properties of materials by applying axial tensile force and measuring force values and deformation synchronously. In the field of polymer materials, such as plastics and rubber, the testing principle is based on the stress-strain behavior of the material under controlled tension. The equipment typically consists of a loading frame, a force sensor, a displacement measurement system, and a control system that can be stretched at a standard rate at a specified temperature and humidity environment until the specimen breaks or reaches a predetermined deformation.
Characterization of toughness of polymer materials
Toughness reflects a material's ability to absorb energy before breaking, which is essential for plastics and rubber. Tensile tests quantify toughness by calculating multiple parameters through stress-strain curves. Among them, elongation at break characterizes the ductility of a material, while tensile strength indicates the ability of a material to resist tensile failure. For many polymer materials, toughness can be estimated approximately by the area under the stress-strain curve, which represents the energy required to break per volume of material. The modulus of elasticity, which is the slope of the initial linear segment of the stress-strain curve, describes the rigidity of the material. Together, these parameters reveal the behavior of the material under stress, providing a basis for product design and material selection.
Test Standards & Conditions
Tensile testing of plastics and rubber follows a series of international and national standards to ensure comparability and reliability of results. Common standards include ISO 527 series (plastics) and ISO 37 (rubber), as well as corresponding national standards such as GB/T 1040 and GB/T 528. The test conditions need to be strictly controlled, including specimen preparation (e.g., molded or injection molded specimens of dumbbell or rectangular sections), ambient temperature and humidity (usually 23±2°C, 50±10% relative humidity), and tensile speed. The speed selection depends on the type of material: 1 to 50 mm/min is commonly used for plastics, and may be higher for rubber. Non-standard environment (e.g., high and low temperature) testing evaluates changes in a material's performance under extreme conditions.
Key test parameters:
After processing, a number of key mechanical parameters can be obtained from the raw data output by the tensile testing machine. The following table summarizes the main parameters and their significance:
| Tensile strength | The maximum tensile stress that the specimen will withstand before it breaks |
| Elongation at break | The percentage of strain at the time of fracture of the specimen |
| modulus of elasticity | The slope of the linear region of the stress-strain curve |
| Yield point stress | The stress of plastic deformation begins to occur in the material |
| Fracture energy | Area under the stress-strain curve, estimating toughness |
When analyzing the data, the stress (σ) and strain (ε) are calculated according to the following formulas: σ = F/A₀ and ε = ΔL/L₀, where F is the instantaneous force value, A₀ is the initial cross-sectional area, ΔL is the elongation, and L₀ is the original gauge. For materials with higher toughness, such as certain rubbers or toughened plastics, the stress-strain curve may show a large area, indicating high energy absorption capacity. Conversely, brittle plastics have a smaller curve area and low elongation at break.
Application examples
In the automotive industry, rubber seals and plastic components are tested for long-term durability and fatigue resistance. The packaging industry uses test data to evaluate the tear and ductility properties of film materials to ensure safe transportation. The field of building materials, such as polymer waterproofing membranes, relies on tensile properties to ensure they can adapt to structural deformation. In addition, when developing new polymer composites, tensile testing can visually show the effect of tougheners or fillers by comparing the base resin with the modified data. Through system testing, producers can optimize process parameters, and users can select materials based on data to improve product reliability.
Current testing faces several challenges: for example, the directionality difference of anisotropic materials (e.g., fiber-reinforced plastics) requires multi-axial testing; the measurement of large deformation of high-elastic rubber requires high-precision elongation tracking; Environmental simulations, such as post-UV aging testing, add complexity. The development trends include: the integration of digital image correlation technology to achieve non-contact full-field strain measurement; Combined with dynamic mechanical analysis, the frequency and temperature-dependent mechanical behavior is studied. Develop micro-specimen testing methods suitable for the development of small batch materials. Intelligent data management systems are also gradually popularizing to automate testing processes and dig deep into data.
Epilogue
As a basic tool for the evaluation of the toughness of polymer materials, the tensile testing machine provides a quantitative basis for the performance characterization of plastics and rubber through standardized testing and detailed data analysis. With the advancement of technology and the improvement of standards, its application will further support material research and development, quality control and engineering material selection, and help the safe and efficient use of polymer materials in many industries.
References
ISO 527-1:2019, Plastics — Determination of tensile properties — Part 1: General principles.
ISO 37:2017, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties.
GB/T 1040.1-2018, Determination of tensile properties of plastics - Part 1: General provisions.
GB/T 528-2009, Vulcanized rubber or thermoplastic rubber - Determination of tensile stress and strain properties.
Polymer Material Performance Test Manual, Chemical Industry Press.