The tensile test is the most fundamental method for determining the mechanical properties of materials. By applying an axial tensile force to a standard specimen and recording the force-displacement curve, it further analyzes key mechanical indicators of the material such as strength, plasticity, and elasticity.
By simulating the deformation and failure process of materials under axial force, it quantitatively obtains the material's ability to resist external forces (strength) and deformation capacity (plasticity), providing a basis for material selection, structural design, and quality inspection.
Based on the tensile curve (stress-strain curve), the following core indicators can be extracted. Their physical meanings and application scenarios are shown in the table below:
The stress-strain curves of different types of materials vary significantly, directly reflecting their mechanical property characteristics:
- Plastic Materials (e.g., low-carbon steel): The curve has four stages—elastic stage (recovery after unloading), yield stage (stress remains unchanged while strain increases), strain hardening stage (stress and strain increase simultaneously), and necking-fracture stage. The percentage elongation after fracture is high (δ > 5%).
- Brittle Materials (e.g., ceramics, cast iron): There is no obvious yield stage; they fracture directly after the elastic stage. The percentage elongation after fracture is extremely low (δ < 5%), and the tensile strength is much lower than the compressive strength.
- Highly Elastic Materials (e.g., rubber): The elastic deformation is extremely large (up to 1000%), the elastic modulus is low, there is no plastic deformation, and it fully recovers after unloading.
The accuracy of the test results depends on the control of the following factors:
- Specimen Specifications: Must comply with national standards (e.g., GB/T 228.1) to ensure uniform dimensions (length, diameter) and avoid errors caused by specimen differences.
- Loading Rate: Excessively fast loading will make the material exhibit "increased brittleness" (e.g., low-carbon steel may have no obvious yield). Loading must be carried out at the standard rate (e.g., 1~5 mm/min).
- Environmental Conditions: High temperatures reduce material strength and increase plasticity; low temperatures make materials brittle (e.g., "cold brittleness" of steel at low temperatures). The test temperature must be clearly specified.
