Tensile test means a test method for determining the properties of a material under axial tensile loading. The elastic limit, elongation, elastic modulus, ratio limit, area reduction, tensile strength, yield point, yield strength and other tensile properties of the material can be determined by using the data obtained from tensile test.
4 stages of steel tensile test:
(1) Elastic phase: This phase of the specimen deformation is completely elastic, all the load, the specimen will be restored to its original length. The elastic modulus E of the material can be measured during this phase.
(2) Yield phase: the elongation of the specimen increases sharply, while the load readings on the universal test machine fluctuate in a very small range (zigzag lines in the figure). If the slight fluctuations in this load reading are omitted, this phase can be expressed as a horizontal segment on the drawing diagram. If the specimen is polished, the surface of the specimen will be seen in the 45° direction of the stripe, called the slip line.
(3) Strengthening stage: After yielding stage, the resistance of specimen is increasing because the material is strengthened continuously during plastic deformation.
(4) in the necking stage and the rupture stage, the load reading gradually decreases after the specimen elongation to a certain degree.
Steel Tensile Test Standard:
ASTM E-8 Standard Specifies the metal tensile test steps:
ASTM D-638 Standard, D-2289 standard (high strain rate) and D-882 standard (sheet material) stipulate plastic tensile test; ASTM D-2343 Standard Specifies the tensile test method applicable to glass fiber, and ASTM D-897 standard specifies the tensile test method applicable to the binder; The ASTM D-412 standard specifies the tensile test method for hard rubber.
Tensile strength (tensile strength) refers to the stress that the material produces the maximum uniform plastic deformation.
In tensile test, the maximum tensile stress of the specimen until the fracture is tensile strength, and sometimes it is not scientifically known as tension, tensile, etc. In the report, tensile fracture stress, tensile yield stress, breaking elongation rate and so on can be obtained.
When the specimen is stretched, when the stress exceeds the elastic limit, even if the stress no longer increases, and the specimen continues to produce obvious plastic deformation, this phenomenon is called yielding, and the minimum stress value of yielding is the yield point.
Some samples of the yield point is very not obvious, there is difficulty in the measurement, so in order to measure the yield characteristics of materials, to produce permanent residual plastic deformation is equal to a certain value (usually 0.2% of the original length) when the stress, called the conditional yield strength or simply yield strength σ 0.2.
Elongation rate after breaking
When the metal material is broken by external force (stress), the length of the elongation of the specimen and the percentage of the original length.
Shrinkage Rate of section
The ratio of the area to the original area is called the shrinkage ratio of the section when the material is reduced by tensile fracture.
Tensile Test Fixture
We know that the mechanical locking structure has: bolts pattern (ie thread, screw, nut), bevel, eccentric wheel, lever and so on, fixture is the structure of these fixtures of the combination of the advantages and disadvantages of each.
The significance of tensile test
Elongation and sectional shrinkage indicate the ability of steel to undergo plastic deformation before fracture. The greater the elongation or the higher the shrinkage ratio of the section, the greater the plasticity of the steel. Steel plastic Large, not only easy to carry out a variety of processing, but also to ensure the safety of steel in building use. Because the plastic deformation of steel can adjust the local peak stress, it tends to be smooth, so as not to cause the local damage of the building structure and the whole structural damage caused by it.
The testing equipment used in tensile strength testing of steel is mainly the tensile tester with strong value, which can detect the force value from the 50kn-1000t, and is usually equipped with intelligent operating system. For testing steel Products.