Tensile strength and yield strength

　　Tensile strength and yield strength are two important mechanical properties of metal materials. These two indices are closely related to the fatigue-resistant manufacturing and the service life of components.

　　Tensile strength is an index of mechanical properties of a metal material obtained by a uniaxial tensile test. Tensile strength represents the ability of a metal material to resist deformation and damage under external forces. Tensile strength = breaking load / initial cross-sectional area of the specimen.

　　When the metal has obvious plastic deformation, the cross-sectional area used in the calculation should be the true cross-sectional area measured after the break, and the obtained tensile strength is called the true tensile strength.

　　This tensile strength index is an index against the maximum deformation ability. In other words, when the deformation reaches this level, the material is broken, and under the condition of uniaxial stretching, no larger deformation can be found. It is a limit and is specific. The tensile sample can withstand the limits of the applied load and is therefore called Ultimate Tensile Strength.

　　Yield strength is also one of the important mechanical properties of metal materials. The yield strength represents the resistance of the metal material to the initial plastic deformation, and its English expression is Yield strength. In fact, this is not completely accurate, because some metal materials have obvious yield points on the tensile curve, while other metal materials have no obvious yield point, especially for some materials with uneven microstructure. Therefore, it is necessary to artificially define the corresponding yield resistance strength when the plastic deformation is to a certain extent. In fact, before the artificially defined plastic deformation value, the slip of the internal driving force of the metal has started, so it cannot accurately reflect the plastic deformation. Start.

　　There is also a parameter about yield strength and tensile strength, this parameter is the yield ratio! The yield ratio is the ratio of yield strength to tensile strength. The range is between 0 and 1. The yield ratio is one of the indicators for measuring the brittleness of steel. The greater the yield ratio, the smaller the difference between the yield strength and the tensile strength of the steel, the worse the plasticity of the steel and the greater the brittleness!

　　The destruction of the material begins with the yield point. The lower the yield ratio, the longer the material will break from the beginning to the fracture, and the higher the yield ratio, the shorter the time from the onset of the material to the fracture. The energy is converted into heat energy between the yield point and the break point.

　　Simply saying that the yield strength is high or the tensile strength is high, then the material is necessarily better or safer. Only steels with high yield strength and low yield ratio are safer.