Tensile strength and yield strength

Tensile strength and yield strength are two important mechanical properties of metal materials. These two indexes are closely related to anti fatigue manufacturing and service life of components.


Tensile strength is the index of mechanical properties of metal materials obtained by uniaxial tensile test. Tensile strength indicates the ability of metal materials to resist deformation and damage under external force. Tensile strength = breaking load / initial cross-sectional area of the sample.


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


The tensile strength index is aimed at the maximum deformation capacity. In other words, when the deformation reaches this level, the material breaks and no larger deformation can be found under uniaxial tension. It's a limitation, it's specific.  Tensile sample can bear the limit of applied load, so it is called ultimate tensile strength.


Yield strength is also one of the important mechanical properties of metal materials. Yield strength represents the resistance of metallic materials to initial plastic deformation, which is expressed in English as yield strength. In fact, this is not entirely accurate, because some metal materials have obvious yield points on the tensile curve, while other metal materials have no obvious yield points, especially for some materials with uneven microstructure. Therefore, when the plastic deformation reaches a certain degree, it is necessary to define the corresponding yield strength artificially. In fact, before the artificially defined plastic deformation value, the internal driving force of metal has started to slide, so it can not accurately reflect the plastic deformation. Start.


There is also a parameter about yield strength and tensile strength, which is yield ratio! Yield ratio is the ratio of yield strength to tensile strength. The range is 0 to 1.  Yield ratio is one of the indexes to measure the brittleness of steel. The larger the yield ratio, the smaller the difference between yield strength and tensile strength, the worse the plasticity and brittleness of steel!


The failure of the material begins at the yield point. The lower the yield ratio is, the longer the fracture time from the beginning to fracture is, the higher the yield ratio is, and the shorter the time from the beginning to fracture is. The energy is converted into heat energy between the yield point and the fracture point.


Simply put, if the yield strength is high or the tensile strength is high, the material will be better or safer. Only steel with high yield strength and low yield ratio is safer.