There are two concepts in the introduction of bolts: tensile strength and yield strength. So what is tensile strength and yield strength?
Generally under the action of a certain external force, the material will exceed a certain limit value and be damaged. In general, there are many forces that cause damage to materials, such as tensile force, pressure, shear force, and torsion.
Today's tensile strength and yield strength are both for tensile forces, which are obtained through tensile tests. Generally, the material is stretched by a tensile machine until it breaks or reaches a certain degree of damage. The force that causes final damage to the material is the ultimate tensile load of the material. The tensile force is generally expressed in Newton N or KN. Divide the ultimate tensile force by the cross-sectional area of the test material to obtain the ultimate tensile load per unit area. Forces per unit area are generally expressed in megapascals (MPa = N / mm).
Tensile strength is the ratio of the ultimate tensile load divided by the cross-sectional area of the material. Tensile strength is the limit of the maximum external force that a unit of material can withstand. Beyond this ultimate tensile force, the material will be destroyed.
So what is yield strength? Yield strength is for elastic materials. Inelastic materials have no yield strength. For example, all kinds of metal materials, plastics, rubber, etc. have yield strength. Glass, ceramics, masonry, etc. are relatively brittle, and generally have no elasticity or yield strength.
Generally, the material undergoes elastic deformation under the action of external force (what is called elastic deformation? That is, when the external force is eliminated, the material will return to its original size and shape). When the external force continues to increase, the material will enter plastic deformation after a certain value. Once the material enters the plastic deformation and the external force is eliminated, the original size and shape of the material cannot be restored! The critical point strength that causes the two types of deformation is the yield strength of the material! Corresponding to the applied tension, the value of the tension at this critical point is called the yield point.