Mechanical Property of Steel
1. Yield point（ σ S)
When the steel or sample is stretched, the stress exceeds the elastic limit, even if the stress does not increase, the steel or sample continues to undergo obvious plastic deformation. This phenomenon is called yield, and the minimum stress value is the yield point. If Ps is the external force at the yield point s and Fo is the cross-sectional area of the sample, then the yield point σ S=Ps/Fo (MPa).
2. Yield strength（ σ 0.2)
Some metal materials have extremely inconspicuous yield points, making it difficult to measure them. Therefore, in order to measure the yield characteristics of the material, it is specified that the stress generated when the permanent residual plastic deformation is equal to a certain value (usually 0.2% of the original length) is called the conditional yield strength or simply the yield strength σ 0.2.
3.Tensile strength（ σ B)
The maximum stress value reached from the beginning to the occurrence of fracture during the stretching process. It represents the ability of steel to resist fracture. Corresponding to tensile strength are compressive strength, Flexural strength, etc. If Pb is the maximum tensile force reached before the material is pulled apart, and Fo is the cross-sectional area of the sample, then the tensile strength σ B=Pb/Fo (MPa).
4. Elongation（ δ S)
The percentage of the plastic elongation of a material after breaking compared to the length of the original specimen is called elongation or elongation.
