Tensile strength is the critical value of transition from uniform plastic deformation to locally concentrated plastic deformation. It is also the maximum carrying capacity of metals under static tension. Tensile strength is the resistance that characterizes the maximum uniform plastic deformation of materials. The deformation of tensile specimens is uniform before they bear the maximum tensile stress, but beyond that, the metal begins to neck, i.e. concentrate deformation. For brittle materials without (or very small) uniform plastic deformation, it reflects the fracture resistance of materials. The symbol is Rm (GB/T 228-1987 old national standard stipulates that the tensile strength symbol is_b), and the unit is MPa. Tensile strength is the maximum nominal tensile stress of the specimen before breaking. It is the critical value for metal to transit from plastic deformation of uniform and universal material testing machine to local concentrated plastic deformation, and it is also the maximum load-carrying capacity of metal under static tension. For plastic materials, it characterizes the resistance of material to the maximum uniform plastic deformation. The deformation of tensile specimens is uniform before the maximum tensile stress, but beyond that, the metal begins to neck, i.e. concentrate deformation. For brittle materials without (or very small) uniform plastic deformation, it reflects the fracture resistance of materials. The symbol is Rm and the unit is MPa. During the tensile process, the maximum force (Fb) that the material bears at break is obviously reduced with the transverse section size after the yield stage and the strengthening stage. The stress (_) obtained by dividing the original cross-section area (So) of the specimen is called tensile strength or strength limit (_b), and the unit is N/mm2 (MPa). It represents the maximum resistance of metal materials to damage under tension. The calculation formulas are as follows: _=Fb/Sot: Fb - the maximum force endured when the specimen is broken, N (Newton); So - the original cross-sectional area of the specimen, mm. Tensile strength (Rm) refers to the maximum stress that the material bears before breaking. When the steel yields to a certain extent, its resistance to deformation increases again due to the rearrangement of internal grains. At this time, although the deformation develops rapidly, it can only increase with the increase of stress until the maximum stress is reached. Thereafter, the steel's ability to resist deformation is obviously reduced, and a large plastic deformation occurs at the weakest point, where the section of the specimen shrinks rapidly, leading to necking until fracture. The maximum stress value of steel before tensile fracture is called strength limit or tensile strength. Unit: N/cm2 (kilogram force per unit area) Tensile strength is commonly measured by universal material testing machine in China.