Tensile strength is the critical value of the transition of metal from uniform plastic deformation to localized plastic deformation, and it is also the maximum load carrying capacity of metal under static tensile conditions. Tensile strength is the resistance to the maximum uniform plastic deformation of the material. Before the tensile specimen is subjected to the maximum tensile stress, the deformation is uniform, but after the metal is exposed, the neck begins to shrink, that is, the concentrated deformation occurs; Very small) a uniformly plastically deformed brittle material that reflects the fracture resistance of the material. The symbol is Rm (the GB/T 228-1987 old national standard specifies the tensile strength symbol is σb), and the unit is MPa.

Practical significance of tensile strength

Σb marks the actual bearing capacity of ductile metal materials, but this bearing capacity is limited to the loading condition of uniaxial tension of smooth specimens, and the σb of ductile materials cannot be used as design parameters, because the strain corresponding to σb is far from the actual use. Achieved. If the material is subjected to a complex stress state, σb does not represent the actual useful strength of the material. Since σb represents the maximum load carrying capacity of the actual machine under static tension conditions, and σb is easy to measure and has good reproducibility, it is one of the important mechanical performance marks of engineering metal materials, and is widely used as product specification or quality control. index.

For brittle metal materials, once the tensile force reaches a maximum, the material breaks rapidly, so σb is the breaking strength of the brittle material. For the product design, the allowable stress is judged by σb.

The level of σ depends on the yield strength and the strain hardening index. When the yield strength is constant, the larger the strain hardening index, the higher the σb.

There is a certain empirical relationship between tensile strength σb and Brinell hardness HBW and fatigue limit.