1. Determination of the standard value of yield strength
Yield strength is the critical point at which plastic deformation begins to occur in a material during stress. In the stress-strain curve of a material, the yield strength usually corresponds to a certain strain value. According to international standards and related codes, the standard value of yield strength for steel is generally its 0.2% offset yield strength. This value is a statistical average derived from a large number of tests and represents the strength level of the material under normal conditions.
2. Determination of design value
Design value refers to the value obtained by multiplying the standard value of yield strength by a safety factor in order to meet the predetermined safety requirements in engineering design. The safety factor is determined according to the special circumstances and risk assessment of the project and is used to take into account factors such as material inhomogeneity, load uncertainty and structural reliability. The design value is determined to ensure that the engineered structure will not fail or be damaged during its service life.
3. Relationship between yield strength standard value and design value
The relationship between the standard value of yield strength and the design value can be expressed by the following equation:
Design value = Yield strength standard value × Factor of safety
The safety factor is usually a value greater than 1, which represents a conservative estimate of the strength of the material in the design project. By adjusting the size of the safety factor, the size of the design value can be controlled to meet the safety requirements of the project. When the safety factor is large, the design value will be reduced accordingly and the strength and stability of the structure is ensured to be higher. And when the safety coefficient is small, the design value will increase accordingly, and the economy and lightweight design of the structure are given more consideration. In engineering design, according to different engineering requirements and material properties, different yield strength standard values and safety coefficients can be selected. For some projects with high requirements on strength, such as bridges and high-rise buildings, higher standard values of yield strength and larger safety coefficients are usually selected to ensure the safety of the structure. For some projects with more sensitive requirements on cost and weight, such as automobiles and aircrafts, lower yield strength standard values and smaller safety factors can be selected to achieve lightweight and cost-saving design.
