Welding knowledge – “Yield strength””

Thread Content

The significance of yield strength: In traditional strength design methods, for plastic materials, the yield strength is used as a benchmark; the allowable stress is determined as σys/n, with the safety factor n typically taken as 2 or higher. For brittle materials, the tensile strength is used as a benchmark, and the allowable stress is determined as σb/n, with the safety factor n usually set at 6. Yield strength not only has direct practical significance but also serves as an approximate measure of certain mechanical properties and processing characteristics of materials in engineering. For example, an increase in the material’s yield strength makes it more susceptible to stress corrosion and hydrogen embrittlement ； Materials with low yield strength have good cold working formability and weldability, and so on. Therefore, yield strength is an essential and important indicator of material properties. Factors affecting yield strength The internal factors that influence yield strength include: bonding bonds, microstructure, structure, and atomic properties. By comparing the yield strength of metals with that of ceramics and polymer materials, it can be seen that the effect of bonding bonds is fundamental. From the perspective of the influence of the microstructure, there are four strengthening mechanisms that can affect the yield strength of metal materials, namely solid solution strengthening, strain strengthening, precipitation strengthening and dispersion strengthening, as well as grain boundary and subgrain strengthening. Among them, precipitation strengthening and fine-grain strengthening are the most commonly used methods in industrial alloys to increase the yield strength of materials. Among these strengthening mechanisms, the first three reduce plasticity while increasing the strength of the material; only grain and subgrain refinement can increase both strength and plasticity. The external factors that affect yield strength include: temperature, strain rate, and stress state. As the temperature decreases and the strain rate increases, the yield strength of the material rises. Cubic metals are particularly sensitive to temperature and strain rate, which leads to the low-temperature embrittlement of steel. The influence of the stress state is also important. Although yield strength is an essential indicator reflecting the intrinsic properties of a material, its value varies depending on the stress state. The yield strength of materials, as we usually refer to it, generally denotes the yield strength under uniaxial tension.