Tensile strength and yield strength

Tensile strength: a material to withstand maximum stress before pulling off. When the steel yield to a certain extent, due to the internal grain rearrange its ability to resist deformation increase again, this time deformation has developed rapidly, but it can only increase with stress and increase until the stress reaches the maximum value. Since then, the ability to resist deformation of steel significantly reduced, and large plastic deformation occurs at the weakest point, where the specimen cross-sectional rapidly shrinking, necking occurs until fracture failure. Steel pulled by maximum stress fracture is called before the ultimate strength or tensile strength.

Yield strength: the critical material yield stress value. For the yield phenomenon is clearly a material, the yield strength is the stress at yield point (yield value); for the material yield is not obvious, and stress - strain limit of a linear relationship between the deviation reaches a predetermined value (typically 0.2% permanent deformation) stress. Usually used as the mechanical properties of solid materials mechanics evaluation, the actual use of the limits of the material. Because necking, strain increases yield after material, and the material lost its original function. Yield strength and the yield point corresponding to the yield point is the point, the corresponding strength of the metal is plastically deformed to become yield strength. Allowable stress refers to the mechanical parts in the use for safety reasons, with the yield stress divided by a safety factor. Tensile strength refers to the material's ability to resist external forces, the strength of the pull-off time is generally stretching experiments.

When the stress exceeds the elastic limit, the deformation increased rapidly, this time in addition to elastic deformation, but also to produce parts of plastic deformation. When the stress reaches point B, a sharp increase in plastic strain curve appears a volatile small platform, a phenomenon known as the yield. The maximum and minimum stress at this stage are called the yield point and lower yield points. Since the value of the lower yield point is more stable, and therefore it is as a material resistance index, called the yield point or yield strength.