What is the yield strength?

Yield is the yield strength at yield limit of a metal material phenomenon occurs, i.e., resistance to micro plastic deformation stress. For no obvious yield a metal material, 0.2 to produce a predetermined percentage of residual deformation which yield limit stress value, known as the yield strength or proof stress. External force greater than this limit, will permanently disable the parts can not be recovered. As low yield strength steel is 207MPa, when under external force larger than this limit, the parts will produce permanent deformation, less than this, the parts will restore the original look.

1. Noun interpretation Yield strength

Yield is the yield strength at yield limit of a metal material phenomenon occurs, i.e., resistance to micro plastic deformation stress. For no obvious yield a metal material, 0.2 to produce a predetermined percentage of residual deformation which yield limit stress value, known as the yield strength or proof stress. External force greater than this limit, will permanently disable the parts can not be recovered. As low yield strength steel is 207MPa, when under external force larger than this limit, the parts will produce permanent deformation, less than this, the parts will restore the original look.

2. Detailed yield strength

is also known as the yield strength of the yield limit, common symbols [Delta] S, the material yield is critical stress value.

● material to yield significant phenomenon, yield stress (yield value) is the yield point strength;

● For material yield is not obvious, and the stress – strain limit linear relationship deviation reaches stress (typically from 0.2 percent of the original standard) predetermined value. Evaluation is generally used as a solid material mechanics mechanical properties, it is the actual use limit of the material. Because after necking stresses exceed the yield limit, strain increases, the material damage, not normal.

When the stress exceeds the elastic limit, yield phase into the deformation increased rapidly, this time in addition to elastic deformation, but also generating portion is plastically deformed. When the stress reaches point B, a sharp increase in plastic strain, stress and strain small fluctuations occur, a phenomenon known as the yield. Maximum, minimum stress at this stage are referred to as the yield point and the yield point. Since the value of the yield point is more stable, and therefore it is the material resistance as an index, called the yield point or yield strength (or ReL of Rp0.2).

Some steels (e.g., high carbon steel) yield no obvious phenomenon, usually plastic deformation stress trace amount (0.2 percent) occurs as the yield strength of the steel, the yield strength of the conditions referred (yield strength) .

First, to explain the force deformation material. Deformable material is not elastically deformed (the force revocationYou can recover the original shape) and the plastic deformation (after canceling force can not restore the original shape, shape changes, lengthening or shortening). .

3 Yield Strength

Frequently yield standards construction, there are three:

● proportional limit stress – the highest stresses will be a linear relationship between strain curve, International often used on σp he said more than σp think that is the material starts to yield.

● elastic limit after sample loading unloading to the residual permanent deformation does not appear as a standard, the elastic material can be completely restored highest stress. The international community generally expressed in Rel. When the stress exceeds Rel think that is the material starts to yield.

● yield strength occurs at a predetermined constant residual strain is standard, as is generally 0.2 to stress as a percentage of residual strain yield strength, symbol Rp0.2.

4. Yield strength factors

Internal factors

Effect of the yield strength are: a bond, organization, structure, atomic nature.

The yield strength of the metal and the ceramic, polymeric materials can be seen in comparison affect bond is fundamental. Effect from the organizational structure point of view, there are four kinds of strengthening mechanisms may influence the yield strength of the metal material, which is:

● solid solution strengthening;

● deformation strengthening;

[123 ] ● precipitation strengthening and dispersion strengthening;

● grain and sub-grain strengthening. Precipitation strengthening and fine grain strengthening means is the most common industrial material yield strength alloy improved. In these types of strengthening mechanisms, the other three mechanisms while improving the strength of the material, but also reduces the ductility, grain and sub grain refinement only, and can not only improve the strength of the plastic increases. External factors

Effect of the yield strength are: temperature, strain rate, stress state.

As the strain rate decrease the temperature increased, the yield strength of the material increases, especially in body centered cubic metals are particularly sensitive to temperature and strain rate, which results in a low-temperature embrittlement of steel. The effect of stress state is also very important. Although the yield strength is an essential indicator to reflect the intrinsic properties of the material, but with different state of stress, the yield strength values ​​are different. We usually yield strength of said material generally refers to the yield strength of the uniaxial stretching.

Engineering Significance yield strength of

TraditionalStrength design method, a plastic material, yield strength as a standard, predetermined allowable stress = σys / n, where the safety factor n can vary from 1.1 to 2 or more, brittle material, in a standard tensile strength, a predetermined allowable stress = σb / n, and generally the safety factor n 6.

It is noted that, according to the traditional strength design method, will inevitably lead sided pursuit of high yield strength materials, but with improved material yield strength, resistance to brittle fracture strength of the material decreases, brittle material increased risk of breaking up.

yield strength of not only the direct use of significance in engineering is almost certain measure process performance and mechanical behavior of materials. For example, material yield strength increased, it is sensitive to hydrogen embrittlement and stress corrosion; low intensity, like cold formability and weldability the material yield and the like. Therefore, the yield strength of the material properties is indispensable important indicator.

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