Know how to calculate yield stress

1.

The formula of yield strength is re = Fe / so; Fe is the constant force at yield

The formula for calculating the upper yield strength is Reh = FEH / so; FEH is the maximum force before the first drop in the yield stage

The formula of lower yield strength is rel = FEL / so; FEL is the minimum force FEL less than the initial instantaneous effect

The force collet displacement diagram was drawn with automatic recording device ring

test. It is required that the stress represented by the ratio of force axis per mm is generally less than 10N / mm and 178;, The curve should be drawn at least to the end of the yield stage. The constant force Fe of the yield platform, the maximum force FEH before the first drop of the force in the yield stage or the minimum force FEL less than the initial instantaneous effect are determined on the curve

extended data

the internal factors that affect the yield strength are bond, microstructure, structure and atomic nature

If the yield strength of metals is compared with that of ceramics and polymers, it can be seen that the effect of bonding bond is fundamental. From the influence of microstructure, there are four strengthening mechanisms which can affect the yield strength of metal materials, namely:

(1) solid solution strengthening

(2) deformation strengthening

(3) precipitation enhancement and dispersion enhancement

(4) grain boundary and subgrain strengthening

precipitation strengthening and fine grain strengthening are the most commonly used means to improve the yield strength of instrial alloys. Among these strengthening mechanisms, the first three mechanisms not only improve the strength of the material, but also rece the plasticity. Only refining the grain and sub grain can improve the strength and increase the plasticity

The external factors influencing yield strength are temperature, strain rate and stress state

with the decrease of temperature and the increase of strain rate, the yield strength of the material increases, especially the BCC metal is particularly sensitive to temperature and strain rate, which leads to the low temperature embrittlement of the steel

The influence of

stress state is also very important. Although the yield strength is an essential index reflecting the internal properties of materials, the yield strength values are different with different stress states. The yield strength of materials generally refers to the yield strength under uniaxial tension

2.

Calculation method of steel yield strength:

calculation formula of yield strength: σ= F / s,

where σ Is the yield strength, unit is "MPa",

for reinforcement, f is the force when the plastic deformation of reinforcement is 0.2% of the original length, unit is "n",

s is the cross-sectional area of reinforcement, unit is "m ^ 2"

extended data:

yield strength is the yield limit of metal materials when yielding, that is, the stress resisting micro plastic deformation. For the metal material without obvious yield, the stress value with 0.2% resial deformation is defined as its yield limit, which is called conditional yield limit or yield strength

the external force greater than this limit will make the parts permanently invalid and unable to recover. If the yield limit of low carbon steel is 207mpa, when the external force is greater than this limit, the part will proce permanent deformation, and if it is less than this, the part will return to its original state

(1) for materials with obvious yield phenomenon, the yield strength is the stress (yield value) at the yield point

(2) for the material with no obvious yield phenomenon, the stress when the limit deviation of the linear relationship between stress and strain reaches the specified value (usually 0.2% of the original gauge length). It is usually used as the evaluation index of the mechanical properties of solid materials, and is the actual use limit of materials. Because the necking occurs when the stress exceeds the yield limit of the material and the strain increases, the material is damaged and cannot be used normally

3. There are four stages from tensile to fracture: 1 proportional stage, 2 yielding stage, 3 strengthening stage and 4 necking stage
in the proportional stage, the stress becomes proportional to the stress; Yield stage: because of the metal grain sliding, it temporarily loses the ability to resist failure, and the up-down wave pattern can be seen from the tensile diagram, which is called yield platform; In the strengthening stage, the grain sliding is completed and the material recovers its ability to resist damage; Necking stage: the material completely lost the ability to resist damage
it can be seen from the tensile diagram that there are two yield points: the upper and the lower. The lower yield point is used in engineering, that is, the lowest value ring the yield period, regardless of the initial instantaneous effect
yield strength calculation: divide the value of lower yield point force (n) read from tensile test by the cross-sectional area of the test piece (mm & sup2;), The yield strength is obtained. Unit n / mm & sup2;

4. Yield strength, also known as yield limit, is the critical stress of material yield

(1) for materials with obvious yield phenomenon, the yield strength is the stress (yield value) at the yield point< (2) when the limit deviation of the linear relationship between stress and strain reaches the specified value (usually 0.2% of the permanent deformation) for the material with no obvious yield phenomenon. It is usually used as the evaluation index of the mechanical properties of solid materials, and is the actual use limit of materials. Because the necking occurs when the stress exceeds the yield limit of the material and the strain increases, the material is damaged and cannot be used normally

when the stress exceeds the elastic limit and enters the yield stage, the deformation increases rapidly. At this time, in addition to the elastic deformation, part of the plastic deformation occurs. When the stress reaches point B, the plastic strain increases sharply and the stress and strain fluctuate slightly. This phenomenon is called yield. The maximum and minimum stresses at this stage are called upper yield point and lower yield point respectively. Because the value of lower yield point is relatively stable, it is called yield point or yield strength (REL or Rp0.2) as the index of material resistance

some steels (such as high carbon steel) have no obvious yield phenomenon. Usually, the yield strength of the steel is the stress at the time of slight plastic deformation (0.2%), which is called yield strength

therefore, if other external and internal conditions are the same, increasing the inner diameter by 0.1 mm has no effect on the yield strength

5. 9 + 0 = 9
9-0 = 9
is it meaningful to put it in the formula table?

6. The calculation method of fraction addition and subtraction:
1) if the denominator is the same, only the numerator is added and subtracted, and the denominator remains unchanged
2) if the denominator is not the same, first divide it into the same denominator, then add and subtract.