Question

just need to find out how to find the new yield point of a metal after it has been stretched ?

give the formula and explain it please

Answer 1

Well, before going find new yeild point first we know Yeild point.

Yeild point: It is a point where the elastic deformation converts in to plastic deformation and the corresponding stress is called Yield stress.

If the material elongates beyond the yield point and released it undergoes permanent deformation.If the stress is reapplied ie reelongates agian, firstly undergoes elastic deformation up to new yield point and then goes to plastic deformation this process is also called "Strain Hardening". here the new yield stress is greater than the original yield stress.

to find out new yield stess we have Hollomons equation.

i.e σ = E. eⁿ

where,

σ = Applied strees

e = strain

E = Yeild strees

n = strain hardening Exponent which is vary from 0 to 1

if n=0 means the material is perfectly Plastic

n=1 means the material is perfectly Elastic

Noramlly the n values lies between 0.10 to 0.50

With higher the n, the initial work hardening is less rapid than that of the lower n metals but the stress required to further deformation would continue to high strains.