Why stress falls from upper to lower yield point in case of mild steel?

The solutes (i.e., say carbon in mild steel) migrate to dislocations. Once the dislactions are free, i.e., are unlocked (by the solutes), the stress required to move dislocation is lower and you get the lower Yield stress, i.e., Yield Drop.

What is upper yield point in stress strain curve?

The upper yield point designates the stress up to which no permanent plastic deformation occurs in a material under tensile loading. The yield point ratio is a measurement of the strain hardening up to the tensile strength.

Why does stress increase with strain?

For metals which harden by the development of dislocations, the increase of the rate of deformation induces a multiplication of the dislocations (increase of their density). This causes the increase of work hardening and consequently the increase of the stress.

Why do we have upper yield point and lower yield point?

Upper yield point is the point after which the plastic deformation starts. This is called strain hardening and lower yield point is the point after which strain hardening begins. Beyond the elastic limit plastic deformation occurs and strains are not totally recoverable.

Why upper and lower yield point occurs?

A few materials start to yield, or flow plastically, at a fairly well-defined stress (upper yield point) that falls rapidly to a lower steady value (lower yield point) as deformation continues. Any increase in the stress beyond the yield point causes greater permanent deformation and eventually fracture.

Why is there an upper and lower yield point?

What does the yield point represent in the stress strain diagram?

In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and will return to its original shape when the applied stress is removed.

Does stress depend on strain?

Yes, Stress is depends upon strain. This relation is easily explained through Hooke’s law. This law states that “the strain in a solid is proportional to the applied stress within the elastic limit of that solid”. When a force is applied to a body, after elastic limit the body starts to deform.

What is Upper yield and lower yield point stress strain curve?

The image to the right shows the engineering stress -strain diagram for a typical ductile material such as steel. Upper yield point is the point after which the plastic deformation starts. This is called strain hardening and lower yield point is the point after which strain hardening begins.

What is the cause of upper yield point in low carbon steel during stress strain testing?

It is well-known that the yield point phenomenon in low carbon steels is caused by the dislocation locking mechanism by interstitial atoms such as carbon and nitrogen.