Why are there upper and lower yield points?

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.

What does the yield point represent in 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.

Why does steel have 2 Yield points?

This Yield Point phenomenon is due to locking and unlocking of dislocations (from the solute atmosphere). Then you get the yield point elongation and notice the Luders Band. If one does unloading, then after ageing, if reloaded one gets higher yield stress and is well known as static strain ageing.

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.

What does yield point mean?

The yield point is defined as the stress beyond which a material deforms by a relatively large amount for a small increase in the stretching force.

What is the lower yield stress point?

A point at which Maximum load or stress required to initiate the plastic deformation of material such point is called as Upper yield point. And a point at which minimum load or stress required to maintain the plastic behavior of material such a point is called as Lower yield point.

Which point on the stress strain curve occurs after the lower yield point?

Which point on the stress strain curve occurs after yield plateau? Explanation: After the yield plateau the curve will go up to its maximum limit of stress which is its ultimate point.