Stree-strain Curve

 Stress-Strain Curve

The stress-strain relationship for materials is given by the material’s stress-strain curve. Under different loads, the stress and corresponding strain values are plotted. An example of a stress-strain curve is given below.

Explaining Stress-Strain Graph

The stress-strain graph has different points or regions as follows:

• Proportional limit
• Elastic limit
• Yield point
• Ultimate stress point
• Fracture or breaking point

(i) Proportional Limit

It is the region in the stress-strain curve that obeys Hooke’s Law. In this limit, the ratio of stress with strain gives us a proportionality constant known as young’s modulus. The point OA in the graph is called the proportional limit.

(ii) Elastic Limit

It is the point in the graph up to which the material returns to its original position when the load acting on it is completely removed. Beyond this limit, the material doesn’t return to its original position and a plastic deformation starts to appear in it.

(iii) Yield Point

The yield point is defined as the point at which the material starts to deform plastically. After the yield point is passed, permanent plastic deformation occurs. There are two yield points (i) upper yield point (ii) lower yield point.

(iv) Ultimate Stress Point

It is a point that represents the maximum stress that a material can endure before failure. Beyond this point, failure occurs.

(v) Fracture or Breaking Point

It is the point in the stress-strain curve at which the failure of the material takes place.