## Tuesday, 3 January 2017

### Stress Strain Curve for Mild Steel :

When the relationship between Stress and strain for any material on a Graph Paper will gives us the Stress Strain Curve.Stress strain curve is the behavior of material subjected under loading. To Draw Stress Strain curve we require a Graph paper. We will take Stress component on Y-axis and Strain component on the X-axis. Then we can draw a curve as shown in figure for respective values of stress and strain which will gives us a Curve. Here I am going to Explain you buddies about the Stress Strain Curve for Mild Steel.

Fig 1 : Stress Strain Curve for Mild Steel

Generally Stress Strain Curve is unique for each material and is found by recording the amount of deformation (Strain) at distant intervals of tensile loading (Stress). These curves will reveal many of the properties of a material,including data required to calculate Modulus of Elasticity (E).

Thus before drawing Stress strain curve we have to know the values of stress and strain of a material subjected to various loading. I will Discuss in detail How to Calculate the values of Stress and Strain of a mild steel material in upcoming Article.But By Now Let's Discuss about Stress Strain curve for Mild Steel.The Stress Strain Curve for mild steel looks as Shown in the Figure 1 .

In Above Figure You can Look at Various Points Marked.They are nothing but the stages involved before fracture of Mild Steel During Tensile Test.

Let me Simplify the above sentence When Mild steel is subjected to Loading it passes through various stages in systematic order and Finally When Load acting exceeds Stress,the material undergoes Fracture.Hope you are clear with above concept.Now lets move to Various Stages involved in Stress Strain Curve of a mild steel .

### Stages involved in Stress Strain Curve :

• Proportionality Limit
• Elastic Limit
• Yield Point
• Ultimate Stress Point
• Breaking Point

#### 1.Proportionality Limit:

Proportionality Limit means the Point up to which Mild Steel Obeys Hooke's Law.
Hooke's Law means Stress is Directly Proportional to Strain within Elastic Limit.
The above law can be explained as that Within Elastic Limit Stress and Strain of a material varies Linearly.

As Proportionality Limit Obeys Hooke's it means that up to the Point "A" Stress Strain will vary Linearly and thus we get Straight line in Graph.The Stress up to the Point "A" from "O" can be named as Proportional Limit Stress.

#### 2.Elastic Limit:

As the name indicated Elastic Limit Means Up to  that Point Material will exhibit Elasticity Property.
Elasticity means regain of material to its original shape after Load is taken off
Thus Up to Elastic Limit When we remove load the material will regain its original shape.Thus Material is Perfectly Elastic Up to Point "B"

#### 3. Yield Point :

Yield Point in Stress Strain Curve are of two types :
• Upper Yield Point
• Lower Yield Point
Upper Yield Point means the point at which yielding initiates due to application or increasing of load

It means that From Upper Yield Point Material will lose the Property of Elasticty.

As we apply Load the Yield increases slowly but at a particular point there will be sudden increase in the yield.This is called as Lower Yield Point.

Lower Yield Point can also be Defined as the Point at which Material yields in large amount even when we apply small amount of load.

In Stress strain curve"C' indicates Upper Yield Point and "D" indicates Lower Yield Point

#### 4.Ultimate Stress Point:

Ultimate Stress Point at which the Material will have maximum amount of Strength in itself.Beyond this point Material will have low or null amount of strength.

Up to this point of Ultimate Stress Point Material can withstand without breaking under loading. This point is also called as Ultimate Strength Point.

In Stress Strain Curve ultimate Strength point is denoted by the letter "F"

#### 5. Breaking Point :

Breaking Point is the Point at which Further loading will leads to failure or fracture of material.

Here at the Breaking Point material will have low amount of Strength.The Strength associated with this point is called as Breaking Strength or Rupture Strength.

In Figure Breaking Point is denoted by letter "G".

From Stress Strain curve ,the curve between Ultimate Stress Point and Breaking Point is called as Apparent Curve.

Hope You got idea about Stress Strain Curve for Mild Steel , If You have any queries Let me see you in Comments.