Before entering the main topic of the **Stress Strain Curve** we have to know about stress and strain.

## What is stress?

The term stress (s) is used to express the loading in terms of force applied to a certain **cross-sectional area** of an object. From the perspective of loading, stress is the applied force or system of forces that tends to deform a body.

**Stress is defined as the Force per unit cross-section area.**

Stress = F/A

**where,**

**σ** = stress,

* F* = force applied, and

* A*= cross sectional area of the object.

**Units of s :** Nm^{-2} or Pa.

## What is strain ?

Change in the dimension with respect to the original dimension due to stress is known as strain. It is denoted by the symbol epsilon.

**Strain is defined as extension per unit length.**

Strain = extension / original length

**Where**:

ε = strain,

lo = the original length

e = extension = (l-lo), and

l = stretched length

**Strain has no units because it is a ratio of lengths.**

### What is stress-strain curve?

The stress-strain curve could be a behavior of fabric once it’s subjected to load. during this diagram stresses area unit aforethought on the vertical axis and as a result of these stresses, corresponding strains area unit aforethought on the horizontal axis. As shown below within the stress-strain curve.

**Stress strain curve** has different regions and points. These regions and points are:

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

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