Consider a block made up of number of molecules is subjected some to amount of externally applied force.
As the block is made up of number of molecules, molecules present in the block will be subjected to externally applied force. Molecules exert an internal force on each other within the block because of the externally applied force. The measure of internally developed forces acting per unit area is called as stress.
In other words, the resisting force or the internal resistance setup within the material is called as stress. Usually stress is denoted by σ.
The SI Unit of stress is N/m2.
Types of stress
- Tensile stress
- Compressive stress
- Shear stress
- Bending stress
- Thermal stress
We can also classify the stress according to the type of force acting on the component,
- Direct stress
Direct stress is the stress developed due force applied which is parallel or collinear to the axis of the component. Examples for this type of stress are tensile stress, compressive stress, shear stress, thermal stress.
- Indirect stress
If the stress is developed due to moment or torsion then it is called as indirect stress. Example: Bending stress, stress due to torsion.
Within elastic limit stress is directly proportional to strain.
Let us assume σ = stress, e = strain, E = Youngs Modulus.
Then according to hooke’s law σ ∝ e
or σ = E x e