Short Answer:

Stresses are the internal resisting forces developed within a material when it is subjected to external loads. These stresses act per unit area inside the body to resist deformation or failure. Depending on how the external force is applied, different types of stresses are produced in a material.

The main types of stresses are tensile stress, compressive stress, shear stress, bending stress, and torsional stress. Each type acts differently depending on the nature of the force. Understanding these stresses helps engineers design strong and safe structures and machine parts.

Detailed Explanation:

Types of Stresses

Definition:

When an external force acts on a body, it tries to deform the shape or size of that body. To resist this deformation, internal forces develop within the material. The intensity of these internal forces per unit area is called stress. Depending on the nature and direction of the applied force, different types of stresses are developed.

In mechanical engineering, understanding these types of stresses is very important for designing safe and reliable components such as beams, shafts, columns, and machine parts. Different loads such as tension, compression, torsion, or bending cause different kinds of stresses, and each must be analyzed carefully to prevent failure.

1. Tensile Stress

Tensile stress occurs when a material is subjected to a pulling or stretching force. The external force tries to increase the length of the material.
In this condition, the internal resisting force developed per unit area is called tensile stress.
Mathematically,

Example: A steel wire or rod being stretched by applying a load at its ends experiences tensile stress.
Effect: The material elongates, and the stress acts along the direction of the applied load.
Application: Tensile stress is considered in cables, tie rods, chains, and structural members under tension.

2. Compressive Stress

Compressive stress is produced when a material is subjected to pushing or squeezing forces. In this case, the external load tries to decrease the length or volume of the material.
The internal force developed to resist this compression per unit area is called compressive stress.

Example: A concrete column supporting a building or a short pillar under weight experiences compressive stress.
Effect: The material tends to shorten or get crushed.
Application: Columns, struts, and walls mainly experience compressive stress in civil and mechanical structures.

3. Shear Stress

Shear stress occurs when two equal and opposite forces act tangentially on parallel surfaces of a material. These forces try to slide one layer of the material over another.
It is given by:

Example: A paper being cut by scissors or a rivet joint holding two plates experiences shear stress.
Effect: The material tends to distort by sliding over itself.
Application: Shear stress is important in bolts, rivets, shafts, and mechanical fasteners.

4. Bending Stress

Bending stress is developed when a beam or structural member is subjected to bending moments or transverse loads.
When a beam bends, the upper fibers are subjected to compressive stress, while the lower fibers experience tensile stress. The neutral axis in between remains free from stress.
Example: A bridge beam or a cantilever beam carrying a load develops bending stress.
Effect: The material bends, and stress varies across the section.
Application: Found in beams, levers, axles, and structural members carrying transverse loads.

5. Torsional Stress

Torsional stress occurs when a circular shaft or rod is twisted by applying torque or twisting moment. The outer layers of the shaft experience maximum shear stress, while the center (axis) has zero stress.
Formula:

Where,

•  = Applied torque
•  = Radius of the shaft
•  = Polar moment of inertia

Example: The shaft of a motor or propeller experiences torsional stress when torque is applied.
Effect: The material tends to twist about its axis.
Application: Common in drive shafts, gear shafts, and rotating machinery.

6. Thermal Stress (Additional Type)

Thermal stress is produced when a material expands or contracts due to temperature changes but is restricted from free movement.
If a structure cannot freely expand when heated or contract when cooled, internal stresses develop within it.
Example: Railway tracks, bridges, and pipelines experience thermal stress due to temperature variation.
Effect: Expansion or contraction causes internal force buildup.
Application: Engineers provide expansion joints to reduce thermal stress in large structures.

Comparison of Stresses (Simple Understanding)

Type of Stress	Caused by	Effect on Material
Tensile Stress	Pulling force	Elongates the material
Compressive Stress	Pushing force	Shortens the material
Shear Stress	Tangential force	Slides material layers
Bending Stress	Bending moment	Curves the member
Torsional Stress	Twisting torque	Twists the shaft

(Note: Only for reference; no need to visualize as a table during notes writing.)

Importance of Studying Different Stresses

Understanding different types of stresses is essential for designing safe, reliable, and efficient structures and machines. By identifying which type of stress acts on a component, engineers can:

• Select appropriate materials with required strength.
• Prevent sudden failure or permanent deformation.
• Ensure that loads are properly distributed.
• Design parts to handle specific stress conditions safely.
• Improve product performance and safety.

For example, a shaft must be strong in torsion, a column in compression, and a beam in bending. Hence, studying types of stresses is the foundation of mechanical design and material analysis.

Conclusion:

The different types of stresses are tensile, compressive, shear, bending, and torsional stress. Each type is caused by different kinds of external forces and has unique effects on the material. Tensile and compressive stresses act along the length, shear stress acts tangentially, while bending and torsional stresses act due to moments or twisting. Understanding these stresses helps engineers design components that can safely withstand working loads without failure, ensuring strength, durability, and reliability in every mechanical system.