Stress and Different Types of Stress

When a force is applied to a body, it deforms due to the induction of stress inside it. If the body has low strength, then the chances of getting deformation are more, while if the body has higher strength, then the chances of deformation are lower. Thus the resistance offered by the body towards deformation is called the strength of the material.

The strength of a material depends on different factors, and one of the important factors that contribute to the strength of the material is its stress-bearing capacity. Therefore it becomes necessary to understand the concept of stress and the different types of stress in physics that a body can experience. 

Stress

Consider a body on which a force F is applied. Due to the application of an external force, a restoring force will act inside the body to prevent the deformation. Although the magnitude of the restoring force will be the same as that of the external force, the direction of the restoring force will be opposite to the direction of the external force. Thus, stress is the restoring force acting per unit area on the body. The formula for stress is as follows: 

                                           σ = F/A

In the above-mentioned formula,

σ = Stress-induced in the body

F = Magnitude of the external force applied

A = Area of the body

The SI unit of stress is N/m2. However, the unit of stress varies depending upon the unit of external force and the area. In the MKS system, the unit of force is kgf while the unit of area is m2; hence the unit of stress becomes kgf/m2. While in the case of the CGS unit system, the unit of area is cm2; hence the unit of stress becomes kgf/cm2. Moreover, the dimensional formula of stress is [ML-1T-2].

Types of Stress in Physics

There are two different types of stress in physics. These are normal stress and shear stress. Normal stress refers to the stress whose direction is perpendicular to the area. It is further divided into compressive stress and tensile stress.

• Tensile Stress

Tensile stress is induced in a body when two equal and opposite forces act on the body such that the length of the body increases. The tensile stress normally acts on the area on which the force is applied, and its development leads to the generation of tensile strain, which is defined as the ratio of increase in length to the original length. 

To understand the working of tensile stress, you can take a rectangular block on which two equal and opposite tensile forces act. Now, consider a section x-x, such that it divides the rectangle into two equal parts. The part to the left of sections x-x will stay in equilibrium if the external force P is equal to the resisting force. Similarly, the section to the right of x-x will stay in equilibrium if an external force is equal to the resisting force. This resisting force acting per unit area is called tensile stress.

• Compressive Stress

Compressive stress is a type of stress in physics that reduces the length of the body. The compressive stress is induced in a body when the body is subjected to two equal and opposite pushes. 

Due to the application of pushes, stress is developed inside the body, which is known as compressive stress. Because of the application of pushes, the body experiences a decrease in length, and the ratio of the decrease in length to the original length is called compressive strain. Compressive stress acts normal to the area where it is applied, like tensile stress.

The tensile stress and compressive stress are also known as longitudinal stress because their line of action is parallel to the object’s horizontal axis.

• Shear stress

Shear stress is the type of stress in physics that acts tangential to the surface of a body. When two equal and opposite forces act on the body in such a manner that they act tangentially across the resisting section, they tend to shear off the section. The strain produced due to shear stress is called shear strain. A great example of the practical application of the shear stress is a riveted joint applied to tensile forces. 

Hooke’s law

According to Hooke’s law, when a material is loaded within the elastic limit, the stress is directly proportional to the strain produced in the body. Thus within the elastic limit, the ratio of stress and strain is a constant. This constant is known as the modulus of elasticity or modulus of rigidity, or elastic moduli.

Conclusion

Understanding the concepts of stress and strain is highly important because the induction of stress and strain in a body can lead to its failure. In this article, we have explained the concepts of stress and strain in depth. The article begins with the definition of the strength of materials and stress. After this, the article explains the different types of stress in physics. Primarily there are two types of stress: normal stress and shear stress. Normal stress is divided into two categories that are tensile and compressive stress. Another important concept related to stress and strain is Hooke’s law, which is explained towards the end of the article.