TYPES OF STRESSES

Stresses are two types they are

               1. Normal stresses, and 

               2. Shear stresses

          Normal stress is the stress which acts in a way perpendicular to he area. It is represented by 'σ' (SIGMA). Normal stress is further divided into Tensile stress and Compressive stress.

Let us discuss each of them briefly

1. Tensile stress:

          The stress induced in a body, when subjected to two equal and opposite pull forces as shown fig., as a result of which there is an increase in length, is known as Tensile stress. The ratio of increase in length to the initial (or) original length is known as Tensile strain. The tensile stress acts normal to the area and it pulls on the area. 

              Let P = Pull force acting on the body,

                     A = Cross-sectional area of the body, 

                     L = Original length of the body, 

                   dL = Change in length 

                    σ  = Stress induced in the body, and 

                     e = Strain 

          Below fig., shows a bar subjected to a tensile force 'P' at its ends. Consider a cross section x-x which divides the bar into two parts. The part left to the section x-x, will be in equilibrium if Tensile force (P)=Resisting force (R). Similarly the part which is right to the cross section x-x, will be in equilibrium if P= Resisting force. This resisting force per unit area is known as Tensile stress or Intensity of stress.

2. Compressive stress: The stress induced in a body, when it is subjected to two equal and opposite push forces as shown in fig., as a result of which there is a decrease in length of the body, is known as Compressive Stress. The ratio of decrease in length to the initial (or) original length is known as Compressive strain. The compressive stress acts normal to the area and it pushes on the area. 

  

3. Shear stress: The stress induced in a body, when it is subjected to two equal and opposite push forces which are acting tangentially across the resisting section as shown in fig., as a result of which the body tends to shear off across the section, is known as Shear Stress. The corresponding strain is known as Shear strain. The shear stress which acts tangential to the area. Which is represented by 'τ' (Tau).

Credits: Mechanical engineers

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STRESS

          Consider some external force acting on a body, the force of resistance per unit area offered by a body against deformation is known as Stress. This external force which is acting on body is called the Load (or) Force. When the load is applied on the body while the stress is induced in the material of the body. The loaded body remains in equilibrium when the resistance offered by the body against deformation and the applied load are equal. 

Stress is denoted by a letter "σ" (SIGMA)

Mathematically stress is written as σ = P/A

          Where σ = Stress (or  Intensity of stress)

                       P = External force (or) Load

                       A = Cross sectional area.

Units of Stress:

          Units of stress depends upon two factors, they are units of Load and Units of area. 

In MKS units, the force is expressed in kgf and area in square meters, so stress units are kgf/m^2.
In SI units, the force is expressed in Newtons and area in meter squares, hence units of stress becomes N/m^2.