Types of strain

Types of strain:-

Here we will discuss types of strain on different basics.

Ø  On the basis of the type of loading

-Tensile strain

            -Compressive strain

            -Shear strain

 

Ø  On the basis of type of deformation

-Temporary or elastic strain

           - Permanent or plastic strain

Ø  Strain is also classified as mentioned here

          -Linear strain   

          -Lateral strain

          -Volumetric strain

Tensile strain

- We have one bar of length L.

- There are two equal and opposite pulling type of forces P, acting axially and trying to pull the bar and this pulling action will result increase in the length of the bar under the action of tensile loading, but diameter of the bar will be reduced under the action of tensile loading. 

-Ԑ_t is the symbol which is used to represent the tensile strain in a member.

-Mathematically                  

                                 Tensile strain (Ԑ_t)= Increase in length (dL) /Original length (L)                                                                       

                                                                         Ԑ_t = dL / L

Compressive strain (Ԑ_c):-

 -We have one bar of length L.

- There are two equal and opposite push type of loading P, acting axially and trying to push the bar and this pushing action will result the decrease in the length of the bar under the action of compressive loading, but diameter of the bar will be increased under the action of compressive loading.

  -Mathematically                            

Tensile strain (Ԑ_t)= Increase in length (dL) /Original length (L)                           

                                                                      Ԑ_c = dL / L

Shear strain-

 - We have two plates and these two plates are connected with each other with the help of a pin or a rivet as shown in figure.

-There are two equal and opposite forces (P) acting tangentially across the resisting section. 

-One force is acting on top plate towards left direction and second force is acting towards right side as shown in figure and hence such type of loading will try to shear off the body across the resisting section.

-This type of loading action will be termed as shear loading and stress developed in material of the body will be termed as shear stress and corresponding strain will be termed as shear strain.

Ø  Temporary or elastic strain

-Temporary strain or elastic strain is such type of strain which will be disappeared on removal of external load or we can say that body will return to its original shape and size.

Ø  Permanent or plastic strain

-Permanent strain or plastic strain is such type of strain which will not be disappeared on removal of external load or we can say that body will not return to its original shape and size.

Ø  Linear strain

          - If length is L and breadth is B.

          -There are two equal and opposite pulling type of forces P, acting axially and trying to pull the rectangular bar and this pulling action will result increase in the length of the rectangular       bar under the action of tensile loading, but breadth of the rectangular bar will be reduced under the action of tensile loading.

          - Linear strain will be basically defined as the ratio of change in length of the body to the original length of the body. Linear strain might be tensile or compressive depending on the type of loading i.e. tensile loading or compressive loading.

     Ø  Lateral strain

     -Lateral strain will be the strain at perpendicular or right angle to the direction of applied force.

      -Lateral strain will be basically defined as the ratio of change in breadth of the body to the original breadth of the body.

Ø  Volumetric strain

     -When an object will be subjected with a system of forces, object will undergo through some changes in its dimensions and hence, volume of that object will also be changed.

      -Volumetric strain will be defined as the ratio of change in volume of the object to its original volume. Volumetric strain is also termed as bulk strain.

Ԑv = Change in volume/Original volume

Ԑv = dV/V

   Ø  Thermal Stress & Thermal Strains

-The Stresses produced due to the change of the materials are known as thermal stresses or temperature stresses.

-If the temperature of the body is lowered its dimensions will decrease and if the temperature of the body is raised its dimensions will increase.

- The corresponding strains caused by thermal stresses known as temperature strains or Thermal strains.

            -Let us assume a bar of uniform cross-section with initial length l 

            -Initial temperature T₁

            -Final temperature is T₂.

            - Coefficient of linear expansion is α.

 Mathematically

 -The expansion of the bar due to a rise in temperature will be:

                                                        expansion of bar = α(T₂ - T₁)l

 If the elongation of the bar is prevented by some external force or by fixing the bar ends

  Thermal strain = α(T₂ - T₁)                  

 

Note: “If the temperature of the bar is decreased, the thermal strain and stress will be tensile in nature.”