Friday, 30 December 2016

TYPES OF STRAIN IN STRENGTH OF MATERIALS

TYPES OF STRAIN IN STRENGTH OF MATERIALS

We were discussing the concept of stress and strain and also we have discussed the different types of stress in our previous post; now we are going further to start our discussion for classifying the strain. Hence, we will see here the types of strain with the help of this post.

Types of strain

There are following types of strain and we will discuss each type of strain in detail with the help of this post.

Strain is classified on the basis of the type of loading

Tensile strain
Compressive strain
Shear strain

Strain is also classified on the basis of type of deformation

Temporary or elastic strain
Permanent or plastic strain

 

Strain is also classified as mentioned here

Linear strain
Lateral strain
Volumetric strain

Tensile strain

Let us see here the following figure; 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. 
Therefore we can define the tensile strain as the strain developed in a member due to the pulling action of two equal and opposite direction of forces. Ԑt is the symbol which is used to represent the tensile strain in a member.

Tensile strain will be determined with the help of following formula.
Tensile strain (Ԑt) = Increase in length (dL) / Original length (L)
Ԑt = dL / L

Compressive strain

Let us see here the following figure; 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. Ԑc is the symbol which is used to represent the tensile strain in a member.
Compressive strain will be determined with the help of following formula.
Compressive strain (Ԑc) = Decrease in length (dL) / Original length (L)
Ԑc = dL / L

Shear strain

Let us see here the following figure; 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.

Shear strain will be determined as displayed in following figure

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.

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.

Linear strain

Let us consider one rectangular bar as shown in figure, its 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. Here in this example, linear strain will be tensile strain because tensile loading is here.

Lateral strain

Consider the same figure as displayed above, Lateral strain will be the strain at perpendicular or right angle to the direction of applied force.

Therefore we can define here lateral strain as; lateral strain will be basically defined as the ratio of change in breadth of the body to the original breadth of the body.

 

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
We will study and analyze each type of strain in detail in our next post.

Reference:

Strength of material, By R. K. Bansal
Image courtesy: Google
We will see another important topic i.e. Elasticity and elastic limit in the category of strength of material.

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