Understanding Young’s Modulus

 

Understanding Young’s Modulus

                Young’s Modulus is one of the three main elastic constants which are: -

1)      Shear Modulus

2)      Bulk Modulus

3)      Young’s Modulus

 

These moduli are used to describe how a material deforms under the loading.

Let’s introduce Young’s Modulus using a tensile test. In a tensile test, we take a test piece, e.g. metal rod and stretch it along its length. It is a uniaxial test which means it applies the load in one direction only. The test machine in test measures the applied load and changes in the dimension of the applied test piece. The main output from this test is the stress-strain curve.

(σ) Stress (pressure)= Force/Area  

 

(ε) Strain = Change in length/Original Length

 

                 


                

                                                                Fig: - Stress-Strain Curve

This curve describes how much the material we are testing will deform for different levels of stress. This test ends when the material fractures. As shown above we can split the curve in two reasons which is the elastic region where the curve is linear and the plastic region.

When applied stress is low and we remain in the elastic region then the original dimension of the component will be completely recovered when the applied load is removed. This means the material acts as a plastic material. For more stress applied then we enter the plastic region. Here permanent plastic deformation will remain after removal of applied stress.

In elastic region, the stress-strain curve is a straight line. This means the strain is proportional to applied stress.

                i.e. (σ) Stress ∝ (ε) Strain => Stress (σ) = Young’s Modulus(E) * Strain(ε)

                                                                        => Young’s Modulus(E) = Stress (σ)/Strain(ε)                                                                                                                                                                                          Young’s Modulus is the gradient of the line in elastic region. Its unit is the same as stress (N/m2).

                Young’s Modulus is actually the measure of how much stiff material is. While calculating the stiffness of a structure Young’s Modulus is also used. The higher the young’s modulus the stiffer the material and so the smaller elastic deformation for the applied load.                                                                               

                If we conduct tests of different other materials then the slope of each material is different from another. Hence, different materials can have vastly different values of Young’s Modulus.

 

 

Mild Steel

High Carbon Steel

Carbon Content

0.05 to 0.25 %

0.6 to 0.95 %

Young’s Modulus

205Gpa

200Gpa

Yield Strength

370Gpa

490Gpa

Ultimate Tensile Strength

440Gpa

635Gpa

 

Notes: -

# Elastic Deformation:

a)          Caused by stretching of the bonds between atoms.

b)         Deformation is reversed when the load is removed.

# Plastic Deformation:

a)          Caused by the breaking of the atom bonds.

b)         Deformation is permanent and remains after the load are removed.

 

Why is Young’s Modulus important in engineering?

                Young’s Modulus is a very important material property when it comes to engineering. In engineering design, a common objective for many different applications is to keep elastic deformation as small as possible which means young’s modulus is a key parameter that needs to be considered in the material selection process. For example, while constructing a bridge if we take the material having low young’s modulus then it will show large deflection when some load moves over it. Selecting a higher stiffness (i.e. higher young’s modulus) material ensures that the elastic deformations remain small for larger loads.



                                                                                                          Prepared by:- Er. Biplov Sapkota

                                                                                                         Reference:-   The Efficient Engineer 

                                                                            

 

 

 

 

                                                                                                                                                                               

Comments

  1. milanOctober 2, 2020 at 9:33 PM

    Thank you so much bro for such an informative blog keep writing such blogs soon i will donate millions of dollars

    ReplyDelete

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