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Monday, 4 November 2019

DIFFERENCE BETWEEN THICK AND THIN CYLINDER


Today, we will start here another important topic of strength of material i.e. thin cylindrical and spherical shells with the help of this post. 


Thin cylindrical and spherical shells

Thin cylindrical and spherical shells are also termed as pressure vessels and such vessels are usually used in various engineering applications such as for storing the fluid under pressure.

Boilers, LPG cylinders, Air receiver tanks are the best examples of thin cylindrical shells.

A cylindrical or spherical shell will be considered as thin cylindrical or spherical shell, if the wall thickness of shell is very small as compared to the internal diameter of the shell.

Wall thickness of a thin cylindrical and spherical shell will be equal or less than the 1/20 of the internal diameter of shell.

Let us consider one cylindrical shell as displayed here in following figure. Fluid is stored here under pressure within the cylindrical shell. We will first find out here the condition to consider the shell as thin cylindrical or spherical shell. 


d = Internal diameter of the shell
t = Wall thickness of the shell
l = Length of the cylinder
P = Internal pressure of the fluid stored inside the cylinder

Condition for thin cylindrical or spherical shell

Wall thickness of thin cylinder < [(1/20) x Internal diameter] 

t < d/20
t/d < 1/20
d/t > 20

This is the condition that we must have to note it to consider a cylindrical or spherical shell as thin cylindrical or spherical shell. 



Radial stress could be neglected when we deal with the thin cylinders. 

Thick cylinder 

Thick cylinders are basically those cylindrical vessels that contain fluid under pressure and ratio of wall thickness to the internal diameter of such cylindrical vessels will not be less than 1/20.  

We can see the practical applications of thick cylinders in various areas such as domestic gas cylinders, oxygen gas cylinders used in medical field, barrel of a gun, water and gas pipelines, nozzle of a jet etc. 

Condition for thick cylinder 

Wall thickness of thick cylinder < [(1/20) x Internal diameter] 

t > d/20
t/d > 1/20
d/t > 20

Radial stress could not be neglected when we deal with the thick cylinders.

This is the condition that we must have to note it to consider a cylinder as thick cylinder.

We will now discuss another topic, stresses in a thin cylinder subjected to internal pressure and thick cylinder lame's equation in the category of strength of material, in our next post.

Reference:

Strength of material, By R. K. Bansal
Image Courtesy: Google

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