Stress Distribution-Finite Element Method-Assignment Solution, Exercises of Mathematical Methods for Numerical Analysis and Optimization

This assignment solution was submitted to Amar Sharma for Finite Element Method course at Aligarh Muslim University. It includes: Stress, Distribution, Tapered, Bar, Finite, Elements, Axial, Load, Idealization, Displacement, Models

Typology: Exercises

2011/2012

Uploaded on 07/08/2012

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Question #1.2:-
Find the stress distribution in the tapered bar shown below using two finite elements under an axial
load of P=1N.
Solution:-
1- Idealization
Let the bar be considered as the assemblage of two elements as shown below:
Assume the bar to be one-dimensional then we have only axial displacement at any point. As there are
three nodes so we have nodal displacements Ø1, Ø2 , Ø3 . These will be unknown.
1
2
2
3
Ø1
Ø2
Ø2
Ø3
pf3
pf4
pf5

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Question #1.2:-

Find the stress distribution in the tapered bar shown below using two finite elements under an axial load of P=1N.

Solution:-

1- Idealization

Let the bar be considered as the assemblage of two elements as shown below:

Assume the bar to be one-dimensional then we have only axial displacement at any point. As there are three nodes so we have nodal displacements Ø 1 , Ø 2 , Ø 3. These will be unknown.

Ø 1 Ø 2 Ø 2 Ø 3

2- Displacement Models

In each element we assume a linear variation of axial displacement Ø.

where ‘a’ and ‘b’ are constants which can be found out by putting the boundary conditions:

Ø=Ø 1 (e)^ at x = 0 Ø=Ø 2 (e)^ at x = l

So by putting the boundary conditions; we get:

a= Ø 1 (e)^ and b= (Ø 2 (e)^ - Ø 1 (e)) / l(e)

3- Element Stiffness Matrix

Using principle of minimum potential energy:

I = Strain Energy – Work Done by External Force = π(1)^ +π(2)^ - Wp

where

and

(Ø 2 (e)^ - Ø 1 (e)) / l(e)

Hence

In Matrix Form

Where

Combining:

[K]=

Global Load Vector:

Overall Equilibrium Equation:

5- Solution of displacement

Inserting Boundary Conditions for nodal displacements:

As Ø 1 =0 So we eliminate the first and first column we have:

Ø 2 = 0.14 x 10-6^ cm

Ø 3 = 0.34 x 10-6^ cm

6- Element Strains and Stresses

And Stresses are: