Section Modulus calculation and optimization

Section Modulus Calculation and optimization

The section modulus of the cross-sectional shape is of significant importance in designing. It is a direct measure of the strength of the design. A section that has a larger section modulus than another will be stronger and capable of supporting greater loads.

The section modulus is given by the ratio of total moment resisted by the section to the stress in the extreme fibre. It gives us an idea about how much load the given structure can take. i.e. If the section modulus increases the moment of resistance increases and hence its load bearing capacity.

Calculation Of Section Modulus

• Here the section selected for the section modulus calculation is the designed Hood.
• The section along the length of the hood will be taken and using the section Inertia analysis tool in Siemens Nx the MOI(Moment Of Inertia) is measured.
• Then using the MOI value section modulus can be obtained using the formula given: S=I/Y where, S - Section Modulus I - MOI value from section Inertia analysis Y - Distance from Neutral axis to outermost fibre(In this case we take it from the centre to the outer edge of hemmed outer panel).

Strength Of Hood Pannel

By using the given equation, the section modulus of the hood, I designed Is computed as given below:

Using section Inertia analysis tool, we got

I_max=4.78x10⁶ mm⁴

I_min=1.39x10⁴ mm⁴

Y= 440.4984mm (Measured from the model)

1. S_max= I_max / Y

=4.78x10⁶ mm⁴ / 440.4984mm

=1.0852x10⁴ mm³(Maximum Strength).

2. S_min= I_min / Y

=1.39x10⁴ mm⁴/ 440.4984mm

=0.0031x10⁴ mm³(Minimum Strength).

Thus the strength of the hood varies from 0.0031x10⁴ mm³ to 1.0852x10⁴ mm³.

To increase the section Modulus The cross sectional area should be increased without noticeable change in ‘Y’.For the same inner pannel was offseted 2mm more.

The MOI of trial section by offsetting the inner panel. Is given below:

Using section Inertia analysis tool, we got

I_max=4.83x10⁶ mm⁴

I_min=1.44x10⁴ mm⁴

Y= 440.4984mm (Measured from the model)

3. S_max= I_max / Y

=4.83x10⁶ mm⁴ / 440.4984mm

=1.0967x10⁴ mm³(Maximum Strength).

4. S_min= I_min / Y

=1.39x10⁴ mm⁴/ 440.4984mm

=0.003287x10⁴ mm³(Minimum Strength).

Thus the strength of the hood varies from 0.003287x10⁴ mm³ to 1.0967x10⁴ mm³.

Hence by comparison the strength of the hood increased compared to the first one.

Conclusion:

The strength of the material is directly proportional to MOI which is proportional to cross sectional area, hence increasing cross sectional area increases strength.