Section Modulus calculation and optimization

QUESTION:

Use the Section from your Hood design and calculate the section modulus using the formula S = I/y

S = Section Modulus

I = Moment of Inertia

y = distance between the neutral axis and the extreme end of the object

Come up with a new section that has improved the section modulus of the previous section and mention what change you made that has increased the strength.

Answer:

Section Modulus:

• It is defined as the ratio of the moment resisted by the section to the stress in the extreme fibre.
• It gives an idea that most of the work in bending is being done by the extreme fibres of the beam, ie the top and bottom fibres of the section.
• The distance of the fibres from top to bottom is therefore built into the calculation.
• If the section modulus increases the moment of resistance increases & hence its load bearing capacity.
• A section that has longer section modulus than another will be stronger and capable of supporting greater loads.

Calculation of Section Modulus:

• In this challenge I have taken my designed hood, for calculation.
• To calculate the moment of inertia, I have taken the hood section along the length of hood & find the inertia using 'section inertia analysis' tool in NX CAD.
• Then, the section modulus is calculated using the given formula i.e.

S = I/y

Where,

S = Section Modulus

I = Moment of Inertia

y = distance between the neutral axis and the extreme end of the object

Section Modulus calculation of the Hood Design:

CASE 1: Initial Hood Design.

Area Moment of Inertia: I(min)

MOI(min):8.280589931e+03[mm^4]

Y distance: 476.6mm

S=I/Y

S = 8.281367601e+03[mm^4]/476.6mm
S = 17.379 mm^3

CASE 2: Optimized Hood Design

Aim: Our Aim here is to increase the I(min)

MOI(min):-8.920673682e+03[mm^4] (increased)

Changes made: I increased the distance between the outer hood panel & the inner hood panel.

S=I/Y

S = 8.920673682e+03[mm^4]/476.6mm
S = 18.717 mm^3

Final result: Thus the stiffness of the car hood has been increased by increasing its area moment of inertia.

Conclusion:
Section modulus is directly dependent on the area moment of inertia and the distance from the neutral axis. Hence, to improve the geometry of the carry more bending load, the section modulus can be improved by increasing the area MOI of a given section.
We can increase the section modulus just increasing the gap between the outer & inner panel.