Section Modulus calculation and optimization

Use the Section from your Hood design and calculate the Section Modulus using the formula

S = I/y

Where,

S = Section Modulus

I = Moment of Inertia

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

WHAT IS SECTION MODULUS?

Section modulus is defined as the ratio of moment of inertia of a section about the neutral axsis to the distance of the outermost layer fromt the neutral axsis.It is defned by the symbol Z.

Hence mathametically section modulus is given by,

I

S = --------- ......... (1)

Y

where,

I = M.O.I. about neutral axsis

and Ymax = Distance of the outtermost layer from the neutral axsis.

WHAT IS M.O.I ? HOW TO CLACULATE M.O.I.?

Moment of inertia is defined as the quantity expressed by the body resisting angular acceleration which is the sum of the product of the mass of every particle with its square of a distance from the axis of rotation or in more simple terms, it can be described as a quantity that decides the amount of torque needed for a specific angular acceleration in a rotational axis. Moment of Inertia is also known as the angular mass or rotational inertia. The SI unit of moment of inertia is kg m².

Moment of inertia is usually specified with respect to a chosen axis of rotation. It mainly depends on the distribution of mass around an axis of rotation. MOI varies depending on the axis that is choosen.

In General form,

Moment of Inertia is expressed as I = m × r²

where,

m = Sum of the product of the mass.

r = Distance from the axis of the rotation.

Calculation:

CASE 1: Before Optimization

The Hood which was already created is imported and the section inertia analysis is done.

We have to make sure that the curve obtained is a single/closed curve.

As per the section modulus equation,

S = I/Y

I = MOI (min) Value is considered i.e 1.470943330e+04

Y = Total distance / 2, Total distance = 880.2107mm

Y =880.2107/2

= 440.10535

S=I/Y

S=1.470943330e+4/440.10535

S=33.422 mm3

CASE 2: After optimization

The hood inner panel’s curve is offset by 1.0mm outwards and section inertia analysis is done same as case 1 for a closed curve.

As per the section modulus equation,

S = I/Y

I = MOI (min) Value is considered i.e 1.569527319e+04

Y = Total distance / 2, Total distance = 880.2107mm

Y =880.2107/2

= 440.10535

S=I/Y

S=1.569527319e+4/440.10535

S=35.627 mm3

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.