Aim:

To calculate section modulus of the pre designed hood in Semens NX. Section modulus calculate the strength in the designed component and helps in optimizing the design. Strength of the component is directly proportional to the section modulus.

Section modulus:

The strength of any cross-sectional region of an object around a reference axis is directly measured by the section modulus.

The formula to calculate section modulus:

S= I / Ymax

Where,

I = Moment of inertia (mm^4)

Y = Distance between neutral axes and outermost fiber (mm)

Moment of inertia:

The term "moment of inertia" refers to the quantity that describes how a body resists angular acceleration and is calculated by multiplying each particle's mass by its square of distance from the rotational axis. The angular mass or rotational inertia are other names for the moment of inertia.

kg m2 is the SI unit for moment of inertia.

Procedure:

A datum plane is created on the surface of the hood. Using intersection curve tool, the intersection between the datum plane and the hood is obtained. Using the tools in sketch workbench the curve is closed and the desired sketch is obtained.

Using section inertia command, the moment of inertia is obtained.

Section modulus calculation:

Case 1:

In this case the inner panel thickness is set to 0.75 mm.

Moment of Inertia (MOI), Imax = 4.81697713 x 10^6 [mm^4]

Moment of Inertia (MOI), Imin = 1.642548651 x 10^4 [mm^4]

Distance between the neutral axis and the extreme end of the object, y = 879.8 mm / 2 = 439.9 mm

Section Modulus, S = Moment of Inertia (MOI), I / Distance between the neutral axis and the extreme end of the object (y)

For Maximum (MOI),

S = (4.81697713 x 10^6 mm^4) / (439.9 mm)

Smax = 10.950164 x 10^3 mm^3

For Minimum (MOI),

S = (1.642548651 x 10^4 mm^4) / (440.556 mm)

Smin = 0.0373391373 x 10^3 mm^3

Case 2:

In this case the inner panel thickness is set to 0.80 mm.

Moment of Inertia (MOI), Imax = 4.819111529 x 10^6 [mm^4]

Moment of Inertia (MOI), Imin = 1.649475236x 10^4 [mm^4]

Distance between the neutral axis and the extreme end of the object, y = 879.8 mm / 2 = 439.9 mm

Section Modulus, S = Moment of Inertia (MOI), I / Distance between the neutral axis and the extreme end of the object (y)

For Maximum (MOI),

S = (4.819111529 x 10^6 mm^4) / (439.9 mm)

Smax = 10.955016 x 10^3 mm^3

For Minimum (MOI),

S = (1.649475236 x 10^4 mm^4) / (439.9 mm)

Smin = 0.0374965955 x 10^3 mm^3

Conclusion:

A table is attached below to understand the changes in the two cases. In the first case is calculated with the inner panel thickness of 0.75mm. In the second case the thickness is altered to 0.80mm. In the second case it is evident that the moment of inertia and section modulus has improved. Increasing the inner panel thickness is not recommended but increasing inner panel thickness increases overall strength of the body.

	CASE 1	CASE 2
MOI (max)	4.81697713 x 10^6 [mm^4]	4.819111529 x 10^6 [mm^4]
MOI (min)	1.642548651 x 10^4 [mm^4]	1.649475236x 10^4 [mm^4]
S(max)	10.950164 x 10^3 mm^3	10.955016 x 10^3 mm^3
S(min)	0.0373391373 x 10^3 mm^3	0.0374965955 x 10^3 mm^3