Section Modulus calculation and optimization

Aim: Doing an analysis of the hood to get the section module and modifying the cross-section area of the hood to increases the section modules of the hood.

Objectives:

Study of the moment of inertia of the hollow parts.
Study about section modulus and on which parameters it depends.
Learn how to do get a moment of inertia in NX software.
Theory:

The Section modulus is usually used in the calculation of stresses in Cross-sections, however the Moment of inertia is often used instead, probably because designers are more familiar with Moment of inertia formulations.

While it’s very important to know how to derive and calculate the Section modulus, the further we get in our studies, the more we can use formulas.

In this post we’ll show, the most important and easiest formulas for Rectangular, I/H, Circular and hollow circular section but also formulas which involve more steps for L-, T- and U- Shapes.

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

steps to calculate the MOI in the NX software as follows:

1.First we have to get the intersection curve of the outer panel and inner panel to get the cross-section of the hood about the XY plane by using the intersection curve as follows

s we can see in this cross-section we need to get to calculate the moment of inertia of the hood in NX software.

2. So after applying the intersection curve command to the surface of the outer panel and inner panel about its center plane we get the following curve as shown:

.Now we have to trim the outer line of the outer panel and inner line of the inner panel and join the breaking lines through studio curve with tangent relation because the inner panel has curvature as shown below:

Now we have a cross-section hood now to get the moment of inertia we are using the section inertia analysis command with an option in that as the existing curve.

from this min MOI is I=1.578350 mm^4

now we have to calculate the Y = distance from the centroid to the outer most point as follows

therefore Y =879.3758/2 = 439.6879mm

section module Z= I/Y = 1.578350/439.6879 = 0.00358 mm^3

Steps to increase the section modulus:

8.Now increase the section modulus which depend on moment of inertia and distance from centroid as per our model we can't change the distance form centroid but we can change the moment of inertia which can increase the section modulus, so this can be done as follows:

a.we increase the mass of the part

b.we can increase the distance of the outer most curve of either inner panel or outer panel from center of rotation axis

So after adding some more areas and offsetting the inner panel curve to 0.5mm outer side, we get the modified new inner panel cross-section which is as follows:

calculate new section modulus

z=I/Y = 1.598142/439.6879 = 0.00363 mm^3

Conclusion: From this project, we can say that the section modulus of the part depends on the moment of inertia and distance from the outer most point to centroid point, so to increase the section modulus we can either increase the cross-section or we can increase the distance of outer most curves from the center of the axis of rotation.