Section Modulus calculation and optimization

Section Modulus Calculation and optimization:

Overview:

The section modulus is the ratio of moment of inertia and the distance from the neutral axis.

It is defined as the bending moment which can be carried by a given section for a limiting maximum stress. It is also called Moment of Resistance. It is the property of the geometry that signifies the resistance towards bending about a reference neutral axis. In simpler words, more the section modulus about an axis, harder it is to bend the object in that particular axis.

Higher the section modulus of the object, higher will be its strength and hence its load carrying capacity will be higher.

S = I/y

Where;

S: Section modulus;

I: Moment of inertia anout the neutral axis.

y: Distance from the neutral axis to the exteme end of the object.

Aim:

The aim of this report is to find the section modulus of the hood using Siemens NX tool, implementing minor revision in the hood design and validating those revision by comparing the section modulus values for both iterations.

Design Tool used : Siemens NX.

MOI Calculation and Section Modulus Calculation:

Moment of inertia can be calculated using the Secion Inertia Analysis tool in NX CAD.

First a datum plane is made in the geometrical centre of the hood panel. The surfaces of the hood outer and inner panel are intersected with the plane. The resultiing curves is used to calculate the MOI.

The intersecting curves are projected on a sketch on the previously made datum plane and the gaps are filled with studio spline. All intersecting curves are made into corners or trimmed.

Using the Section Inertia analysis tool, the MOI is calculated.

(MOI Calculation)

For the calculation of Section modulus is calculated using the minimum value of the MOI calculated by Section Inertia Analysis Method.

For the first section, the calculated MOI(min) is 2.78 x 10⁵ mm⁴ ;

The Distance from the neutral axis y: (879.54/2) mm = 439.77 mm

S= I/y: 2.78 x 10⁵ mm⁴ /439.77 mm

S1: 0.632 10³ mm³ .

To improve the section modulus, the MOI needs to be improved. In this instance, MOI is increased by offfsetting the curve from the inner panel outwards for 0.5mm.

The peviously mentioned steps are repeated for the MOI calculation.

For the second section, the calculated MOI(min) is 2.82 x 10⁵ mm⁴ ;

The Distance from the neutral axis remains the same y: (879.54/2) mm = 439.77 mm

S= I/y: 2.82 x 10⁵ mm⁴ /439.77 mm

S2: 0.641 10³ mm³ .

Conclusion:

The Section Modulus in Case 1: S1: 0.632 10³ mm⁴ .

For Case 2: S2: 0.641 10³ mm⁴ .

The Section modulus is increased by: 0.009 10³ mm⁴ or 9mm⁴ .

Hence, there is a slight improvement in the section modulus of the hood, the strength of hood is increased.