Section Modulus calculation and optimization

Section Modulus

The section modulus of the cross-sectional shape is of significant importance in designing beams. It is a direct measure of the strength of the beam. A beam that has a larger section modulus than another will be stronger and capable of supporting greater loads. In case of Automobiles while designing the Hood it has to made sure that the Section modulus of the hood should be in the considerably good range so that it is capable of supporting greater loads, ie ;during the time of impact if the section modulus is high then the hood section will be able to able to withstand the impact upto a certain extent. With chances of sudden impact on the hood it must be designed specfically to fare against bending due to impact. There are certain factors that affect the section modulus of the hood.

1. Shape of the hood

2. Material used

3. Position of the hood panels

Section modulus is denoted as the ration between Moment of Inertia about neutral Axis upon the farthest point of Section from neutral Axis.

where Section Modulus is denoted By S, moment of Inertia is denoted by I and Y is the distance from the neutral axis.

S = I/Y , Unit of Section Modulus is mm^3

Section Modulus of the Hood Section

Fig shows the section modulus reading of Hood section

Section modulus of the Hood section is claculated by taking a section region from the 0-Y region and the section is modified inorder to be a closed section as shown in the fig below. After setting the losed section region all the curves are joined and once the section is joined then the section modulus is calulated by Section inertia analysis option and we will get the corresponding Moment of Inertia Values.

Section inertia Analysis Chart

CG (mm)			MOI (Max)	MOI (Min)	Principal Directions		Section Length	Section Area
-0.000016446	746.6743343	-912.837126	1.036*10^5 mm^4	4.144*10^5mm^4	Max: (0.000000353,0.9811963868,0.189068669)	Min: -0.000000028,-0.189068669,0.981963868	2.071*10^5 mm	45.286860808 mm^2

Here Minimum Moment of Inertia Value MOI is taken and Y value is calculated by taking distance from two reference end points from the Hood section, the distance will be 476.3mm. The Distance from neutral Axis will give Y Value.

S= (4.144*10^5)/ (238.15)= 1.740*10^3mm^3

The Section modulus for the hood section will be 1.740*10^3mm^3. Now certain modification can be done on the hood section inorder to improve the Section modulus Value.

Improved Section Modulus

By offsetting the outer panel by 0.75mm outwards ie farther to the inner panel the MOI values changes to a Certain dergree.

The New MOI Minimum value becomes 4.426*10^5 mm^4

Then the new Section modulus becomes 1.858*10^5 mm^3

Eventhough there is not a drastic change in Section modulus value but this proves that Hood panel assembly have an impact on the section moduldus of the entire section. The S value can also be furthur improved by the type metal used in Hood.