Roof challenge

Title: Roof design

Objective: To design the roof and its requirements front roof rail, bow roofs, center reinforcement, rare roof rail from given skin data, and doing curvature syudy on the roof performance to place the bows position.

Roof :

The roof is the top patr of the car which protects the car and passangers from all all types of weather conditions, it also protects the passangers from crashes, rolling of car or somthing falls on the car.

Procedure:

From the given skin data create the dich area of the roof and create the front roof rail taking data from master section which is given now create the center roof rail with bow roof in it to give additional strength to the roof, then create the rare roof rail from the given master section data. After creating the front, center and rara roof rails create the bow roof in between them. Create emboos on the roof to give style and strength to the roof and thicken the parts.

Design considerations:

• Visibility criteria
• head clearence
• curvature study
• heat distorsition and snow load criteria
• draft analysis.

Roof components:

1) front roof rail:

Tthe front roof rail is located at the front of the roof where windshild is fixed. The front ends of the roof is spot welded and the rare ends are attached to the roof with mastics.

2)Bow roof 1:

Bow roof gives additional strength to the roof so that it can satisfy the norms. Bow roof is attached to the roof with mastics and also bow roof is designed in such a way that we can add more mastics points which gives more strength to the roof.

3) center roof rail :

Center roof rail is located at the center of the roof to give support at the center of the roof in the center roof rail to give massive strength we added a bow roof. Both center and bow roof is spot welded and both together attached to the roof with mastics.

4)Bow foor 2:

Bow roof gives additional strength to the roof so that it can satisfy the norms. Bow roof is attached to the roof with mastics and also bow roof is designed in such a way that we can add more mastics points which gives more strength to the roof.

5) Rare roof rail:

It is located at the back end of the roof, it is designed in such way that as the hings of the back door and back visibility criteria.

Calculations:

heat distortion curvature study:

It is use to find the hest distortion temperature of the material where it starts to soften when it exposes to the fixed loads. To avoid damage and bending of the roof based on the calculations the position of the bow roof is desided on the roof.

Bow–roof prediction Formula :

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Judgement Condition : OK< 2.7> 3.1

Where

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

Result:

Bow possition	Rx	Ry	l	L	t	R	W	OK/NG
FR	2423.27	5733.95	363.63	2030.99	0.65	3406.77	1.61	OK
bow 1	6199.91	9835.64	450.17	2030.99	0.65	7605.61	3.02	OK
center	10539	6599.77	451.41	2030.99	0.65	8116.72	3.25	OK
RR	14812.71	3242.71	338.96	2030.99	0.65	5320.61	2.06	OK

Snow load criteria:

To know the snow load on the roof this calculation is done to place the bows in better place on the roof.

Snow load Prediction formula

section inertia:

Qr = [Iy x t²] / [α x s x [(Rx + Ry)/2]² x 10^-8]

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where

α = My x Lx² x 10^-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

250 ≤ s ≤ 380

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]

Length of Roof panel with the center point between Roof rail Front /Rear as the front and rear reference point.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

Roof panel X curvature radius of length s in Side view

Result:

Bow possition	Iy	α	Lx	Ly	Y	S	Rx	Ry	t	Qr	determination
Case 1	484.69	0.937	1135	2030.99	464.6	406.90	2492.20	4410.20	0.65	1.18	NG
Case 2	5.21*10^3	0.910	1083.3	2030.99	510	450.70	6112.16	5709.56	0.65	3.74	OK
Case 3	481.81	0.860	1053.8	2030.99	509.6	395.18	11034.55	12760	0.65	1.24	NG

Section modulus:

Section modulus is defined as the ratio of moment of inertia of the cross section about the nutral axis to the distance of extreme fiber from the nutral axis. If a section has high section modulus than compare to others it has higher strength and supports great loads. It is denoted by S

Here,

S=I/Y

S= section modulus

I= moment of inertia

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

Section modulus at.

Front roof rail:

Imin=2.18*10^5mm^4

Imax=1.68*10^6mm^4

Smin=1.70mm^3

Smax=13.11*10^3mm^3

Bow roof 1:

Imin=481.81mm^4

Imax=9.57*10^3mm^4

Smin=13.88mm^3

Smax=2.75*10^2mm^3

center roof rail:

Imin=5.21*10^3mm^4

Imax=2.15*10^5mm^4

Smin=65.12mm^3

Smax=26.87*10^2mm^3

Bow roof 2:

Imin=484.69mm^4

Imax=1.05*10^4mm^4

Smin=13.95mm^3

Smax=3.02*10^2mm^3

rare roof rail:

Imin=2.49*10^5mm^4

Imax=1.41*10^6mm^4

Smin=20.73*10^2mm^3

Smax=11.73*10^3mm^3

Draft analysis:

Before we give the part for manufacturing we have to some analysis ourself to check all the constrains and to check if we have any negative draft on a part.

we have a tool called draft analysis in nx cad to check the following.

when the color is green it means it has a positive draft it means area which are more than 3 degree is shown as green. If it is shown in yellow that means it has less than 3 degree and if in blue or red then it means it has negative draft.

Top view:

Front view:

Back view:

Side view:

Conclusion:

In this project designed roof, front roof rail, bow roofs, center roof rail and rare roof rail. Performed section modulus, moment of inertia and draft analysis to check the manufacturing fesibility.