Roof Design

Report:

INTRODUCTION

An automobile roof is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, rain andn other external elements. Weather conditions are taken into consideration while designing the roof. Roof are vulnerable to high heat conditions and load so heat load and snow load calculations are done to get proper design.

OBJECTIVE:

To design the roof and associated reinforcements from given styling surface and do the heat load and snow load calculations to know the effectiveness of roof reinforcement and draft analysis for each reinforcement to access manufacturability.

PARAMETERS:

We have to create the number of roof rails to withstand the load.

BOW roof rail-fixed in flatter region to enhance strength.

Front and rear roof rails-Fixed to the ditch area using spot weld operations. These parts are fixed to roof using mastic sealants. Gap between roof rails and row roof should be less for better for NOISE, VIBRATION, HARSHNESS. The criteria are.

1.Visibility criteria 2.Head clearance 3.Curvature study 4.Hear distortion and snow load criteria 5.Draft analysis.

Master sections of parts:

Here are some Reference images for the Master sections - These images are just to give you a brief idea about the design

Front roof rail:

Centre roof rail:

Its imparts the strength to outer roof.

BOW roof rail:

bow rail1, 2

Rear roof rail:

section modulus:

for bow roof-1

for centre roof:

for bow roof-2

CALCULATION FORMULA :

for Heat Distortion Criteria

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

Judge mental Condition: OK< 2.7

Were,

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]

for Snow Load Criteria

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

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

CALCULATION:

TABLE:

SECTION	R(x) mm	R(y) mm	R mm	t mm	L mm	I mm	W	RESULT
FRR-BWR1	5737.972	2564.022	3544.277	0.75	2034.3	382.673	1.5703	pass
BWR1-CBWRR	4949.341	6289.821	5285.684	0.75	2034.3	425.106	1.9964	pass
CBWRR-BWR2	3981.374	10561.286	5782.770	0.75	2034.3	414.856	2.1205	pass
BWR2-RRR	3297.710	14473.286	5371.527	0.75	2034.3	353.206	1.9395	pass

sections- roof rails	I(y) mm	L(x) mm	L(Y) mm	L(1) mm	L(2) mm	R(x) mm	R(y) mm	t mm	Y mm	s	M(y)	α	[(Rx + Ry)/2]2	Q(r)	result
fr-bow1	1580.7	1136.811	1936.282	476.948	502.584	4518.131	2618.361	0.75	476.948	489.766	696026.43	0.899502	12732379.51	15.851553	pass
bow1-crr	1829.08	1085.625	1936.282	502.584	488.841	3768.904	6201.819	0.75	979.532	495.712	937167.24	1.104528	24853829.28	7.5605886	pass
crr-bow2	1513.31	1057.901	1936.282	488.841	467.908	4273.815	11056.753	0.75	1468.374	478.374	687063.94	0.768930	58756578.80	3.9385793	pass