Challenge

Roof challenge

NNobal Nagar17 Jun 2022

ROOF DESIGN

OBJECTIVE - Design a Roof, Front Roof Rail, Rear Roof Rail, Centre Roof Rail, Bow Roof 1, Bow Roof 2 with given Mastersection and also check for the Heat distortation and Snow Load condition.

INTRODUCTION - An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.

In later years, many variations on the automobile roof developed.

Convertible roofs
Hardtops
Sunroofs
I-tops
Targa tops
Vinyl roofs

The Roof consists of the following parts:

Front Roof Rail
Centre Roof Rail
Rear Roof Rail
Bow Roof 1
Bow Roof 2

Front Roof Rail -The Front Rail Roof is created on the front end of the roof to strengthen it from front.

Centre Roof Rail - It is created in the centre of the roof.

Rear Rood Rail - It is created on the rear end of the roof and while designing we have to consider the tailgate position as well.

Bow Roof 1- it is created in between the Front Rail Roof and Cetre rail roof.

Bow Roof 2 - it is created in between the the Centre rail roof and Rear rail roof.

DRAFT ANALYSIS -

The Draft Analysis is done each and every components with a minimum draft angle of 7 degree.

Front Roof Rail-

Roof-

Rear Roof Rail

Center Roof Rail-

Bow Roof 1-

Bow Roof 2-

HEAT DISTORTION CRITERIA -

Heat distortion temperature is the temperature at which the metal softens and deforms under a specific load. This study is done to check the ability of the roof to withstand high temperature with respect to the positioning of the reinforcements which contribute to increased strength.

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) (R2)/t] + [ 1.10x10^(-3) x 1] - 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]

I = Bow Roof Span [mm]

HEAT DISTORTION CALCULATION
SR NO.	BOWs	Rx	Ry	R	I	L	t	R^2/t	W	OK/NG
1	FR & 1ST	2977.846	5759.648	3925.918	540.47	2032.259	0.75	20550444.2	1.81	OK
2	1ST & CTR	3702.905	6491.013	4715.675	250	2032.259	0.75	29650120.3	1.66	OK
3	CTR & 2ND	3917.855	3844.355	3880.757	392	2032.259	0.75	20080367.7	1.64	OK
4	2ND & RR	3248.024	3274.221	3261.07	291	2032.259	0.75	14179435.8	1.42	OK

From the above table ,it is concluded that the designed roof satisfied the Heat distortion Criteria.

SNOW LOAD CRITERIA

Snow load criteria study is done to check the ability of the roof to withstand snowfall and bounce back to its original shape without any permanent deformation once the load is removed

Snow load Prediction formula

Qr = [ly x t2] / [axs 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

a = My x Lx2 x 10-12, My = Y(Ly-Y)

Judgement condition = Qr 23.1

250 SS S 380

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the vehicle along with OY[mm]
Length of Roof panel with the center point between Roof rail Front /Rear as the reference point of the front and the rear.

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

ly = Geometrical moment of inertia of Roof BOW (Y cross-section [mm]

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

srNo.	Bows	ly	a	Lx	Ly	Y	s	Rx	Ry	t	Qr	Determination (Qr)
1	FR & 1ST	103.8068	1	1148.25	2032.259	495.1	505.3	2977.846	5759.65	0.75	11.85	ok
2	1ST & CTR	466.0359	1	1095.97	2032.259	515.4	479.8	3702.905	6491.01	0.75	8.53	ok
3	CTR &2ND	111.6565	0.79	1062.09	2032.259	444.1	431	3917.855	3844.36	0.75	21.63	ok