Roof Design

Roof Desgin

Objective: -

1.To Create Reinforcement for roof outer panel and flanges

2. To do curvature Study to determine position of flanges

Software Used

. NX CAD

Introduction

Roof

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 drwan carrages, early automobile roofs used similar materials and designs.

Morden Roof have thee varition

1. Normal Roof

2. Sunroof

3. Convertible

For this project we are using normal roof

Methdology

1. Get the roof outer pannel model in NX Cad

2. Create a Working Surface

3.Understand the Master Section of Front roof rail and draw accordingly

below is the image of created Front Roof Rail

4. Similarly by following the master section create Rear Roof Rail

5. Now create the center roof rail, and bow roofs according to master section

also create bow roof one and bow roof two same as center roof rail

Calculation

Now as the reniforcements have been made we have to do curvature study for the roof

we are doing

1. Heat Distortion

2.Snow Load Condition

1. Heat Distortion

Heat distortion temperature is the temperature at which the metal softens and deforms under a specific load. Roof of a car is probably the only component which is exposed to sun for almost all the time, so 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.

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

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]

W = OK< 2.7

According to that we get a table

BOW	Rx	Ry	R	I	L	W
FR - 1	1304	3244	5197	497	2028	2.03
1 - CTR	8836	4020	5525	257	2028	1.85
CTR - 2	6167	4684	5324	207	2028	1.73
2 - RR	2642	5450	3558	546	2028	1.73

By the table above we can summarize that this roof pass the heat distortion test

2. Snow load test

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.

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

Where,

α = My x Lx² x 10^-12 , My = Y(Ly-Y)

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]

The width of the roof panel is 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]

Qr ≥ 3.1

250 ≤ s ≤ 380

Table

BOW	Rx	Ry	S	ALPHA	My	QR
FR - 1	2654	2236	478	1.003	841158	37.85
1 - CTR	6023	3462	314	1.07	930170	14.35
CTR - 2	8967	3068	488	0.91	823004	6.74
2 - RR	14330	3145	319	5.2*10^-4	1929	8.5

From the above table we can conclude that Qr value for all section is above accebtable limit but s value for

front roof rail section and 2 roof rail section is high

Soultion

Repostion the first bow roof more towards front bow roof

Conclusion

Hence we desgined and testes the roof