Roof Design

ROOF DESIGN ON CATIA

Aim:To design roof as per given the master sections ,to do a curvature study as per bow roof heat distortion and snow load condition and do a draft analysis .

Theory:

An automobile roof or car top that sits above the passenger compartment ,protectng the vehicle occupants from sun,wind,rain,and the other external elements .An automobile roof also has features like sunroof(it is used to release the warm air inside the car into the atmosphere) and the attachments to tie the luggages.

Sunroof

Roof rack

Following are the types of automobile roofs:

1.Convertible roof

Convertible roof cars are the cars which has the feature to enable or disable the roof as per requirement.

2.Hardtop roof

A hardtop is a rigid form of automobile roof ,typically metal ,and integral to the design ,strength and style of the vehicle .

3.T top roof

A T top is an automobile roof with a removable panel on each side of a rigid bar running from the center of one structural bar between pillars to the center of the next structural bar.

4.Targa top roof

Targa top is a semi convertible car body style with a removable roof section and a full width roll bar behind the seats.

5.Vinyl roof

Vinyl roof refers to a vinyl covering for an automobile's top.This covering was originally designed to give the appearance of a convertible to models with fixed roofs and eventually evolved into a styling statement in its own right .

An automobile roof consists of the following major components :

1.Outer roof

2. BOW roof

3.Center roof

4.Front roof rail

5.Rear Roof rail

Manufaturing process of Automobile roof:

The manufacturing process of the automobile component comprisess of the following steps respectively consists of an outer plate processing process, a strip shaped assembly and annular assembly processing process and an automobile roof side beam processing process,and an automobile roof combining process .

The center roof and bow roofs are attached to outer roof with the help of mastics whie the outer edges of front and rear rail are welded and inner edges are attached with the help of mastics.

Crash tests done on roof:

For vehicles to be approved within EU and in most other countries of the world ,they must subit to various crash scenarios and fulfill certain safety criterias.The Insurance institute for highway safety evaluates and rates the roof strength of motor vehicles

An overall rating is assigned on the basis of peak Strength to Weight ratio(SWR) measured within 127 mm of displacement.

The testing process

Roof strength evaluations are conduted on a quasi static test system manufactured by MGA research corporation .

The system consists of an upwright assembly and an attached loading head that an be fixed at varying hieghts from the ground and the pitch angles ranging from -5 to 5 degrees to accomodate testing on the driver or on the passenger side

The roll angle is fixed on 25 degrees.

Four hydraulic actuators control the movement of the platern along two linear guides

The entire sytem is mounted on a T slot bed plateanchored to the floor of the test facility .

Curvature Study:

1.Heat distortion calculation

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

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

Values from measurements taken and calculation

Sr.No	Description	Rx	Ry	R	l	t	L	W	Ok/NG
1	F R and 1st bow roof	5624	3559	4359	657	0.75	2033	2.028	OK
2	1st bow roof & 2nd bow roof	4885	6579	4118	233	0.75	2033	1.51	OK
3	2nd bow roof & center bow roof	4372	8747	5830	251	0.75	2033	1.95	OK
4	Center bow roof and bow roof 3	4035	10390	5813	235	0.75	2033	1.93	OK
5	Bow roof 3 and RR	3445	13779	5512	561	0.75	2033	2.20	OK

2.Snow load condition

The behaviour of roof is checked for snow load conditions so that during winter season roof can with stand the load of snow without getting deformed permanently .

Snow Load Prediction Formula

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)

s = L1/2 + L2/2

Values from measurements taken and calculation

Sr.No	Description	Rx	Ry	Lx	Ly	Y	L1	L2	Iy(mm4)	t	My	α	s	Qr
1.	F R and 1st bow roof	4048	3502	1187	2033	657	657	233	7470	0.75	904032	1.27	445	52.17(OK)
2.	1st bow roof & 2nd bow roof	3804	6497	1109	2033	889	233	251	55350	0.75	1017016	1.25	242	21475021.89(OK)
3.	2nd bow roof & center bow roof	4056	8880	1079	2033	1138	251	235	150.29	0.75	1018510	1.185	243	0.7017(NOT GOOD)
4.	Center bow roof and bow roof 3	4256	10808	1070	2033	1371	235	561	238.29	0.75	907602	1.039	398	1.358e-14(NOT GOOD0
5.	Bow roof 3 and RR	4194	15142	1039	2033	1984	na	na	14990000	0.75	97216	na	na	na

Draft Analysis:

1. Outer roof

2.Front roof rail

3.Rear roof rail

3.Bow roofs

4. Center roof

Results:

For curvature study

The roof design is correct as per heat distortion as all the values of W are less than 2.7.

But,the roof design doesnt clears the snow load condition as the values of Qr is less than 3.1 for two bow roofs also values of S are not within the given range.

For draft analysis

Front roof rail doesnt have a correct draft angle .

Bow roofs doesnt have proper fillet radius

Conclusion:

In order to make the roof suitable for snow load condition it would be better to reposition bow roofs and make it equidistant from front roof rail to rear rail,changing the curvature of roof or adding more embosses on outer roof can also make it suitable for snow load conditions

Front roof rail draft angle needs to be increased on the red portion.

Fillet radius needs to be reduced on the embosses and bow roofs.