Roof Design

AIM:

To a given roof styling, create essential flanges and reinforements.

OBJECTS :

To develop the essential flanges and reinforements with appropriate dimensions and checking draft analysis. Calculating the heat distortion, snow load section inertia on roof.

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.

The roof is a styling surface part which is fixed with the BIW body through the rails and panels inside the upper roof to provide it strength and stiffness.

The roof part which starts from A-pillar and goes upto D-pillar.The roof purpose is to provide cover to the passenger inside the car and protect the passenger from elements like sun,rain,wind,etc.The roof also prevents unwanted object from falling inside the car.Roofs are generally made up of Aluminium.Aluminium based roof panel may reduce the overall weight of the assembly.

TYPES OF CAR ROOFS :

• Convertable roof
• Hardtops
• Sunroof
• T-tops
• Targa roofs
• Vinyl roofs

CONVERTABLE ROOF :

HARDTOP ROOF :

SUNROOF :

T TOP ROOF :

TARGA TOPS :

VINYL ROOF :

The following factors should be considered for the roof design:

• Visibility criteria
• Head clearance for comfort
• Safety Parameters
• Draft analysis
• Heat distortion and Snow Load

COMPONENTS OF ROOFS :

• Front roof rail
• Rear roof rail
• Bow roof
• Bow roof center
• Ditch area

Front roof rail :

Front roof rail is used to provide strength of roof panel and also to support windshield glass, roof panel , headliner. Spot weld are applied at windshield glass end of the rail and other end is joined with roof using th mastic sealent which is increase the strength.

The front roof should design with the help of master section and maintain the proper dimension.

REAR ROOF RAIL :

Rear roof rail is again used to strengthen the roof and it acts as a link between back glass and roof which connected to the backdoor of the car.Spot welds are applied at back doorend of the rail and the other end is joined with roof using mastic sealent.

BOW ROOF :

The major portion of the area, which is used to strengthen and rigitity of the roof, If we use he sun roof the bow roof will doble to strengten the roof balance. Here the bowroof rail is joint with the roof through mastic sealent.

Ditch area:

Ditch area is a extended portion of the maim roof concellled by other BIW pannels.The rails support of the roof are attached to the ditch area using spot weld.

Analysis:

It is done to justify the position of the bow roofs.

1.Roof crash test.

2.Snow load test.

3.Heat distortion criteria

ROOF CRASH TEST :

It is a government car safety program tasked with evaluating new automobile designs for performance against various safety threats.

Heat distortion criteria:

When Heat distortion temp is high howlong it will sustain the on the roof. so, the study is done to check the ability of the roof with respect to position of reinforements, which is used to increase the 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]

Judgment Condition

OK< 2.7

HEAT DISTORTION ON ROOF
SL NO	BOWS	I	RX	RY	R	T	L	W	RESULTS
1	FR TO BW 1	410.77	5734.75	2607.88	3585.33	0.75	2025.07	1.592298	OK
2	BW 1 TO BW C	371.44	4970.1	6202.1	5518.171	0.75	2025.07	1.98306	OK
3	BW C TO BW 2	404.42	4038.35	10268.28	5796.88	0.75	2025.07	2.097127	OK
4	BW 2 TO RF	385.18	3296.46	14474.74	5369.97	0.75	2025.07	1.958371	OK

Above the values are statisfied the as per condition.

Snow Load criteria:

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

Snow Load Prediction Formula

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)

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]

Roof panel X curvature radius of length s in Side view

Judgment condition

Qr ≥ 3.1

SNOW LOAD
SL NO	BOWS	RX	RY	R	LY	LX	Y	S	T	IY	ALFA	QR	RESULTS
1	FR TO BW 1	4489.79	2657.74	7147.53	2025.07	1131.13	481.145	481.145	0.75	1761.5	0.950445499	0.03693	NG
2	BW1 TO BW C	3763.79	6110.84	9874.63	2025.07	1081.92	472.88	472.885	0.75	2231.5	0.859183891	0.031054	NG
3	BW C TO BW2	4244.45	10699.84	14944.29	2025.07	1054.95	525.79	525.795	0.75	2480	0.877321601	0.011689	NG

Above the values are not statisfied the condition.

MOMENT OF INERTIA FOR BOW ROOFS :

Draft analysis:

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.Here the draft angle is given as 7 degree.

CONCLUSION :

Finally the roofs are designed by the used master section and also done all test, draft analysis. But, snow load onlt failed the test.