Roof Design

ROOF DESIGN

Aim:

Design of the front roof rail, rear roof rail, and bow roof for the roof of the vehicles with the help of the given skin data of the roof according to snow load condition and hear distortion criteria.

Objective:

• To learn about headroom clearance.
• Study about heat distortion criteria to improve the roof strength.
• Study about snow load criteria.

Roof:

• A headliner is the material that covers the ceiling of a vehicle, but it does more than hide bare metal with color-coordinated soft fabric.
• 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.

FRONT ROOF RAIL

• The front roof rail is used as the reinforcement to the roof surface to increase the strength and also used to mount the brackets.
• The front roof rail has to clear visibility criteria.
• The width of the front roof rail is decided in such a way that there should be enough headroom clearance between the head of the driver and the end surface of the roof rail to avoid injuries to the person.

REAR ROOF RAIL

• The rear roof rail is used as the reinforcement to the roof surface at the rear side.
• The joining method used for this rail is the same as that of the front roof rail.

BOWS

• We are making two bows one is in between the front roof rail and central roof rail and another is in between the central roof rail and rear roof rail.
• Both ends of the bow are joined to the roof outer flanges by the spot welding and the inner sides of the bow are joined to the inner surface of the roof with the help of mastic points.

HEAT DISTORTION CRITERIA

In this criteria to check the roof capacity with temperature and a fixed load.

so to calculate whether the roof deform or not, according to the position of the bow we do these calculations as follows

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]

CALCULATION:

For the front roof rail and bow 1

Rx= 2656.35mm

Ry= 5731.56mm

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

R = 2(2656.35*5731.56)/(2656.35+5731.56)

R = 3630.23mm

l = 401.79mm

L = 2116.55mm

t = 0.75mm

Putting all values in the equation,

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

W = [1.73 x 10^(-3) x 2116.55] + [1.85 x 10^(-8) x (3630.23^2)/0.75] +

[1.10x10^(-3) x 401.79] - 2.68

W = 1.74

The condition for the heat distortion criteria is W>2.7 so the given is less than 2.7 so the position of the bow 1 is correct according to the hear distortion criteria.

we do the calculation for the remaining Bows positions as shown in the following table,

ROOF RAIL	Rx(mm)	Ry(mm)	Rx*Ry(mm)	Rx+Ry(mm)	R(mm)	L(mm)	t(mm)	l(mm)	W	RESULT
FR-BOW1	2656.35	5731.56	15225029	8387.91	3630.23	2116.55	0.75	401.79	1.74	PASS
BOW1-CENTER	6342.64	4935.13	31301752	11277.77	5551.05	2116.55	0.75	339.74	2.11	PASS
CR-BOW2	10342.39	4023.60	41613640.4	14365.99	5793.35	2116.55	0.75	419.85	2.27	PASS
BOW2-RR	14392.26	3309.02	47624276.19	17701.28	5380.88	2116.55	0.75	374.52	2.10	PASS

SNOW LOAD CALCULATION

• This snow load condition calculation is done to check the strength of the roof when there is dead weight on the roof.
• As we know that in some regions we have snowfalls so when snow falls on the roof then this act as dead weight because in some the rate of snowfall is more so the roof should sustain this dead weight for that we do this calculation to check the position of the bow and its sectional area.

The formula for snow load condition:

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

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

FOR BOW1

FOR CENTER ROOF RAIL

FOR BOW ROOF 2

CALCULATION

For front roof rail and Bow1:

Iy = 5273.1mm^4

Y = 443.78mm

My = Y(Iy−Y)

My = 443.78(5.2731-443.78)

My = 233985

Lx = 1041.51

α = My⋅Lx^2⋅10^−12

= 233985* 1041.51^2*10^-12

= 0.25

S = L1/2 + L2/2

= 443.78/2+339.74/2

S = 391.76

t = 0.75mm

Rx = 4414.50mm

Ry = 2773.98mm

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

= [5273.1 x 0.75^2]/[0.25 x 391.76 x [(4414.50+2773.98)/2]^2 x 10^-8]

= 26.30

Judgemental criteria is QR>3.1

ROOF RAIL	ly	My	Lx	Ly	Y	S	Rx	Ry	t	Qr	RESULT
FR-BOW1	5273.1	233985	1041.51	1955.40	443.78	391.76	4414.50	2773.98	0.75	26.30	PASS
BOW1-CR	7017	15785	1041.51	1955.40	399.54	422.53	11784.42	3771.16	0.75	15.56	PASS
CR-BOW2	5483	235675	1041.51	1955.40	412.59	510.3	10790.61	3224.25	0.75	25.10	PASS

Joining Method used for manufacturing of Roof:

1.Spot welding points:

2.Mastic Points:

Position of these points on Roof

Draft analysis to check the manufacturability of roof and its parts:

FRONT ROOF

BOW ROOF 1

CENTER ROOF

BOW ROOF 2

REAR ROOF

CONCLUSION

I learned types of roofs and reinforcement used to increases the strength of roof and to the heat distortion criteria and snow load conditions and to join the front roof rail, central roof rail, rear roof rail and Bows to the roof.