Roof Design

 REPORT

AIM

The project aims to design a car roof with essential flanges and reinforcements, including ditch area, front roof rail, bow roofs, central roof rail, and rear roof rail from the given styling surface. The roof's curvature will be studied, and calculations will be performed for heat distortion and snow load criteria to determine the correct bow roof positions. The moment of inertia and section modulus will be found for Bow roofs, central roof rail, front roof rail, and rear roof rail. Finally, draft analysis will be performed for each reinforcement.

METHODOLOGY FOR PART CREATION

Roof Outer Panel creation from the styling surface and the master section as the reference.

Front roof rail creation with respect to the master section.

Rear roof rail creation.

Bow roof rail creation.

ROOF OUTER PANEL

FRONT ROOF RAIL (FR)

REAR ROOF RAIL (RR)

CENTER ROOF RAIL (CR)

BOW ROOF RAIL 1 AND 2 (BR1 AND BR2)

ROOF ASSEMBLY

DRAFT ANALYSIS

Heat Distortion Criteria

Heat Distortion refers to the point where metal loses its shape and bends under a certain amount of pressure due to high temperature. The purpose of conducting this study is to assess the roof's ability to withstand high temperatures while taking into account the placement of reinforcements that enhance its 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

 

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y) Excluding the ditch area.

L = 2018.1056 mm

t = sheet thickness

t = 0.75 mm

ROOF RAIL	Rx	Ry	R	I	L	t	W	Result
FR- BR1	3006.72333544	5693.81685814	3935.3262	514.2765	2018.1056	0.75	1.759	PASS(W<2.7)
BR1- CR	7187.20525652	4726.36220241	5702.6302	391.5177	2018.1056	0.75	2.044	PASS
CR- BR2	11094.68218425	3878.00560376	5747.1631	350.6551	2018.1056	0.75	2.011	PASS
BR2- RR	14717.47012807	3260.64315438	5338.5377	343.7956	2018.1056	0.75	1.892	PASS

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

250 ≤ s ≤ 380

Section Modulus Analysis

 BOW ROOF RAIL 1

CENTER ROOF RAIL

BOW ROOF RAIL 2

ROOF RAILS	Iy (mm4)	Lx(mm)	Ly(mm)	L1	L2	Rx	Ry	t	Y	s	My	α (alpha)	Qr	RESULT
FR-BR1	677.625379178	1134.993	1969.1435	607.1722	468.4718	3389.62690709	4453.74173225	0.75	607.1722	537.822	731368.2383	0.0939693567	49.039	PASS(Qr>3.1)
BR1-CR	1.976042369e+03	1078.801	1969.1435	468.4718	427.6052	4657.40945413	2983.76904107	0.75	1075.6440	448.0385	712184.0674	0.0864460767	196.606	PASS
CR-BR2	673.438845225	1056.174	1969.1435	427.6052	465.8943	6241.12320024	6379.66332805	0.75	1503.2492	446.74975	558434.2172	0.0635975479	33.481	PASS
BR2-RR	-	1042.606	1969.1435	465.8943	-	17194.54512932	3862.65510114	0.75	1969.1435	-	-	-	-	-

CONCLUSION

Based on the curvature study conducted on the roof, the results were satisfactory. It was observed that positioning the bow roofs over the flat areas can enhance the roof's strength. Additionally, embossments can be incorporated to improve the roof's strength and aerodynamics, but their inclusion may lead to an increase in manufacturing costs and can be avoided if not deemed necessary.