Roof challenge

AIM: To create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements for the given Roof styling.

INTRODUCTION:

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 water from external elements and the roof is a styling part that is fixed with the BIW body through the rails and panels inside the upper roof to provide it strength and stiffness.

There are many types of roofs available:

• Convertible roof
• hardtops
• Sunroofs
• T-tops
• Targa tops
• Vinyl roofs

Factors should be considered while designing a Roof:

• Head clearance
• Visibility criteria
• Heat distortion and snow load condition
• draft analysis
• safety parameters

Components that are used in Roof:

• Outer panel
• Front roof rail
• Bow roof
• Center roof rail
• Rear roof rail
• Ditch area

Procedure for Designing the Roof:

Outer panel

Front Roof Rail: Front roof rail is used to provide strength to the roof panel front and it also acts as a link between windshield glass, roof panel, and headliner. Spot welds are applied at the windshield end of the rail and the other end is joined with the roof using mastic sealant which also increases the strength

The master sketch which I used to design the Front roof rail:

Bow Roof Rail: Bow roof rail is mostly used for strengthening purposes. and it gives strength to the area between the front roof and the center roof rail. also, it was created in the area between the center roof rail and the rear roof rail to provide enough strength. And the position of the bow roofs is to be justified by the curvature study

The master sketch which I used to design the Bow roof rail:

Center Roof Rail: This is a roof rail that will be at the center of the roof to provide strength and stability to the roof.

The master sketch which I used to design the Center roof rail:

Rear Roof Rail: Rear roof rail is also used to strengthen the roof and it acts as a link between the back glass and the roof which connected to the backdoor of the car

The master sketch which I used to design the Rear roof rail:

FINAL ROOF DESIGN

Heat Distortion criteria: Heat distortion temperature is a temperature at which the metal softens and deforms under a specific load. this study is done to check the ability of the roof to withstand high temperature with respect to the position of the reinforcements which contribute to the 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]

Judgment Condition

OK< 2.7

CALCULATIONS

CASE 1 (front roof rail to bow roof 1)

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

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y) in mm
L = 2028.7 mm

R = Roof curvature
Rx = X curvature in mm
Ry = Y curvature in mm
Rx = 3272.7735 mm
Ry = 14637.2045 mm
R = (2*(Rx*Ry))/(Rx+Ry)

R = 4.8298e+03

Roof plate thickness [mm]
t = 0.75 mm

l = Bow Roof Span [mm]
l = 334.2 mm

W = ((0.0017*2028.7) + (1.8500e-08 * (4.8298e+03^2)/0.75) + ( 0.0011 *334.2))- 2.68

W = 1.7551 [Judgment Condition OK< 2.7]

CASE 2 ( bow roof 1 to center roof rail)

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

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y) in mm
L = 2028.7 mm

R = Roof curvature
Rx = X curvature in mm
Ry = Y curvature in mm
Rx = 4968.4032 mm
Ry = 6213.1294 mm
R = (2*(Rx*Ry))/(Rx+Ry)

R = 5.5215e+03

Roof plate thickness [mm]
t = 0.75 mm

l = Bow Roof Span [mm]
l = 417.7mm

W = ((0.0017*2028.7) + (1.8500e-08 * (5.5215e+03^2)/0.75) + ( 0.0011 *417.7))- 2.68

W = 1.9803 [Judgment Condition OK< 2.7]

CASE 3(center roof rail to bow roof 2) and CASE 4 (Bow roof rail2 to rear roof rail are also the same as the above procedure

CASE 3

R =5.7770e+03

W =2.0794 [Judgment Condition OK< 2.7]

CASE 4

R =5.3494e+03

W =1.8423 [Judgment Condition OK< 2.7]

complete calculations placed in the table :

Therefore, According to the judgment condition OK< 2.7 all the values W should be within the satisfied limits

Snow Load criteria:

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

250 ≤ s ≤ 380

Section modulus of the cross-section shape is of significant importance in designing the structure. it measures the strength of structure a structure has a larger section modulus than another will be stronger and capable of supporting greater loads

Front roof rail

Bow roof rail 1

Bow roof rail 2

Center roof rail

Calculations for snow load condition:

CASE 1 (Front roof rail to bow roof rail 1):-

(ALL DIMENSIONS ARE IN MM)

t = 0.75

Lx = 1144.5

Ly = 2028.7

Y = 472.9

Iy = 178.975 mm^4

L1 =472.9
L2 = 498.5

Rx = 3359.4862
Ry = 2637.0377

s = (L1/2) + (L2/2)

= (472.9/2) + (498.5/2)

= 485.7000

My = Y(Ly-Y)
My = 472.9*(2028.7-472.9)

= 7.3574e+05

α = My* Lx^2 * 10^-12

= 7.3574e+05 * 1144.5^2 * 10^-12

= 0.9637

Qr = (Iy * t^2)/(α*s*((Rx + Ry)/2)^2 * 10^-8)

= (178.975 * 0.75^2) / (0.9637 * 485.7 * ((3359.4862 + 2637.0377 )^2 )* 10^-8)

Qr = 2.3925 Judgment condition Qr ≥ 3.1 (Not satisfied the snow load judgement criteria)

Remaining cases are displayed in the below table:-

Reason of failure that i have noticed the moment of inetria very much less that means the cross section also very less for that reason snow load critiria doesnt satified. And Fom the above the result of the snow load criteria all the value are not satisfied according to the snow load judgement condition (Judgment condition Qr ≥ 3.1)

Draft analysis: The draft analysis command used to detect the part drafted will be easily removed this type of analysis is performed based on color images identifying zones on the analyzed element

Outer panel draft analysis & center roof rail

Bow roof rail

CONCLUSION: Finally I have completed the roof design by using the master sketch and also I have done heat-distortion calculations to check the ability of the roof to withstand higher temperatures with respect to the position of the reinforcements which can contribute to increase the strength

• whereas all the values of heat distortion come under the satisfactory condition
• And also snow load condition values do not follow the judgment criteria condition
• and also done draft analysis