Roof challenge

Objective: Devlope and design the given car roof with proper reinforcement by following the master section to creat the roof ditch area, Front roof rail, Rear roof rail and Bow-roofs.

Introduction:

Roof is a part of an automobile essential to protect and keep the passenger safety from harsh weather condition, accidents etc. the conventional task of the roof panel is that of compartment shielding, passenger protection and connecting of the body sides, front and roof cross members, In case of roll over compartment integrity is provided by the compartment frames, while the roof target is only to avoid the ejection of the passengers, providing protection against hard local contact.

Correspondingly a wide selection of suitable materials are available: Steel, aluminum, thermosetting plastic sheet, glass. In case of steel grade FEP04, the usually thickness is in the range of 0.65 to 0.85mm. In all cases, any roof panel material requires braces to prevent panel flexing and vertical waviness, commonly known as oil canning: for this purpose light steel bows are introduced, which are welded or riveted or screwed to the body side and bounded to roof panel by smooth flexible adhesives such as butyl mastic (in order to avoid sink marks on roof surface), mainly providing a damping effect.

Another task of roof bows is to support the interior roof liner which requires a number of fittings both in central and boundary areas to avoid deflection and vibrations. Fittings are usually plastic clips or Velcro strips. Some roof liners, mostly on less expensive vehicles ae bonded directly to roof panel.

Procedure:

First we have to devlope and design the roof with given master section and creat the ditch area. After that we need to design Front and rear roof rail and bow roofs. After that we need to assemble those with the roof.After completing assembly we need to do inspection and test the strength, heat distortion and snow load capacity of that aseembly.

Ditch Area:

Ditch area is the extended part of the roof to which Roof rails and bow roofs are concealed using spot welds. For designing the part there are some factors we consider and those are Headroom clearence, Driver visibilty criteria, wind sheild clearence and Back door. The thickness we give is 0.75mm.

Front Roof Rail:

Front roof rail is joined with the wind sheild glass, Body side outer panel and inner panel. While designing a 3-5 degree draft angle we provide as per the visibility criteria and head room clearence of the driver.The wind sheild end is joined with the rail by using spot weld and the other end of the rail is joinf with roof using mastic seals as they give proper strenth to it.

Rear Roof Rail:

This is also joined with exactly considering the same criterias we followed in front roof rail. This is also joined with the back door, body outer panel and inner pannel. Head room cleareance and back side visibility everything should be considered. Here also one end of rail is spot welded with back door and other end is sealed using mastics with the inner panel.

Center Bow Roof:

This bow roof is also designed as considering the head room clearence and strengthing the roof. This roof is joined with the inner panel using mastic points. As this is the center part so we are adding extra reinforcement to increase the strenght

Bow Roofs:

Bow roofs are also we put for increasing the strenght of the car roof. For reducing weight and we did some styling and emoboses also. Two of them were used and each are diffenerntly designed as per the postion we are going to fix with inner panel of the roof.

Front Bow Roof

Rear Bow Roof

Calculations to determine bow position:

1. Heat Distortion Criteria:

Heat distortion temperature is the 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 positioning of the reinforcements which contribute to increased strength.

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

Judgement Condition : OK<2.7<NG

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]

ROOF	L	Rx	Ry	R	t	l	W	Condition
FR & B1	2027.323	6367.56	2511.72	3602.44	0.75	373.12	1.54	OK
B1 & CRR	2027.323	5336.7	6109.52	5697.02	0.75	433.355	2.05	OK
CRR & B2	2027.323	4056.7	11331.78	5974.55	0.75	417.91	2.11	OK
B2 & RR	2027.323	3361.1	16412.92	5579.59	0.75	351.903	1.89	OK

From the above table, it is concluded that the designed roof satisfies the heat distortion criteria.

2. Snow Load Criteria:

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

Judgement condition = Qr ≥ 3.1

250 ≤ s ≤ 380

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 reference point of the front and the rear.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel 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	AREA MOMENT OF INERTIA I(y)	t	Y	Ly	Lx	My	alpha	L1	L2	S	Rx	Ry	Qr	CONDITION
FR & B1	1589	0.75	471.6	2027.323	1109.21	699147	0.860207	455.5	514.4	494.9	4336.6	2513.6	17.89	OK
B1 & CRR	1662	0.75	518.4	2027.323	1071.47	744266	0.854468	514.4	492.6	510.55	3798.5	6121.4	8.71	OK
CRR & B2	1604	0.75	502.7	2027.323	1053.14	729618	0.809223	492.6	450.3	485.05	4517	11270	3.71	OK

From the above table, it is concluded that the designed roof satisfies the snow load criteria.