Roof Design

Objective:

1. To Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.
2. To Calculate the Heat distortion and snow load criterion for the roof.
3. To create front roof rail, rear roof rail, bow roof 1 and bow roof 2 according to the master section.
4. To perform draft analysis on the roof and its assembly.

Roof Ditch area Design:

From the given input styling data, we going to create the roof ditch areas on front , rear and sideways according to the given master section:

Front Roof rail:

Since the roof is made of thin material, it is necessary to add roof reinforcements at the front end of the roof to support the roof outer panel. This provides good load bearing capacity and also prevents the passengers from injury during rolling over condition.

Bow Roofs:

Centre roof:

Rear Roof Rail:

Heat Disortion Calculation:

Heat Distortion 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 contributes to increase the 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

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

Rx,Ry Calculation:

After infering the values from the design, the results are tabulated and the value of W is found out by substituting the values in the formulae.

S.NO	Description	Rx	Ry	R	I	L	t	R^2/t	W	OK/NG
1	FRR- BR 1	5493.352	1999.586	2931.942	372.2	1121	0.75	11461708.2	-0.11921	OK
2	BR1- CR	4704.695	5294.909	4982.384	440	1082	0.75	33098867.1	0.288189	OK
3	CR - BR 2	3910.957	9860.882	5600.63	390.9	1060.4	0.75	41822741.6	0.358203	OK
4	BR2- RR	3296.644	14890.12	5398.148	378.4	1046	0.75	38853341.1	0.264607	OK

Snow Load Criteria Calculation:

Snow load is the downward force on a Car’s roof by the weight of accumulated snow and ice. The roof or the entire structure can fail if the snow load exceeds the weight the car. Or if the car was poorly designed or constructed.

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

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

S.NO	Description	Iy	α	Lx	Ly	Y	s	Rx	Ry	t	My	(Rx+Ry)/2	Qr	OK/NG
1	FRR- BR 1	1268	0.916931	1121	2033.705	465.2	489.5	2535.4067	1999.586	0.75	729668.4	2267.4961	30.90717	OK
2	BR1- CR	2883	0.913307	1082	2033.705	513	490	3180.21174	5294.909	0.75	780121.5	4237.5605	20.18006	OK
3	CR - BR 2	4063	0.823939	1060.4	2033.705	468	481	4200.35894	9860.882	0.75	732749.8	7030.6204	11.66653	OK
4	BR2- RR		0.8322	1046	2033.705	494	0	3600.27375	14890.12	0.75	760614.2

From the tabulated values, we know that the values found out satifies the heat disortion and snow load criteria and hence our bow roof placement is correct.

Draft Analysis:

Final Assembly: