Roof challenge

Objective:- To design a Roof with Roof rails

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 other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.

The Automobile roof consists of the following parts:

• The outer panel
• Front roof Rail
• Bow Roof
• Centre Roof Rail
• Rear Roof Rail

The outer panel:-

 

Front rof rail:-

Bow roof:-

Centre roof rail:-

 

Rear roof rail:-

 

Roof Images

 

HEAT DISTORTION CRITERIA:

Heat distortion temperature is the temperature at which metal softens and deforms under a specified load. While designing roof, this criteria is taken into consideration. We create bow roofs when the roof is long and flat to increase its strength. The position of the bow roofs is to be justified and this justification is done by curvature study:

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            

Judgement Condition : OK< 2.7> 3.1

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]

To measure L

 

HEAT DISTORTION CRITERIA

S.NO	BOWS	RX	RY	R	i	L	t	R^2/t	W	OK/NG
1	FR & 1ST BOW	5697.37	2977.55	3911.09	586.53	2033.67	0.75	20395518.29	1.83	ok
2	1ST BOW & CTR	4691.28	7335.86	5722.81	266.87	2033.67	0.75	43667544.71	1.91	ok
3	CTR & 2ND BOW	4073.44	10100.77	5805.59	261.57	2033.67	0.75	44939953.00	1.93	ok
4	2ND BOW & RR	4396.32	14387.28	6734.71	506.24	2033.67	0.75	60475091.71	1.84	ok

Here we can see that the roof is completely satisfying the conditions of heat distortion.

SNOW LOAD PREDICTION FORMULA:

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

So there is a formula to predict the strength of the roof.

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 front and rear reference point.

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 panel X curvature radius of length s in Side view

After calculating all these values the Qr is found out.

S.N0	BOWS	Rx	Ry	Lx	Ly	Y	Iy(mm^4)	My	S	Alpha	t (mm)	Qr	OK/NG
1	FR & 1ST BOW	6344.57	2990.04	1352.69	2033.70	671.60	6702.36	914786.36	505.19	1.67	0.75	20.51	ok
2	1ST BOW & CTR	3858.77	7307.19	1407.92	2033.70	338.78	1686.36	574204.99	334.77	1.13	0.75	8.04	ok
3	CTR & 2ND BOW	6189.25	49197.86	1399.81	2033.70	330.76	6580.80	563264.43	480.91	1.10	0.75	0.91	NG
4	2ND BOW & RR	5828.88	79126.13	1050.70	2033.70	631.07	5001.88	885157.71	0	0.97	0.75	-	-

It is observed that the roof is satisfying the condition only in the area between bow roof 1 and centre roof. in the other areas it is not satisfying the condition. So in order to strengthen the roof at these areas embosses are created on the outer roof.

L1	L2
671.60	338.78
338.78	330.76
330.76	631.07
631.07	0

 

SECTION MODULUS STUDY OF THE SECTION OF THE ROOF RAILS:

The section modulus of the cross-sectional shape is of significant importance in designing of structures. It is a direct measure of the strength of the structure

A structure that has a larger section modulus than another will be stronger and capable of supporting greater loads.

Section modulus (S) = I/y

Where,

I = Moment of inertia in (mm⁴)

y = Distance between the neutral axis and the extreme end of the object (mm)

FRONT ROOF RAIL:-

REAR ROOF RAIL:-

BOW ROOF 1:-

 

BOW ROOF 2:-

CENTRE REINFORCEMENT BOW ROOF:-

S.NO	Component	I (mm4)	y (mm)	Section Modulus (S) (mm3)
1	Roof	1414.75	1016.85	1.39
2	Front Rail Roof	8558	62.02	137.98
3	Rear Rail Roof	5001	83.76	59.70
4	Bow Roof 1	6702	32.48	206.34
5	Bow Roof 2	6580	32.49	202.52
6	Centre Reinforcement & Bow Roof	1686	43.96	38.35

DRAFT ANALYSIS:-

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.

FRONT ROOF RAIL:-

REAR ROOF RAIL:-

 

BOW ROOF 1:-

BOW ROOF 2:-

 

CENTRE REINFORCEMENT BOW ROOF:-

 

CONCLUSION :-

The Design a Roof from the given skin data and the master section provided with rear roof rail, centre roof rail, bow roof and reinforcement has been successfully created, considering the design rules as mentioned in the given data.