Challenge

Roof challenge

VVijay Bharga22 Aug 2022

MATLAB

Aim : To create the design of roof of the car using CAD software and peform Curvature study and draft analysis .

Roof :

The roof of a vehicle or car is the top part of it , which protects passanger from the wheather and injury when the car gets crashed.
The roof is a styling surface part which is fixed with the BIW body through the rails and panels inside roof to provide its strength and stiffness .
The rails and reinforcement are joined to the ditch area with a spot weld where it is not the styling part.

Components of roof :

Front roof rail
Rear roof rail
Bow roof
Centre roof rail
Ditch area

Front roof rail :

It is made with the help of the given master section .
Front roof rail is provided to strengh to the roof panel .
It act as a link between windshield glass , roof panel and headliner .
Spot welds are applied at wind shield end of the rail and other end is joined with roof using mastic sealent .

Rear roof rail :

Rear roof is made by using the master section which is given to us.
It is also used to strengthen the roof and it acts as a link between back glass and roof which connected to the backdoor end of the rail.
Other end is joined with roof using mastic sealent .

Centre roof rail and Bow roof rails :

bow roof are provided where there is more straightness to increase the strength of the roof .
Centre roof is also provide to increase the strength of roof .

Different views of roof assembly :

Curvature study :

After getting the final body it has to be checked and justify that it passes the standards.

It is done to justify the position of the bow.

Heat distortion criteria .
Snow load test.

Heat distortion criteria :

Heat distortion temperature is a temperature at which the metal softens and deform under a specific load .
This study is done to check the abality of the roof to withstand high temperature eith respect to the position of the reinforcement which contribute to the increase the strength.

To calculate the heat distortion criteria by the formula,
first creare sketch ,then draw a line on tyhe centre of the roof on Y axis .
Now draw a line of 300 mm distance from centre line .
Now draw a line of 100 mm distance on both side of 300 mm distance.
Draw aline between the centre of roof rails and draw the line from the centre line by distance of 100 mm both side .
Now make intersection of both line .

MATLAB code for heat distortion calculation:

clear all
close all
clc

l = input ('Total length : ' );
Rx = input ('Rx : ' );
Ry = input ('Ry : ' );
R = 2*((Rx*Ry)/(Rx+Ry))
i =  input ('i : ' );

t = 0.75
s = R*R/t

x = 1.73 * 10^(-3)*l
y = 1.85 *10^(-8)*s
z = 1.1 * 10^(-3)*i

W = x+y+z-2.68

Table of heat distortion calculation:

Sr No.	Bow	Rx	Ry	R	I	L	t	R^2/t	W	OK/NG
1	FR - BOW1	5740.34	2423.35	3.408 X 10^3	544.74	2037.72	0.75	1.54 X 10^7	1.7	OK
2	BOW1 - CR	4856.06	6660.21	5.61 X 10^3	400.61	2037.72	0.75	4.2 X 10^7	2.06	OK
3	CR - BOW2	4008.00	10421.04	5.78 X 10^3	310.38	2037.72	0.75	4.46X 10^7	2.01	OK
4	BOW2 - RR	3247.93	14795.03	5.32 X 10^3	557.30	2037.72	0.75	3.78 X 10^7	2.15	OK

Snow load calculation:

This test is done to check the behaviour or strenghth of roof when there is dead load applied on roof .
In some part of world there is heavy snow fall , due to that there is dead load weight is applied on the roof.
Normally due to dead load roof will bend and should be design in such a way that when the load is removed it should be regain its original shape..

Calculation approach:

Here we have done same things which we have done in heat distortion calculation.
Here we have projected curve at the center of hood .

Moment of inertia calculation:

Front roof :

Moi MAX = 1.67 x 10^4 mm^4

MOI min = 749.22 mm^4

BOW :

Moi MAX = 2.96 x 10^3 mm^4

MOI min =182.85 mm^4

BOW :

Moi MAX = 5.08 x 10^3 mm^4

MOI min = 227.73 mm^4

BOW :

Moi MAX = 1.45x 10^3 mm^4

MOI min =89.93 mm^4

Rear roof :

Moi MAX = 2.75 x 10^3 mm^4

MOI min =1306.32 mm^4

Matlab code for snowload calculation:

clear all
close all
clc

iy = input ('Iy = : ') ;
Ly = 1998.321;
Lx = input ('Lx = : ');
s = input ('s= : ');
Y = input ('Y = : ');
t = 0.75;
Rx =  input ('Rx = : ') ;
Ry =  input ('Ry = : ') ;
My = Y * (Ly - Y)
alphaa = My * Lx*Lx * 10^(-12)


u= iy *t*t;
v = alphaa * s* (((Rx +Ry)/2)^2);

Qr = u/(v*10^(-8))

Table for snowload calculation:

Sr No.	Bow	Iy	My	alpha	Lx	Ly	s	Y	Rx	Ry	Qr	ok/NG
1	FR - BOW1	749.22	7.81 x 10^5	1.2	1145.71	1998.32	457.83	533.25	2653.33	2283.95	14.7	ok
2	BOW1 - CR	182.85	9.9x 10^5	1.19	1094.80	1998.32	432.88	1011.24	2954.92	9988.85	.64	NG
3	CR - BOW2	227.73	8.3 x 10^5	0.9	1071.82	1998.32	505.62	1399.21	6254.76	10845.35	.04	NG
4	BOW2 - RR	89.93	1.3 x 10^5	0.1	1056.31	1998.32	533.25	1991.31	2521.19	16077.49	7.041	ok

Solution for failed condition :

Here we have created embosed on the roof for increasing the strenght of the roof .

Draft Analysis :

Draft nalysis is used to detect the part we have drafted should be easily removeable during manufacturing .
This type of analysis is performed based on color range identifying zones on the analysed element where the deviation from the draft direction at any point corresponding to specific angle .
The draft allow the easy removal of thew part.
In draft analysis the green colour indicate that the angle is sufficient enough for the removal of part during manufacturing process .

Rear roof :