Roof challenge
Roof
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.
In order to give strength, it is provided with embosses on top of the roof.
The bow roofs are provided with mastic sealant as they are assembled with the surface, so welding is not possible, were as the ditch area, front and rear area is welded with the roof.
Front and rear roof rails are cut a part as there will be mounting on A and C pillars.
Section Part
Front Roof Rail
Rear Roof Rail
Bow Roof 1
Centre Roof Rail
Bow Roof 2
Section Modulus Calculation :
Front Roof Rail
Rear Roof Rail
Bow Roof 1
Centre Roof Rail
Bow Roof 2
Heat Distortion Criteria
It is the temperature at which the material starts softening when exposed to a fixed load at elevated temperature.
Above this temperature the material can't be used.
In order to know whether the design is safe or not according the positioning of bow roofs, the theoritical analysis is performed by considering the below given formula -
W = 1.73x10^-3 x L+1.85x10^-8 x (R^2)/t + 1.10x10^-3 x l-2.68
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]
Judgement Condition: OK<2.7mm<NG
Results obtained –
|
Sr no |
Bow |
Rx |
Ry |
R |
T |
I |
L |
W |
W<2.7 |
Ok/Ng |
|
1 |
FRR & 1st bow roof |
4305.1 |
2788.6 |
3385 |
0.75 |
336.5 |
2027 |
1.47 |
<2.7 |
Ok |
|
2 |
1st bow roof & CRR |
4714.6 |
6367.7 |
5417.8 |
0.75 |
376.2 |
2027 |
1.96 |
<2.7 |
Ok |
|
3 |
CRR & 2nd bow roof |
3739.1 |
10929 |
5571.9 |
0.75 |
378.6 |
2027 |
2.008 |
<2.7 |
Ok |
|
4 |
2nd bow roof & RRR |
2644 |
12323 |
4355 |
0.75 |
379.6 |
2027 |
1.71 |
<2.7 |
Ok |
So as per the results obtained the roof is safer to produce as the W values are below 2.7 as per the standard condition.
Thus, the design passes the Heat Distortion Test.