Roof challenge
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2021 |
|
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SKILL-LYNC roof design |
By
ABHIJNA K
CHAPTER 1
INTRODUCTION
An automobile roof is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Though it just looks like a styling surface that protects from sun, wind and other elements, various environmental conditions are taken into account for designing of the same. Roof should be provided with proper reinforcements for strengthening. Vehicle roof can be subjected to high heat conditions or load during snowy conditions. To make the roof withstand these conditions, various calculations are done. This ensures the safety of the passengers in the vehicle.
OBJECTIVES
The main objective of the project is to design a roof and roof reinforcements from the styling surface received using NX CAD. After the design is done, heat load and snow load calculations will be done on the OY section of the roof.
CHAPTER 2
COMPONENTS OF ROOF
The components of the roof are:
- Roof
- Front roof rail
- Bow roof rail 1
- Center roof rail
- Bow roof rail 2
- Rear roof rail
- 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. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.
- Front roof rail:
The front roof rail is located on the front of the roof where the wind shield joins with the roof. The visibility criteria and the head room clearance of the passenger are taken into consideration for the bottom flange. One end of the rail is joined using spot welding while the other end is joined with the roof using mastic sealants for increased strength.
- Bow roof rail 1:
Bow roof is an additional stiffening member for the roof to increase the strength and so that it can satisfy the norms. Both the ends are joined together using mastic sealants to increase strength and also since this would not affect the styling of the roof.
- Center roof rail:
Centre Roof rail or the reinforcement centre is located at the centre of the roof. The cross section of this is more since it needs to provide more strength to the roof. Here both are ends are joined together using mastic sealants.
- Bow roof rail 2:
This bow roof also have the same purpose as that of the first one. This one is located between the centre bow roof and rear roof.
- Rear roof rail:
This roof rail joins with the back door and the roof. Inputs from the backdoor are taken into consideration for designing this roof rail. Here one end is joined using spot welding while the other end is joined using mastic sealants.
CHAPTER 3
CALCULATION
Heat Distortion Curvature Study:
This study is used to find out and predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load. So in order to avoid bending or damage of the roof based on this calculation we will decide the position on the roof bows on the roof.
Formula:
W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x I] - 2.68
Judgement Condition: OK<2.7> 3.
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] I = Bow Roof Span [mm]
|
S.no |
bows |
Rx (mm) |
Ry (mm) |
R (mm) |
I (mm) |
L (mm) |
[R^2]/t (mm) |
T (mm) |
w |
OK/ NG |
|
1 |
BR1 -CR |
7031 |
2584 |
3779.11 |
429.30 |
2032.08 |
19042229.85 |
0.75 |
1.659 |
OK |
|
2 |
CR -BR2 |
11181 |
2986 |
4713.27 |
448.98 |
2032.08 |
29619885.45 |
0.75 |
1.905 |
OK |
|
3 |
BR2 -RR |
4923 |
3435 |
4046.54 |
446.12 |
2032.08 |
21832647.96 |
0.75 |
1.728 |
OK |
Snow load Prediction formula:
formula:
Qr = [ly x t^2] / [ x s x [(Rx + Ry) / 2]^2 x 10^-8]
Where
α = My x Lx^2 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 OY[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 from front Roof Rail to Roof BOW mm.
S = Distance for which Roof BOW bears divided load [mm]
Ly = Geometrical moment of inertia of Roof BOW
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 Root BOW [mm]. Roof panel X curvature radius of length in Side view
MOMENT OF INERTIA
Front roof rail:
Bow roof rail 1:
Center roof rail:
Bow roof rail 2:
Rear roof rail:
|
S.no |
bows |
Iy |
α |
Lx |
Ly |
Y |
s |
Rx |
Ry |
t |
Qr |
OK/ NG |
|
1 |
BR1- CR |
446.12 |
1.401 |
1407.5 |
2032 |
446.12 |
447.54 |
7110 |
9345 |
0.75 |
0.221 |
NG |
|
2 |
CR -BR2 |
448.96 |
1.361 |
1384.3 |
2032 |
448.96 |
439.13 |
6363 |
2254 |
0.75 |
2.471 |
NG |
|
3 |
BR2 -RR |
429.30 |
1.294 |
1371.6 |
2032 |
429.30 |
214.65 |
14736 |
7900 |
0.75 |
0.950 |
NG |
The values for the snow load does not satisfy the condition, So that to make the roof stronger we create embosses on the roof.
CHAPTER 5
VIEWS OF ROOF ASSEMBLY
CHAPTER 5
CONCLUSSION
Finally the design of roof is done with the help of NX-CAD software by following master section
Google drive link:
https://docs.google.com/document/d/1-JRQclk2hLhbhtdwu5TDmmvyDsAW9Bw8/edit?usp=sharing&ouid=100421040390010035010&rtpof=true&sd=true