Roof challenge
ROOF DESIGN
OBJECTIVE:
For the Given Roof styling, Develop the essential flanges and reinforcements, Provide appropriate dimension and check for Draft analysis and also submit your section modulus report on the 0-Y section.
Start with the creation of a roof ditch area the tool opening angle is only 3 degrees.
Do a curvature study on the roof and perform calculations to determine the position of the Bow-roof.
AUTOMOBILE ROOF:
An automobile or car top is the portion of an automobile that ssits above the passenger compartment,protecting the vehicle occupants from sun,wind,rain and other external elements.because the earliest automobile were designed in an era of horse drawn carriages,early automobile roofs used in similar materials and designs.
COMPONENTS:
- Front roof rail
- Rear roof rail
- Roof outter
- Bow roof rail
- Reinforcements
Number of bow roofs are depends upon the the size of the outter roof surface.
ROOF OUTTER PANEL:
The roof is made from a sheet of atleast 0.75mm.This protects the cabin from external conditions and objects.The dich areas are spot welded to the pillers of the car and certain areas of the roof rails,welding on the upper surface is avoided in order to maintain a good aesthetic.
FRONT ROOF RAIL:
The front roof rail is used to rovide strength to the roof panel front and it also acts a link between windsheild glass, roof panel, and headliner (interior trim)
The Front roof rail is made from a sheet of at least 1.25mm thickness.This part acts as a support for the roof sheet on the front it also provides a mounting area for the windsheild.It is designed with support requirements,visibility creiteria and headroom space in mind.The roof is fixd to the roof rails with the use of mastics while the ends are spot welded.
REAR ROOF RAIL:
The rear roof rail is used to provide strength to the roof panal front and italso acts as a link between wndsheild glass,roof panel and headliner
BOW ROOF:
The bow roof rail provides additional support to the roof and are atleast 1mm thick they are positioned insuch a way that they provide maximum support to the roof,care must be taken so that they do not intrude nto the headroom requirements of the car.Bow roof rails are optional feature provided as required by the design.Small cars may have none while large ones may have 3 or more,they may also be integrated into the centre roof rail in some cases.the roof is fixed to the roof railswith the use of mastics while the ends are spot welded.
REINFORCEMENT:
This is the roof rail that runs between B-piller of the car and provide a support area for the centre of the roof sheet they usually 1- 2mm thick and also provide support area for the centre cabin light mount.The roof is fixed to the roof rails with the use of mastics while the ends are spot welded.
CALCULATION:
HEAT DESTORTION CRITERIA:The roof of the vehicle is the most exposed to changes in temperature, these changes cause deformation in the roof. In order to prevent failure of the roof due to excessive thermal stress, the roof rails must be placed in the correct locations. Improper designing of the roof may cause warping, cracking, and failure of mounts.
This calculation is done to find if the roof under thermal stress deforms within set limits.
It is calculated using the formula
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]
| SI.NO: | BOW'S | Rx | Ry | R | I | L | t | W | OK/NG |
| 1 | FR & 1st | 5714.2 | 2429.4 | 3414.11 | 332.1 | 2022.5 | 0.75 | 1.18 | OK |
| 2 | 1st & CTR | 4870.3 | 1587.4 | 2394.4 | 439.5 | 2022.5 | 0.75 | 1.44 | OK |
| 3 | CTR & 2nd | 559 | 15119.3 | 1078.14 | 444.1 | 2022.5 | 0.75 | 1.34 | OK |
| 4 | 2nd & RR | 3237.5 | 1387.5 | 1972.5 | 372.5 | 2022.5 | 0.75 | 1.33 | OK |
So the design meets the requirements of heat distortion criteria and the values are got from the formula and calculation are within the limits.
SNOW LOAD CONDITIONS:
Snow load is the downward force on a 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 roof was designed to shoulder. Or if the roof was poorly designed or constructed.
The roof of a vehicle is normally not designed to hold up weight but for regions with snowfall, it must be properly reinforced to hold up the weight of accumulated snow on the roof, if done improperly it may cause the roof to bend and intrude into the passenger compartment which is dangerous.
This calculation is done in order to check if the location and strength of the roof rails are enough to avoid plastic deformation of the roof.
Snow load Prediction formula
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)
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 reference point of the front and the rear.
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
| SI.NO: | BOW'S | Iy | α | Lx | Ly | Y | S | Rx | Ry | t | Qr | DETERMINATION (Qr) |
| 1 | FR & 1st | 1.0862e+004 | 0.9236 | 1135.63 | 2022.5 | 457.64 | 486.395 | 4604.95 | 2497.38 | 0.75 | 191.74 | OK |
| 2 | 1st & CTR | 3.686 e+003 | 0.9101 | 1082.63 | 2022.5 | 515.15 | 517.58 | 3762.98 | 6068.70 | 0.75 | 1329.6 | OK |
| 3 | CTR & 2nd | 3.6852e+003 | 0.8676 | 1053.77 | 2022.5 | 520 | 493.04 | 4276.41 | 110992.12 | 0.75 | 8.207 | OK |
| 4 | 2nd & RR | - | 0.7830 | 1038.96 | 2022.5 | 466.08 | 233.04 | 3934.44 | 16796.45 | 0.75 | - | #DIV/0! |
So the design meets the requirements of snow load criteria and the values are got from the formula and calculation are within the limits.
MOMENT OF INERTIA:
Section moment of inertia is used to predict the amount of deformation and deflection of a part. A higher moment of inertia is preferable as it reduces the amount of deflection for a given force. The thickness of the part and the addition of flanges and embosses increase the section inertia of the part.
Here the master sections of the roof and roof rails and their section analysis are given.
MOI OF FRONT ROOF RAIL:
MOI OF BOW ROOF-1:
MOI OF BOW ROOF-3 AND REINFORCEMENT:
MOI OF BOW ROOF-2:
MOI OF REAR ROOF RAIL:
DRAFT ANALYSIS:
The draft angle for all parts is passing the 7 degress minimum draft angle.
DRAFT ANALYSIS OF ROOF OUTTER:
DRAFT ANALYSIS OF FRONT ROOF RAIL:
DRAFT ANALYSIS OF BOW ROOF-1:
DRAFT ANALYSIS OF BOW ROOF-3:
DRAFT ANALYSIS OF REINFORCEMENT:
DRAFT ANALYSIS OF BOW ROOF-2:
DRAFT ANALYSIS OF REAR ROOF:
GOOGLE DRIVE LINK:
https://drive.google.com/file/d/1iWegGBDgHYRIwOzR7KbW_o-lcnD8NYsT/view?usp=sharing
CONCLUSION:
Thus as per the objective essential flanges and reinforcements are developed for the given roof styling and section modulus , draft analysis are carried out for the designed roof.In addition to that curvature study of the roof and calculations to determine the position of the bow roof are perormed.