Roof Design
Aim
- Provide appropriate dimensions and check for Draft analysis.
- Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.
- Develop the reinforcements as separate parts
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.
Design of any product starts from a requirement. While considering the Roof, f the roof is flat it is very weak and cannot able to with stand the forces like snow, So the design engineer sketches the product based on the requirement in order to increase the strength of the roof these reinforcements like front roof rail, central roof rail, rear roof rail and the bow roofs are introduced and joined to the flat surface of the roof with the different joining process.
- 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 (Front/Rear)
Front Bow Roof
Rear Bow Roof
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.
- Central 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.
- 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.
CALCULATION
Bow–Roof Prediction/Heat Distortion Analysis
The heat distortion study plays a major role in sheet metal usage. heat distortion temperature is a temperature limit above which the material cannot be used for the structural applications. This study is used to predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load at elevated temperature. In order to avoid bending or damages on the roof, based on the heat distortion temperature, this study will predict the bow roof position which helps to strengthen the roof.
W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68
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]
Conditions
True IF < 2.7
RESULT
From the above table it can be concluded that all values of w<2.7 And the current position of the bows are ok
Snow Load Prediction Analysis
This test is done to know how is the roof behaving when there is a snow over. normally due to the snow weight the dent will happen. But the roof should be designed in such a way that when the snow is removal the roof should go it its original position. This is the basic requirements for snow load criteria.
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)
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]
The width of the roof panel is 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
Judgment Condition
True if Qr ≥ 3.1
Result
From the above table it can be concluded that all values are True and the position of the bows are ok
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 colour ranges identifying zones on the analysed element where the deviation from the draft direction at any point, corresponds to specified values.
Front Rail
Front Bow Rail
Centre rail
Rear Rail
Conclusion
As from the given roof rail i can able to generate different Bows to different position of the roof, so that Heat dispation analysis and snow load analysis is also done along with the draft analysis.