Roof challenge
Report on roof design
Aim: To develop the essential flanges and reinforcements with appropriate dimensions and checking draft by performing draft analysis ,calculating Section inertia ,Heat distortion and snow load on the roof.
Roof :An automobile roof of a 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.
Many variations on the automobile roof developed .these include:
Convertible roofs :
A convertible roof is a passenger car that can be driven with or without a roof in a place .The methods of retracting and storing the roof between models.
Hardtops:A hardtop is a rigid form of automobile roof ,which form of automobile roof ,which for modern cars is typically constructed from metal.
Sunroofs:A sunroofs is a movable panel that opens to uncover a window in an automobile roof ,allowing light and /or fresh air to enter the passenger compartment .sunroofs can be manually operated or motor driven and are available in many shapes ,sizes and styles .while the term sunroof is now used generically to describe any glass panel in the roof.
The automobile roof consists of the following parts:
the outer panel
Front roof rail
Bow roof
Centre roof rail
Rear roof rail
Front roof rail:
The front roof rail is created at the front side of the roof to provide strength to the roof .Headroom clearance and the driver visibility are the two important factors to be considered while designing the front roof rail.the front roof rail is connected to the roof outer panel with the help of mastic seal.
Bow roof:
It is used to give strength to the area between the front roof and the centre and the centre roof rail.also it created in the area between the centre roof rail and the rear roof rail to provide enough strength .it can be created in any numbers depanding upon the roof length but the position of the bow roofs is to be justified by curvature study.
Centre roof rail :
It is created at the centre of the roof .it is connected to the roof by mastic seal.
Rear roof rail:
it is created at the the rear end of the roof .The fitment of the backdoor is to be considered while designing the rear roof rail.
Heat distortion criteria:
Heat distortion temperature is the temperature at which metal softens and deforms under a specified load .while designing roof, this criteria taken into consideration .we create bow roofs when the roof is long and flat to increase its strength .The position of the bow roofs is to be justified and its justification is done by curvature study.
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]
Here we can see that the roof is completely satisfying the condition of heat distortion.
Snow load prediction formula:
Snow load is the downward force on a car s roof by the weight of accumalated snow and ice .The roof can fail if the snow load exceeds the weight the roof was designed to shoulder .
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)
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
Qr ≥ 3.1
It is observed that the roof is satisfying the condition only in the area between front roof and bow roof 1 and bow roof 1 amd centre roof .in other area it is not satisfying the condition .So in the order to strenghten the roof at these areas embosses are created on the outer roof .
EMBPOSS TO STRENGTHEN
Section modulus:
The section modulus of the cross sectional shape is to significant importance in designing of structure .it is a direct measure of the strength of the structure .
A larger structure that has a larger section modulus than another will be stronger and capable of supporting greater loads.
Section modulus (S):l/y
l= Momnt of inertia
y= Distance between the neutral axis and the extreme end of the object (mm).
Bow roof section inertia analysis
Bow roof 1 section inertia analysis:
Centre Roof rail section inertia analysis:
Draft Analysis:
IN nx to check weather the sheet metal part we have designed can be deep drawn ,there is an option called draft analysis is performed based on colour ranges identifying zones on the analyzed element where the deviation from the the draft direction at any point ,corresponds to specified value.
Roof draft:
Bow roof analysis:
Bow roof 1:
Centre roof draft analysis:
Front roof draft analysis:
Rear roof draft analysis:
