Roof challenge
ROOF CHALLENGE
Objective
To design the Roof Reinforcement and Bow roofs for the given Roof styling using NX CAD 11 and to perform the calculations to determine whether the positioned Bow roofs are as per the Heat Distortion and Snow Load conditions.
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.
Roof is connected to A pillar, B pillar and C pillar. Thus the roof is supported by reinforcement with front and rear roof rails.
Front Roof Rail:
The Front roof rail supports the wind shield glass (3.7-4.7 mm thick) and a rubber is pasted below that (4-5mm) sticked with a sealant. 21.5 mm length is measured featured design purposefully (8+5+7+2). 3 degree angle is also designed for a reason. Visibility criteria will deteriorate the wind shield glass. Visibility criteria are used for the driver. Head room clearance is also need to be maintained. Min of 80 mm is followed.
Construction:
For the construction for the bow roofs it was taken on an average of four so that the entire given roof model is divided into 4 types so that 2 bows roofs of thickness 0.75 mm and 1.15 mm was used. Then the reinforcement roof at the centre was modeled with a thickness of 0.75 mm was modeled. The width of the 2 bow roofs was taken as 75 mm and the reinforcement centre width was around 120 mm. Then at the end all the roofs were fixed on the ditch area so that it could be welded.
Front Roof - Master Section:
Master Section Design:
Rear Roof Rail:
The Rear roof Master Section
Rear Roof Design:
Reinforcement Roof Section
Bow Roof Section
Bow Roofs
Roof Down View
Roof Curvature Study:
The designed roofs and reinforcements positions are determined by the following Criterias
- Heat Distortion Criteria
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]
Calculation:
Thus from the calculation made it is clear that all the roof positions are positioned in the accepted range .i.e OK< 2.7> 3.1
- Snow Load Criteria
Formula:
Qr = [Iy x t^2] / [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
Calculation:
Thus from the table it is clear that the snow load condition for the roof has been found that it is within the permissible limit. So that it also clears the snow load condition. It is also found that the thickness of the second bow roof thickness was changed to 1.15 mm to get the expected output.
Section Modulus Results:
For Bow Roof 1:
For Bow Roof 2:
Reinforcement Roof:
Thus these values are used for the calculation of the Snow Load Calculation.
Conclusion:
Thus from the calculations made the heat distortion criteria and snow load condition criteria was satisfied and the positioning of the bow roofs were determined.