Roof challenge
OBJECTIVE
To design the Front roof rail, Bow roof rail, Center roof rail, and Rear roof rail using the given roof styling and the master section using the NX cad. To calculate the Heat distortion criteria and Snow load criteria on the designed roof.
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.
Roof components
- Front roof rail
- Bow roof rail
- Center roof rail
- Rear roof rail
1. Front roof rail
2. Bow roof rail 1
3. Center roof rail
4. Bow roof rail 2
5. Rear roof rail
Master section of front roof rail
Section inertia roof rails
Section inertia of Bow rail 1
Minimum moment of inertia 19.942 mm^4
Section inertia of Bow rail 2
Minimum moment of inertia 20.108 mm^4
Section inertia of Center roof rail
Minimum moment of inertia 39.497 mm^4
Heat distortion criteria
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]
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)
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 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 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
CONCLUSION
Thus the design of the front roof rail, bow roof rails, center roof rail, rear roof rail was completed on Nx cad. Heat distortion criteria satisfy the condition and snow load criteria do not satisfy the condition. So we can provide emboss to the roof surface for more strength.