Roof challenge
Aim: To design a car roof with all its members like the front, rear, reinforcement, and bow roof rails. Also, calculate the heat distortion and snow load conditions and determine whether the designed roof satisfies the conditions.
Theory:
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.
Parts of a Roof
Typically, the roof of a car will have 4 major components; the front roof rail, rear roof rail, reinforcement roof rail, and bow roof rails. The number of bow roof rails varies according to the size of the roof and other factors like existence of sunroof/panaromic sunroof etc.
Challenge:
Given class A skin
Front roof rail outer and inner master section
Front roof rail outer has been made
Rear roof rail outer and inner master section
Rear roof rail outer has been made
Front roof rail
Rear roof rail
Bow roof rail master section
Bow roof rail (rear)
Providing mastic points
Bow roof rail (front) with mastic points
Reinforcement roof rail
Finally doing symmetry and making everything a solid body (0.75mm thickness)
Making embossings on the rooftop for extra rigidity and strength
Final Design
Draft Analysis
BRR (rear)
BRR (front)
RRR
Front Roof Rail
Rear roof rail
Rooftop
Calculations:
Heat Distortion
Formula
Roof length in 0-Y direction (L) came to be 2028.483 mm
Sketch for plotting points to find Rx and Ry values
Projection the points onto the styling surface and connecting them with curves
Find Rx and Ry values
Rx
Ry
Find 'l' values
Calculated W values with the help of Excel sheet
We find that all values of W satisfy the condition of OK<2.7>3.1
Snow Load
Formula
Plotting points
Finding Rx and Ry values
Finding Lx values (vertical distance of the rail)
Y values (distance b/w the midpoints of the rails)
To find section modulus of the 3 rails
Making intersection
Filling the intersection
Finding section modulus using "measure inertia" tool. Take the lower value of M (which is M1 here).
Finally calculating Qr using Excel sheet
We find that one of the areas does not satisfy the Qr condition of Qr >= 3.1.
Conclusion:
Therefore, we can conclude that the roof that we have designed does well to satisfy the heat distortion criterion but fails in the case of snow load. Therefore this roof is not suitable for application.