Roof challenge
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.
Objective:
- To design a Car Roof with the given input model and drawing.
- Calculation for Heat Distorsion and Snow Load Criteria is done to check whether the designed roof withstand the standards.
DESIGN CONSIDERATION
1. Visibility criteria
2. Head clearance
3. Curvature study
4. Hear distortion and snow load criteria
5. Draft analysis.
Final Roof Design along with components:
Components of Roof:
Outer Panel:
Front Roof Rail:
The front roof rail is the front part of the roof. It is degined considering the driver's visibilty criteria. One end is joined using Spot welding and other end is joined using mastics.
Bow Roof -1:
The bow roof is a stiffner part which gives strength to the roof.
Center Roof:
The Center roof is the center most part in the roof. It gives strength to the roof. It is located connecting the B pillar. The Center roof is joined with the help of mastrics.
Reinforcement:
Reniforcement is used to give strength to center roof.
Bow Roof-2:
The bow roof is a stiffner part which gives strength to the roof.
Rear Roof Rail:
The rear roof is joined with the back door of the roof. It is designed with the design consideration of the back door design.
Outer Panel with Rear Roof Rail:
Calculations for Heat Distorsion:
Bow–roof prediction 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 for Heat Distorsion Criteria: (Rx & Ry)
Calculation for Heat Distorsion Criteria: (l value)
Calculation for Heat Distorsion and Snow Load Criteria:
Calculation for Snow Load Criteria:
Snow load Prediction formula
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
Snow Load Criteria Calculations
Moment of Inertia for Bow Roof-1:
Center Roof Moment of Inertia:
Moment of Inertia for Bow Roof-2:
Calculations for Snow Load Criteria
Total Calculation for Heat Distorsion and Snow Load Criteria:
The Snow load criteria is not achieved. The moment of inertia is found lower.
So emboss is created on the outer panel to provide strength to the roof part.
The Outer Panel of Roof with Emboss
Conclusion:
We were successfully able to design the roof with all the roof rails for better support and strength. We designed it so as to satisfy the norms and regulations by calculating the heat distortion criteria and the snow load critera. While doing this we also understood about the methodology behind designing the roof of the car and what all we take into consideration while designing so.