Roof Design
ROOF DESIGN
ROOF
An automobile roof is a component which sits above the passenger to protect from sun,wind,rain and other external substances. It also provides strength to the car in case a roll over situation occurs. So the design of roof is an important part in design with flanges,reinforcements,and other design elements to improve the strength.
BASIC ELEMENTS OF ROOF
- OUTER PANEL
- FRONT ROOF RAIL
- REAR ROOF RAIL
- FRONT BOW ROOF RAIL
- REAR BOW ROOF RAIL
- CENTER BOW ROOF RAIL WITH REINFORCEMENT
OUTER PANEL
Outer covering of the roof,it provides strength and an aesthetic look to the car.
FRONT ROOF RAIL
This is the roof assembly located at the front side of the car it comes in contact with the car glass and side body of the car. It provides strength to the front side of the roof. The design considerations to be taken care while designing this is Head room clearence and visibility.
FRONT AND REAR BOW ROOF
These bow roofs are added to provide extra strength to the roof. The number of bow roofs is fixed according to the length of the roof. The position of the bow roofs is determined by performing roof curvature study of the roof surface.
CENTER BOW ROOF RAIL AND REINFORCEMENT
As the name indicates this is located at the center portion of the roof. It consist of a Primary bow roof assembly embedded with an secondary bow roof assembly for increasing the strength of the roof.It also acts as a support if their is an roll over occurs. These embedded roofs are joined using spot welding.
REAR ROOF RAIL
This is the support which comes in contact with the backdoor,side body and inner panel of the car. While designing the rear roof we have to consider design criterias such as head room,visibility criteria.
DRAFT ANALYSIS
OUTER PANEL ROOF
FRONT ROOF RAIL
BOW ROOF RAIL
CENTER ROOF RAIL
REAR ROOF RAIL
CURVATURE STUDY OF ROOF AND ROWS
Curavture study is to be performed on the roof styling surface and bow roofs to determine their position to decide where the bow roofs to be placed and get the strenght and tests and analysis within the safe design limit. Their are various tests to be conducted for curvature study we will focus on two tests.
- Heat-Distortion Criteria
- Snow Load Calculation
HEAT DISTORTION CRITERIA
HEAT DISTORTION 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]
SNOW LOAD CALCULATION
SNOW LOAD 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 lengths in Side view