Roof challenge

Introduction:

Roof of an automobile is the assembly which is at the top of passenger cabin . The primary objective of roof is to protect the passengers from external factors like rain ,sun,snow and protect the passengers in case of a roll over .

The types of roofs are:

1) Hardtops - When we talk about hardtops, we refer to the common rigid forms of automobile roofs we see around. This type of roof is made from metal or plastic in modern-day cars. So, the common Toyota Corolla, Camry, and many of the cars in Nigeria are all Hardtops.

2) Sunroof - A sunroof is an operable type of roof that allows for an opening in the roof of an automobile; say a window in a roof. It can allow either light or air or both to enter the vehicle. They are either operated manually or automatically.

3) Convertibles - convertibles are passenger cars that can be driven with or without the entire roof in place. They have first introduced as open-air vehicles; no roofs, no sides.

There are various types of roofs presently in the market .Eg: Convertible roof

Hardtop (Retractable type)

sunroof

T-roof

Under the styling surface of the roof. Other structures contribute to its strength and stability. They are mainly installed on the flatter surface of the roof. The other structures that lie inside the roof are:

• Front roof rail - Front roof rail is used to provide strength to the roof panel and it also acts as a link between windshield glass, roof panel, and headliner. Headroom clearance and visibility criteria should be considered the important factor while designing the front roof rail
• Bow roof - Bow roofs are again the roofs that will provide support to the roof panel by increasing its strength. The position of the bow roofs is the very factor that needs to be considered. The bow roofs should be straight.
• Center roof rail - This is a roof rail that will at the center of the roof to provide strength and stability to the roof. The center roof rail will be a straight roof rail.
• Rear roof rail - Rear roof rail is again used to strengthen the roof and this acts as a link between the roof panel and the backglass which is connected to the backdoor of the car

We will be concentrating more on the hardtop as it is the most widely used and provides best structural strength .

Roofs are provided with reinforcements in the front, center and rear by rails . Additional supports called bow roofs are also provided to ensure strength in case of rollovers .

The position and dimension ofroof rails and bow roofs are of utmost importance because it has to clear certain parameters in order to ensure safety and longer life. There are 2 main criteria used to calculate this

a) Heat Distortion Criteria

Used to ensure that the vehicle roof withstands thermal expansion in various geographical conditions

b) Snow Load Criteria

Used to ensure that the vehicle roof withstands loads caused by snowfall in cold regions .

PROCEDURE

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 - This study is done to check the ability of the roof to withstand snowfall and bounce back to its original shape without any damage once the load is removed.

• Again for calculating the Rx and Ry value
• Create one sketch on the plane which is at top of the roof surface. so againdraw an 0-y-axis on the sketch and will draw lines 100 mm apart on both sides and then mark the center between the rails and roofs and from that center,
• Draw a vertical centerline and will create lines 100mm apart on both sides of that line. Then create intersection points between horizontal and vertical lines. The sketch is shown below

The snow load Prediction formula is shown below:

Qr = [Iy x t²] / [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

SECTION MODULUS OF THE ROOF

From the above result, the roof structure is added with reinforcements in form of embosses on the roof

DRAFT ANALYSIS