Roof Design

REPORT OF ROOF DESIGN

Aim:- To develop the enssential flanges and reinforcement of bow roof with appropriate dimensions and checking draft by performing Draft analysis ,calcluating scection inertia ,Heat distortion and snow load on the roof.

Roof:- An automobile roof panel or car top of the portion of an automobile that fixed or sits above the passenger compartment, proctecting the vehicle occupants from sun, wind,rain,and other external elements.

Roof is designed by following some criteria:-

• Head clearance for easy and comfort
• visibility criteria as safety and functionality
• Draft analysis for easy to manufacturing and tooling
• safety parameter for users
• Heat distortion
• snow load criteria
• accidental load criteria

Roof skin panel:-

Front roof rail master section:-

Center Bow roof master section:-

Bow roof master section:-

Rear roof rail master section:-

Front Roof Rail View :-

Embosses are created to given stiffness and strength to the rail and mounting for brackets are given in which lights and switches will position.

Center Bow roof view:-

Bow roof -1

Bow roof -2

Rear roof rail view:-

Embosses are created to given inner strength of the material.

Roof rail position:-

Outer panel flange are created:-

Rear flange is created in which back door hinges will position and back door sit over the outer hinges its.

Complete Assembly view :-

completion after designing of roof some calcluation, due to calcluate the strength of Designed roof

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

Where,

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+R)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span

Except Rx and Ry all values can be measured on the model.

To get the Rx and Ry curvature a sketch was required

• A sketch was created on a plane on top of the Roof
• 0-Y line was created in the X-Direction in center of roof
• Then a Horizontal line below 300mm was created named as -3Y Line
• Two lines on both sides at 100mm were created from -3Y Line
• Intersection point on line was created and projected on outer Panel of Roof

Projected points

this projected points are projected on the outer roof surface

Then this using points to create three point arc

Then Minimum Radius of curvature was messured to get Rx and Ry value

Rx1 value:-

Rx2 value:-

Rx3 value:-

Rx4 value:-

Ry1 value:-

Ry2 value :-

Ry3 value:-

Ry4 value:-

By using all value heat distortion by using Excel:-

According to Judgement Condition : OK< 2.7> 3.1

All Values are under Judgement Condition.

Snow Load Calculation

During Winter Season the snow gets clogged over the top surface/roof of the car and the snow has some mass on it. Due to this, the roof can fail if the snow load exceeds the capacity of the roof that was designed to sustain.

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

To get the values a sketch was created on top of Roof

• O-Y line was created in the center of roof
• A line between First and center Roof rail was created
• Then two lines on both sides at 100mm was created
• Similar lines were created between other center roof rail, both Bow Roof rails and rear roof rails
• Intersection points were created and projected on the roof

Projected points for snow load calcluation:-

Then three point arc was created by using this points

Then minimum radius values was created Rx and Ry values:-

Rx1 value obtained:-

Rx2 value obtained:-

Rx3 value obtained:-

Rx4 value obtained:-

Ry1 value obtained:-

Ry2 value obtained:-

Ry3 value obtained:-

Ry4 value obtained:-

By using all the values Snow load was calculated in the MS Excel

Snow Load Calculation

So, according to the Judgement condition = Qr ≥ 3.1

And, Here one result of Qr is not fulfilling the demand. So, there are some solutions, that the model can pass over to the styling team to change the curvature to improve the strength, Bow Roof rails position can be changed to the weaker side of roof or Embosses could be created on the outer panel to improve the strength.

To improve the strength, the embosses are created

Section Modulus:-

Section modulus is a geometric property for a given cross-section used in the design of beams. Other geometric properties used in the design include an area for tension, radius of gyration for compression, and moment of inertia for stiffness. The Section modulus is defined as

S=Iy

Where

S = Section Modulus

I = Moment of Inertia

y = Distance from the neutral axis to any given part.

Front Roof rail

The intersection was created and then Section Inertia command was used to obtain MOI

Center bow roof:-

Bow roof 1:-

Bow roof 2:-

Rear rail bow roof:-

Conclusion:-

all the required parameters and different Calculations were done for safety concerns.