Roof challenge

Objective:

For the given Car Roof styling, design and develop the essential flanges and reinforcements, namely the Ditch Area, Front Roof Rail, Rear Roof Rail, Centre Roof Rail and Bow-Roofs.

INTRODUCTION:

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.

Under the styling surface that is seen on the outside, there are many other structures under the roof which contribute to its strength and stability. The number of such structures/supports differ with respect to the size of the vehicle. They are primarily installed on flatter areas of the roof to enhance the strength. These are the Front Roof Rail, Rear Roof Rail, Centre Roof Rail and Bow Roofs and they are joined to the roof by the Ditch Area.

DESIGN CONSIDERATION:

• Visibility criteria
• Head clearance
• Curvture study
• Heat distortion and Snow load criteria
• Material thickness

FRONT ROOF RAIL:

Front roof rails are used in the assembly of a roof in which it provides mounting provisions to windshield glasses and the changes in the front roof rail influences the frontal visibility of the passenger. The major design factor considered is the headroom clearance. The front roof rail also provides provisions for mounting the inside rearview mirror.

DRAFY ANALYSIS FOR FR:

BOW ROOF 1:

BOW- Roof center 1 is an additional stiffening member used in the roof assembly for the localised strength improvement and it is join directly to roof itself with several spot welding or even with the mastic sealent.

DRAFY ANALYSIS FOR BOW ROOF:

Centre Roof Rail:

Centre Roof rail or the reinforcement centre is located at the centre of the roof . The cross section of this is more since it needs to provide more strength to the roof. Here both are ends are joined together using mastic sealants.

DRAFY ANALYSIS FOR CENTER ROOF:

BOW ROOF 2:

The bow roof center 2 is similar to that of bow roof center1 which serves the same purpose as the previous but with a limited extend and hence it is used with a smaller cross section.

DRAFY ANALYSIS FOR BOW ROOF 2:

REAR ROOF RAIL:

The rear roof rail is the one of the importent component of roof assembly which is used for the back door mounting.similar to front roof rail importen design consideration include rear passanger head clerance rear visibility of the vehicle.

DRAFY ANALYSIS FOR REAR ROOF:

Heat Distortion Curvature Study:

This study is used to find out and predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load. So in order to avoid bending or damage of the roof based on this calculation we will decide the position on the roof bows on the roof.

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 Criteria:

We predict the snow load in this of the roof bows and then place and change the design of the load accordingly to satisfy the condition.

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 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]

This shows that first and third section, design does not fulfil snow load criteria.

Hence, to increase the strength of the roof, embosses are provided on the roof surface

Draft analysis of Outerpanel was done to check for proper draft angle.

BOW ROOF OVERALL :

CONCLUSION:

Design of roof was done and checked for heat load and snow load criteria. Designed passed the heat load criteria but failed at some sections in snow load criteria. To overcome this, embosses are provided on the roof surface