Roof challenge

                                      DESIGNING A ROOF OF A CAR

Objective: 

       To design a Roof of a car & do the curvature study to resist Heat distortion & snow load condition.

Automobile 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. Automobile roofs are conventionally supported by pillars on each side of the body.

Design of Automobile roof:

      The first step in designing an automobile roof is to create an outer surface (skin surface), which are usually designed by styling team based on parent car design and aesthetics.

Procedure:

• Using surface modeling techniques, necessary ditch areas are designed on all the sides of the roof.
• In addition to that, Rails and spoiler are designed on the top of the roof.
• To increase strength and to join the roof with the body of the car, some reinforcements are provided on the roof, such as

     1. Front roof rail

     2. Rear roof rail

     3. Reinforcement centre

     4. Bow roofs

Detailed Design

Front Roof rail:

• It is used to join the roof with front glass, and chassis via A-pillars.
• The thickness of 1.5mm is given to the surface.
• Necessary embosses are provided on the surfaces, if required.

Rear Roof Rail:

It is used to join the roof with back door and chassis via C-pillars.

• The thickness of 1.5mm is given to the surface.
• Necessary embosses are provided on the surfaces, if required.

Reinforcement centre:

• It is used to join the roof with the B-pillar.
• The thickness of 1.5mm is given to the surface.
• Reinforcement centre consists  of two parts- The inner part and outer part.

Bow Roofs:

• It is used to increase the strength of the roof.
• A number of bow roofs are decided based on the length of the roof and stength required.
• The thickness of 1.5mm is given to the surface. Strength of the roof will increase with the number of bow roof.
• In some cases, the bow roof itself is used as reinforcement centre.
• In this project, two bow roofs and one reinforcement are used.

Section Modulus calculation of the Roof:

Section modulus is a geometric property for a given cross-section used in the design of beams or flexural members. The elastic section modulus is defined as 

We have,

S= I/y

Where I - Second moment of area

          y- the distance from the neutral axis to any given fibre.

Front roof rail:

2. Bow roof rail 1:

3. Centre roof rail:

4. Bow roof rail 2:

5. Rear Roof rail 2:

Roof Curvature study:

1. Heat Distortion Criteria Calculation of the Roof:

       Heat distortion test is a type of static load test which plays an important role in maintaining roof strength. Heat distortion temperture at which metal softens and deforms under a specified load. From Heat distortion criteria, roof strength can be enhanced by appropriate positioning of bow roof rails.

Calculations:

Observation:

     As per the heat distortion criteria, positions of all the bow roof and reinforcement centre are under acceptable conditions.

2. Snow load criteria Calculation of the Automobile roof:

      The snow load test  is a type of static load test used to verify that roof assembly exhibits no permanent deflection due to a distributed load representing snow load.

        Snow load Prediction Formula

    Qr = [Iy *t2]/[a*s+[(Rx+Ry)/2]^2*10^-8]

Where 

  a= My x Lx^2 x 10^-12 , My = Y(Ly-y)

Judgement condition = Qr > 3.1

250

t = Roof plate thickness (mm)

Ly = Distance between the front and rear roof rails on the vehicle along OY (mm)

       - length of roof panel with the center point between roof rail front/ rear as the reference point of the front and 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 roof rail to roof bow

S= Distance for which roof bow bears divided load

     - S = L1/2 + L2/2

ly = Geometric moment of inertia of Roof Bow (Y cross section)

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 vew

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.

Observations:

   As per the heat distortion criteria, positions of all the bow roof and reinforcement centre are under acceptable conditions.

Images:

Conclustion:

    All the parts of the roof are designed based on the required parameters and are assembled together to form the roof using NX CAD. 

Google link:https://drive.google.com/file/d/1GmDaufyoAlGv5HRR66TTuIDzVtoV6OIB/view?usp=sharing