Roof challenge

Roof definition

The roof is the topmost structural member in an Automobile. The main purpose of the roof is to protect the passenger and Compartment from all types of environmental factors such as dust, wind, Rain, Sunlight etc. As the component is exposed to such rigorous conditions, careful material selection is really important. Generally, alloys of aluminum are preferred as they are lightweight and results in lower CG and more stability. Steel is also used to develop a panel for the roof.

The outer panel of the roof is supported by the Roof rails. Roof Rail and Roof part are joined by Mastic glue preferably butyl mastic as it retains flexibility even after adhesion and helps in maintaining flexibility and reducing NVH. Generally, the roof rails are developed from scrap material; from the blanks used to manufacture the rest of the body panel. Front and Rear roof rails are present in every car body. But, the number of bow roof and Reinforcement centre depends upon the curvature and length of the roof outer panel.

• Heat Distortion - it is an important factor to determine the position of the roof. Heat Distortion temperature is the temperature at which the material is no longer suitable for structural applications. When exposed to high temperature and load the material begin to soften and cannot be used.

Formula - W = (1.73*10^-3*L)+[1.85*10^-8*R^2/t]+(1.10*10^-3*l-2.68)

Were,

L - Length in X-direction(mm)

Rx - Value of X curvature

Ry - Value of y Curvature

R - Roof curvature - 2*(Rx*Ry) /(Rx+Ry)

t - Thickness of the component

l - Bow roof Span

Snow Load Condition - The roof of an automobile must be able to withstand load especially snow which results in heavy load acting on the roof. If the roof is not able to withstand it, there will be deformation of the roof. To prevent that, Snowed criteria calculation helps us to determine whether the roof design will withstand the snow load.

Formula - 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 centre 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]