Roof Design
AIM : For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.
OBJECTIVE :
1.The main goal of the project is to design the roof sheetmetal in NX cad, as well as the front roof rail, rear roof rail, bow roof front, bow roof rear, centre roof rail, and reinforcement to make a sturdy roof.
2. Carry out a curvature research on the roof and performance calculations for the criterion of Heat distortion and Snow load.
3. Determining the section modulus and moment of inertia for Bow-roofs and the centre roof rail.
4. In addition, locate the Draft Analysis for each section.
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.
When it is seeing from outside of the car, it is just closing the top portion. But in design point of view, it is hard to create the design. Because of you have to create no of support rails for enough strength to withstand the load. Bow roofs are primarily fixed in flatter region to enhance strength.
Front roof and rear roof rails are fixed to the ditch area using spot weld operation. But front, rear bow roof and center roof rails are fixed to roof using mastic sealants. We don’t want so much gap between roof rails and bow roof area. So, we reducing the NVH issues.
DESIGN CONSIDERATION OF ROOF:
- Visibility criteria
- Head room clearance
- Bow roof position
- Heat distortion and Snow load criteria
- Draft analysis
Roll Over Test On Roof
- The rollover test is given by the Insurance Institute of highway safety ( IIHS). After analyzing many accidents IIHS has fixed some regulations about how to perform the test.
- IIHS rating is based on the following things which are how fast a car can reform its original shape after rollover and how deep a protrusion is.
- The aim of this test is to minimize the protrusion of the roof.
- Two conditions need to be followed while performing this test. One is to lock all the doors of the car properly and the second is to close all the windows of a car.
- Also, it is mandatory to fix the chassis on the hard lever surface horizontally.
- Load is applied at 25 degrees tilt when view from the front over the length of 762 mm.
- Load is applied at 5 degrees tilt when view from the side, over the length of 1829 mm.
DESIGN OF FRONT, REAR ROOF RAILS AND BOW ROOFS.
CENTER ROOF RAIL :
CENTER ROOF RAIL and its's Master Section.
BOW ROOF 1 :
BOW ROOF 1 and its's Master Section.
CENTER ROOF RAIL :
CENTER ROOF RAIL and its's Master Section.
BOW ROOF 2 :
BOW ROOF 2 and its's Master Section.
REAR ROOF RAIL :
REAR ROOF RAIL and its's Master Section.
DRAFT ANALYSIS :
OUTER ROOF
CENTER ROOF RAIL
BOW ROOF 1
CENTER ROOF RAIL
BOW ROOF 2
REAR ROOF RAIL
HEAT DISTORTION ANALYSIS :
Analysis of Heat Distortion
The strength of the roof panel is significantly influenced by heat distortion analysis. Above this temperature, a material cannot be used for structural purposes.
The material begins to soften when exposed to a fixed load at an increasing temperature, and this study is used to forecast the heat distortion temperature at which this happens.
By altering the position of bow roofs, the heat distortion temperature can be recalculated using the trial-and-error method to prevent any bending or damage to the roof. This allows it to fall within the range that is depicted below.
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+Ry)
Rx = X curvature
Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
Judgment Condition
OK< 2.7
CALCULATION :
Snowload Analysis
- The purpose behind this analysis is to check the strength of the roof when snow is present on it acting as a load.
- A roof should be designed in such a way that it should rebound to its original shape after the removal of snow.
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)
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]
The width of the roof panel is 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
Judgment condition
Qr ≥ 3.1
MOI OF BOW ROOF 1
MOI OF CENTER ROOF RAIL
MOI OF BOW ROOF 2
CALCULATION :
Judgment condition
Qr ≥ 3.1
Conclusion :
As we can see the Qr value of Center Roof to Bow Roof 2 IS not meeting the condition as it is less than 3.1, So Embosses are provided on the outer roof panel to increase the strength of the roof
FINAL IMAGES
