Roof Design
Roof Design
Objectives:-
1. For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements.
2. Provide appropriate dimensions.
3. Check for Draft analysis.
4. Do a curvature study on the roof and perform calculations to determine the position of the Bow-roofs.
5. Suggest and implement remedies in the design if the criterion is not full-filling.
6. Develop the reinforcements as separate parts
Given:-
1. Thickness = .75mm
2. Draft angle = 7 degree
3. Front Roof Rail Master section
4. Master section of the Rear Roof Rail
5. Master section of Bow Roof
6. 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+Ry)
Rx = X curvature
Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
Judgment Condition
OK< 2.7
7. Snow Load Prediction 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)
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
250 ≤ s ≤ 38
Theory:-
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. The roof is the structure above the windshield glass having the reinforcements to provide strength to the overall structure and to withstand overhead forces like snow
Reinforcements
If the roof is flat it is very weak and cannot able to withstand the forces like snow, so in order to increase the strength of the roof these reinforcements like the front roof rail, central roof rail, rear roof rail, and bow roofs are introduced and joined to the flat surface of the roof with the different joining process
Different types of reinforcements present on car roofs:
- Front roof rail
- Bow roofs
- Central roof rail
- Rear roof rail
- Central roof rail reinforcement if the sunroof is present.
METHODOLOGY
We get the model of the roof from the styling team. Then we will have to do all the engineering work. We create the ditch area for the roof and also the roof bows and roof rails for the roof which would we designed by us considering all the safety norms and regulations.
DESIGN CONSIDERATION RULES
-
Visibility criteria
-
Head clearance
-
Curvature study
-
Hear distortion and snow load criteria
-
Draft analysis.
Roof Design
1. Roof Flanges
Draft Analysis of Roof Flange
2. Front Roof Rail Design
Draft Analysis of Front Roof Rail
3. Design of Rear Roof Rail
Draft Analysis of Rear Roof Rail
4. Central Roof Rail Design
Draft Analysis of Central Roof Rail
5. Front Roof Bow Design
Draft Analysis of Front Roof Bow
6. Rear Roof Bow Design
Draft Analysis of Rear Roof Bow
7. Central Roof Rail Reinforcement
Draft Analysis of Central Roof Rail Reinforcement
Roof Assembly
ROOF CRUSH TEST :
The roof crush test is the design given by the IIHS ( insurance institute of highway safety ). After analyzing the many accidents IIHS has then fixed some regulations, that how to perform the crush test.
IIHS gives the rating based on this test. For this, they consider two points while giving the rating
- How fast the car can reform to its original shape after the rollover and
- How deep is the protrusion after the rollover
GOAL OF ROOF CRUSH TEST :
To minimize the protrusion into the occupant compartment, so that the seat belts and airbags can do their job in protecting the occupant
CONDITIONS TO FOLLOW FOR ROOF CRUSH TEST :
There are two conditions that should be followed for the roof crush test, they are
INITIAL CONDITION :
- Close and lock all the doors
- Close all the windows
SECOND CONDITION :
Fix the body sill or chassis frame on a hard lever surface horizontally
METHOD OF APPLYING THE FORCE :
The load is applied in such a way that 50 is tilted from the front end to the rear end and the load will be 1800 mm in length and 750 mm in width. The load is applied at the position of 250 from the flatness of the roof. The load is applied on the roof for almost 120 sec and the crushing speed at which the load is applied is 13 mm/sec or less than that
RESULTS :
If the displacements go above the requirements level then we have to increase the bow roof thickness or add more mastics points to increase the strength. the stronger the roof the better it can protect the occupants in rollover crashes.
HEAT DISTORTION STUDY ON THE ROOF :
The heat distortion study plays a major role in sheet metal usage. heat distortion temperature is a temperature limit above which the material cannot be used for structural applications. This study is used to predict the heat distortion temperature at where the material starts to soften when exposed to a fixed load at an elevated temperature. In order to avoid bending or damage on the roof, based on the heat distortion temperature, this study will predict the bow roof position which helps to strengthen the roof.
Curvature study
1. 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) =
Rx = X curvature
Ry = Y curvature
R = Roof curvature
R = 2(Rx*Ry)/(Rx+Ry)
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
Judgment Condition
OK< 2.7
Values of Curvature
Rx1
Ry1
Rx2
Ry2
Rx3
Ry3
Rx4
Ry4
Calculation Table
2. Snow Load Prediction Formula
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
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 from 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
250 ≤ s ≤ 380
Values of Moment of Inertia
Iy1
Iy2
Iy3
Values of Curvature
Calculation Table
Results
1. The heat distortion study:- Given Judgemental Condition:- W< 2.7
From the above table, we can conclude that our design satisfies the heat distortion condition because all the values of w is less than 2.7 Which means that all reinforcement position is perfect and it will helpful in returning to its original condition when heat distortion happened.
2. Snow Load Criteria study:- Given Judgemental Condition:- Qr ≥ 3.1
250 ≤ s ≤ 380
From the above table, we can conclude that our design satisfies the Snow Load Criteria study because all the values of Qr are lies between 250 and 380 Which means that the Front and Rear Bow and Central Roof Rail are strong enough to withstand snow load conditions and it will return in its original condition when Load will remove.