Roof Design

 Roof Design

 Aim:- For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof with calculation of roof heat distortion and snow load.

 

Roof strength test

This protocol explains how the Insurance Institute for Highway Safety (IIHS) evaluates and rates the roof
strength of motor vehicles.
Roof strength evaluations consist of a quasi-static test conducted on a vehicle’s roof in a manner similar
to tests used to judge compliance with U.S. Federal Motor Vehicle Safety Standard (FMVSS) 216 (Office
of the Federal Register, 2009). The main differences between the IIHS roof strength test and that specified
by FMVSS 216 are that the IIHS test:
• Specifies testing one side of a vehicle’s roof,
• Does not include a headroom criterion,
• Specifies testing to a given displacement instead of a given force level, and
• Specifies setting the vehicle’s pitch angle during testing based on the measured on-road pitch
angle.
An overall rating is assigned based on the peak strength-to-weight ratio (SWR) measured within 127 mm
of plate displacement.
Supporting documents for the Insurance Institute for Highway Safety (IIHS) roof strength program are
available from the Technical Protocols section of the IIHS website.

TESTING
Roof strength evaluations are conducted on a quasi-static test system manufactured by MGA Research
Corporation (Figure 3).
The system consists of an upright assembly and an attached loading head that can be fixed at varying
heights from the ground and at pitch angles ranging from −5 to +5 degrees to accommodate testing on the
driver or passenger side.
The roll angle is permanently fixed at 25 degrees.
Four hydraulic actuators control the movement of the platen along two linear guides.
The entire system is mounted on a T-slot bed plate anchored to the floor of the test facility.

Provided master sections

Front Roof Rail Master section 

 

Master section of the Rear Roof Rail 

Master section of Bow Roof 

Master section of Center Reinforcement Rail

 

Different types of reinforcements that our design roof has  :

• Front roof rail
• Bow roofs rail 1
• Central roof rail
• Bow roof rail 2
• Rear roof rail
• Roof outer panel

 

FRONT ROOF RAIL :

Front  roof rail is the one which joins the wind shield glass , body side outer and the inner panel  also. Here the front roof rail is designed based up on the master saection and then it is sewed and thicken 0.75mm

 

 

REAR ROOF RAIL :

Rear roof rail is the one which joins the back door and the body side outer and it is sew and thicken 0.75mm

   

 

CENTRAL ROOF RAIL : 

centre roof rail is created according to master section and then the it is sewed and thicken 0.75mm

 

BOW ROOF 1  :

The bow roofs are give to improve the torsional stiffness and load bearing capacity of the roof structure . The number of bow roof present is depends on the overall size of the roof . Presently in this project two bow roofs are added.thicken 0.75mm

 

 BOW ROOF 2  :

 

 

Roof outer panel

Outer panel is created according to master section and then it is sewed and thicken to 0.75mm

 

 

Final assembly

 

 

JOINING PROCESS :

Mastics are introduced between the roof outer panel and the reinforcements for joining .  where ever the mastic are introduced there is remarkable improve of the strength

Spot welding is also introduced to join the reinforcements and the outer panel

DESIGN CONSIDERATIONS FOR A ROOF :

• Visibility criteria
• Head clearance
• Curvature study
• Heat distortion and snow load criteria
• Draft analysis

 

 

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 the 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 elevated temperature . In order to avoid bending  or damages on the roof, based on the heat distortion  temperature , this study will predict the bow roof position which helps to strengthen the roof .

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]

 Judgement Condition : OK< 2.7> 3.1

 

APPLY THE VALUES IN THE FORMULA :

In order to find the heat distortion apply all the necessary values from the roof to the give formula

ROOF RAILS	I	Rx(mm)	Ry(mm)	L(mm)	t (mm)	R = 2(Rx*Ry)/(Rx+Ry)	W	Result
FR-BOW1	526.590	5686.72	3048.34	2029.26	0.75	3969.07	1.79	PASS
BOW1-CRR	380.866	4715.67	7226.37	2029.26	0.75	5707.09	2.05	PASS
CRR-BOW2	330.125	3893.67	11007.74	2029.26	0.75	5752.54	2.01	PASS
BOW2-RR	363.95	3273.95	14622.65	2029.26	0.75	5350.04	1.93	PASS

 

 CALCULATIONS  RESULT :

From the above table it can be concluded that all values of w<2.7 so design is OK

 

SNOW LOAD CRITERIA :

This test is done to know how is the roof behaving when there is a snow over . normally  due to the snow weight the dent will happen. But the  roof  should be designed in such a way that when the snow is removal the roof should go it its original position . This is the basic requirements for snow load criteria .

 

 

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 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]

APPLY THE VALUES IN THE FORMULA :

In order to find the snow load criteria  apply all the necessary values from the roof to the give formula

 CALCULATIONS :

ROOF RAILS	Iy	Rx(mm)	Ry(mm)	Lx(mm)	Ly(mm)	L1(mm)	L2(mm)	t(mm)	s	My	α	Y	[(Rx + Ry)/2]2	Qr	Result
FR-BOW1	1.84x103	4253.56	3057.73	1127.17	1976.18	618.29	458.31	0.75	538.2	839569.80	1.0666	618.29	13363740.36	13.49	PASS
BOW1-CRR	2.413X103	3847.41	7198.75	1078.37	1976.18	485.31	407.29	0.75	432.79	968487.82	1.126	1076.60	30504412.69	9.13	PASS
CRR-BOW2	1.85X103	4308.44	11611.53	1056.43	1976.18	407.29	492.29	0.75	449.78	730504.20	0.815	1483.89	63361361.2	4.48	PASS

  CALCULATIONS  RESULT :

It is observed from the values that obtained values of QR > 3.1

 

Section analysis:

                     Section moment of inertia is used to predict the amount of deformation and deflection of a part. A higher moment of inertia is preferable as it reduces the amount of deflection for a given force. The thickness of the part and addition of flanges and embosses increase the section inertia of the part. Here the master sections of the roof and roof rails and their section analysis are given.

BOW ROOF 1

Create an intersection curve with the help of the plane and select the bow roof 1

Moment of inertia maximum,( MAX)  I _max  =2.683×10⁴ ( mm⁴)

Moment of inertia minimum ,( MIN)  I _min =1.846 x10³ ( mm⁴)

 

 

BOW ROOF 2

 

Moment of inertia maximum,( MAX)  I _max  =4.639×10⁴ ( mm⁴)

Moment of inertia minimum ,( MIN)  I _min =2.413 x10³ ( mm⁴)

CENTRAL ROOF RAIL :

Moment of inertia maximum,( MAX)  I _max  =2.684×10⁴ ( mm⁴)

Moment of inertia minimum ,( MIN)  I _min =1.856 x10³ ( mm⁴)

 

Draft analysis 

The Draft Analysis command enables you to detect if the part you drafted will be easily removed. This type of analysis is performed based on color ranges identifying zones on the analyzed element where the deviation from the draft direction at any point, corresponds to specified values.

Minimum draft angle of 7⁰ is considered for analysis . green colour infer on the parts that all face along the tooling direction has positive draft angle greater than 7⁰ and passed in analysis

 

DRAFT ANALYSIS FOR FRONT ROOF RAIL :

 

DRAFT ANALYSIS FOR BOW 1 ROOF RAIL :

 

DRAFT ANALYSIS FOR CENTRAL ROOF RAIL :

 

DRAFT ANALYSIS FOR BOW 2 ROOF RAIL :

 

DRAFT ANALYSIS FOR  REAR  ROOF RAIL :

 

views

 

Top view

 

Bottom view

 

section view

 

Conclusion:- so I can conclude that I have properly design the  roof according to master section and also rood also pass the heat  distortion and snow load calculations and draft analysis is also done