Automobile roof design using NX12 and optimization by calculating heat distortion criteria, snow load criterion, section inertial analysis.

Automobile roof design using NX12 and optimization by calculating heat distortion criteria, snow load criterion, section inertial analysis.

OBJECTIVE: The main objectives of this project are

• developing essential flanges and reinforcements from the input styling surface
• Provide appropriate dimension and check for Draft analysis and perform section modulus analysis on the 0-Y section
• To do a curvature study on the roof and perform calculations to determine the position of the Bow-roof

INPUTS:

project insight:

ROOF: An automobile roof can be termed as a protective structure that keeps the passengers of the vehicle safe from external elements like weather(sun, rain,fog..etc.), flying debris, and one of its main purposes is to protect the inhabitants of the vehicle from sustaining any injuries during rollover incidents and sudden impacts on roof.

• The roof itself is not a single component but an assembly of various parts and structures that form the roof assembly.
• it consists of an outer panel that provides covering and forms the top portion of the vehicle and also provides good aesthetics and strength to the vehicle.
• they are various components under the outer panel that form an internal structure which adds a lot of strength to the roof portion.
• and these components are the reason for the roof not getting caved in during rollover incidents of the vehicle.

• 

Structural components of the roof

1. front roof rail reinforcement (FR)
2. bow roof rail reinforcement 1 (BR1)
3. center roof rail reinforcement primary(CR)
4. center roof reinforcement(secondary)
5. bow roof rail reinforcement 2 (BR2)
6. rear roof rail reinforcement (RR)

the number of bow roof rails may vary depending on the size of the vehicle

STRUCTURAL COMPONENTS OF THE ROOF:

front roof rail reinforcement (FR): It is the support that joins the windshield glass, bodyside outer, and the inner panels. It is usually made from body side outer scrap and therefore the thickness of the rail is 0.65 mm. A draft angle of 3-5 degrees is provided for deep-drawing operation. The visibility criteria and the headroom clearance of the passenger are taken as design considerations

bow roof rail reinforcement 1 (BR1)& bow roof rail reinforcement 2 (BR2): these are the intermediate structural components of the roof that are added in order to provide support along with the three primary roof rails(FR,CR,RR). the number of bow roof rails may vary depending on the class of the vehicle. some vehicles may not have bow roof at all.it all depends on the design intent.these are joined to the roof by using mastics.embosses are added for additional strength.

BR1

BR2

center roof rail reinforcement(CR): the center roof rail is placed at the exact middle portion of the roof ,in some cases a secondary rail is embeded in to the center rail for added strength,the design inputs are taken from curvature of the roof at the CR position it is joined with mastics to the roof instead of spot welds as it is placed under styling surface.

rear roof rail reinforcement (RR):

It is the support that is joined to the backdoor, the bodyside outer and the inner panels. Inputs from the backdoor design is also taken to accommodate therequired clearance along with headroom clearance and the rear visibility criteria while designing the rear roof rail. Spot welds are applied at the backdoor end ofthe rail and the other end is joined with the roof using mastic sealants.

calculations to determine bow roof position:

heat distortion criteria:

Heat distortion temperature is the temperature at which the metal softens and deforms under a specific load. This study is done to check the ability of the roof to withstand high temperature with respect to the positioning of the reinforcements which contribute to increased strength.

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Judgement Condition : OK< 2.7> 3.1

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]

BOW	Rx	Ry	R	I	L	t	R^2/t	W	OK/NG
FR&BR1	5711.0	2779.3	3738.9	400.3	2031.8	0.75	18639164	1.61	OK
BR1&CR	4849.6	6613.9	5595.9	407.6	2031.8	0.75	41753322	2.04	OK
CR&BR2	3933.1	11711.4	5888.6	334.2	2031.8	0.75	46234146	2.04	OK
BR2&RR	3219.8	16729.1	55866.4	320.8	2031.8	0.75	41614166	1.94	OK

From the above table, it is concluded that the designed roof satisfies the heat distortion criteria.

Snow load criteria:

Snow load criteria study is done to check the ability of the roof to withstand snowfall and bounce back to its original shape without any permanent deformation once the load is removed

Snow load Prediction formula

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)

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]

Roof panel X curvature radius of length s in Side view

S.NO	BOW	IY	α	Lx	Ly	Y	S	Rx	Ry	t	QR	OK/NG
1.	FR&BR1	103.8068	1.0	1148.25	2031.8	495.1	505.3	5529.8	3086.9	0.75	8.96	OK
2.	BR1&CR	466.0359	1.0	1095.97	2031.8	515.4	479.8	4380.8	8634.6	0.75	6.86	OK
3.	CR&BR2	111.6565	0.7	1062.09	2031.8	444.1	431.0	3911.7	13857.5	0.75	3.79	OK

From the above table, it is concluded that the designed roof satisfies the SNOWLOAD CRITERIA

section modulus study:

front roof rail:

bow roof 1:

center roof rail :

bow roof 2 :

rear roof rail :

THIS CONCLUDES THE DESIGN AND ANALYSIS OF AUTOMOBILE ROOF WITH ITS INTERNAL COMPONENT ASSEMBLIES

NOTE: GO TO THE BELOW LINK FOR PART AND ASSEMBLY FILES

https://drive.google.com/file/d/19VouFVxnnalfzvDlfmzFN964SsjtgZeK/view?usp=sharing