DESIGN AND MODEL OF ROOF

DESIGN AND MODEL OF ROOF

Objective: To model the ROOF according to Engineering Standard using NX CAD.

Software : NX CAD.

Introduction of Car Roof design:

Roof is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from Climate and other external condition. Strength of the roof is suggested as an appropriate counter measure for such injuries.

It introduce reinforcement in the form of are as follows:

1. Front roof rail
2. Rear roof rail
3. Centre roof rail & centre bow roof rail
4. Bow roof rail

Front roof Rail:

• It is act as a reinforcement of front roof area & its design factor to maintain the visibility criteria, Headroom area & the space required for the windshield glass, rubber pad & sealent.
• Minimum thickness should be maintain of 0.65mm. Draft angle = 3-5°

Rear roof Rail:

• It is act as a reinforcement of rear roof & its design factor to maintain the visibility criteria, Headroom area for the rear seat passenger.
• Minimum thickness should be maintain of 0.65mm.

Centre roof rail and bow roof rail:

• All the bow reinforcement placed in the flat surface area to maintain strengthened.
• Minimum thickness should be maintain 0.65mm.

Fig. Centre roof and centre bow roof rail

Fig. Bow roof rail 1 and 2

Section modulus of reinforcement:

Bow Roof Rail-1:

Minimum Moment of Inertia Imin = 19145.69 mm4

Centre Bow Roof Rail:

Minimum Moment of Inertia Imin = 20621.21 mm4

Bow Roof Rail-2

Minimum Moment of Inertia Imin = 23093.41 mm4

Roof Calculation:

Heat Distortion Criteria:

Heat distortion test is a type of static load test which plays an important role in maintaining roof strength. Heat distortion temperature is the temperature at which metal softens and deforms under a specified load. From Heat distortion criteria, roof strength can be enhanced by appropriate positioning of bow roof rails.

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

Where,

L = Roof Length in X-Direction [mm] (Roof dimension in 0-Y)

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

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

Heat Distortion Test Result
S.NO	BOWS	Rx	Ry	R	I	L	t	(Rᶺ 2)/t	W	OK/NG
1	FRR & BR1	2612.13	3258.9	2899.89	258.34	2058.5	0.65	12937479.6	1.404722	OK
2	BR1 & CRR	4590.2	7447.3	5679.684	305.415	2058.5	0.65	49628934.3	2.135297	OK
3	CRR & BR2	3741.21	11737.37	5673.901	307.7	2058.5	0.65	49527924.62	2.135942	OK
4	BR2 & RRR	3098.09	15361.08	5156.246	247.8	2058.5	0.65	40902877.12	1.910488	OK

From above observed results shows that the designed roof passes Heat Distortion

Criteria.

Snowed Criteria:

The snow load test is a type of static load test used to verify that roof assembly exhibits no permanent deflection due to a distributed load representing snow load: the distributed pressure applied is in the range 10-15 N/dmᶺ2.

Ly = Distance between front and rear roof rails [mm]

Lx = Distance between left and right end roof rails [mm]

Y = Distance between centre of front roof rail to centre of bow roof rail [mm]

S = Distance for which roof bow bears divided load [mm]

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

Ry = Longitudinal direction curvature radius of roof panel X cross section on roof bow

t = Roof plate thickness [mm]

From below observed results shows that the designed roof passes Snowed

Criteria.

Embossed Roof:

Roof embossing is a bonus reinforcement for the roof which Provide an additional strength.

Roof Models:

The final design of the Roof with all the rails are shown below

Conclusion:

By applying solid and surface modelling methodologies and accord of Engineering Standards, developed essential flanges and ditch area for the given roof styling surface the design of Roof was completed using NX CAD.