Roof Design

NOTE TO THE EVALUATOR : IN THE FRONT ROOF RAIL THICKNING HAS DONE TWO TIMES DUE TO SOME ISSUES IN MY SOFTWARE I CAN'T ABLE TO DO THICKNING AFTER THE SEWING OPERATION SO AFTER CONSULTING WITH THE SUPPORT ENGINEERS I HAD DONE LIKE THIS .

OBJECTIVE

• The objective of this project is to design a car roof with essential flanges and reinforcement like Front Roof Rail, Bow Roof 1&2, Centre roof rail, and Rear Roof Rail for the given styling surface.
• And perform the study on the roof by calculating the Heat distortion and Snow Load criteria to determine whether the bow roof are in the correct position
• And finding the Moment of Inertia for Front Roof Rail, Bow Roof 1&2, Centre roof rail, and Rear Roof Rail, and performing the draft analysis for all the components.

INTRODUCTION

Design of any product is starts from an requirement .the design engineer sketches the product based on the requirement .then the 2d sketch with the proper dimension is converted into the 3d model using the advance cad software .the other important thing In the design is that every product that is designed is should b able to manufacture so the role of the design engineer is to design a product that can be easily manufactured and with the less cost effective .the process of the development carries until the design satisfy the customer needs.

CAR ROOF

An automobile roof or car top is the portion that sits above the passenger compartment protecting the vehicle occupants from sun , wind , rain, and other foreign particles while looking from outside of the car the roof is just an portion that covers the top .the roof is the structure above the wind shield glass having the reinforcement to provide the strength to the overall structure and to withstand heat distortion and the snow load.

WHY REINFORCMENT

If the roof is flat it is very week and cannot able to withstand the forces like snow so in order to increase the strength of the roof these reinforcement are introduced like Front Roof Rail, Centre Roof Rail, Bow Roof 1&2,and Rear roof rail ad it is joined to the flat surface of the roof with the different joining process.

METHODOLOGY

We get the model of the roof from the styling team .then we should do all the engineering work we create the roof bows roof rails and ditch area for the roof which we would consider all the safety norms and regulation.

TYPES OF REINFORCMENT:

• FRONT ROOF RAIL
• BOW ROOF 1
• CENTER ROOF RAIL
• BOW ROOF 2
• REAR ROOF RAIL

FRONT ROOF RAIL:

Front roof rail is the one which joins the windshield glass body side outer and the inner panel also and here the front roof rail is designed based upon the master section given.

REAR ROOF RAIL

Rear roof rail is the one which joins the back door and body side outer.

CENTRAL ROOF RAIL:

Central roof rail helps in providing effectively support the flat area of the roof as it is more susceptible to failure under the action of the load generally the centre roof rail is placed at the centre of the roof which is connected to the B-pillar support structure. this central roof rail helps in adding the strength to the roof during the roll over test.

BOW ROOFS

The bow roofs are given to improve the load bearing capacity of the roof structure. The no of the bow roof present is depends on the overall size of the roof. In this design there are two bow roofs are added.

BOW ROOF 1:

BOW ROOF 2:

JOINING PROCESS

Mastics are introduced between the roof outer panel and the reinforcment for joining and whenever the mastics are introduced there is a remarkable improve of the strength .and spot welding is also introduced to join the reinforcement and the outer panel

DESIGN CONSIDRATION OF THE ROOF

• DRAFT ANALYZIS
• CURVATURE STUDY
• HEAD CLEARENCE
• HEAT DISTROTION
• SNOW LOAD CRITERIA
• VISIBILITY CRITERIA

ROOF CRUSH TEST

Roof crush test the IIHS makes use of the roof crush test where by a machine pushes an angled metal plate down on one side of the roof the peak force applied by the machine before the roof is crushed by 5 inches

13(cm) is determined and compared to the vehicle’s weight to determine the roof strength-to-weight ratio

IIHS gives the rating based upon 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 roll over
• How deep is the protrusion after the roll over

GOAL OF THE ROOF CRUSH TEST

To minimize the protrusion into the occupant compartment so that the seat belts and air bags can do their job in protecting the occupant.

CONDITION TO FOLLOW FOR ROOF CRUSH TEST

There are two condition that should be followed that should be followed for the roof crush test

INITIAL CONDITION

• Close and lock all the doors
• Close all the windows

SECOND CONDITION

Fix the body sill or chassis frame on the harder level surface horizontally.

METHOD OF APPLIYNG THE FORCE

The load is applied in a way that 5 degree is tilted from the front end to the rear end and the load will be in 1800mm in length and 750mm in the width and the load is applied at the position of 25 degree from the flatness of the roof and the load is applied on the roof for almost 120 sec and the crush speed at which the load applied is 13mm/sec or less.

RESULTS:

If the displacement goes above the requirements level then we should increase the bow roof thickness or add more mastic points to increase the strength the stronger the roof the better it can protect the occupants in the roll over crashes.

HEAT DISTROTION STUDY ON THE ROOF

The heat distortion study plays a major role in the sheet metal usage heat distortion temperature is a limit above which the material cannot be used for the structural applications the study used to predict the heat distortion temperature at where the material starts to soften when the exposed to a fixed load at elevated temperature. In order to avoid bending or damages on the roof based on the heat distortion temperature and 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]

Judgment Condition

OK< 2.7

APPLY THE VALUES FROM THE FORMULA

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

CALCULATION:

HEAT DISTROTION CALCULATION
	L	R	T	I	RX	RY	W	RESULT
CASE1	2029.12	4116.227385	0.75	577.332	5656.483	3235.2669	1.883378221	PASS
CASE2	2029.12	5733.109585	0.75	329.95	4663.4421	7439.5385	2.004080056	PASS
CASE3	2029.12	5752.594609	0.75	330.096	3893.7896	11007.1561	2.009761037	PASS
CASE4	2029.12	5350.098895	0.75	364.036	3274.0068	14622.2933	1.936864969	PASS

From the above table it can be conclude that all the values are <2.7 and that proves that current position of the bow roof are in the good state as per the design and it is ok.

SNOW LOAD CRITERIA

this test is done to know how the roof is behaving when there is a snow on the car, normally due to the snow weight a dent can happen but the design of the roof should be in a way when the sow is remove the roof should go to its original place this the basic requirement for the snow load criteria.

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)

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]

Judgment condition

Qr ≥ 3.1

250 ≤ s ≤ 380

APPLY THE VALUES THAAT ARE GIVEN IN THE FORMULA

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

CALCULATION

BETWEEN	IY	RX	RY	LX	LY	L1	L2	l3	l4	S	Y	MY	ALPHA	T	IY+T^2	(RX+RY/2)^2	QR
FRR-BR1	1176.38	4212.05	3141.57	1125.26	2029.12	669.13				538.27	669.13	910010.1087	1.152263961	0.75	1176.9425	33441180.6	5.674420157
BR1-CRR	1855.22	3876.18	7466.82	1076.3	2029.12		407.41			407.335	1076.55	1025489.234	1.187948971	0.75	1855.7825	57905860	6.623004428
CRR-BR2	2232.19	4306.2	11569.8	1056.31	2029.12			407.26		444.675	1483.82	809127.046	0.902816527	0.75	2232.7525	101830299	5.461618363

My answer is greater than > 3.1 hence the roof as passed snow load criteria.

SECTION INERTIA ANALYSIS:

FRONT ROOF RAIL

MOI(MAX):1.929824024e+04[MM^4]

MOI(MIN)1.176382478e+03[MM^4]

BOW ROOF 1

MOI(MAX):2.673125510e+04[MM^4]

MOI(MIN):1.855224820e+03[MM^4]

CENTER ROOF RAIL:

MOI(MAX):4.388962412e+04[MM^4]

MOI(MIN):2.232190051e+03[mm^4]

BOW ROOF 2:

MOI(MAX):2.678177905e+04[MM^4]

MOI(MIN):1.868649290e+03[mm^4]

REAR ROOF RAIL:

MOI(MAX):5.1679500300e+05[MM^4]

MOI(MIN):3.645195734e+04[mm^4]

DRAFT ANALYZIS

draft analyzis is used to predict he manufacture fesability of the part.

FRONT ROOF RAIL:

REAR ROOF RAIL:

CENTER ROOF RAIL:

BOW ROOF 1

BOW ROOF 2:

ROOF:

CONCLUSION:

hence the front roof rail,rear roof rail,bow roof 1,bow roof 2,center roof rail is designed by the following master section and draft analysis and section modulus are done for all the parts to check the manufacturing feasibility