Roof Design

AIM:

The main objective of the project is to create the Roof Sheetmetal design in NX cad, and also designing Front roof rail, rear roof rail, bow roof front, bow roof rear, center roof rail and Reinforcement are creating to build the strong roof these are all create by using nx cad.

Objective:

Do curvature study on Roof and performance calculations for Heat distortion and Snow load criteria to determine the position of the Bow roofs.Finding the moment of inertia and section modulus for both Bow roof and center roof rail. And also finding the Draft Analysis of each part.

Introduction of Automobile roof or car top:

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. Because the earliest automobiles were designed in an era of horse drawn carriages early automobile roofs used similar materials and designs.

Types of car roofs:

• Convertible roofs
• Hardtops
• Sunroofs
• T-tops
• Targa tops
• Vinyl roofs

The basic criteria to design the roof they are

• Visibility criteria
• Head room clearance
• Bow roof position
• Heat distortion and Snow load criteria
• Draft analysis

Crush test on the roof:

Roof crush test means to crush the roof by adding more loads to the top side of the roof at one one edge why to do this step because to know the material is really withstand the load or not to be tested in this crush test we will elaboratelly see in given below.and i will refer some point by using insurance institute of highway safety report

Curb Weight Measurement:

Curb weight values used for calculating the SWR are based on IIHS measurements of a vehicle, not the
manufacturer’s specified curb weight.
Vehicle curb weight is measured with full fluid levels using scales manufactured by Longacre Racing
Products (Computerscales DX series 72634).

Test Vehicle Selection:

For information on how we select vehicles for our crash test programs, including how we define typically
equipped vehicles, see Test Vehicle Selection (IIHS, 2021).Whenever possible, the vehicle acquired for testing is the same vehicle used for the curb weightmeasurement. At times, it is necessary to test a vehicle that does not meet the IIHS definition of atypically equipped vehicle, and the curb weight measurement is applied from another vehicle that doesmeet the definition. In these cases, the test vehicle does not differ from our typically equipped vehicledefinition in any way that might influence the roof strength (e.g., a vehicle with a sunroof would not betested if the typically equipped vehicle lacks this option).Once the test vehicle has been acquired, either the driver or passenger side of the vehicle is selected for testing. For most vehicles, the test side is chosen at random. However, for roof designs that appear asymmetrical, engineering judgment is used to select the side of the roof that may result in a lower peak force.

TEST VEHICLE PREPARATION:

With the vehicle on a level surface, the on-road pitch angle at the front door sill is measured on both sides
of the vehicle. Unless the vehicle manufacturer requests otherwise, roof racks and other nonstructural
items that may be contacted during the test are left as installed from the factory. Any trim or other
components are removed if they interfere with supporting the vehicle along its rocker panels.
For vehicles with vertical pinch weld flanges on the bottom of the rocker panels, the vehicle support
system consists of one I-beam (HR A-36, W4X13) for each rocker panel. Each I-beam has a clamping
system incorporated on the top that is tightened against the pinch weld flange to clamp the system in place
(Figures 1 and 2).When the pinch weld flange has a bend that prevents supporting the sill with one I-beam, more than oneI-beam can be used on each side of the vehicle. For vehicles with no pinch weld flange, or with a nonvertical flange angle that precludes clamping, mounting by another method may be necessary, such as
that described in the National Highway Traffic Safety Administration’s Laboratory Test Procedure
(2006). Prior to testing, the front-row seat back on the side being tested is reclined to prevent interaction with the crushing roof. Rear seats are latched in their upright position. All windows are closed and doors are locked.

TESTING THE STRENGTH OF THE ROOF:

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 varyingheights from the ground and at pitch angles ranging from −5 to +5 degrees to accommodate testing on thedriver 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.

Two I-beams (HR A-36 W10x88) are mounted on the bed plate perpendicular to the longitudinal axis of
the platen. The vehicle, with the attached rocker panel support system, is placed on these beams. The
vehicle is adjusted so that:
1. The longitudinal centerline of platen is within 10 mm of the initial roof contact point.
2. The yaw angle of the vehicle relative to the longitudinal axis of the platen is 0 ± 0.5 degrees.
3. The midpoint of the platen’s forward edge is 254 ± 10 mm beyond the most forward point of the
roof (including the windshield trim if it overlaps the roof) lying on the vehicle’s longitudinal
centerline.
To minimize the potential for loading the edge of the platen during the test, there should be a
minimum clearance of 150 mm between every point along the forward edge of the platen and
the structurally significant body components, when measured normal to the platen’s face
(Dimension “A” in Figure 4).
Note: Structurally significant body components include the roof, roof pillars, and any glass
(windshield, side windows, roof glass) but not the side mirrors, trim, removable roof rails, roofmounted antennas, and generally any component that consumers can remove.
If the 150-mm clearance is not achieved, then the vehicle is moved rearward longitudinally
until the 150-mm clearance is achieved at the front edge of the platen, or an equal measure of
clearance (±20 mm) less than 150 mm at the front and rear edges of the platen is obtained
(Dimensions “A” and “B” in Figure 4), whichever occurs first.

The pitch angle of the vehicle matches the on-road angle, while also accounting for any difference
between the platen’s pitch angle and the nominal −5 degrees.
The maximum combined difference of the vehicle and platen pitch angles from their targets is ±
0.5 degrees. (For example, if the on-road vehicle pitch angle is −0.2 degrees and the platen
pitch angle is −5.2 degrees, the target sill angle for the test is −0.4 ± 0.5 degrees.) If necessary
to achieve this angle, shims are inserted between the rocker panel supports and the W10x88 Ibeams attached to the bed plate.
Once the vehicle is positioned correctly, the rocker panel supports are clamped to the two perpendicular Ibeams, and the beams are marked to confirm that the vehicle position is maintained during the test. For
body-on-frame vehicles, the frame is supported to prevent the weight of the chassis from stressing the
body at the body mounts.
The roof is crushed to a minimum displacement of 127 mm at a nominal rate of 5 mm/second. Some tests
are conducted to a greater displacement to collect additional strength data for research purposes. Force
data are recorded from five load cells (Interface Inc., model 1220) attached to the loading platen.
Displacement data are recorded from four linear variable displacement transducers (LVDTs) (MTS
Temposonics model GH) integrated into the hydraulic actuators. Figure 5 shows the locations of the load
cells and LVDTs on the loading platen

Force and displacement data are collected with a National Instruments USB-6210 data acquisition system
and reported at 100 Hz. These data are based on a sampling rate of 2,000 Hz, with every 20 points being
averaged to produce the output data at 100 Hz.
The displacement-time histories from the LVDTs are compared to verify that the platen’s roll angle and
pitch angle (relative to the vehicle’s on-road pitch) were maintained at 25 ± 0.5 degrees and −5 ± 0.5
degrees, respectively.The precrash and postcrash conditions of each test vehicle are documented with still photographs. The position of the vehicle in the test fixture also is recorded. Motion picture photography is made of the test with real-time video cameras.

Styling roof:

ROOF:

i am design the Roof, front roof rail, rear roof rail, bow roof, center reinforcement rails are create by the help of styling surface and i to do the offset surface and untrim the surface

MASTER SECTION of FRONT ROOF RAIL:

FRONT ROOF RAIL:

Front roof rail is used for supporting the roof for externally applied forces occurring at accidents. When we increasing the front roof rail is good for strength but also it is not for drivers because of it hide visibility of road.When considering the parameters of roof rail, give them 60-80mm length, proper draft angle and also using the embosses for increasing the strength. Front section of front roof rails spot welded to the front ditch area and other end is fixed with help of mastic sealants.

Sheetmetal thickness t = 0.75mm

Flange length = 13.2 > 3t+R

Radius = (3mm or 5mm) > t

MASTER SECTION FOR REAR ROOF RAIL:

REAR ROOF RAIL:

Rear roof rail is creating to length 80-100mm with proper draft angle. Give embosses on the sheet to ensure the enough strength for holding the roof structure. When considering the all parameters like length, width, sealants, rubber materials, wind shield to create the design properly.

Head room clearance = 120mm

Sheetmetal thickness = 0.75mm

Radius = (3mm or 5mm)

MASTER SECTION OF FRONT BOW ROOF RAIL:

FRONT BOW ROOF RAIL:

The bow roofs are given to the improve the torsional stiffness and load bearing capacity of the roof structure. When number of bow roofs are given by the roof dimension. Longer the roof area we have to give the more bow roof to the structure.Positioning of the bow roofs are decided by the curvature study. The Heat distortion and Snow load criteria are checked to analyze the bow roof position by various condition.We also give the Mastic area for fixing the Bow roof to the roof outer. Each mastic sealants are having 80mm circular effective area of surroundings. Thickness of the Bow roof is 0.75mm.

MASTER SECTION OF REAR BOW ROOF RAIL:

REAR BOW ROOF RAIL:

It is also same to the Front bow roof but the positioning bow roof only change. The bow roofs are given to the improve the torsional stiffness and load bearing capacity of the roof structure. When number of bow roofs are given by the roof dimension. Longer the roof area we have to give the more bow roof to the structure.

MASTER SECTION OF CENTER ROOF BOW RAIL:

CENTER BOW ROOF RAIL:

it is the one of the main roof to support the outer panal and the front and rear panal are uses to support the outer panal but center support is the main supporting system to hold the roof in the same position to thicken the center bow roof to thickess of 0.75mm.

REINFORCEMENT MASTER SECTION OF CENTER BOW ROOF RAIL:

REINFORCEMENT OF CENTER BOW ROOF RAIL:

Reinforcement Center roof rail is effective support to the flat area structure roof. Because of center area of roof is more susceptible to failure under action of load. Usually, Reinforcement center roof rails are fixed at the center of the roof for connecting to the B – Pillar support structure, it will used for roll-over test.Center bow roof and reinforcements are placed at the center of the roof structure. They two are connecting to help of spot - welding operation. Thickness of the Reinforcement center roof rail is 0.75mm.

they are two methods to ensure that the roof is strong and if the load is applied on the panal it is withstand or not will be identifty by,

• Heat distortion prediction
• Snow load prediction

HEAT DISTORTION:

The heat distortion study the plays an important role in Sheetmetal application. Heat distortion is temperature limit above which material cannot be used for structural application. This study is useful to fin the where the material starts to soften when exposed to a fixed load at elevated temperature. In order to avoid the bending, damage to the roof based on the heat distortion temperature. This study will provide the which position of the bow roof give enough strengthen to 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]

All the support in the inner panal bows are all in 0.75mm thickness (t)

Roof length L:

the total length of the outer panal is 2033.7 mm

BOW ROOF SPAN (I):

Here we want to take the distance from front roof rail to bow roof front for finding the bow roof span(I), we want to measure another bow roof span

Rx & Ry:

From 0-Y axis, at -3Y about distance 300mm is drawn parallel on the perpendicular plane. After that 100mm lines are offset to either side of -3Y line. Now center lines are drawn between each adjacent roof rail edges respectively. Intersection points are marked on the sketch. Make all geometry lines are construction lines except points.Project the intersection points on sketch to the Roof surface.Join the intersection points in roof surface using the arc curve an measure the radius using the minimum radius comment.

Heat distortion of final calculation:

FRONT INNER PANAL - FRONT BOW ROOF = A

FRONT BOW ROOF - CENTER ROOF = B

CENTER ROOF - REAR BOW ROOF = C

REAR BOW ROOF - REAR INNER PANAL = D

ROOF RAILS	Rx	Ry	Rx*Ry	Rx+Ry	R mm	L	t mm	I mm	W	FINAL
A	5738.41	2530.83	14522940.18	8269.24	3512.521146	2030.99	0.75	415.3129	1.5947	PASS
B	4888.62	6529.36	31919559.88	11417.98	5591.104536	2030.99	0.75	440.9258	2.0897	PASS
C	3915.52	10894.34	42657006.16	14809.86	5760.622471	2030.99	0.75	420.9934	2.1152	PASS
D	3219.82	14982.66	48241468.32	18202.48	5300.537984	2030.99	0.75	308.0387	1.8658	PASS

When We have the necessary values for finding the heat distortion value(W):

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

Apply the all the values,From the above table we, conclude that all the values are of W< 2.7 and also W> 3.1. So, that all bow roofs areas are placed at the right place.

SNOW LOAD PREDICTION:

WHY TO DO this snow load prediction because in india it is an tropical climate so the snow will not happen in winter climate but in foreign countries they have an snow fall in all the year during winter time so the snow load prediction it is used to check the if the the snow is happen in the top of the roof it will put the too much of load on the outer panal so that reason only to apply this prediction to pass this test car will be applicable for snow countries. to identify this by using this formula they are,

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 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

FRONT INNER PANAL - FRONT BOW ROOF = J

FRONT BOW ROOF - CENTER ROOF = K

CENTER ROOF - REAR BOW ROOF = M

ROOF RAILS	Iy mm^4	Lx mm	Ly mm	L1 mm	L2 mm	Rx mm	Ry mm	t mm	y mm	S mm	My mm	((Rx+Ry)/2)^2	α	Qr	FINAL
J	1149.28	1137.76	2030.99	501.75	520.74	3377.37	2177.39	0.75	501.75	511.245	767296.17	7713839.664	0.993263218	16.50381481	PASS
K	1109.11	1084.39	2030.99	520.74	500.57	3783.54	3280.12	0.75	520.74	510.655	786447.585	12473823.15	0.92478503	10.59081022	PASS
M	2342.04	1057.04	2030.99	500.57	441.08	3018.34	11084.08	0.75	500.57	470.825	766082.3394	49724639.46	0.856552649	6.57049918	PASS

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.

There are two types of section modulus we have,

• Elastic section modulus
• Plastic section modulus

CENTER BOW ROOF:

I = MOMENT OF INERTIA

Y = distance between the neutral axis to extreme end of the object.

S = section modulus

Imax = 4.094x10^4 mm^4

Imin = 121.526x10^3 mm^4

Section modulus = moment of inertia / distance between the neutral axis to extreme end of the object.

S= I/Y

S= Imax/y=4.094x10^4 mm^4/45

S max= 909.7777mm^3

S= Imin/y= 121.526x10^3/45

S min= 2700.5777mm^3

REINFORCEMENT:

Imax =3.793 mm^4

Imin = 24.781 mm^4

S max= 8428.88 mm^3

S min= 550.68 mm^3

FRONT INNER PANAL:

Imax =1.605 mm^4

Imin = 924.87 mm^4

S max= 2662.57 mm^3

S min=15342.89 mm^3

FRONT BOW:

Imax =2.2261 mm^4

Imin = 91.7959 mm^4

S max= 740.30 mm^3

S min= 24619.22 mm^3

REAR BOW:

Imax =2.2350 mm^4

Imin = 94.5606 mm^4

S max= 745 mm^3

S min= 3152.02 mm^3

REAR INNER PANAL:

Imax =3.4674 mm^4

Imin = 6.5471 mm^4

S max= 3409.43 mm^3

S min= 643.76 mm^3

DRAFT ANALYSIS:

Draft snslysis it is very easy and effective and handy command which is mostly used in while manufacturing a component it will clears the draft angle then only the component will be easily manufacture while it is not clear the draft angle it is very difficult to manufacture. i will take the 7degree draft angle for all the creation of panal it is very useful to easily manufacture the material Minimum draft angle of 7degree is considered for analysis . green colour infer on the parts that all face along the tooling direction has positive draft angle greater than 7 degree and passed in analysis.

DRAFT ANALYSIS OF INNER PANAL:

DRAFT ANALYSIS OF OUTER PANAL:

FINAL OUTPUT:

CONCLUSION:

Hence i designed all the inner and outer panal (roof , front roof rail, bow roof rails , centre roof rail and rear roof rail) they are all designed by the following by the master section. and to take the draft analysis, heat distortion, snow load, section analysis it will be used to check the feasibility of the component it will be used while manufacturing.