Roof challenge

REPORT OF ROOF DESIGN

AIM-

To develop the essential flanges and reinforcements with appropriate dimensions and checking draft by performing Draft analysis, Calculating Section inertia, Heat distortion and Snow load on the roof.

• The aim of this project is to design car roof with essential flanges and reinforcement like ditch area, front roof rail, bow roofs, central roof rail and rear roof rail for the given styling surface.
• Perform the calculation for the heat distortion and snow load criteria to determine whether the bow roofs are at the correct positions.
• Finding moment of inertia and section modulus for bow roof rails.
• Perform the draft analysis for each reinforcement.

ROOF-

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.

An automobile roof or car top is the position of an automobile that sits above the passenger’s compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements, Roof is the structure above the wind shield glass having the reinforcements to provide the strength to the overall structure.

In later years, many variations on the automobile roof developed. These include:

• Convertible roofs. Roof modules. Roof modules.
• Hardtops.
• Sunroofs.
• T-tops.
• Targa tops.
• Vinyl roofs.
• Solar panel roof

• • Convertible roofs - A convertible or cabriolet is a passenger car that can be driven with or without a roof in place. The methods of retracting and storing the roof vary between models. A convertible allows an open-air driving experience, with the ability to provide a roof when required. Potential drawbacks of convertibles are reduced structural rigidity (requiring significant engineering and modification to counteract the effects of removing a car's roof) and cargo space.
• 

• Hardtops - A hardtop is a rigid form of automobile roof, which for modern cars is typically constructed from metal.

• Sunroofs - A sunroof is a movable panel that opens to uncover a window in an automobile roof, allowing light and/or fresh air to enter the passenger compartment. Sunroofs can be manually operated or motor driven, and are available in many shapes, sizes and styles. While the term sunroof is now used generically to describe any glass panel in the roof, the term "moonroof" was historically used to describe stationary glass panes rigidly mounted in the roof panel over the passenger compartment. A moonroof has a glass panel that is transparent and usually tinted. Previous terms include Sunshine Roof, Sliding Head and Sliding Roof.

• T-Tops - A T-top is an automobile roof with a removable panel on each side of a rigid bar running from the center of one structural bar between pillars to the center of the next structural bar. The panels of a traditional T-top are usually made of auto grade safety glass.

• Targa Tops - Targa top, or targa for short, is a semi-convertible car body style with a removable roof section and a full width roll bar behind the seats. The rear window is normally fixed, but on some targa models, it is a removable plastic foldable window, making it a convertible-type vehicle. Any piece of normally fixed metal or trim which rises up from one side, over the roof and down the other side is sometimes called a targa band, targa bar, or a wrapover band.
• Targa tops are different from T-tops, which have a solid, non-removable bar running between the top of the windscreen and the rear roll-bar, and generally have two separate roof panels above the seats that fit between the window and central t-bar.

• Vinyl Roofs - This covering was originally designed to give the appearance of a convertible to models with a fixed roof, but eventually it evolved into a styling statement in its own right. When leather, canvas and vinyl were sometimes used along with landau bars, to give a fairly accurate reproduction of a horse-drawn carriage's movable top.
• Oper Manta with Vinyl Roof

• Solar Panel Roof- The Solar panel roofs are newly developed for electric cars, to charge the batteries by using sunlight without stopping at charging stations which consumes a good time to recharge the batteries. So that the solar panel roofs were developed for on going recharging of batteries.

Roof is designed by following some criteria-

1. Visibility criteria as safety and functionality
2. Head clearance for ease and comfort
3. Draft analysis fro easy manufacturing and tooling
4. Safety parameters for users
5. Heat distortion
6. snow load criteria
7. Curvature study

To create the Roof Given data is-

ROOF SKIN DATA

FRONT ROOF RAIL MASTERSECTION

Embosses are created to give strength to the roof rail and mounting for brackets are given in which lights and switches will position.

REAR ROOF-

REAR ROOF WITH EMBOSSES-

CENTRE ROOF -

BOW ROOF-1

BOW ROOF 2

FRONT ROOF-

ROOF RAILS POSITION -

OUTER SURFACE-

OUTER PANEL FLANGE-

ASSEMBLY VIEW-

After completing design there are some calculation can be done by us to calculate the strength of the Designed

Roof.

Roof Bow Calculations

Heat Distortion Calculation

HEAT DISTORTION CALCULATIONS

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]

Except Rx and Ry all values can be measured on the model.

To get the Rx and Ry curvature a sketch was required-

PROCEDURE TO MEASURE THE PARAMETERS:

• On Plane parallel to the top plane draw sketch in which OY line is offset by 300mm.
• Draw lines perpendicular to OY line passing through point exact midpoint of the two adjacent parts (e.g., midpoint between front rail and bow roof 1)
• Offset these reference line on both side by 100mm
• Mark intersection points of reference line and 100mm offset lines.
• These reference points are then projected on to roof outer panel surface to create curves.
• Take all necessary measurements required to calculate W value as per mentioned formula.

Projected Points

Then Three point Arc was created by using these points

NOW CALCULATE RX & RY VALUE-

RX

FRONT TO BOW 2 =5739.7mm

BOW 2 TO CENTRE =4984.16mm

CENTRE TO BOW 1=3975.84mm

BOW 1 TO REAR =3288.61mm

RY MEASURED FOR 4 SECTIONS

FRONT TO BOW 2 =2475.86mm

BOW 2 TO CENTRE =6144.61mm

CENTRE TO BOW 1=10533.06mm

BOW 1 TO REAR =14525.2mm

RX & RY VALUE-

L CALCULATION-

L=2051.2961mm

I CALCULATION-

SECTION 1

I=380.2617mm

SECTION 2-

I=431.19mm

SECTION 3-

I=431.255mm

SECTION 4-

I=338.3561mm

By using all Values Heat Distortion was Calculated in the MS Excel

Judgment Condition

OK< 2.7

According to Judgement Condition : OK< 2.7> 3.1

All Values are under Judgement Condition.

HERE WE SEE THAT THE ROOF IS COMPLETELY SATISFYING THE CONDITION OF HEAT DISTORTION.

now Load Calculation

During Winter Season the snow gets clogged over the top surface/roof of the car and the snow has some mass on it. Due to this, the roof can fail if the snow load exceeds the capacity of the roof that was designed to sustain.

Snow load is the downward force on a cars roof by the weight of accumulated snow and ice. The roof can fail if the snow load exceeds the weight the roof was designed to shoulder or if the roof was poorly designed or constructed.

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]

Roof panel X curvature radius of length s in Side view

Judgment condition

Qr ≥ 3.1

250 ≤ s ≤ 380

To get the values a sketch was created on top of Roof

• O-Y line was created in the center of roof
• A line between First and center Roof rail was created
• Then two lines on both sides at 100mm was created
• Similar lines were created between other center roof rail, both Bow Roof rails and rear roof rails
• Intersection points were created and projected on the roof

SNOW LOAD CALCULATION-

POINTS-

10 POINT ARE PROJECTED-

USING 3 POINT ARC CURVE ARE CREATED-

RX VALUE FOR 4 SECTION ARE SHOWN IN DIAGRAM-

FRONT TO BOW 2 =4601.23mm

BOW 2 TO CENTRE =3763.400mm

CENTRE TO BOW 1=4272.91mm

BOW 1 TO REAR =3970.54mm

RY VALUE FOR 4 SECTION ARE SHOWN IN DIAGRAM-

FRONT TO BOW 2=2500.65mm

BOW 2 TO CENTRE =6093.37mm

CENTRE TO BOW 1=11030.51mm

BOW 1 TO REAR =16598.3357mm

RX & RY VALUE-

LX CALCULATION-

LX1=1126.36mm

LX2=1088.58mm

LX3=1068.49mm

LY CALCULATIONS-

LY=LY1=LY2=LY3=LY4=1933.3116mm

L1 & L2 FOE SECTION 1

L1=456.6468mm

L2=511.3432mm

SECTION L1 & L2

L1=511.3432mm

L2=510.84mm

SECTION 3

L1=510.84mm

L2=454.4772mm

SECTION 4

L1=454.4772mm

L2=0

Y CALCULATION-

SECTION 1

Y1=456.646mm

SECTION 2

Y2=967.99mm

SECTION3

Y3=1478.8344mm

SECTION 4

Y4=1933.3116mm

Section Modulus:

Section modulus is a geometric property for a given cross-section used in the design of beams. Other geometric properties used in the design include an area for tension, radius of gyration for compression, and moment of inertia for stiffness. The Section modulus is defined as

S=Iy

Where

S = Section Modulus

I = Moment of Inertia

y = Distance from the neutral axis to any given part.

Front Roof rail

The intersection was created and then Section Inertia command was used to obtain MOI

IY MIN=1.381*10^3mm^4

BOW ROOF 2

IY MINM=1.630*10^3mm^4

CENTRE ROOF RAIL=

IY MIN=1.871*10^3mm^4

BOW ROOF 1

IY MIN=1.64*10^3mm^4

REAR ROOF

IY MIN=4.15*10^3mm^4

By using all the values Snow load was calculated in the MS Excel

Snow Load Calculation

It describes the snowed condition which the roof should satisfy, if not satisfied then the roofs should should change the dimension till it satisfy the snowed condition.

So, according to the Judgement condition = Qr ≥ 3.1

here all result are statis fieds that condition so not need to do any thing

all result are passed the criteria

DRAFT ANALYSIS

In NX to check whether the sheet metal part we have designed can be deep drawn, there is an option called draft analysis. This type of analysis is performed based on colour ranges identifying zones on the analysed element where the deviation from the draft direction at any point, corresponds to specified values.

Draft analysis was performed with 7 Degrees Value(generally given in sheet metal)

Front Roof rail

2nd Bow Roof

centre roof-

bow roof 1

rear roof

OUTER SURFACE-

ALL DRAFT ANGLE ARE OK

After Completing the Design there are physical test of vehicle is done to check the strength of the Roof with vehicle.

There are various Car Roof Designs to check their strength some tests are done which are:

• Car Roll-over Test - The Roll-over test is conducted because a rollover is a type of vehicle crash in which a vehicle tips over onto its side or roof. Rollovers have a higher fatality rate than other types of vehicle collisions.

Vehicle rollovers are divided into two categories: tripped and untripped. Tripped rollovers are caused by forces from an external object, such as a curb or a collision with another vehicle. Untripped crashes are the result of steering input, speed, and friction with the ground.

The vehicles which have a higher center of gravity like SUV or Small Trucks are more prone to Roll-over. Rollover accidents typically involve a singular vehicle that loses control due to icy or snowy road conditions, soft road shoulders, uneven ground, collision with curbs or guardrails after a vehicle has lost traction, or hitting an obstacle while driving.

During a rollover accident the regional body distribution of injuries normally effects five main areas: head and neck, thorax, abdomen, upper limbs, and lower limbs. The majority of rollover crash victims sustain multiple injuries throughout these regions with the head and neck being the most vulnerable area. Some of the most common rollover injuries include: traumatic brain injury, spinal cord injury, broken bones, and cuts, scrapes, and bruises. These injuries are caused from slamming into another vehicle or obstacle, impact with unsecured cargo, contact with broken glass or torn metal, or from being tossed within the vehicle or ejected from the vehicle.

Volvo Roll-Over Test

• Roof Crush Test - In this test the load is applied on the roof to test the strength in static car postion. The standard does not apply to school buses and passenger cars that conform to the dynamic rollover test requirements of FMVSS 208, Occupant Crash Protection, and S5.3 by means that require no action by passenger car occupants. It also does not apply to convertibles, except for optional compliance with the standard as an alternative to the rollover test requirements in S5.3 of FMVSS. In April 1991, the National Highway Traffic Safety Administration (NHTSA) announced that FMVSS 216 was to be extended to light trucks, buses and multi-passenger vehicles not exceeding 6000 pounds, and that requirement came into force in September 1993. American statistics have long indicated that the fatality rate when light trucks (including four-wheel drives and utility vehicles) are involved in rollover accidents is twice that for passenger cars.
  

FMVSS 216 Roof Crush

The purpose of the FMVSS 216(Federal motor vehicle safety standard) is to reduce the head injuries, neck injuries and deaths by the roof crush of the car in to the passenger compartment in rollover crashes.

The resistance of the vehicle roof to deformation is dictated by a static test, in which the force of 1.5 times the unloaded vehicle weight or 5000 pounds, which is less, is progressively applied to the roof of the vehicle in the region of the “A” pillar. Force is applied to the plate at a roll angle of 25 degree and a pitch angle of 5 degree to the direction of the forces simulation can be experienced in rollover crashes. At the t time of the test, displacement of vehicle roof should not more than 5 inches of intrusion, as estimated by the movement of the test device.

Some Views of Roof created

Front View

TOP VIEW-

BOTTOM VIEW

ISOMETRIC VIEW

BACK VIEW

SIDE LEFT VIEW

SIDE RIGHT VIEW

5 MM GAP BETWEEN INNER AND OUTER PANNEL

Learning:

• Here we learned how to create a rails with the given standards by using Master Sketch.
• Learned How to calculate Heat Disorsion and Snow load criteria
• Learned how to do Draft analysis.

Conclusion:

The roof was created with all required parameters with a certain rails, and calculation the heat distortion, snow load are done and performed Draft analysisfor safety concerns. The result is satisactory.

THANKS