Roof challenge

OBJECTIVE: To Develop the essential flanges and reinforcements, Provide appropriate dimensions and check for Draft analysis, and submit your Section Inertia report on the 0-Y section.

INTRODUCTION: Automotive roof plays an important role in the aerodynamics and internal strength of a vehicle. The roof’s BIW influences the aftermath effects of crush load, snow load, and heat distortion criteria. The roof has internal structures like front roof rail, rear roof rail, bow roof 1, bow roof 2, rear roof rail, and reinforcement roof rail. In this project, these structures were designed accordingly. Their position was also justified by the required criteria. Generally, roofs are given a curvature along with Xc and Yc. But some places of the roof have flatness compared to other sections, mostly while approaching the trailing edge of the roof, the roof becomes flat relatively. Sometimes this flatness is intentionally given to reduce the creation of a wake region while moving faster. The roof is like building a house. The house needs pillars. similarly, the roof needs the above-quoted internal structure to ensure safety and performance. The roof has to perform well in the roll-over test. The outer panel of the roof is considered a class A surface, so there cannot be any spot welds or any visible fastening. Mastics play a major role in engaging the roof panel and the internal BIW parts.

TYPES OF AUTOMOBILE ROOFS:

• Convertible: A convertible, cabriolet, or spyder is a passenger car that can be driven with or without a roof in place.
• Hardtop: A hardtop is a rigid form of automobile roof, which for modern cars is typically constructed from metal. A hardtop roof can be either fixed, detachable for separate storing, or retractable within the vehicle itself.
• Sunroof: An Automotive sunroof is a movable panel that is operable to uncover a window in an automobile roof which allows light and fresh air into the passenger compartment.
• T-top: 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 Top: It is a semi-convertible car body style with a removable roof section and a full-width roll bar behind the seats.
• Vinyl roof: Vinyl roof refers to a vinyl conversion for an automobile’s top. This conversation 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.

DESIGN CONSIDERATION:

• Visibility criteria.
• Head clearance.
• Curvature study.
• Heat distortion and snow load condition.
• Draft analysis.
• Safety parameters.

COMPONENTS OF ROOF:

• Front Roof Rail
• Rear Roof Rail
• Bow Roofs
• Centre Roof Rail
• Ditch Area

STYLING SURFACE:

ROOF CRUSH TEST FOR PASSENGER CAR:

Safety point of view vehicle roof plays a very crucial role especially roll over kind of accidents, in which vehicle tips over onto its side of the roof. And vehicle rollover crashes are the cause of many fatalities and head, neck, and spine trauma around the world.

Therefore, passenger safety is also a very important parameter in front of OEMs. It is not only a marketing strategy but also it is an obligation stipulated by international standards that are now placed in several countries, as well as a governmental requirement. For this reason, strength is a very important criterion for designing a vehicle roof.

The strength of the roof structure to occupant protection in real-world rollover crashes, requiring the maximum moving distance of the roof structure should be less than 127 mm (5 in.) when the induced load is 1.5 times the vehicle weight.

For the test, the passenger car shall be rigidly placed or positioned on a horizontal surface with the doors locked and the window closed. Furthermore, a flat, rigid block with a lower surface a rectangle measuring 30 inches wide by 72 inches long (762mm x 1829mm) shall not move more than 5 inches(127mm), measured as the distance between the original location of the lower surface of the test device and its location as the specified force level is reached, when it is used to apply a force of 1.5 times the unloaded vehicle weight (UVW) or 5000 lbs(22224N), whichever is less, to either side or forward edge of the vehicle.

This test can be conducted on either side of the roof structure, the front left or the front right side but not on both sides in one single test and still meet the requirements of the test. The rigid plate shall not move faster than 0.5 inches/second and the force applied on the plate shall not exceed the lesser of 1.5 times the unloaded vehicle weight (UVW) expressed in kilograms multiplied by 9.8 or 5000lbs (22240N).

Also, the direction of the force shall be downward and perpendicular to the lower surface of the rigid plate and such that it moves in a straight line without rotation. The duration of the test shall not exceed 120 seconds. The longitudinal axis of the plate is pitched forward at a 5 º angle as viewed from the side of the passenger car.

The lateral axis or the roll of the plate is such that it forms a 25 º outboard angle with a horizontal surface as viewed from the front of the passenger car.

FRONT DITCH AREA:

REAR DITCH AREA:

ROOF:

FRONT ROOF RAIL: This part joins the windshield glass and the bodyside outer. The master sketch has all the geometrical details for the front roof. A space of about 21 mm is provided for the windshield, rubber lining, and mastic. The drawing angle is kept open for about 3 degrees. The sealant requires at least of minimum 5mm gap. Whenever the inclination was provided for flanges the visibility criteria and the draw ability have to be considered. The offset surface distance of 32mm depends on the visibility of the driver and enough headroom clearance. The 80mm length depends on a surface match with the outer panel and also provides enough cabin clearance. On the right side of the roof rail, a clearance of about 3mm is given for mastic. Corner relief is given to deviate the stress concentration point.

REAR ROOF RAIL: This part joins the back door and the bodyside outer. The rear roof provides enough space for back door hinge placement. The field of vision and headroom clearance are to be considered while dimensioning.

CENTER ROOF RAIL: Centre roof rail is provided to effectively support the flat area of the roof as it is more susceptible to failure under the action of the load. Usually, the center reinforcement roof rail will be placed at the center of the roof connecting the B pillar support structure which results in added support in the roll-over test.

BOW ROOF: The Bow roofs are given to improve the torsional stiffness and load-bearing capacity of the roof structure. The number of bow roofs provided will depend upon the overall dimensions of the roof. The longer the roof more the bow roofs are integrated into the BIW frame They are attached to the outer panel using mastic sealants. Each mastic point will have up to 80 mm circular effective area. The positioning of bow roofs is done based on a curvature study. The heat distortion criteria and snow load criteria are checked to analyze the position of the bows in various conditions.

BOW ROOF 1:

BOW ROOF 2:

ROOF CALCULATIONS:

Heat Distortion Criteria Calculation:

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]

According to the Judgement Condition: OK< 2.7> 3.1 all the values are satisfactory.

Snow load Prediction:

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

According to the Judgement condition = Qr ≥ 3.1, it passed at only two positions and fails at Centre Roof Rail to Bow Roof 2 Positon. To improve we can provide ribs on the roof to provide some extra strength to the roof or we can increase the thickness of the Bow Roof 2 it will improve the Geometrical moment of inertia of Roof BOW hence improved strength.

DRAFT ANALYSIS:

Front Roof Rail:

Rear Roof Rail:

Center Roof Rail:

Bow Roof 1:

Bow Roof 2:

Roof:

ROOF ASSEMBLY: