Roof Design

ROOF DESIGN

INTRODUCTION

      The vehicle's total structural strength is greatly enhanced by the car roof, especially in the case of an impact or rollover. Engineers use cutting-edge materials like high-strength steel or aluminium alloys in their meticulous construction of the roof to ensure that it can resist the forces applied during such catastrophes.Many safety elements that are built into the roof structure of modern cars are installed. Rollover protection systems, side curtain airbags, and reinforced pillars are a few examples of this. These parts are carefully designed by engineers to give occupants the best possible protection in the event of an accident.Aerodynamic performance is influenced by the form and contour of the automobile roof, which impacts high-speed stability and fuel efficiency. In order to improve vehicle efficiency and reduce drag, engineers test and optimise the roof design using wind tunnel testing and computational fluid dynamics (CFD) simulations.

MATERIAL SELECTION

Achieving a balance between strength, weight, and cost for the automobile roof depends heavily on the materials selected. A growing number of advanced composites are being employed to reduce weight without sacrificing structural integrity, such as carbon fibre reinforced polymers (CFRP). However, because of their affordability and track record of durability, conventional materials like steel and aluminium continue to be widely used.

MANUFACTURING PROCESS

     Engineers use a variety of production processes to quickly and effectively build automobile roofs that adhere to strict quality standards. These procedures could involve hydroforming, stamping, or even more sophisticated methods like resin transfer moulding (RTM) for composite roofing. Based on variables including material characteristics, manufacturing volume, and cost considerations, each technique is carefully chosen.

ROOF RAILS

FRONT ROOF RAIL

     A crucial part of guaranteeing both safety and structural integrity, the front roof rail is a basic structural component in contemporary car design. Located at the vehicle's front roof edges, it is vital to the overall structure's reinforcement, especially in frontal collisions and rollover accidents. Its design carefully strikes a balance between strength, weight, and cost factors. It is made of sturdy materials like high-strength steel or aluminium alloys. Designed to be a seamless integration with the vehicle's body structure, the front roof rail distributes loads efficiently and reduces penetration into the passenger compartment during collisions, making it a crucial component of the safety cage.The front roof rail serves not just a crashworthiness purpose but also enhances the vehicle's aesthetic appeal. Designers and engineers work closely together to ensure that form and function are harmoniously blended. Engineers work hard to ensure that vehicles meet strict safety regulations while maintaining a high level of performance and design coherence through rigorous testing and validation procedures.

According to the given master section the front roof rail was designed by following all the design norms.

MASTER SECTION OF FRONT ROOF RAIL

BOW AND CENTRE ROOF RAIL

     A crucial aspect of a car's structural design, the bow roof rail—also called the B-pillar or centre pillar—is found on traditional body types like sedans, SUVs, and trucks. It is positioned between the front and back doors and gives the roof structure the vital support and stability it needs, greatly enhancing overall stiffness and occupant safety.The bow roof rail is made of sturdy materials, such as aluminium alloys or high-strength steel, and is carefully engineered to handle a range of pressures and stresses that arise during vehicle operation. Its strategic placement strengthens the car's structural integrity, particularly in side-impact and rollover situations when it keeps the passenger compartment intact.

According to the given master section the bow and centre roof rail was designed by following all the design norms.

MASTER SECTION OF BOW ROOF RAIL


REAR ROOF RAIL
      The main purpose of the rear roof rail design is to reinforce and sustain the vehicle's roof structure structurally. The rear roof rail is meticulously engineered to handle a range of loads, including those encountered in rollover and collision events. In order to maximise structural integrity and guarantee occupant safety, the shape, thickness, and material choice are all carefully considered.The strength, weight, and longevity of the rear roof rail design are largely dependent on the materials selected. Because of their superior mechanical qualities, alloys made of high-strength steel or aluminium are frequently utilised. More recently, it has also been possible to reduce weight without sacrificing strength by using cutting-edge materials like carbon fibre composites.The rear roof rail and the vehicle's other structural elements, like the side pillars and rear quarter panels, must blend together flawlessly. This integration improves the overall stiffness and crashworthiness of the vehicle by ensuring a cogent and sturdy body structure.The European New Car Assessment Programme (Euro NCAP) and the National Highway Traffic Safety Administration (NHTSA) are two regulatory bodies that have established a number of safety standards and regulations that must be followed in the construction of the rear roof rail. To make sure that the rear roof rail satisfies or surpasses these specifications, engineers carry out extensive testing and research.

According to the given master section the Rear roof rail was designed by following all the design norms.

MASTER SECTION OF REAR ROOF RAIL

DRAFT ANALYSIS OF ROOF RAILS

     All the roof rail clears the draft analysis.Minimum Draft angle of 7 degree is given to the surfaces and all the embosses of the roof rails. 

FRONT ROOF RAIL

BOW ROOF RAIL 1

CENTRE ROOF RAIL

BOW ROOF RAIL 2

REAR ROOF RAIL

 HEAT DISTORTION CRITERIA

     Car roof heat distortion standards are essential for maintaining the structural stability and safety of automobiles, especially in extreme temperatures. The thermal distortion criteria indicate the highest temperature at which the automobile roof's material can withstand without deforming or breaking down. It is an important factor to take into account because extended exposure to high temperatures can cause materials used in automobile roofs, such as composite panels, plastic, or metal, to soften, warp, or even melt. The material composition, design, thickness, local climate where the car will be used, legal requirements, and strict testing procedures followed by the manufacturers are some of the variables that affect the criterion.By adhering to stringent heat distortion criteria, automotive engineers strive to ensure that car roofs maintain their structural integrity, functionality, and safety standards across diverse environmental contexts.

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

     We can infer from the above table that all values are W<2.7, fulfilling the judgement criterion. so that every location with a bow roof is positioned suitably.This demonstrates that the design meets heat distortion standards successfully.

SNOW LOADING CRITERIA

     When designing automobile roofs, snow loading parameters are crucial to take into account, especially in areas that are prone to severe snowfall. Snow on a car roof puts a lot of pressure downward, therefore roof systems that can bear pressures like this are needed to keep the roof from collapsing or deforming. When designing automobile roofs, engineers carefully consider a number of aspects to make sure they can withstand snow loading safely. These include the site itself, where regions that see a lot of snowfall require designs that can support higher weights, the materials selected, and the structural soundness of the building. Furthermore, it is crucial to follow building norms and standards that are particular to snow loading requirements. Strict testing procedures, such as controlled load tests and simulated snow accumulation scenarios, are used to evaluate a roof's robustness.To improve the roof's ability to hold weight, strategic design elements like reinforced roof rails and extra bow roofs are also used. Through careful consideration of these factors, automotive engineers guarantee that automobile roofs maintain safety regulations, especially in areas with significant snowfall, protecting the vehicle's structural integrity and the safety of its occupants.

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

 From the above table we can see that Qr values are above 3.1 , so the design passes the snow loading criteria successfully.

CONCLUSION

     Thus the roof is designed from the given Class A surface by developing roof outer , bow roofs , centre roof rail, front and rear roof rail. The roof is designed according to the design norms and master sections. All the roof rail clears the draft analysis. Minimum Draft angle of 7 degree is given to the surfaces and all the embosses of the roof rails. The roof design passes both heat distortion criteria and snow loading criteria sucessfully.