Challenge

Roof challenge

MMohammad Shuhail U5 Jul 2022

Automobile Roof

An automobile roof otherwise known as a rooftop is an automobile body part that protects passengers in the compartment from the sun, wind, rain, and other external objects.

Hardtops

These are a common modern type of rooftops. Hardtops are made up of metal or plastic. There are two types of hardtops roofs detachable hardtops and retractable hardtops. Hardtops roofs are popular because of their solid structure and noise-free structure. Apart from protecting the passengers' hardtop roofs also provide more sense of privacy. Hardtop roofs are suitable for most climates.

2)Sunroof

One of the most popular types of roof. This type of roof allows the operator or passenger allows the light, and air to enter the passenger compartments by making it transparent or opening a part of the rooftop. There are mainly three types of sunroof pop-up roof, spoiler, and a panoramic sunroof.

3)Convertibles Roofs

These types of roofs allow the operator to ride the automobile with or without a rooftop. Mainly there are three types of convertible roofs.

Retractable hardtops: These are automatic retractable type rooftops made up of metal, plastic, or both.

Detachable Hardtops: These are common hardtop roofs that can be detached from their place and kept in the trunk.

Soft Tops: Rooftops are made up of textiles, there are automatic and manual convertible roofs

Important Manufacturing Process Involved

Blanking: Process in which a flat or a geometrical shape is created by feeding a coil of sheet metal into a press and die.
Stretch Forming: Process of stretching and bending a sheeting metal with help of a die
Edge Cutting: The cutting edge is the intersection of two tool point surfaces.
Deburring: Machining process of removing burrs from machined metal products.
Weld: Process of fusing to metal parts by means of pressure, heat, or by other means.
Polishing: Chemical process performed for a shiny and smooth surface.

Crash Test on Roof

Apart from protecting passengers from extreme weather, the roof plays an important role in safety during accidents especially if there is a rollover condition. Thus, while designing a roof these safety measures need to be considered. FMVSS 216 (Federal Motor Vehicle Safety Standard) determines the rollover crashworthiness of a vehicle by determining the roof strength. During a rollover crash

The process of crash testing involves applying a gradually increasing load on an automobile roof. All the doors and the windows need to be closed before applying the load. The load is applied through 72in long and 30in a wide flat rectangular block. The load is increased gradually up to 1.5 times the unloaded vehicle’s weight. The vehicle should not deform more than 5in. The 1.5 times load is called the strength to width ratio. The force is applied at a roll angle of 25 degrees and a pitch line angle of 5 degrees to the direction of the force.

Design Consideration

Passenger safety
Number of bow roofs
Bow roof position
Manufacturing ability
Quality and attractive

Design Approach

Thickening dimension: 0.75mm

Skin Data

Master Diagram

Front Roof Rail

Rear Roof rail

Center Roof

Roof Top

Front Rail

Rear Rail

Center Roof Rail

BOW Roof-1

BOW Roof-2

Assembly

BOW Roofs

Curvature Study

Heat Distortion Test

The heat distortion test is conducted to determine the deformation at flexural load. Heat distortion study is essential for the roof because it can be exposed in harsh climates.

Sketch For Heat Distortion Study

The radius of curvature in between the front rail and bow roof-1.

The radius of curvature in between the bow roof-1 and the center rail.

The radius of curvature in between the center roof and bow roof -2.

The radius of curvature in between the bow roof-2 and the rear roof.

Calculation

Conclusion

The curvature study of the design comes positive Since all the values of 'W' lice are below 2.7. Hence it satisfies the heat distortion criteria.

Snow Load Study

The snow load study is conducted to determine the snow accumulation limit over the roof.

Sketch

The radius of curvature in between the front rail and bow roof-1.

Radius of curvature in between bow roof-1 and center rail.

Radius of curvature in between center roof and bow roof -2.

Radius of curvature in between bow roof-2 and rear roof.

Calculation

SNOW LOAD
Sl No	BOWs	Lx	Ly	L1	L2	Rx	Ry	(Rx+Ry)/2	Iy	t	Y	s	My	α	Qr	Determination
1	Front_Bow1	1095.1	2028.64	566.2347	303.361	4390.7251	2812.4352	3601.5802	25.9336	0.75	153.547	153.547	287915	0.34531	2.121	NG
2	Bow1_Center	1072.7	2028.64	303.361	468.425	3763.5057	6095.9105	4929.7081	288.422	0.75	303.361	234.86	421287	0.48473	5.864	OK
3	Center_Bow2	1051.7	2028.64	468.425	609.651	4149.9472	9747.8398	6948.8935	26.1613	0.75	468.425	305.594	526551	0.58239	0.171	NG

Conclusion

The judgment condition 250 ≤ s ≤ 380 is not satisfied in two conditions hence the bow rail has to be repositioned. Since the snow load condition 3.1 ≤ Qr is not satisfied in two positions the curvature also has to be changed after the repositioning of the BOW roofs.

Section Modulus

Section modulus is a geometrical property related to the cross-section area of a flexural member. Section modulus is of two types, elastic section modulus, and plastic section modulus.

The expression to calculate the elastic section modulus is,