Roof Design
report on roof design
objective:-
- To design roof of a car using nx, considering all design consideration of a roof for, reinforcements , drip area, dich area, front roof rail, rear roof rail, bow roof.
- Perform a curvature study on the roof and perform the calculations 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 roofs , central roof rail . front roof rail and rear roof rail .
- Perform the draft analysis for each reinforcements.
introduction:-
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.The component of an automobile that lies above the passenger compartment and protects the occupants from the sun, wind, rain, and other external elements is known as the roof or car top.A car roof is responsible for protecting the passenger from rain, wind, sunlight, accidents etc. It also offers aerodynamic support to the car when it is in motion.
DESIGN CONSIDERATION OF ROOF:
- Visibility criteria
- Head room clearance
- Bow roof position
- Heat distortion and Snow load criteria
- Draft analysis
ROOF CRUSH TEST:
Roof strength evaluations consist of a quasi-static test conducted on a vehicle’s roof in a manner similar to tests used to judge compliance with Federal Motor Vehicle Safety Standard 216 (Office of the Federal Register, 2009).
The main differences between the procedure specified by the Insurance Institute for Highway Safety (IIHS) and that specified by the U.S. federal government are that the IIHS procedure are,
- Specifies testing one side of a vehicle’s roof
- Does not include a headroom criterion
- Specifies testing to a given displacement instead of a given force level
- Specifies setting the vehicle’s pitch angle during testing based on the measured on-road pitch angle.
An overall rating is assigned based on the peak strength-to-weight ratio (SWR) measured within 127 mm of plate displacement.
objective of test
- To ensure pedestrian saefty for side collusion and car roll over impact on roof.
- To withstand the minimum load for a roof crash test for fisible design and manufacturing of product.
design procedure for roof :-
componants to design:.
- FRONT DITCH AREA
- FRONT ROOF RAIL
- REAR DITCH AREA
- REAR ROOF RAIL
- BOW ROOF FRONT
- BOW ROOF REAR
- CENTRE ROOF RAIL
GIVEN DATA:.
Front Roof Rail Master section
Master section of the Rear Roof Rail
Master section of Bow Roof
Master section of Center Reinforcement Rail
ROOF CLASS A
DESIGNING THE COMPONANTS:.
FRONT DITCH AREA
We have to create the extension sheet with minimum 15mm, and give the positive draft angle 3 degree considering the following drawing operation.
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.
- emboss are given to increase strength and cutouts in emboss reduceses weight in componant with keeping its strength constant.
REAR DITCH AREA
- It’s same to the front roof ditch area but we have to fix the rear door in this area, when considering the parameters to design the rear roof ditch area.
- this is designed as per given data.
REAR ROOF RAIL
- Head room clearance = 120mm
- Sheetmetal thickness = 0.75mm
- Embosses height 2 < 3t
- Radius = (3mm or 5mm)
BOW ROOF FRONT
DICH AREA FOR BOW ROOF FRONT
- 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.
- 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.
- Ditch area is made for to have spot weld with body.
BOW ROOF REAR
CENTRE 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.
- Centre roof rail is attached to B piller of a car, which together provides a rigid and good impact resistance.
- central roof rail is wider than BOW roofs .
CURVATURE STUDY ON THE ROOF:.
- Heat Distortion critera.
- Snow Load critera.
Heat Distortion critera.
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
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]
I = Bow roof span [mm]
Thickness for the Roof(t):
Roof Outer Panel, t= 0.75mm
Front Roof Rail, t = 0.75mm
Rear Roof Rail, t = 0.75mm
Bow Roof Rail Front, t = 0.75mm
Bow Roof Rail Rear, t = 0.75mm
Reinforcement roof rail, t = 0.75mm
CALCULATION FOR FIRST SECTION
W1 = [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
where,
RX = 5733.6695mm
RY = 2244.9761mm
t =0.75
l =279.0750mm
L = 2025.6107mm
R = 8604.268
{W1= 1.131}
pass
CALCULATION FOR SECOND SECTION
W2 = [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
where,
RX =5088.0980mm
RY = 5735.7730mm
t = 0.75
l = 535.3702mm
L = 2025.6107
R = 14380.15
{w2=1.413 }
pass
CALCULATION FOR THIRD SECTION
W3 = [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
where,
RX =4030.4576mm
RY = 10307.92mm
t = 0.75
l = 373.9088mm
L = 2025.6107
R = 15453.4008
{w3=1.764 }
pass
CALCULATION FOR FORTH SECTION
W4 = [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
where,
RX =3345.4616 mm
RY =13693.6074 mm
t = 0.75
l = 387.7092 mm
L = 2025.6107
R = 14339.262
{w4=1.251 }
pass
CURVATURE values
SNOW LOAD:.
Snow load criteria study is used to check the durability of the roof to withstand the snow fall on the roof and reflex it is original shape without any permanent deformation after load being removed.
SNOW LOAD CRITERIA:
Qr = [IY x t2] / [α x s x [(RX + RY)/2]2 x 10-8]
Where,
α = My x LX2 x10-12, 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 rails 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],
With of the roof panel exposed on the surface.
Y = Distance between Front roof rails 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 [mm4],
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[mm4],
Roof panel X curvature radius of length s in side view.
result:.
movement of inertia:.
BOW Roof 1:.
CENTER ROOF RAIL:.
BOW Roof 2:.
DRAFT ANALYSIS:
roof draft analysis:.
Front Roof Rail:.
BOW Roof 1:.
Center Roof Rail :.
BOW Roof 2:.
Rear Roof Rail:.
top view
top view
conclusion:.
The section modulus study for the Master sections and create for the Front roof rail, Rear roof rail, Bow Roof Rail and Rear Roof Rail and creation of the Ditch area,and to perform the draft analysis all are sucessfully done by using nx software.