Roof Design
ROOF is an very important compant in automobile that it should protect the passengers from the environmental impacts as well as it should provide increase in star rating in ncap ,
Design considerations of a roof are follows
1. Front roof rail
2. Center bow roof rail
3. Rare roof rail
4.Bow roof1
5. Bow roof2
1.Front roof rail it should be designed such a way it should be in certain limits such it should have enough head roof clearence, and it should not have any disturbance in driver site , it also follows the benchnmarking study it should have enogh space to deform during accidents.
Draft analysis of a front roof rail shown below
2.Centre bow roof rail it is provided at the center of the bow roof to provide strength to the the roof it should be bent like a bow to withstand the strevgth when there is a accciedent or roof test .it is designed such a way that to follow these all criteria .
draft analysis of a centeral bow roof
Rare roof rail is a part in the roof assembly as it should designed such a way to provide strengthen to the roof it is placed at the rare side of the roof that there is a hinge which is connecting between roof and the back door.
it should also has the enogh space to deform the sheet and with stand the impact to the car.
Draft analysis of rare roof rail
Bow roof1 should be placed on the roof by at a distancs on which it should follow certain criteria they are heat distortion criteria and snowload criteria.
Draft analysis of a bow roof1 shown below
Bow roof2 it is also an an additional bow roof to tsrengthen the roof on certian forces these are caluclated by the formulae by doing trail and error we fix a position on which it can withstand the forces on the roof.
Draft analysis of a bow roof 2 shown below
Heat distotin is a phenomena in which metal tends to expand which will create strength issues in cars because of high tensile strength of steeel , which is most versatile material for manufacturing of cars to meet this criteria there are some formulaes which can numerically estimate the positions to meet the heat distortion phenomena
Required data to caluclate the heat distortion criteria is taken from the sketch
caluclations for the heat distortion
case1
Radius are measured in this way
l=421.3
L=2016.9
Rx=572.198
Ry=2231.7615
R=(Rx+Ry)/2
w=(1.73x10^-3xL)x(1.85x10^-80((R^2/t))+(1.10X10^-3xl)-2.68
w=1.66
case 2
Required inputs are taken from the sketch
l=384.2
L=2016.9
Rx=6360.736
Ry=4932.755
R=(Rx+Ry)/2
w=(1.73x10^-3xL)x(1.85x10^-80((R^2/t))+(1.10X10^-3xl)-2.68
w=1.99
case 3
Radius ofcurvature from the projections
l=479.5
L=2016.9
Rx=3934.98
Ry=4120.8
R=(Rx+Ry)/2
w=(1.73x10^-3xL)x(1.85x10^-80((R^2/t))+(1.10X10^-3xl)-2.68
w=1.736
case 4
l=296.4
L=2016.9
Rx=7011.412
Ry=2190.77
R=(Rx+Ry)/2
w=(1.73x10^-3xL)x(1.85x10^-80((R^2/t))+(1.10X10^-3xl)-2.68
w=1.409
all dimenssions are inmm
Snow load criteria
During winter heavy snowfall falls to withstand the additional weight of asnow on the roof of acar it should be designed such a way that it resist the load and when the load is removed it should be return back to its initial position so to meet this design consideration the caluclations are carried out ,
Case1 bow roof1
Lx=1166.9
l1=515.4
l2=462.5
y=515.4
Ly= 1951.9
My= y( Ly-y)
My=740372.1
α = My x Lx2 x 10-12 ,
α=1
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Iy=2.27*10^3
t=0.75
α=1
Rx andRy values are taken from the abiove figure
Rx= 2660.5648
Ry= 2717.989
s = l1/2+l2/2=489
Qr=36.1
Case2 center bowroof
Lx=1089.5
l1=462.5
l2=557.8
y=977.9
Ly= 1951.9
My= y( Ly-y)
My=501999.6
α = My x Lx2 x 10-12 ,
α=0.60
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Iy=2.27*10^3
t=0.75
α=0.60
from the figure values are obtained
Rx= 2941.183
Ry= 6275.7276
where iy=2.15*10^3
s = l1/2+l2/2=510.4
Qr=19.6
Case3 bow roof2
Lx=1061.2
l1=557.8
l2=416.2
y=1535.7
Ly= 1951.9
My= y( Ly-y)
My=639158.34
α = My x Lx2 x 10-12 ,
α=0.719
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Iy=2.27*10^3
t=0.75
α=0.719
Rx= 2611.857
Ry= 11356.5201
iy=2.71*10^3
s = l1/2+l2/2=487
Qr=7.2
Case4
From the sketch the input value is taken which is shown below
Lx=1047.4
l1=416.2
y=1951.9
Ly= 1951.9
My= y( Ly-y)
My=0
α = My x Lx2 x 10-12 ,
α=0
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Iy=2.27*10^3
t=0.75
α=0
Rx= 166639.8143
Ry= 5645.7651
s = l1/2+l2/2
Qr>3.1