Roof challenge
introduction
roof of an automobile sits above the passenger compartment.roof houses the vehicle as a shelding part which safegurds the occupants from sunlight,heat,rain,wind,dust and other external elements.in case of convertibiles.it is called roof.
in the past roof was introduced as cover of of passengers compartment but later on,it was also used as a luggage carrier,sunroof and in resent past years with with the introduction of the solar paneled electric vehicle got a major boost in the automotive industry.
roof has following functions ;
- protect from external damage
- act as asafety gear when a roll over acctident occurs
- luggage carrier
- desgin of the roof also affects in giving aerodynamic shape of vehicle
- sunroof
- solar paneleld roof in ev.
since the roof has numerous functions.therfore the roof has to be stronger enough to with stand and damage experienced by it while roll over.for that,the roof should have good strength and stiffnes.so the roof is made with embosses and some reinforcement ,such as.
- front roof rail
- rear roof rail
- center roof rail
- bow roof
they are bonded with roof through spot welding and mastic sealant.
while designing the roof.few creteria sholud be followed they are visibility headroom clearance heat distoration snow load curvature study
ditch area is provided on all the four sides of the roof.roof ditch area are provided to mount roof to the main body of the car also to mount windsheld glass for the front ditch area and to mount taligate to rear ditch area .
front roof rail.
front roof rail design should considerd headroom clerance and visibility criteria and has mounting area for windshiled glass.for additional strength embosses are been provided.
commands used ;
offset,fill,join,parallel,curve smooth,spilt,extract,sweep,multi section surfaces,edge fillet,plane sketch,project,extrapolate,symmentry,thichsurface,etc.
rear roof
rear roof similar to the front roof rail.rear headroom and rear visibility criteria are considered and also taligate will be mounted on the rear roof rail so taligate conditions have to be considered while designing the rear roof rail .
the thickness of rear roof rail is 0.65mm
center roof rail
center roof rail is reinforcement support to the roof and it has the bracket for cabin light mount .
The thickness of center roof rail is 1.3mm
The thickness of lamp bracket roof rail is 0.65mm
commands used ;
offset,plane,spilt,sweep,curve smooth,multi section surface,join,edge fillet,extract,sketch,extrude,line healing,thicksurface,etc.
Bow roof.
bow roof has been provided for additional strenght especially against snow conditions and rollover situations in this model one bow roof has been provided between front roof rail and center roof rail and another bow roof has been provided between center roof rail and rear roof rail.but the number of bows on the roof is based on the size of the car like small cars do not require a bow because it increses the weight of the car as well as the other rails are enough to provid the support for the roof.but for large cars 3 or more bows are neeed to support the roof.
The thickness of bow roof rails are 0.65mm
commands used
offset,fill,join,parallel,curve smooth,spilt,extract,sweep,multi section surfaces,edge fillet,plane sketch,project,extrapolate,symmentry,thichsurface,etc.
main roof ;
main roof modelled using the styling surface as reference,then the ditch area and emboss are created on it .
the thicknes of main roof is 0.75mm
commands
offset,plane,sketch,projesct,spilt,sweep,extract,fill,join,edge fillet,extraplate,symmentry,extrude,healing,thickness,etc.
assembly
front and rear rails are mated in the front and rear of the main roof respetively.the bow roof center rail and the lamp bracket are placed and mated with the main roof. the rails are mounted with the main roof through the mastic sealants and spot welds.
position analysis
the postion and moment of all the reinforcements are taken and checked,whether it satisfies the hest distraction test and snow load test. necessary modification should be taken if it falls to meet requriments .
heat distoration criteria
the roof is directly exposed to sunlight.the temperature changes with respect to time and season,it causes deformation in the roof.in order to prevent failure it should be designed in such a way else it gets failure .
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]
TABLE-1 ;HEAT DISTORATION CRITERIA ;
RX(MM) RY(MM) L(mm) I(MM) R(MM) T(MM) W
fr bow 5771.602 2739.185 2027.244 380.896 3715.164 0.75 1.586578
bowl cr 4964.424 6135.713 2027.244 259.699 5488.271 0.75 1.855789
cr-bow2 3985.18 11069.37 2027.244 259.903 5860.479 0.75 1.960207
bow2-rr 3319.538 16169.63 2027.244 369.091 5508.26 0.75 1.981542
fr ; front rail
cr ; center rail
rr ; rear rail
satisfying condition is w is lesser than 2.7
from the above table it is found that the value of W is lesser than the 2.7,therfore the heat distoration condition is satisfied with this model .
snow load condition ;
the roof designed in such a way that the roof would be bend slightly when the load is applied and regain its shape once the load idd removed here by the roof is tested to avoid plastic deformation .
it is checked using the fromula .
TABLE-2;SNOW LOAD CONDITION PARAMETERS
RX RY LX LY IY(MM4) T(MM) Y(MM)
FR-BOW 5084.687 3929.765 1098.478 1947.06 1.10E+03 0.7 516.549
bow-cr 4446.932 8174.768 1065.706 1947.06 9.20E+03 0.7 449.581
cr-bow2 3848.156 13222.96 1046.817 1947.06 1.16E+0.3 0.7 449.821
bow2-rr 1947.06 0.7 530.83
TABLE-3 SNOW LOAD CONDITION (Qr).CALCULATION
MY=Y(LY-Y) A=MY LX^2*10^-12 S=(L1/2)+(L2/2) QR
738931.0927 0.891634097 483.065 6.176759
673239.9046 0.764618271 449.701 32.90416
673491.3435 0.738029211 490.3255 2163353
751779.4942 0 265.415
to satisfy the snow load condition ,the qr value should be greater than or equal to 3.1
from above caluculation shown in table 3.it is found that the snow load condition (Qr).value is lower than 3.1 at the rear portion .therfore the embosses are created
thus the roof was modeled .