Simple Surface Method

8/11/2019 Simple Surface Method

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To demonstrate the use of the SSS method ona real vehicle body

To ensure the structure has satisfactory load-

To determine load in beams, panels, andsubassemblies


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The SSS method is most effectively appliedduring the conceptual state, and also used tohelp resolve issues on existing structure.

idealized.

The baseline load paths for both bending andtorsion load cases are determined.


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Structure of medium size saloon car(Courtesy of General Motors)


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SSS model of structure (right-hand halfonly shown)


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The side-frame (1)

The front suspension tower (2)

The engine rail-Z shape (3)

The dash (4) The cowl (5)

The windscreen frame (6)

The centre floor (7)

The floor cross-beams (9), (10) The rear floor (11)

The rear longitudinal (12)

The rear cross-beam (13)

The angled beam (14)

The rear panel (15) The boot top (16)

The backlight frame (17)

The roof (18)

A total of 18 SSSs for only half model


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Typical load distribution for a medium size passenger carTypical load distribution for a medium size passenger carTypical load distribution for a medium size passenger carTypical load distribution for a medium size passenger car

Using the factor 10simplifies the arithmetic(9.81 m/s2)


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SF and BM diagram Slope and Deflection


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SSS model-bending loads

(right-hand only shown for clarity)

Point load (single load)Point load (single load)Point load (single load)Point load (single load)- Suspension reactions (F/SUSP, R/SUS)- bumpers (F/Bumper, R/Bumper)

Distributed loadDistributed loadDistributed loadDistributed load-Power train (Power-train)-Passengers (F/Pass, R/Pass) at Z, T, G-Fuel tank (F/Tank)-Exhaust (Exhaust)


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Center of gravity: x = Mx / Mass= 3,682,981/ 1,706.75= 2157.9 mm

Moment equilibriumRear axle load = 825.7 kg

Front axle load = 881 kg


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Front suspension tower

Has high shear loads

Good shear connection must be made to theen ine rail & the u er fender rail

Bending loads are not significant

The tower is not very wide but very deep


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Front Bulkhead

Bending moment on the dash panel is a hoggingmoment

deep

Side shear force is significant

May indicate the need of stiffeners (swaging)


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Rear seat cross-beam

Bending moment on the dash panel is a saggingmoment

It is significant as the rear seat cross-beam is not

deep

Side shear force is significant

Good shear connections are required to the rockers


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Applying equal and opposite wheel loads

Pure torsion moment

Assuming , the track is 1.45 m

The Applied load at node O


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Front suspension towers and engine railsFront suspension towers and engine railsFront suspension towers and engine railsFront suspension towers and engine rails


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The main torsion boxThe main torsion boxThe main torsion boxThe main torsion box


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Torsion case edge loadsTorsion case edge loadsTorsion case edge loadsTorsion case edge loads

q = Q / L


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High forces and moments occur at the rearsuspension mounting point (node O)

The SF and BM are different and higher than


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The loading on engine rail shows muchhigher SF and BM than bending case

On the main torsion box, it shows the

path.

The windscreen and backlight frames musthave adequate section stiffness and goodcorner joints. (max bending)


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Require a good shear connection between theinner wing and dash panel.

Require a stiffening member between the top.

The cowl carries a significant BM includingthe SF transferred between the dash panel

and the windshield frame.


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At the real panel acts as beam is not requireto carry shear between the floor and boot top

frame.

,

required carry shear between the rear paneland the backlight frame.

The alternative model has shear flow valueshigher than in the original model because ofthe reduced area main torsion box.

Simple Surface Method

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