Bracket Design Competition

8/2/2019 Bracket Design Competition

1/31

ME240 Bracket Design

Eric Grossman

Jim Lovsin

Mike Worth

Spring 2003, Northwestern University


2/31

Background


3/31

Setup and Rules To Note

Adhesives allowed

Bracket does not have to be 1

piece

Can touch ground until point D

B doesnt have to be used.

Allowed 30mm clearance

instead of 20mm


4/31

Performance Index

mc

PI

*

=

2

1

3

Priority:

1. Load

2. Mass

3. Cost


5/31

Material Selection

1018 Steel, and 3 grades of Al.

1018 steel is our choice.

Considering cost and strength

advantage. highest yield stress,

(smaller deformation).

Costs significantly less than allAl alloys.

Only candidate that can be

welded together (rivets or bolts

arent as strong and heavier).

Much heavier, but we can

minimize mass in design, not

material.


6/31

Design Directions

Maximize moment of inertia in an easily manufacturableshape

Use welding Get bracket as close to edge as possible

No need for mount at B

Start with thickest steel then shave weight

Not welding all connections/interchangeability


7/31

Preliminary Designs


8/31

Jims Design


9/31

Jims FEM


10/31

Erics Design

S-shape: bringcompression column asclose as possible toload (reduce moment)

Square cross-section:

high moment of inertia Reinforced joints

Only mounted at A

Simple 3-tube design

Notch to preventslipping of appliedload


11/31

Erics FEM

High deformation

Hard to manufacture

Needed tension component

Finite Element Analysis:

1. Stress concentrated near

applied load.

2. Large displacement of top

beam.

3. No buckling in column


12/31

Mikes Design


13/31

Mikes FEM


1. Blah.

2. Add your comments

3. here


14/31


15/31

Iterations


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Iteration 1

1.5mm steel

Duct tape and spotwelding

Reinforced lip

U beam cantilever

600N failure ofcantilever

Tensile and columnnot deformed

Weight: ~250 g Load: 600N


17/31

It.1: Interchangeable beams

Cantilevers to interchange, none tested.

Alignment problems

Edges not crisp, contributed to misalignment

Thinner steel used,not likely tosupport load

Shapes that didnt

require weldingtried. Shear forces


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Iteration 2

Slightly taller 3 u shaped

members not

welded

Forming square

shape

Much heavier


19/31

Iteration 2


1. Deformation confined to cantilever but high displacement

2. Little displacement of tensile member



20/31


21/31

Iteration 3

T-beam shape (manuf.)

Reinforcing top plate

Column grips cantilever to top Tensile width decreased

Filler added to make columnwide enough

Corners cut to reduce massand add clearance


22/31

Iteration 3


1. Deformation still concentrated at front of column

2. Strange behavior in tensile member



23/31

Iteration 3

Thinner steel incolumn

Tensile weld

narrow tensile

Tensile andcolumn notdeformed

Crease at column

Weight: 240 g Load: 1780N


24/31

Final Design


25/31

Final Dimensions

All dimensions in mm.

Mounting (no B)

A


26/31

FEM


1. Strange tensile behavior not observed in testing

2. Less displacement of cantilever tip



27/31

The Bracket

Thin steel incolumn (1.5mm)

Tensile weld

Free column

Change inphilosophy abouthow to proportionleaving distance to

displace vs. tallercantilever Weight: 190g Load: 2000N


28/31

Clearance/Thickness Tradeoff

Al 2024 and Al 7075

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

0 0.05 0.1 0.15 0.2 0.25 0.3

Strain (in/in)

Stress

(psi)

AL 2024

AL 7075

.1% offset


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Conclusions


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Performance Index

Reduce weight in cantilever holes T-beam

Use thinner column

In the problem statement, the performance index is given as I = P / (c*m).

Our final bracket yields an index of:

I = (2000 N) / (($0.195/kg)*(.19 kg)) = 54.0 kN/$

Future Improvements


31/31

Thank youQuestions

Bracket Design Competition

Documents

Transcript of Bracket Design Competition