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Kimberly Liu

Kimberly Liu

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titleBackground

  • There are 4 wheel covers, each with a thickness of 1/4”

    • The front covers are different from the rear covers

  • The wheel covers sit flush against a flange (1”) on the side panel (also 1/4” thicknegligible thickness due to no core)

Research and Concept Development

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titleResearching Options:

1.0 Nuts and Bolts

  • Nuts and bolts provide a simple solution to mounting the wheel covers (similar to the windshield mounting on MS12)

  • simple initial assembly procedure: only requires holes to be drilled into panels

  • difficult installation/removal process due to the presence of the bottom face of the wheel cover

    • requires access from the door or trunk opening to tighten the nut

  • NOT FEASIBLE

2.0 Adhesive Base Nut

Base NutImage RemovedBase NutImage Added

3.0 Quarter-Turn Fasteners

4.0 Clip-on or Snap-in Nuts

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titleDecision Matrix

Decision Matrix

Criteria

Adhesive Base Nut and Fastener

Quarter Turn Fastener (QTF)

Notes

Cost

0

-1

  • QTF generally have higher costs

Installation

0

-1

  • QTF require a receptacle to be installed (more tools, parts, time)

Ease of Use / Tools required

0

+1

  • both require only 1 tool to undo

  • QTF is more efficient as it only requires a 90 deg turn

Part/Material Compatibility (composite sandwich panels)

0

-1

  • adhesives are a reliable bonding method for composite panels

  • rivets can produce a stresentraion on the panel and also ru nthe risk of pulling through

Aero-dynamics

0

+1

  • Dzus QTF heads are flush with the panel

TOTAL

0

-1

Chosen Method: Adhesive Base Nut + Fastener

Calculations

Minimum Length of Bolt Required:

L_min = (total panel thickness) + (bolt thickness)

L_min = (0.25” + 0.25”)(25.4 mm) + (8 mm)

L_min = 20.7 mm

Closest Available Length → 25 mm
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Failure Modes:

Failure Criteria: Safety Factor (SF) < 2.0

Calculations for possible failure modes are shown below. A 5G bump* loading scenario is used.

Info

(*note: this is actually supposed to be a 2G bump (not 5G), so the safety factor is actually 5.)

Loading Condition - 5G Bump

(maybe use a different loading scenario? side impact?)

Assume the vehicle (720 kg) undergoes a 5G bump and the load is evenly distributed amongst the 4 wheel covers and each of its 6 fasteners.

1. Plate Tear out - CF panel fails/yields

  • Assumptions

    • Material - Carbon Fibre (AX-5201 XL)

Image RemovedImage Added

Material testing to be carried (if time and resources are available) to validate hand calculations.

2. Bolt shear - bolt fails/yields

  • Assumptions:

    • bolt is in single shear

    • bolt material is 316 stainless steel: Mechanical Properties

    • Image RemovedImage Added
Image RemovedImage Added

3. Fastener Pull-through - CF panel fails/yields

  • In order for this to happen, there must be a large force acting from inside the vehicle, pushing outwards - this is unlikely (according to regs, wheels should never come in contact with the panels).

  • Alternatively, frequent tightening/loosening of the bolt during the removal/installation of the wheel cover can cause the mounting hole to deform/expand.

  • For preventative measures, a washer can be added to the outside face of the wheel cover. This increases the area of applied force and distributes the load.

4. Adhesive Base nut shears off - Adhesive joint fails

  • The adhesive base nuts are not directly under any loading. For this adhesive joint to fail, there must be large shear stresses acting parallel to the panel. This could be due to bolt movement during tear-out (see 1).

  • Assumptions

    • adhesive - Loctite EA E-120HP

      • Lap shear strength with steel: 30 MPa

    • using F_bolt is not accurate since this is the loading seen on the panel (not on the base nut), however, it is an overestimate and will give a conservative result.

    • For adhesive joints, it was determined that a safety factor of 6 should be used. The calculated safety factor is less than 6 however, as stated before, the force was overestimated.

...

Minimum Length of Bolt Required:

** Side panel flange no longer has core material - assume a panel thickness of 0 mm

L_min = (total panel thickness) + (nut thickness)

L_min = (0” + 0.25”)(25.4 mm) + (8 mm)

L_min = 14.35 mm

Closest available bolt length → 20 mm

Screws:

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titleOff the Shelf Component Selection

Adhesive Mount Nut:

Material

McMaster-Carr P/N

Price

316 Stainless Steel

98007A319

$8.38 / 5

Zinc Plated Steel

98007A128

$7.38 / 10

$13.18

Profile

Material

McMaster-Carr P/N

Price

ultra low

316 Stainless Steel

91223A453

$9.98 / each

Alloy steel

90358A027

$7.71 / each

low profile

Alloy Steel, black oxide

93070A175

$10.95 / 25

alloy steel, zinc plated (partial thread)

90327A158

Alloy Steel Low-Profile Socket Head Screws, Hex Drive, Zinc Plated,

M8 x 1.25 mm Thread, 20 mm Long

90327A157

$12.70 / 25

super corrosion resistant 316 stainless steel (partial thread)

90666A139

$7.86 / 10

18-8 stainless steel

92855A722

$7.86 / 10

Alloy Steel, Zinc plated 8.8 Steel

97050A239

$1.48 / each

Adhesive Mount Nut:

Material

McMaster-Carr P/N

Price

316 Stainless Steel

98007A319

$8.38 / 5

Zinc Plated Steel

98007A128

$7.38 / 10

Washers:

Material / Size

McMaster-Carr P/N

Price

Zinc plated steel, 24 mm OD

91100A160

$11.83 / 100

Zinc plated steel, 16 mm OD

91166A270

$4.07 / 100

Expand
titleFinal BOM

Bill of Materials:

Item

Material

Size

McMaster-Carr P/N

Price

Quantity

Adhesive Mount Nut

Zinc plated Steel

M8 x 1.25 mm

Base Diameter 23 mm

98007A128

$7.38 / 10

3-4 packs

Low-Profile Socket Head Screw, Hex Drive

Image Removed

Zinc plated alloy steelImage Added

Alloy Steel , Black Oxide

M8 x 1.25 mm
25 mm long

90327A158

$13.18 Thread, 18 mm Long

93070A163

$14.90 / 25

1-2 packs

*Check bay inventory

Washer

Zinc plated Steel

16 mm OD

8.4 mm ID (M8)

91166A270

$4.07 /100

1 pack
* Check bay inventory for spare washers

Manufacturing and Assembly Plans

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Left To Do:

  • manufacturing/assembly plan

  • update CAD (add washers)

    • hole location drawings

    General Notes:

    • Wheel cover integration requires at least 2 people. The process is estimated to take 2-3 hrs (not including cure time).

    • These guidelines are just recommended steps. Feel free to make adjustments where necessary for a more effective and efficient process.

    • The wheel cover panels will be installed using low profile bolts, adhesive mount nuts and washers. Note that the front and rear panels have different geometries.

    • The adhesive mount nut will be permanently bonded to the side panel flanges. Holes will be drilled into the side panel and wheel covers. The bolts can be undone to remove the panel.

    Image AddedImage Added

    Preparation:

    • Ensure that the side panel and wheel covers have been trimmed to the correct geometry (follow mold outlines)

    • Dry Run: clamp the wheel covers to the side panel flanges to ensure there are no interferences or major gaps

    Procedure:

    Mounting Holes:

    1. Mark mounting hole locations on the wheel covers based on attached drawings. (Note: Hole centres are 12.70 mm (0.5 in) from the outer edge of the panel.) The opposite hand panels will be mirrored versions.

    Image AddedImage Added

    2. Drill M8 clearance holes (9mm) through the wheel covers.

    3. Clamp the wheel cover onto the side panel flange. Use a marker to mark the centre of each mounting hole from the wheel cover onto the side panel flange.

    Image Added

    4. Unclamp and remove wheel cover. Drill M8 clearance holes (9mm) into the side panel flange.

    Adhesive Mount Nuts:

    5. Place the adhesive nuts on the back face of the side panel flange and align to the holes. Follow the adhesive instructions to glue in place.

    Image Added

    • Ensure the surface is clean and dry.

    • Find 50 ml cartridges of LOCTITE EA E-120HP - Epoxy adhesive. Wear gloves when handling the epoxy adhesives. The working time of the adhesive is 2 hours. Start a timer once mixing has started in the nozzle.

    • Apply adhesive and align the centre of the nut to the hole in the side panel. Apply enough adhesive so that some of it flows through the holes on the adhesive nut.

    Base NutImage Added

    • Let the adhesive cure for 24 h before applying any load (i.e. before installing wheel cover)

    Installation:

    6. : Place the wheel cover against the side panel flange. Add a washer onto the outside face of the wheel cover. Insert the screw through the holes in both panels and tighten. Do not over-tighten the screws as this will apply excessive clamping force and can damage the carbon fibre panel.

    Image Added