Decision Matrix

Failure Modes:

Failure Criteria: Safety Factor (SF) < 2.0

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

Loading Condition - 5G Bump

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.

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1. Plate Tear out - CF panel fails/yields

• Assumptions

  • Material - Carbon Fibre (AX-5201 XL)

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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

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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.

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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.

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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:

Adhesive Mount Nut:

Washers:

Bill of Materials:

Item	Material	Size	McMaster-Carr P/N	Price	Quantity
Adhesive Mount Nut Image Added	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 Added	Alloy Steel , Black Oxide	M8 x 1.25 mm Thread, 18 mm Long	93070A163	$14.90 / 25	1-2 packs *Check bay inventory
Washer Image Added	Zinc plated Steel	16 mm OD 8.4 mm ID (M8)	91166A270	$4.07 /100	1 pack * Check bay inventory

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.

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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.

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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.

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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.

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• 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.

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• 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.

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