• 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 (negligible thickness due to no core)

Open

Open

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

• A base nut can be mounted to the inside face of the side-panel flange.* A low-profile fastener can be installed from the outside of the vehicle through the wheel cover and side panel.

  • * consider glueing these on before installing the side panels to the chassis

  • ensure the fastener heads are as flush as possible to the vehicle’s outer surface

• relatively simple installation/removal process and initial assembly (drill holes and glue base nuts)

• grommets/inserts can be added in the holes drilled through the sandwich panels for added greater strength Panel Fasteners

3.0 Quarter-Turn Fasteners

• Involves a mounted receptacle on the side panel flange and a quarter-turn fastener through both panels (only requires a 90-degree turn to secure)

  • receptacles can be riveted, welded, or adhered

• Links:

  • Dzus fasteners: DZUS Quarter Turn Fasteners

    • installation video: The Ultimate Dzus Fastener Installation Guide

  • Quarter Turn Fastener Selection Guide

    • (could we glue a weld nut instead?)

  • Quick Access fasteners catalog

  • Quarter-Turn Fasteners

• McMaster-Carr

   

  https://www.summitracing.com/parts/ear-pane6600-erl#overview (Dzus panel fasteners)

4.0 Clip-on or Snap-in Nuts

• These are more commonly used with thinner panels (usually sheet metal)

  • not suitable for our panel thicknesses

• Clip On Quarter Turn Fastener Receptacle

• NOT FEASIBLE

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.

1. Plate Tear out - CF panel fails/yields

• Assumptions

  • Material - Carbon Fibre (AX-5201 XL)

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

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:

Adhesive Mount Nut:

Washers: