1.0 Overview

• Different materials and mounting methods are explored to determine an optimal choice for the structural panel solution.

• These panels will be installed along the longitudinal planes of the chassis.

2.0 Summary of Options

Possible panel materials are listed below along with suggested mounting methods.

The suggesting mounting methods will likely require additional tabs to be installed onto the chassis.

* tabs must have sufficient bonding area. (see section 2.2 for details on adhesive bonding)

** fasteners can cause high-stress concentrations and lead to tear-out

2.1 Why is aluminium difficult to weld to steel?

https://www.twi-global.com/technical-knowledge/faqs/aluminium-welding/aluminium-to-steel#:~:text=Aluminium%20alloys%20can%20be%20joined,alloys%20to%20steel%20is%20difficult.

• Aluminium and steel vary in thermal conductivity and melting temperature

  • Tm_steel = 1370 C compared to Tm_Al = 660 C (~2X difference)

• the metals are insoluble in each other

• in the molten state, they react to form brittle intermetallic phases

1. Since welded joints between aluminium and steel raise many issues, we can conclude that this option is not suitable for our application.

• However, there are other options for mounting aluminium to steel (adhesive bonding, mechanical fasteners)

2.2 Structural Adhesive vs Welding and Mech. Fastening

https://www.assemblymag.com/articles/92741-how-to-use-structural-adhesives-to-replace-welding-and-mechanical-fasteners#:~:text=Unlike%20welding%2C%20structural%20adhesives%20have,necessary%20fatigue%20and%20force%20resistance.

Bonding Metal Substrates | 3M

• Adhesives enable joining between dissimilar materials.

• They can eliminate the stress concentration caused by spot welds or mechanical fasteners since the load is spread over the entire bonded area.

• Unlike welding, there is no metal distortion or weakening due to heat. Additionally, it does not require highly skilled labour.

• Adhesives allow for the use of thinner sheets of metal without concerns of tear-out with mechanical fasteners or burn through and distortion with welding.

2.2.1 How strong is structural adhesive in comparison to welding?

For reference, the epoxy structural adhesive used in aero-chassis integration has a tensile strength of 41 MPa after curing for 7 days at room temperature. Its lap shear strength with steel is 30 MPa after curing for 12 hours at 65 degrees celsius.

However, we should look for an adhesive better suited for metal-metal bonding.

• 3M™ Scotch-Weld™ Structural Adhesives has a shear strength of 4500 psi or about 31 MPa.

Welded joints can be stronger than the base material depending on the type of weld. Weld strength can be approximated by tensile strength. [1] (The tensile strength (yield) of 4130 steel is 460 MPa)

Full penetration welds tend to fail outside the weld joint itself, and on the heat-affected area of tubing. Partial penetration welds tend to fail at the weld joint. [2]

Open

3.0 Comparing Options

1 → 3 (worst to best)

* Need to know more about weight. It is not an issue unless it surpasses the weight limit (see S2021 Updated Masses of Sub-Team Assemblies ). We can remove weight as a criterion if the limit is not surpassed.

3.1 Discussion

1. If it is determined that weight is not a critical factor, the best option would be steel sheet metal. Its main advantages are ease of installation and overall reliability.

• The only advantage of using carbon fibre is the weight savings.

• The advantages of aluminium over steel are weight savings and cost. However, this option presents challenges in the installation stage.

4.0 Conclusions