Goal: Compare the mechanical properties, prices and processes (wet lay vs infusion) for different types of sandwich cores
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Cores to Investigate
Nomex (honeycomb core used in MSXIV)
Soric (flexible foam core)
Grade SF (standard), XF (thicker with large channels) and LRC (narrow resin channels)
Divinycell (PVC foam core)
Grade H (lower weight) & HM (higher strength)
Nomex | PP Infusion Honeycomb | Soric |
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Divinycell |
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Properties | ||||
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Price | ~$0.50/in3 (Dec.4 2021) | N/A (required to request a quote) | ~$0.10/in3 (Dec.4 2021) | |
Process | Prepreg |
Infusion | Infusion |
Nomex
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Honeycomb Core
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Used is MSXIV, 1/4” thickness [1]
Available at [7]
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Thicknesses of 2.16mm, 5.33mm, 8.51mm (thicker sizes also available)
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Thickness of the Core
The required thickness of the core depends on the force/load on the specific panel of the car. MSXIV used Nomex cores between 1/4” and 1” depending on the panel. MSXII had a strategy to minimize the core material cost that included using significantly thinner core materials (or no core) on panels that experience less force like the doors and trunk.
The different core materials below can vary in thickness. So the panel design and load capacity will play a role in determining the necessary thickness/material.
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Honeycomb Cores (Nomex and Infusion Grade Honeycomb)
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Properties
Nomex was the honeycomb core used in MSXIV. It has the best strength-to-weight ratio of the core materials, consisting of mostly empty space.
Nomex: Thicknesses between ~2.16mm- 24.38mm available (~0.085”-0.96”), in sheets of 12”x12’’, 24’’x24’’, 24”x48’’, 48x48’’
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Price: if you buy 2.16mm in sheets of 12”x12”, the cost is roughly $62.30/m²
May be available cheaper at a different place
gets more expensive when you buy larger sheets
Process
The standard process for honeycomb seems to be prepreg. There may be a way to do infusion as well [5]
There is a specific honeycomb core made for infusion manufacturing at [8]
Soric
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Foam core
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Available in 2mm and 3mm thicknesses at [6]
Significantly thinner than the core used in MSXIV
Price: sold in rolls of 1.2m width, ~$10.03/m²
or 50”x100”
Infusion Grade Honeycomb: available in a thickness of 1/4”- 6”, in sheets up to 48” wide and 144” long.
Manufacturing Method
The standard process for making a sandwich with a Nomex core uses prepreg, which is expensive. Infusion is supposed to be possible as well, but the team has had problems in the past with the Nomex filling with resin during the infusion process.
There is a type of honeycomb core that is designed for infusion manufacturing: https://www.plascore.com/honeycomb/honeycomb-cores/thermoplastic/closed-molding/
Carbon Fiber with Nomex Core Process Comparison: Prepreg and Infusion
https://www.youtube.com/watch?v=EyXWXHC1adg
https://www.youtube.com/watch?v=EHLSzEmWzJs
Data Sheets
There aren’t as many options for the infusion grade honeycomb as there are for standard Nomex. The shear and compressive strengths of the infusion honeycomb are lower than that of Nomex when comparing products of similar density. Samples of the data sheets with links to their full documents are given below.
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Purchasing
Nomex: The cost depends on the thickness of the material and the size of the sheet. Generally, buying thicker material or larger sheets is more cost-effective, but the prices are mostly in the $0.50/in3-$1.50/in3 range (as of December 4th, 2021). Available at https://www.rockwestcomposites.com/aramid-honeycomb-series
Infusion Grade Honeycomb:doesn’t have prices posted. The website instructs you to contact them to request a quote.
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Soric (SF, XF and LRC)
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Properties
Soric is a foam core made from a series of small foam honeycombs, with resin channels in between them. There are 3 different grades of Soric that may be useful.
SF: the standard Soric, available in 2mm and 3mm thickness
XF: has larger hexagons with wider resin flow channels, available in 1.5mm, 2-6mm and10mm thickness
LRC: very thin channels minimize resin consumption, available in 1.5mm, 2mm and 3mm thickness
Manufacturing Method
All Soric foam cores and most commonly used with infusion.
Examples:
https://www.youtube.com/watch?v=qXKPaYyeUVE
https://www.youtube.com/watch?v=V_mBVKgJyJc
Data Sheets
Soric has a much higher density than Nomex and other honeycomb cores because of the lack of open space. It has a higher average compressions strength and a higher compression strength than Nomex (especially XF), but its increased density and resin consumption means it still has a worse strength-to-weight ratio.
LRC has the lowest density and weight, but also the lowest strength of the three options.
XF has a much higher strength, but a high resin consumption making it denser and heavier. It is also the only Soric available in thicknesses greater than 3mm.
Samples of the data sheets with links to their full documents are given below.
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Purchasing
Soric SF: Sold in 2mm or 3mm, in rolls 1.2m wide and any specified width. The longer the rolls you buy the more cost-effective the purchase is. Prices start around $0.10/in3 (as of Dec 4th, 2021), but a discount is added as you buy longer rolls.
Available at https://www.easycomposites.co.uk/lantor-soric-sf , this is shipped from the UK so extra fees may apply.
Resources:
Past Confluence Pages
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Compares the sandwich cores of different university design teams
UofT was found to use Nomex for their core as well
Carbon Fiber with Nomex core Process Comparison: Prepreg and Infusion
[4] https://www.youtube.com/watch?v=EyXWXHC1adg
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Prices
[6] https://www.easycomposites.co.uk/lantor-soric-sf
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