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NigelGroom
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I am working on the design of an impact attenuator for a Formula Student car. I am interested in using aluminium honeycomb, specifically the 19.1mm cell size as it is the most cost effective, and I am in the process of testing a design using this in solidworks. One concern I have is how the sheets and honeycomb layers will be bonded together. I have attatched an image of the current attenuator design because it is a little bit difficult to explain. I would like to know, along with what the best resin/adhesive to use is, what material exactly should be selected and used during the cad process. I can see that it is of the 3003 series, however I am unsure what material out of this series specifically as they are given properties in solid form rather than treated as a honeycomb section. All help and feedback is greatly appreciated! I am also open to using a different material providing it is not ridiculously expensive. The budget for this project is around £500 so it is limited.
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Dravis
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You can use Permabond ET538 .. this is specifically formulated for bonding Alu honeycomb, both to composites and to aluminium .
I would recommend keying the alu sheet surfaces before bonding the honeycomb to it.
You could also use a purely composite structure, by using kevlar/Carbon sheets, and nomex honeycomb.
This will have the added advantage of being able to cope with repeated impacts.
I'm not sure of the sizes involved, so I find it a bit difficult to assess the costs of building of the structure, so determining if the alternative solution will be too expensive depends on the size of the structure and demands om its performance.
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Warren (Staff)
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Dravis is correct.
Unless this is a technical exercise, you may well find it cheaper and easier to buy an off the shelf attenuator pre-made either from honeycomb or foam to meet the FS technical regulations.
Another important factor in attenuator design is initial peak loadings. You will find most honeycomb attenuators are made from a "pre-crushed" honeycomb to elimate the initial peak loading. It then crushes in a linear and predictable way and is hence relatively easy to calculate with.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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NigelGroom
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Thank you for your reply and feedback. I feel those materials are a little out of the price range. I am also curious as to what you meant by keying? I have not heard of this process done with regards to these materials before. Repeated impacts are not a concern. The attenuator is designed to be used only once, as per the regulations of IMechE.
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NigelGroom
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Yes this is a technical exercise, it is my final year individual project. There already exists an off the shelf attenuator which the university purchased a couple of years ago, that can be used as a back up.
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Warren (Staff)
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keying is the process of leaving a rough finish on the surface, in this case usually with sand paper. Keying helps adhesion.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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NigelGroom
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Oh right I wasn't aware of that but I shall look into it, thanks.
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NigelGroom
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The other issue I have is when modelling it, what should the thickness of the aluminium be set at? I don't mean the cell size or the thickness of the aluminium honeycomb layer, I mean the thickness of the actual material. Right now this is being modeled at 0.5 mm, however I am concerned that this is too thick, or just not accurate. I have attached a screenshot of a creo sketch, consider the area shaded orange, this is the thickness that needs to be correctly defined.
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Warren (Staff)
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You will need to be more precise than 0.5mm. The foil thickness is the figure you are after, and in that case is 50 micron. Other technical and mechanical data on the honeycomb can be downloaded here. You also will want to consider the cell construction of the sheet. The honeycomb is manufactured, in simple terms, using multiple layers of thin aluminium foil perforated and bonded at the nodes. The critical point here is that 2 faces of each cell are in effect 2 foils bonded together. You would need to take this into account with any modelling you perform.
Warren PenalverEasy Composites / Carbon Mods - Technical Support Assistant
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NigelGroom
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Ok perfect, I shall use 50 microns in my modelling from now on. Your description of the cell construction makes sense, I shall ensure that the top and bottom faces (assuming a regular hexagon) are 100 microns in my modelling. Thank you so much for all your feedback and support, you have been very helpful.
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