Composite Frame Proposal(ish)

What is the Composite Frame project?

The main goal of this project is to develop/ test the techniques needed to design and manufacture a chassis for a solar car which is completely made of composite panels. There is a lot of room for weight savings by pursuing this, and it should in theory be easier for our car to pass regulations for impact cases due to composite panels much stronger in compression compared to conventional materials. (Based on what Chris said in Aeroshell CDR, their frame weighed around 30 lbs)

This project is JUST to ensure that we can actually manufacture and design something of this sorts with our resources, and build our knowledge on the technical side. This will not necessarily be the validation we need for passing scrutineering/ satisfying whatever bs BB want, but is more a proof of concept type thing.

The manufacturing testing (phase 1) of this research is already pretty much done since we needed to ensure that we could make a panel without any major defects, and ensure that it could hold up at least to an eye test before investing in further testing.

We are also limiting the scope of our testing to 1/8th inch cell size aluminum honeycomb with a 0.78in thickness since we are primarily designing this prototype frame for the areas of the car which will take the most load under operation - the dynamics mounting areas. If our panel can withstand that as well as the impact regs, it will prove a frame of this sorts is viable, and then we will look into lighter alternatives of materials. We will also be starting of using a 4ply/core/4ply panel, with a 0/45/-45/90 fiber orientation for each face skin, as this is one of the most common and easy to manufacture quasi-isotropic arrangements of carbon fiber.

Goals of research/testing (not in any specific order)

1. Ensure that it is possible to manufacture a composite frame panel given our resource restrictions

2. Validate strength of self made composite components compared to commercial panels

3. Test and optimize different joint methods

4. Test and optimize different insert methods

5. Figure out how to calc or model composite panels

6. Is corrosion a factor that we should consider?

1. Manufacturing

• Manufacturing method

  • We are using a method of manufacturing which is unconventional. This is primarily due to the fact that we do not have consistent access to a composites grade oven, and the one we can use is not long enough for our needs.

  • Instead of using pre preg, we are doing wet layups, co-curing our panels.

  • Our method has downsides in adhering the face sheets to the core as since there is no adhesive sheet, there is a less consistent bond gap, adhesive fillets aren’t as consistent, and resin distribution isn’t constant. Our face sheet strengths are also aren’t as strong due to a lower fiber volume fraction than can be afforded with pre preg, and we have no real way of ensuring that our resin is properly distributed

• Manufacturing process testing results

  • We have already finished a few different styles of test panels, and with the honeycomb size/ cell size we are currently thinking of using, we shouldn’t have any issues with face sheet dimpling/wrinkling

  • [insert pic of test panel here]

2. Strength Validation

• Strength testing/validation of this panel will come in 2 main methods, the testing of our face sheets and the testing of the panel as a whole. We are doing this since some of the panels properties are dependent primarily on the face sheet whereas some depend on the complete panel.

• Face sheet testing

  • We are planning to conduct face sheet tests with 2 different types of resin. Both will be using the same carbon fiber and fiber volume fraction. The first resin will be West Systems 105/209 epoxy, the same one we use in the rest of our wet layups. The second will be Fiberglast 2000/2120, which is a higher strength resin with properties which should be more suited to this project. The reasoning for testing both of these is that the properties we collect from here are vital in creating more accurate Ansys material data cards of our parts.

  • Due to lack of resources (mainly specialty jigs for the Instron), there are only a few tests that we can conduct easily, namely tensile, shear, flexural strength. The rest we are still trying to figure out how to test or will have to estimate from the CF data we have. These will give us the main properties of the face sheets except for compressive strength from which we should be able to create an Ansys data card.

• Full panel testing

  • There are several tests that we need to conduct on this. First and foremost is a tensile shear test to see when the panel fails in shear, as this will likely be its primary loading condition. We will also be testing compression, both edgewise and in plane. The goal is to use these tests to create a fairly accurate representation of our panels in Ansys

• Strength Validation

  • In order to validate that our panel is viable, over comp and in general during the summer once we start getting results, we will reach out to solar teams who have composite chassis asking for either testing data of their own panels or the manufacturer's datasheets. This will be done to see how our panel compares to the strengths of other teams panels. I expect that our panels will be worse than those most teams use since we are making our own, and are using different manufacturing methods, but this also allows us to increase the strength of our panels by adding plies as needed in order to reach the strength requirements needed.

3. Joints

• Joints will also need to be excessively tested in order to ensure that a chassis of this nature can be created. These connections will all have to be manually tested and validated, as doing this through sims will most likely not be too accurate. The plan is to use a method of initial testing similar to what UMNSVP used, loading joints with things like human weight + buckets of sand in order to test and mainly optimize joints. Final values will hopefully be obtained by using an Instron but that would require complicated jigging.

• Factors being considered in optimization

  • Joint type (T joint, L joint etc)

    • All types of joints will most likely be used in the car but it is likely that one type of joint is stronger than the other and will try to favor that in our future design decisions

  • Adhesive used to connect joints

    • DP-460

    • Loctite EA-120 HP

  • Reinforcements

    • Pins

    • L Brackets

    • Composite Reinforcement(?)

4. Inserts

• The current goal for this project is to have a completely composite frame and that means that components like the roll cage and dynamics will be mounting to the composite panels. Due to this it is going to be subjected to large amounts of both static and dynamic loading. We need to make sure that our frame panels and inserts can take these loads so that we can successfully make such a chassis

• Factors being considered with inserts

  • Type of inserts

    • Potted, through, regular inserts, etc.

  • Insert material

    • Currently will start testing with aluminum due to easiness of machining and weight savings

      • Another factor is bond from aluminum-epoxy-aluminum may be different to steel-epoxy-aluminum

  • Adhesive

  • Insert size

5. Hand Calcs/FEA

• We want to be able to develop some way to calculate/predict stresses and resulting deformations within our panels in order to better design our panels in the future. This will happen after we know its possible to create panels with the strengths we need for a composite frame.

Other concerns that need to be addressed

• Is galvanic corrosion an issue?

  • Dr Kiryakides (Composites prof, UT) said its not something we have to worry about, however the one industry person I talked to about this said that we should have a non conductive layer between the CF and aluminum honeycomb to prevent galvanic corrosion