If the auto industry CAFE is going to reach 54.5 mpg in the next 15 years, it's going to have to draw from a variety of new technologies, including materials similar to these. I would think the high stiffness bodes well.
I understand the stiffness part of the lightweight materials. And I am willing to bet the overall structure is still considerably stronger than anything else on a lb for lb basis. The overall characteristics of these new materials are really impressive in every respect.
I can't wait to see some of these materials and designs formulated for production vehicles and then subjected to crash tests. Eventually the combination of lightweight, stiffness, impact resistance, deformability and strength will be engineered into vehicles capable of protecting the passengers during high impact crashes, probably assisted by air bag devices.
Although the specific strength of the car is still very good, on absolute terms it is not. For example if this car would have a collision with a regular road car then safety is quite a concern.
The materials used are very high tech and at the moment also very expensive, this is why carbon fibre is still mainly used in race cars and high performance road cars. And when carbon fibre is used at the moment, it is usually solid laminate. The problem with this is the same as the problem with high strength steel, thin sheets offer enough strength but are very easy to bend (low stiffness).
This is were sandwich construction comes in, the thin carbon fibre facings are placed outwards and low density foam is used to fill the gap. Because now the thickness is increased, the stiffness is also increased tremendously.
But this technique comes with a price, you basically have a low strength high stiffness structure and this means that impact resistance is not especially high. I am sure that safe structures can be designed light with these techniques, but versus heavy current cars safety is still less.
Use of light weight components will be the way to 54.5 mpg. The wheel configuration is reminiscent of the Dale that was two wheels in the front and one in the back which was supposed to reduce the weight enough to get 70 mpg. Overall, that vehicle was a hoax, but there were some parts of the design that could be used today to get to the 54.5 mark.
Beth, We do use analysis software for our calculations. Without it, we could have never designed such a lightweight structure. We use software from ANSYS called Composite PrepPost that is based on ANSYS mechanical. Basically we model the car with shells and apply composite material properties on the meshed elements.
Materials can be defined as plies and core materials, which are then stacked to simulate the sandwich construction.
@Woytek Bode: Thanks for elaborating on the role of simulation software. Many organizations using composites still don't tap into analysis software or do so late in the design cycle. Do you use the ANSYS tools upfront in the design cycle or later on in the process as more of a validation tool?
Many oranizations design and develop overdimensioned structures where the use of such software might be not useful yet. We are with thirteen students and only have one year to design and build a completely new solar car. I guess that because we are with so many young engineers, the design philosophy is very different to that of 'old fashioned' companies.
This alone would result in very different methods of designing and also building. But ofcourse also time forces us to finish the final designs quickly so the production process can be started.
The ANSYS package is also used for all structural aluminium and magnesium parts for the suspension. Furthermore, CFD calculations on the aerodynamics are also done in the same suite.
So in conclusion: yes we use these tools upfront in the design cycle. We first focussed on the materials allowing us to build light (TeXtreme, Rohacell foam, Turane resin) and did tests to ensure we enter the correct material data in ANSYS. This allowed us to set detailed demands on the structure and introduce complicated load cases. Also, the weight of the structure can be estimated to good accuracy and this helps us determine the optimum in problems like facing thickness vs. core thickness and solid (L-like) vs. sandwich stiffeners.
Once again, thanks for clarifying. To your point about the team being 13 "young engineers": So you think they are more open to the role of analysis tools early on the design cycle and using simulation in general compared with more established engineers or more traditional engineering processes?
I agree sleek design. Looking at it, there is a wheel in the front and two in the rear. The design is more like a 3 wheelers (similar to scooter). Do you know what considerations drove the design to be a 3-wheelers type? Will this be able to support more than one passenger? I wonder?
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