Quote:
Originally Posted by kbui
 I spent years of research in the crashworthiness of composites for structural components. Number 3 misses the point about composites usage in automotive. Up to now, composites have been used mainly as non-structural components and you can only reduce so much weight with this stuff, body panels, interior, bumpers....ALL of the crash structural parts are still metal. Strong light weight metals are being used. A few manufacturers are experimenting with composites (CF) structural parts but they are not cheap and they are certainly not ready for cheap mass produced cars.
The major difference in the design requirements of cars versus aircrafts and others is: the structural parts must be able to dissipate energies during the crash to protect the occupants. The ductility in metal allows for this plastic work (converting kinetic energies into the crumbled metals). This ductility in metal is a huge advantage that composites do not have. In aircraft design for example, the composites can be used to up to its brittle failure limit minus the safety factor and engineers do not have to worry about post brittle failure, i.e. if the stresses in the composite parts are exceeding the brittle failure, you already have a failure. In cars, we have to continue to work with the metals post yield because plastic flow and work hardening are what we rely on for energy dissipation.
Personally, I believe we will have to come up with more active safety systems so that we can keep the occupants safe without completely relying on the plasticity of metals before we can truly have composite structural components in cars. Got up too early this morning to run some "blast on composites" simulations and couldn't stay away. I have spent way too many years doing this stuff and it's still as interesting as it was when I got started in the 80's  I love getting paid for doing stuff I enjoy doing anyway. |
What point did I miss exaclty? I've worked on cars and trucks using all of the materials we are discussing so I'm not sure what I missed?
You are bringing up energy management when we were simply discussing mass.
As I also have done crashworthiness in my career we can have that discussion as well so if you want to throw engergy management into the discussion we can. Just remember that the steel doesn't just crumple and absorb energy. If you look in detail you will see crush initiation points that are designed in to manage where the steel folds and hidden you will see many extra reinforcement and doublers and inserts to add strength in crush to other areas. This can also be done with SMC and CF as well. That just wasn't the topic of the post.
Every material has it's plusses and minuses. Walk your way simply from low carbon steel to the higher strength steels and you suddenly find yourself with materials that are also harder to form and cut. And those too behave differently in crash. So not every material lends itself to any application. It isn't as simple as how much you want to pay.