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Originally Posted by Number 3
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.. |
The main different in designing for automotive crash versus other applications is the crash structural parts are not simply designed to the material's elastic limit. High strength materials give you stronger structures due to higher yield points, but they take away the ductility. The area beneath the stress-strain curve is the plastic work that the material can absorb. Metals have these plastic works and composites don't.
When dealing with crash structures, you can't separate mass from energy management. With regards to the crush initiators in metal parts, they are there to control how and where the crush initiates and progress, you still need ductility to dissipate the energy. I like the analogy of a spring/damper/mass system for metals and only spring/mass for composites. Composites are great, strong and light, it's just very difficult to use in automotive crash for the time being.
Didn't mean to offend you, but I worked on a small team that started the crash simulation technology via computers at GM in the mid 80s and subsequently, I worked for the software company that developed and sell that piece of software that is being used by most auto makers today. Before the crash by computers was available, the crash design was an arduous task for any new platform.