helicopters rotorblades are made of honeycombed aluminum to give them strength, so isn't it a good idea for automakers to use the same technology to strengthen the frames of autos to make them lesslikely to cave in during a side impact auto accident?
hmm, so if a helicopter rotor collided with say a tree, you think the rotor would survive?
Cost is everything - if they get enough design margin from a single sheet that is the choice. Especially in fabrication costs. Besides cars are designed to crumple and a honeycomb structure may be too strong to dissipate crash forces as the body deforms in an accident. Aerospace uses that structure for light-weigh performance and can literally eat the extra cost.
Honeycombed materials are not strong in all directions. Honeycombed materials are strong in a force at 0 degrees, but will collapse under a teensy force at 90 degrees. Since a car can be damaged from many directions, the use of honeycombed materials would not be ideal. The website I've listed is about the strength of honeycombed materials and is interesting, but does not specifically address your question.
Sure you could do this, but the reason it won't happen is cost. If your target is today's strength car, you could make the car lighter. If your target is today's weight car, you could make the car stronger. Honeycombed aluminum is not so much a strong material as a strong material at a given weight. For just a little more weight though, other less exotically manufactured materials have even greater strength, so I doubt that this will be seen in cars. Airplanes have an entirely different cost function, and weight is everything so they can afford these materials.
I'm not sure you are using Honeycombed aluminum in the right context. Honeycombed aluminum is generally a method of taking a solid sheet of aluminum and carving out areas so that rails of honeycombs are left on one side and the other still looks solid. However this is not done for strength, it is done for the weight savings. Like you said, helicopter rotors are milled so that the aluminum is honeycombed, but this is to shave off a few hundred pounds of metal, which means more passengers or lifting capability. Now honeycombed aluminum has about 70% of the strength of solid aluminum, given its impacted at the right angle. In this respect it could be used on cars to give comparable strength but give far better fuel economy just because your not lugging around all that weight.
