Cars and truck crumple because it was designed to. Look at the frame inside engine compartment you'll see weak spots placed in frame so upon impact they crush. "Weak metal"? Metal can be hard and brittle or soft and modulous (bendable) Using metal with wrong modulous or hardness than design makes end product weak. Also metals lattice stucture (molecular crystal) needs to be uniform or else it would produce metal that is not within design parameters. This is very hard to detect without the use of special equipment. US gov is lazy it would ask the suppliers to test and provide data. Which can easily be faked. But who risks pissing off their largest costumer unless protected by cabal or an enemy of the US like china.