October 25, 2013

Hard, Strong, & Tough: Choose Two?

I don't know enough materials science to be sure that this is one of these meme-y "choose two" situations, but I got the impression from a Popular Science story that if you're manufacturing a bike lock—or anything, for that matter—you can't contrive for it to be hard, strong, and tough. (At least not in the technical sense. For those of you who don't have the relevant definitions committed to memory, I've included them below, courtesy of "the industry leader in manufacturing training," Tooling U.) 

Technical Definitions (source)

compressive strengtha material's ability to resist a squeezing force
shear strengtha material's ability to resist forces that attempt to cause the internal structure of the material to slide against itself
tensile strengtha material's ability to resist forces that attempt to pull it apart
hardnessa material's ability to resist penetration, indentation, or scratching; hard materials tend to be very wear resistant
toughnessthe measure of a material's ability to absorb mechanical forces before it breaks; impact toughness is a particular category of toughness
impact toughnessthe amount of energy that a material can absorb from a sudden, sharp blow before it breaks or fractures

Popular Science only introduced the trio of macho adjectives hard, strong, and tough, though, as prelude to what PS writer Theodore Gray terms a "fatal flaw" of nearly all materials: They become less flexible when very cold.

Cooling a tough-looking (informal usage, that) lock to –13°F with compressed difluoroethane, for instance, leaves it vulnerable to attack by a hammer:

Don't think bike thieves employ to such tactics? I've been tracking down and reading interviews with reformed bike thieves, and my research indicates...well, I'll save that for another post.

1 comment:

  1. That video is interesting, but luckily the compressed air / hammer approach does seem to be a pretty conspicuous way to steal a bike...