

Auxetic Materials: Hook's Law - viviantan
http://www.economist.com/blogs/babbage/2012/10/auxetic-materials?fsrc=scn/tw/te/bl/Hookslaw

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mistercow
>And a less obvious application is in an easy-to-clean filter: stretch this
filter and its pores grow, allowing stuff stuck in them to be flushed through
when the filter is washed.

That doesn't make sense to me. If the auxetic threads making up the filter
expand, then the negative space between them will shrink, so you'll get
smaller pores, not larger ones.

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graeham
The threads themselves don't expand, its that they re-arrange themselves so
the material is larger in total volume, but the voids within the material are
also larger. The solid material itself, of course, must be conserved. Think of
a sponge: normally if you stretch it the pores get smaller. Auxetic materials
can be engineered so the pores get larger, but the amount of sponge stays the
same.

~~~
mistercow
Ah, that makes sense.

