Graphics Reference
In-Depth Information
until it breaks. When we can strategically embed soft material inside a brittle
material, those soft material patches can cushion the cracks and stop their
propagation, delaying their catastrophic effect on the hard material, making
it even tougher. Clamshells have interesting properties like this, but until
recently, making such materials was the purview of Mother Nature. We cer-
tainly couldn't injection-mold materials like that. But with multimaterial print-
ing, we might be able to fabricate them at will.
Here's another example. This one pertains to the elastic properties of mate-
rials and how they delect and stretch under load. If you have ever stretched a
rubber band, you will have noticed that as it gets longer, it also gets thinner.
Most materials do that; it's called the Poisson effect, after the French math-
ematician and physicist Siméon Denis Poisson who irst characterized it sys-
tematically. Yet it is possible to print hard and soft material in such a pattern
that causes the material to
expand
laterally when it is pulled longitudinally.
This bizarre, unnatural material property is a material with a negative Poisson
ratio, also known as an
auxetic
material.
Auxetic materials are not found in nature and are dificult to manufacture
using conventional manufacturing techniques. But with a high-resolution
multimaterial 3D printer, you can make auxetic materials on demand and
embed them within other structures to make strange and beautiful machines.
For example, cars made with materials designed using auxetic materials
to absorb energy upon impact so that the passengers are safe. The front
bumper would absorb the impact and send the energy in different directions
using patterns of auxetic and conventional materials.
Other patterns could have even more unusual and useful behaviors. It is
possible, to print hard and soft materials in laminated patterns that make
a material be lexible in one direction but stiff in a different direction. This
property may not be so exciting by itself, until you realize that you can
print objects with tailored elastic properties. For example a custom brace
or implant could assist a patient after a knee injury by allowing that patient
to bend their knee freely in one direction while supporting the knee in
another direction. A custom glove could enhance a rock climber's ability to
hang on protrusions.
