John B. wrote:

I suspect that it may be at least partly to
the loading of the device (the direction and
amount of force applied to a device). Kevlar,
that you mention has tremendous tensile
strength - The specific tensile strength
(stretching or pulling strength) of both
Kevlar 29 and Kevlar 49 is over eight times
greater than that of steel wire. But on the
other hand it has very poor compressive
strength (resistance to squashing or
squeezing). Rather difficult to design
a three dimensional device using a material
that has strength in only one direction :-)

Easy. Make a new composite material,
Kevlar/Kevlar, and put them perpendicular to
each other

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