COMPLIANT JOINING APPROACHES AND THEIR USES IN MACHINE DESIGN AND DAY-TO-DAY LIFE.
The most popular joining approaches used to join two or
more bodies together also rely on elastic deformations to achieve their
objectives. Most consumer products consist of multiple manufactured parts that
need to be joined together during assembly. The joining approach chosen to
attach these parts often determines the final product's quality and performance
because most failures occur at the interface of the product's joined parts. Although
some joining approaches don't rely on elastic deformations such as welding or
gluing. The vast majority of such approaches do rely on elastic deformations to
fix their parts together.
Compliant
joints (Screw and Bolts)
Screws and bolts are common but unlikely examples of
joining elements that rely on compliance to function. At first glance bolted
joints may seem like a collection of rigid parts but the bolt itself doesn't
successfully join the parts together until its shank begins to stretch as the
joint's nut is tightened. It is only at that point that the bolt begins to
permanently join its parts together through compression such that the forces
required to shear them apart are far greater than those expected to load the
joint during its lifetime, thus it's the elastic nature of the parts
deformations that actually joins them together.
Some latches also appear to be made of rigid pieces but they too use compliance to join their parts together only when this joint's switch is pushed down so that its compliant strap is elastically stretched around its drum.
Compliance
press fit (Dowell pins)
Press fit joints also rely on elastic deformation to join
their parts together. Dowel pin joints are a good example. The outer diameters
of dowell pins are intentionally made larger than the holes into which they are
hammered so that the material surrounding the pins compresses them with a
significant enough elastic force to hold them firmly in place.
Other press-fit
examples include bottle corks, legos and other toy building blocks. Plugs on
the inlets of inflatable beach balls, the fasteners on the back of some
baseball caps, removable erasers poster tube caps and the lids of many
containers.
Compliant
snap fit (Buckle)
Another joining mechanism that uses elastic deformations to
function is a compliant snap fit. Unlike the previous joining approaches
discussed, the flexible elements that constitute snap fits elastically deform
as they are being joined together. But once the parts are in place the elements
snap back to their original configuration where they become anchored in place
like this common snap buckle. Many laptop cases use internal springs within
latches that achieve snap fit behavior to help their cases remain shut. Other
compliant snap fit examples include ethernet cable connectors, phone cases,
plastic eggs binder rings, clips for vacuum cords or sun visors, pen caps, some
cd cases, close buttons and hangers that deform to clamp clothing in place
fasteners like the one used to join the ends of goggle straps together or to
clip children into car seats and latches like the one used for cake lid, coin
pouch, clock's battery panel and styrofoam food container. In fact many
container lids use snap fits to seal themselves. Shut once they have been
closed for e.g soda lid not only snaps onto its cup but it also possesses
compliant flaps for pinching straws in place preventing backsplash.
Compliant
snap fit (ziploc seals)
ziploc seals also
use snap fit principles to join two sides of a bag together a parallel track of
opposing j-shaped grooves or hooks on one side of the bag snap onto another
arrowhead-like stem on the other side of the bag when pressed together thus
causing an airtight seal so food within the bag can remain fresh zip ties are
another snap fit inspired device but the neat thing about zip ties is that
there are many different positions into which the teeth on its compliant band
can snap as they are pulled past a deforming beam within the zip ties ratchet
head. Since the compliant beam in the ratchet head is only allowed to deform in
one direction users can easily adjust how tightly objects are bound together
but once snapped in place the zip ties compliant band can't be pulled out the
other direction.
Velcroves
Nature has also leveraged elastic deformations to devise a
variety of simple but ingenious joining approaches that have inspired numerous
products the concept for touch fasteners was for instance inspired by nature. Swiss
engineer george demestral invented the first man-made touch fastener in 1941
after he went on a walk in the woods and noticed how easily burdock seeds would
cling to his coat upon closer inspection of these and other hooked seeds that
passively attach themselves to almost anything that brushes against them he was
inspired with the idea for velcro. Velcro consists of two mating sides one side
consists of looped fibers and the other side consists of tiny elastic hooks
that deform around and tangle themselves with the loops of the other side. when
they are pressed together, since the loops elastically deform when the sides of
the resulting joint are forced apart, velcro can be used multiple times until
the sides become overly clogged with dirt and debris. Velcro is often used as
an easy alternative for rapidly fastening shoes gloves and other wearable items
such as t elbow pads, suction cups.
Leverage another nature inspired joining approach that also
relies on elastic deformation to function similar to the suckers on an octopus
or a squid suction cups push the air out from underneath them as they are
elastically deformed onto the part to which they are intended to be joined. If
a load tries to pull the suction cup off of the parts surface atmospheric
pressure pushes back on the cup against the vacuum created within the sealed
chamber below it and thus the cup remains firmly attached to the surface.
So there are many more compliant examples and even entire
categories of compliant examples that we could have discussed such as art or
photography but hopefully by now you're starting to realize the extent to which
compliant devices have completely infiltrated your daily life despite how
ubiquitous compliant products are though. Although compliant machines have
limitations but there are numerous solutions to overcome it. Examples in nature suggest that the advantages
of compliant deformations are still majorly underutilized by society instead of
using them for toys and toilet plungers. We could be using the advantages of
compliant deformations to create technologies that push the limits of what's
physically possible and unlock the door to transform our current perception of
science fiction into a compliance enabled reality.
COMPLIANCE
IS THE FUTURE.
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