Force, Stress, Strain
Actuators for the promotion of:
Muscles and Tendons
What are some of the physics we are
looking at for artifial tendons and muscles?
- From its commercial beginnings in the late 1930s up to recent years, the
fundamental marketing strategy of the plastics industry has been to develop
and refine polymeric materials that could replace "traditional" materials
- metals, wood, rubber, glass, paper, et al. - in existing, high-volume and/or
high-value applications (Ashley 2003).
- Whereas there are also advanced composites with high-modulus fibers available
to compete against the great strength of steel, the one characteristic of
steel and other metals that has consistently eluded polymer scientists is
electrical conductivity, until recently.A measure of conductivity was achieved,
but there were generally compromises in terms of processability or performance
or total part economics.
- Thus, the search for "inherently conductive" polymers commenced in earnest
in corporate, academic and government-supported research laboratories around
the world - in the U.S., Europe and Japan, in particular. And in the 1950s
and 1960s, as the implications of the microelectronics revolution became apparent
to all, the search for such materials accelerated further, taking on the trappings
of the search for the Holy Grail.
- In the mid-1970s, quite by accident, the first polymer capable of conducting
electricity - polyacetylene - was discovered at the University of Pennsylvania.
The announcement of this discovery quickly reverberated around the polymer
science community, and the intensity of the search for others magnified dramatically.
By 1984-1985 the number of patents issued in the field of electrically conductive
polymers had shot up, and by 1987 the first application - a polymer electrode
in a miniature ("button") battery - was registered.
- In the early years and decades of the 21st century, the processes and the
products in a host of vital industries:- aircraft/aerospace - automobiles
- biotechnology - chemical processing - electrical/electronic equipment -
military hardware will be completely transformed by the integration of these
conductive polymers into an ever-widening menu of materials.
- U.S. and global manufacturers and their material/part suppliers have always
faced a choice between the known and the unknown in materials decision-making.
The companies that are willing to plumb the unknown and learn to enhance their
total processing/performance spectrum will enter the next century as vital
competitors in the evolving global marketplace for products and services.
Those that don't will soon face technological obsolescence and disappear.
This certainly applies all along the product/service supply chain in the industries
cited above and others as well.
- The companies that succeed in developing and marketing electrically conductive
polymers and other novel molecular transformations will be those driven by
"patient money." These are hardly materials that offer quick rewards "going
right down to the bottom line." Rather, this is a field where careful, time-consuming
and very often cooperative research will eventually be rewarded with applications
beyond any contemporary crystal ball-gazing. And in our research we have identified
many companies - in North America, Europe and Asia - determined to participate
in those applications in the future with materials currently dubbed "exotic."
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Hooke's Law: materials
deform in linear proportion to the load (force) applied to it. F~KS where
K is a constant and S is the amount deformed (Newman 2003).
this looks like pressure, which also is a type of stress. There are two
types of stress: 1)normal-which is perpendicular to the material 2)shear
stress-which is parallel to the material.
The response of
a material to a stress is called a strain.
Strain= change in
There are two types
of normal stress: 1)tensile 2)compressure
All materials have
a stress/strain diagram.
Elastic moduli: 1)Young's modulus Y for tensile stress:
(F/A)/(delta L/L not) this is related to K-- F= (YA/L not) times delta
L where (YA/L not) is K which is Hookes Constant. This entire equation
is Hooke's Law
volumetric stress/volumetric strain
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Physics 103 Fall 2003 Dr.
last updated on 24-Nov-2003