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Portal To Architecture
Portal To Art & Design
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Portal To Becoming Bucky
Portal to Biotensegrity
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Types and Polyhedra
Index to all Forms and Types of Tensegrity
Index to all concept articles
Index to all People
Index to all pages in this wiki
Artifacts and Procedures
ADAM Collapsible Truss System
Biot Tensegrity Robot
Blur Building by Diller & Scofidio
How To Build A 3 Strut Copper Base for a Table
How To Build A 30 Strut Soda Straw Dodecahedron
Icosahedron WIth Mitch Amiano's Connectors
Jakob Tensegrity Torus
Photonium, Tower of Light by Snelson
Table of Contents
Comparing Tendon Materials
Inventory of Tendon Materials
Thermodynamics of Rubber Bands
Rubber band sizes
Read here about physical materials that are suitable for tension members of models and tensegrity structures. For general tendon concepts and issues, see
Comparing Tendon Materials
All tendons stretch under load in a tensegrity structure, but some materials stretch more than others. See below for a chart of approximate stretch in rope under 30 percent of its breaking load.
Stretch patterns in tensegrity tendons vary by material. For example:
Nylon stretches far more than Dacron.
Polypropylene has little elasticity but has only about 60 percent the strength of Dacron.
Kevlar and Spectra stretch about 1 to 2 percent or less. Kevlar is several times stronger than steel, but it’s not durable when bent sharply, so it is not suitable for tensegrities where the tendons bend around a strut-end. Spectra is even stronger than Kevlar and accepts bending. It’s also good at resisting chafe. however, it tends to “creep” slightly under a heavy sustained load such as it bears in any pre-stressed tensegrity.
Inventory of Tendon Materials
A review of materials used for tendons.
Dacron, a polyester fiber, stretches only about 3.5 to 5 percent under the same conditions, so it is preferred to nylon.
preferred Dacron for his models. Dacron is known outside North America as Terylene, Duron, Fortrel, A.C.E., and Kodel.
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced by Dupont in 1935. Nylon is one of the most commonly used polymers.
Nylon stretches about 10 to 15 percent under a load equal to 30 percent its breaking strength; therefore, it is used in light models only.
used nylon in his original
tensegrity sculpture, Early X-Piece (1948). "For George" (1970) was composed of black bamboo and nylon.
Bruce Hamilton's kits are made of 70lb Jinkai nylon monofilament line that is attached to nylon washers, with the fasteners being 8 - 32 threaded nylon machine screws. See
his website for details
Spectra is ultra-high molecular weight polyethylene (UHMWPE) fibers yield very high strength and cut resistant ropes that can stand-in for steel cables at one tenth their weight. WV prefers it for his
Spectra, like Kevlar, stretches about 1 to 2 percent or less. Spectra is even stronger than Kevlar and accepts bending. It’s also good at resisting chafe. however, it tends to “creep” slightly under a heavy sustained load such as it bears in any pre-stressed tensegrity.
Kevlar stretches about 1 to 2 percent or less. Kevlar is several times stronger than steel, but it’s not durable when bent sharply, so it is not suitable for tensegrities where the tendons bend around a strut-end. Compare with Spectra, above.
Natural rubber is made from latex which is acquired by tapping into the bark layers of the rubber tree. Once the latex has been “tapped” and is exposed to the air it begins to harden and become elastic, or “rubbery.” Synthetic rubber is made by mixing petroleum byproducts in a reactor with soapsuds which produces milky liquid latex. The liquid is then coagulated into rubber chunk and then sold to rubber manufacturers who in turn melt the rubber down and pour it into molds to create various products. See rubber band, below.
A rubber band (in some regions known as a binder, elastic band, lackey band, laggy band, lacka band or gumband) is a short length of
formed in the shape of a loop. While other rubber products may use
, rubber bands are primarily manufactured using
because of its superior elasticity.
Thermodynamics of Rubber Bands
Temperature affects the elasticity of a rubber band in an unusual way. Heating causes the rubber band to contract, and cooling causes expansion.
An interesting effect of rubber bands in
is that stretching a rubber band will produce heat (press it against your lips), while stretching it and then releasing it will produce an
reaction, causing it to become cooler. This phenomenon can be explained with
Gibb's Free Energy
. Rearranging ΔG=ΔH-TΔS, where G is the free energy, H is the
, and S is the
, we get TΔS=ΔH-ΔG. Since stretching is nonspontaneous, as it requires an external heat, TΔS must be negative. Since T is always positive (it can never reach
), the ΔS must be negative, inferring that the rubber in its natural state is more entangled (fewer
) than when it is under tension. Thus, when the tension is removed, the reaction is spontaneous, leading ΔG to be negative. Consequently, the cooling effect must result in a positive
, so ΔS will be positive there.
Rubber band sizes
A rubber band is given a [quasi-]standard number based on its dimensions. Generally, rubber bands are numbered from smallest to largest, width first. Thus, rubber bands numbered 8-19 are all 1/16
wide, with length going from 7/8 inch to 3 1/2 inches. Rubber band numbers 30-34 are for width of 1/8 inch, going again from shorter to longer. For even longer bands, the numbering starts over for numbers above 100, again starting at width 1/16 inch.
The origin of these size numbers is not clear and there appears to be some conflict in the "standard" numbers. For example, one distributor has a size 117 being 1/16 inch wide and a size 127 being 1/8 inch wide. However, an OfficeMax size 117 is 1/8 inch wide.
notes plastibands last much longer than rubber bands.[Aug 2010]
Plastibands are made with latex-free polyurethane. Baumgartens.com, the manufacturer, says they are much stronger than ordinary plastic bands and contain no additives or plasticizers. They are marketing them as a "green" product. The bands are available from a variety of art supply stores and amazon.com. They're listed on the staples.com website, but the local store has never stocked them. (
, Aug 2010)
uses plastibands instead of rubber bands for his tensegrity constructions, he says they last much longer than rubber bands.[Aug 2010]
Steel is usually deployed in the form of wire, though it can be deployed as a chain: see chain.
A wire is a single, usually
, string of metal. Wires are used to bear mechanical
and to carry
. Wire is commonly formed by
the metal through a hole in a
are determined by various
. Not all metals and metallic
possess the physical properties necessary to make useful wire. The metals must in the first place be
and strong in tension, the quality on which the utility of wire principally depends. The metals suitable for wire, possessing almost equal ductility, are
, aluminium and
; and it is only from these and certain of their
with other metals, principally
, that wire is prepared. By careful treatment extremely thin wire can be produced. Special purpose wire is however made from other metals (e.g.
filaments, because of its high melting temperature). Copper wires could be plated with other metals, such as tin, nickel, and silver to handle different temperatures.
Inox is stainless steel.
used stainless steel in his sculpture "Forest Devil" (1975), "Rainbow Arch" (2001), "Sun River" (1967) and others. His most common choice for deployments is aluminum struts with stainless steel tendons.
Steelon is a brand name for plastic or nylon coated wire roap.
used Steelon and aluminum in his sculpture "Spring Street" (1964), "Sun Run" (1967), and others.
Piano wire is a specialized type of
made for use in
and other musical instrument strings, as well as many other purposes. It is made from
, also known as
. General-purpose, high-carbon steel, drawn music wire (such as
A228) is manufactured in both
music wire gauges (m.w.g.) in diameters as small as 0.006 inch up to 0.192 inch (0.15 to 4.8 mm). A small number of companies produce the tough, high tensile polished wire intended for limited music instrument markets, which is manufactured from steel of a specific composition by
. Musical instrument strings, modern electric guitars in particular, are among the most demanding of all its applications. Placed under high tension, they are subject to repeated blows, repeated bending, are stretched and slackened during tuning and, in piano service, are still expected to last for decades. The wire must also be extremely consistent in size: variations greater than 0.0003 inch (8 μm) will produce audible falseness in modern instruments.
"Music wire" is the USA name for high strength steel wire, it's also available in stainless steel which might look nicer?
Music wire is sold by weight and packaged in tight coils. It springs back to a gentle curve but can be straightened using a series of opposed rollers. It requires careful handling for safety and appearance, since it can be marred by
, and it requires special cutters, as the hardened steel will otherwise quickly dull the cutter.
It is hard and springy, you will need to think carefully about connections, perhaps neatly twisting the ends like guitar strings. Normal wire cutters (for soft wire) will be nicked by this hard wire, there are special wire cutters with hardened edges just for music wire. Also, be careful to not puncture your fingers or other body parts with the sharp wire ends.
A sample supplier:
Amsteel is a registered trademarked brand name for a nonrotational, Samthane-coated 12-strand single braid that yields high strength and low stretch; equivalent to wire rope with one-seventh the weight. The manufacturer claims the product is flexible, spliceable, and resists flex-fatigue and abrasion. It floats-will not absorb water, is easily spliced, extremely lightweight, durable-outlasts wire rope, and is spliceable--Class II 12-strand. Sample link:
wire (often abbreviated to EL wire) is a thin diameter
coated in a
which glows when an
is applied to it. It can be used in a wide variety of applications- vehicle and/or structure decoration, safety and emergency lighting, toys, clothing etc - much as rope light or
are often used. Unlike these types of strand lights, EL wire is not a series of points but produces a 360 degree unbroken line of visible light.
See Spectra, below.
used bead chain in his sculpture "Harry's Hen" (1960), "Bead Chain Helix" (1959), and others.
A rope is a length of
, twisted or
together to improve strength for pulling and
. It has
but is too flexible to provide
(i.e. it can be used for pulling, but not pushing). Rope is thicker and stronger than similarly constructed cord, line,
See Spectra, above.
used thread and cardboard in his earliest tensegrity sculpture "Bat Wing Piece" (1948).
Comparing stretch of materials under 30% of breaking load.
Portal to Model Making
A series on physical materials, methods, procedures. For CAD, see
You Can Touch This
Rhode Island Program
Cardboard Model Building
Models by # of Struts
Johansons'/Ioganson's 1921 structure:
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