## January 22, 2009

### Understanding Strength of Materials and History of Improvement

This article will go over some basic background about tensile strength of material and then discuss historic material strength improvement to understand what industrial production of new carbon nanotube tethers relates to past improvements in strength of materials.

Understanding Tensile Strength of Material and the Measurement Units
A Gigapascal is unit of measure for strength of material. The strength of tethers (ribbons or rope) is usual the tensile strength. Tensile strength is how much force is needed to pull the tether until it breaks/fails. How strong a tether for a given amount or density of material is important. Grams per cubic centimeter (g/cc or g/cm**3) are used to measure the density. 1 gram per cubic centimeter is the density of water

Specific tensile modulus
Tensile modulus related to the specific gravity.
It is expressed in N/tex (1 N/tex = 10.2 g/dtex or 11.3 g/den).
It is calculated by the relation:
Specific tensile modulus (N/tex) = Tensile modulus (GPa) / Specific
gravity (g/cm3)

One N/Tex is the same as One GPa per gram per cm3 is the same as one mega Yuri.

The units for measureing specific strength (or tenacity) are confusing - traditionally, people use either GPa-cc/g for the former, and N/Tex for the latter. These two units are the same in fact, and are equal to 1E6 N-m/kg [one million newton meters per kilogram], which is what the pure metric unit should be - force per linear density.

To end confusion once and for all, we propose to name the pure metric unit for both specific strength and tenacity as a Yuri (in honor of Yuri Aatsutanov), and so a tether with a linear tensity of 0.001 kg/m that breaks at 1000 N will have a breaking strength of 1 Mega Yuri.

Tensile Strength of Different Material
Wood 0.001 N/tex
Steel 0.05 N/tex
Alumina 0.5 N/tex
Nylon 0.84 N/tex
Spider silk 1 N/tex
E-glass 1.4 N/tex
S-glass 1.8 N/tex
Kevlar #29 has 1500 denier and 1.42 grams per cc of material
Kevlar #29 has 2.03 N /Tex
Kevlar #49 has 2.08 N/Tex
Spectra 1000 has 3.10 N/Tex
The strongest fibers ever before this had gotten to about 4.1 [Zylon] N/Tex

Steel has strength properties [not necessarily just tensile strength] that are two to three times more than cast iron.
Titanium is about half the weight of steel and a little stronger, plus it can remain strong at higher temperatures.

Carbon Nanotube fiber with 10 N /Tex has FIVE times the strength of common Kevlar.
The strength difference is more than the difference between Kevlar and Nylon.

So we are talking about moving from the age of iron to the age of steel or even from bronze the copper/brass ages to the iron age was also a similar step up in material strength. [Bronze was stronger than iron. The switch to iron was because of tin to make bronze became too expensive. The ages also had to do with shifts in society, technology and culture that coincided with the shifts in materials.]

If we get the 30 N/Tex that is like the step from copper up to steel. Researchers believe that 20-30N/Tex carbon nanotube tethers are possible.

Being able produce the new carbon nanotube tethers/material in large volumes and at affordable prices is vital for realizing the large potential impact on civilization.

100 kilometer high towers.
1800 kilometer long orbiting tethers.

Being able to go mach 10 with a rocket and then handoff to a tether means that cargo/payload becomes 1/3 of what the rocket is hauling instead of 1% or less.

References on material strength:

This link has is another table of materials with costs (includes glass and other more common material)

Educational reference that teaches polymer science and material strength

Historic Periods Dominated By Particular Material
Originally archeological classifications had the stone, bronze and iron age. Copper and other ages were added later.

Another set of strengths and elasticity of materials tables.

`Tensile Strength Brass (66% Cu, 34% Zn)  (cast)  150–190  MPa Brass      (rolled)             230–270  MPa   Copper (cast)                   120–170  MPa   Copper      (rolled)            200–400  MPa   Iron (cast)                     100–230  MPa  Iron (wrought)                  290–450  MPaSteel (castings).               400–600    Steel (mild) (0.2% C)         430–490   High-carbon spring steel:        (annealed                  700–770 `

The Stone Age

The Stone Age is a broad prehistoric time period during which humans widely used stone for toolmaking. Stone tools were made from a variety of different kinds of stone. For example, flint and chert were shaped (or chipped) for use as cutting tools and weapons, while basalt and sandstone were used for ground stone tools, such as quern-stones. Wood, bone, shell, antler and other materials were widely used, as well. During the most recent part of the period, sediments (like clay) were used to make pottery.

The Copper Age

The copper age is a phase in the development of human culture in which the use of early metal tools appeared alongside the use of stone tools.

The Bronze Age

Bronze was also stronger than iron, another common metal of the era, and quality steels were not available until thousands of years later. Nevertheless the Bronze Age gave way to the Iron Age as the shipping of tin around the Mediterranean Ocean ended during the major population migrations around 1200 - 1100 BCE, which dramatically limited supplies and raised prices. Bronze was still used to a considerable extent during the Iron Age, but for many purposes the weaker iron was sufficiently strong to serve in its place. As an example, Roman officers were equipped with bronze swords while foot soldiers had to make do with iron blades.

Iron Age

In archaeology, the Iron Age was the stage in the development of any people in which tools and weapons whose main ingredient was iron were prominent. The adoption of this material coincided with other changes in some past societies often including differing agricultural practices, religious beliefs and artistic styles, although this was not always the case.

In history, the Iron Age is the last principal period in the three-age system for classifying prehistoric societies, preceded by the Bronze Age. Its date and context vary depending on the country or geographical region.

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