Everything about Tensile Strength totally explained
Tensile strength , or
measures the engineering stress applied (to something such as rope, wire, or a structural beam) at the point when it fails. It is an
intensive property of the material, which not only depends on the type of material but also the preparation of the specimen and the temperature of the test.
Explanation
The tensile strength (TS) is the stress at the maximum on the stress-strain curve.
There are three typical definitions of tensile strength:
Yield strength: The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently.
;Ultimate strength: The maximum stress a material can withstand.
Breaking strength: The stress coordinate on the stress-strain curve at the point of rupture.
Concept
The various definitions of tensile strength are shown in the following stress-strain graph for
low-carbon steel:
Metals including steel have a linear stress-strain relationship up to the yield point, as shown in the figure. In some steels the stress falls after the yield point. This is due to the interaction of carbon atoms and
dislocations in the stressed steel.
Cold worked and alloy steels don't show this effect. For most metals yield point isn't sharply defined. Below the yield strength all deformation is recoverable, and the material will return to its initial shape when the load is removed. For stresses above the yield point the deformation isn't recoverable, and the material won't return to its initial shape. This unrecoverable deformation is known as
plastic deformation. For many applications plastic deformation is unacceptable, and the yield strength is used as the design limitation.
After the yield point, steel and many other
ductile metals will undergo a period of
strain hardening, in which the stress increases again with increasing strain up to the
ultimate strength. If the material is unloaded at this point, the stress-strain curve will be parallel to that portion of the curve between the origin and the yield point. If it's re-loaded it'll follow the unloading curve up again to the ultimate strength, which has become the new yield strength.
After a metal has been loaded to its yield strength it begins to "neck" as the cross-sectional area of the specimen decreases due to plastic flow. When
necking becomes substantial, it may cause a reversal of the engineering stress-strain curve, where decreasing stress correlates to increasing strain because of geometric effects. This is because the engineering stress and engineering strain are calculated assuming the original cross-sectional area before necking. If the graph is plotted in terms of
true stress and
true strain the curve will always slope upwards and never reverse, as true stress is corrected for the decrease in cross-sectional area. Necking isn't observed for materials loaded in compression. The peak stress on the engineering stress-strain curve is known as the
ultimate strength. After a period of necking, the material will rupture and the stored elastic energy is released as noise and heat. The stress on the material at the time of rupture is known as the
tensile strength.
Ductile metals don't have a well defined yield point. The yield strength is typically defined by the "0.2% offset strain". The yield strength at 0.2% offset is determined by finding the intersection of the stress-strain curve with a line parallel to the initial slope of the curve and which intercepts the abscissa at 0.002. A stress-strain curve typical of aluminum along with the 0.2% offset line is shown in the figure below.
Brittle materials such as
concrete and
carbon fiber don't have a yield point, and don't strain-harden which means that the ultimate strength and breaking strength are the same. A most unusual stress-strain curve is shown in the figure below. Typical brittle materials don't show any plastic deformation but fail while the deformation is elastic. One of the characteristics of a brittle failure is that the two broken parts can be reassembled to produce the same shape as the original component. A typical stress strain curve for a brittle material will be linear. Testing of several identical specimens will result in different failure stresses. The curve shown below would be typical of a brittle polymer tested at very slow strain rates at a temperature above its glass transition temperature. Some engineering ceramics show a small amount of ductile behaviour at stresses just below that causing failure but the initial part of the curve is a linear.
Tensile strength is measured in units of
force per unit
area. In the
SI system, the units are
newtons per
square metre (N/m²) or
pascals (Pa), with
prefixes as appropriate. The non-metric units are
pounds-force per square inch (lbf/in² or PSI). Engineers in North America usually use units of ksi which is a thousand psi.
The breaking strength of a
rope is specified in units of force, such as newtons, without specifying the cross-sectional area of the rope. This is often loosely called tensile strength, but this isn't a strictly correct use of the term.
In brittle materials such as rock, concrete, cast iron, or soil, tensile strength is negligible compared to the compressive strength and it's assumed zero for many engineering applications. Glass fibers have a tensile strength stronger than steel
(External Link
), but bulk glass usually does not. This is due to the
Stress Intensity Factor associated with defects in the material. As the size of the sample gets larger, the size of defects also grows.
In general, the tensile strength of a rope is always less than the tensile strength of its individual
fibers.
Tensile strength can be defined for
liquids as well as solids. For example, when a
tree draws water from its roots to its upper leaves by
transpiration, the column of water is pulled upwards from the top by
capillary action, and this force is transmitted down the column by its tensile strength. Air pressure from below also plays a small part in a tree's ability to draw up water, but this alone would only be sufficient to push the column of water to a height of about ten metres, and trees can grow much higher than that. (See also
cavitation, which can be thought of as the consequence of water being "pulled too hard".)
Typical tensile strengths
Some typical tensile strengths of some materials:
| Material |
Yield strength
(MPa) |
Ultimate strength
(MPa) |
Density
(g/cm³) |
| Structural steel ASTM A36 steel |
250 |
400 |
7.8 |
| Steel, API 5L X65 (Fikret Mert Veral) |
448 |
531 |
7.8 |
| Steel, high strength alloy ASTM A514 |
690 |
760 |
7.8 |
| Steel, prestressing strands |
1650 |
1860 |
7.8 |
| Steel Wire |
|
|
7.8 |
| Steel (AISI 1060 0.6% carbon) Piano wire |
2200-2482 MPa |
|
7.8 |
| High density polyethylene (HDPE) |
26-33 |
37 |
0.95 |
| Polypropylene |
12-43 |
19.7-80 |
0.91 |
| Stainless steel AISI 302 - Cold-rolled |
520 |
860 |
|
| Cast iron 4.5% C, ASTM A-48 |
130 |
200 |
|
| Titanium alloy (6% Al, 4% V) |
830 |
900 |
4.51 |
| Aluminium alloy 2014-T6 |
400 |
455 |
2.7 |
| Copper 99.9% Cu |
70 |
220 |
8.92 |
| Cupronickel 10% Ni, 1.6% Fe, 1% Mn, balance Cu |
130 |
350 |
8.94 |
| Brass |
approx. 200+ |
550 |
5.3 |
| Tungsten |
|
1510 |
19.25 |
| Glass |
|
50 (in compression) |
2.53 |
| E-Glass |
N/A |
3450 |
2.57 |
| S-Glass |
N/A |
4710 |
2.48 |
| Basalt fiber |
N/A |
4840 |
2.7 |
| Marble |
N/A |
15 |
|
| Concrete |
N/A |
3 |
|
| Carbon Fiber |
N/A |
5650 |
1.75 |
| Spider silk |
1150 (??) |
1200 |
|
| Silkworm silk |
500 |
|
|
| Aramid (Kevlar or Twaron) |
3620 |
|
1.44 |
| UHMWPE |
23 |
46 |
0.97 |
| UHMWPE fibers (Dyneema or Spectra) |
|
2300-3500 |
0.97 |
| Vectran |
|
2850-3340 |
|
| Polybenzoxazole (Zylon) |
|
5800 |
|
| Pine Wood (parallel to grain) |
|
40 |
|
| Bone (limb) |
104-121 |
130 |
1.6 |
| Nylon, type 6/6 |
45 |
75 |
1.15 |
| Rubber |
- |
15 |
|
| Boron |
N/A |
3100 |
2.46 |
| Silicon, monocrystalline (m-Si) |
N/A |
7000 |
2.33 |
| Silicon carbide (SiC) |
N/A |
3440 |
|
| Sapphire (Al2O3) |
N/A |
1900 |
3.9-4.1 |
| Carbon nanotube (see note below) |
N/A |
62000 |
1.34 |
- Note: Multiwalled carbon nanotubes have the highest tensile strength of any material yet measured, with labs producing them at a tensile strength of 63 GPa, still well below their theoretical limit of 300 GPa. However as of 2004, no macroscopic object constructed of carbon nanotubes has had a tensile strength remotely approaching this figure, or substantially exceeding that of high-strength materials like Kevlar.
- Note: many of the values depend on manufacturing process and purity/composition.
(Source: A.M. Howatson, P.G. Lund and J.D. Todd, "Engineering Tables and Data" p41)
Further Information
Get more info on 'Tensile Strength'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://tensile_strength.totallyexplained.com">Tensile strength Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
