Youngs Modulus is a Measure of Stiffness
YOUNG'S MODULUS also called Modulus of Elasticity quantifies the stiffness of an elastic material. The Stiffness of Carbon Fiber can be compared using its Young's Modulus
It is one of the important characteristic of a material. Being able to compare and quantify stiffness is fundamental to Engineering and construction. Young Modulus is how stiffness is expressed for engineering types.
Anyone doing research on materials used to make masts and in particular carbon fiber, will run into youngs modulus sooner or later.
It's important to stress that stiff is not equivalent to strong. A stiff material might not deflect much under load but may break at a lower stress (force) than another less stiff material.
Defining a few words we already know!
- An Elastic Material:
- is a material that is able to resume its normal shape after a load is removed. In other words if you bend or stretch something and it springs back to its original shape, with no damage, it's an elastic material.
- A Stiff material
- Is a material that needs a large force applied to it to change its shape.
- a Flexible material
- is one that only requires a small force to change its shape.
- is a measure of force
- is a measure of deformation (amount of bend or stretch)
Young's modulus predicts how much a material bends or extends under tension or shortens under compression. The higher the young's modulus, the stiffer the material.
It is expressed as a ratio of stress over strain. In other words, how much something bends (strain) under a given load (the stress).
Unit: 10 9 N/m2 Or Gpa (GigaPascal)
N = Newton, m = Meter. A Newton is equal to the force that would give a mass of one kilogram an acceleration of one meter per second per second. A Pascal is equal to one newton per square meter.
Young's modulus is not always the same in all orientations of a material.
Most metals and ceramics, along with many other materials, are isotropic, their mechanical properties are the same in all orientations.
Some materials are made or can be modified or physically treated to modify their structure and make it directional. These materials are or become anisotropic, and Young's modulus will be different depending on the direction of the force. Anisotropy can be seen in many composites. Carbon fiber has much higher Young's modulus (is much stiffer) when force is parallel to the fibers (along the grain). Other anisotropic materials include wood and reinforced concrete.
Young's modulus can vary due to differences in sample composition and test method.
These values are offered for comparison only. Units are GPascal
|Rubber (small strain)||0.01-0.1|
|Low density polyethylene||0.2|
|Pine wood (along grain)||8.963|
|Oak wood (along grain)||11|
|High-strength concrete (under compression)||30|
|Magnesium metal (Mg)||45|
|Aramid (such as Kevlar)||70.5-112.4|
|Brass and bronze||100-125|
|Glass-reinforced plastic (70/30 by weight fibre/matrix, unidirectional, along grain)||40-45|
|Carbon fiber reinforced plastic (70/30 fibre/matrix, unidirectional, along grain)||181|
|Silicon carbide (SiC)||450|
|Single-walled carbon nanotube||1,000+|
The units of measure are not so terribly important for the amateur boat and mast maker, what is more to the point is the comparison of materials. It's interesting to compare Carbon Fiber with Glass Fibre and Aluminium. Carbon Fibre stiffness is about 4 times that of fiberglass and over twice the stiffness of Aluminium. Carbon fibre is also about twice as stiff as Kevlar.
How is Young's Modulus Measured?
There are several different tests such as the 3 point test, or a stretch test. Essentially a sample is prepared and a force is applied to it. The deflection or stretch is measured.
When testing composites like carbon fibre or fiberglass, it is tricky to prepare samples that are exactly comparable and a great deal of attention needs to be paid to the sample preparation, matrix and density of fibres and weave. In any research paper I have read, a significant amount of detail goes into describing the way the samples are made. Because materials like aluminium or copper are more uniform the preparation is not as critical. If there are crystal orientations then these have to be matched and noted.
Measuring the bending of a carbon fibre tube. They are not testing to destruction. This is a 3 point test. The material to be tested is placed on 2 supports and a third point comes down and applies a force. The machine then measures how much deflection there is for a given force. The higher the Young's modulus, the lower the deflection before the piece breaks.
Here a part is being tested to failure. It is actually a test of strength. Fun video for Lotus driveshafts.
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