what is poisons ratio?

Question

it is related with applied mechanics.

Answer 1

Poisson's ratio

When a sample of material is stretched in one direction, it tends to get thinner in the other two directions. Poisson's ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. For a perfectly incompressible material, the Poisson's ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. Some materials, mostly polymer foams, have a negative Poisson's ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.

Gore-Tex PTFE valve packing gets thicker in diameter when it is pulled along its length. This is reversible upon compression.

A Poisson's ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material "negative volume".

Answer 2

When a sample of material is stretched in one direction, it tends to get thinner in the other two directions. Poisson's ratio (ν, μ), named after Simeon Poisson, is a measure of this tendency. Poisson's ratio is the ratio of the contraction strain (normal to the applied load) divided by the extension strain (in the direction of the applied load). For a perfectly incompressible material, the Poisson's ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. Some materials, mostly polymer foams, have a negative Poisson's ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.

A Poisson's ratio greater than 0.5 does not make sense because at a specific strain the material would reach zero volume, and any further strain would give the material "negative volume".

I hope this is a good lead.

Answer 3

When a sample of material is stretched in one direction, it tends to get thinner in the other two directions. Poisson's ratio (ν, μ), named after Simeon Poisson, is a measure of this tendency. Poisson's ratio is the ratio of the contraction strain (normal to the applied load) divided by the extension strain (in the direction of the applied load). For a perfectly incompressible material, the Poisson's ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. Some materials, mostly polymer foams, have a negative Poisson's ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.

A Poisson's ratio greater than 0.5 does not make sense because at a specific strain the material would reach zero volume, and any further strain would give the material "negative volume".

Answer 4

This is a topic you can look up in the Handbook of mechanical engineering. The spelling is wrong. The ratio is named after the scientist who defined it .

Hint:

Go to your local library.

Get a book on Machine Design or The Hand book of Mechanical Engineering.

Go to index (at the back of the book, it is alphabetically arranged).

It may be under Elasticity or Ratio or P.......

Answer 5

If a square bar is stressed in a testing machine in the direction of its length so that the length increases, there is a contraction in each opposite direction, which produces a decrease in the thickness of the bar. The ratio between the contraction at right angles to a stress and the direct extension is called the Poisson's ratio. Its value in steel is in the order of 0.28.

Answer 6

Definition of Poisson's ratio
Poisson's ratio n is the ratio of transverse contraction strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio.

n = - etrans / elongitudinal

Strain e is defined in elementary form as the change in length divided by the original length.
e = DL/L.

Poisson's ratio: why usually positive
Virtually all common materials become narrower in cross section when they are stretched. The reason why, in the continuum view, is that most materials resist a change in volume as determined by the bulk modulus K more than they resist a change in shape, as determined by the shear modulus G.

In the structural view, the reason for the usual positive Poisson's ratio is that inter-atomic bonds realign with deformation. Stretching of honeycomb by vertical forces, shown on the right illustrates the concept.

Poisson's ratio: relation to elastic moduli
Poisson's ratio is related to elastic moduli K, the bulk modulus; G as the shear modulus; and E, Young's modulus, by the following. The elastic moduli are measures of stiffness. They are ratios of stress to strain. Stress is force per unit area, with the direction of both the force and the area specified.

n = (3K - 2G)/(6K + 2G)
E = 2G( 1 + n)

The theory of isotropic elasticity allows Poisson's ratios in the range from -1 to 1/2. Physically the reason is that for the material to be stable, the stiffnesses must be positive; the bulk and shear stiffnesses are interrelated by formulae which incorporate Poisson's ratio.

Poisson's ratio in various materials
Poisson's ratio of the elements are via Web Elements, which adduce references [2-4]. In a large compilation of properties of polycrystalline materials [5], most have Poisson's ratio in the vicinity of 1/3.

Answer 7

Poisson's ratio: The ratio between lateral strain to the longitudinal strain of a body is called Poisson's ratio.
That means, if a wire of length L1 is stretched to length L2, then its width decreases from W1 to W2(say), then according to Poisson's ratio,
lower-case sigma=lateral strain/longitudinal strain.
(It's not Poison's ratio but Poisson's ratio by the way)

Answer 8

poisson's ratio is the measure of universal behaviour of almost all matter that whenever it is distorted(stressed) in any one direction , it changes its shape in other 2 axis in opposite way. i.e. if you strech a wire lengthwise, its cross section will reduce. the ratio of lateral strain to longitudinal strain in this case will be the poisson's ratio for this material.

Answer 9

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Answer 10

poison ratio is defined as the ratio of lateral strain to the longitudnal strain......== as u know whn we stretch a bar, it Elongates and its length increses with dicrease in width and viceversa== the ratio of dat change in width to the change in length is called as POISON'S RATIO.

its just the a Ratio of length hence hav no dimensions and No units.....hope u know wht Strain is ........as u can get this esily if u know wht strain is......as ratio of change in length to the original length of any streched piece.