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In engineering mechanics, deformation is a change in shape due to an applied force. This can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). Deformation of a cylinder under compressive loading File links The following pages link to this file: Deformation Categories: GFDL images ... Engineering mechanics is a branch of the physical sciences which looks to understand the actions and reactions of bodies at rest or in motion. ... In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ... The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before it breaks. ... Compressive strength is the capacity of a material to withstand axially directed pushing forces. ... Jump to: navigation, search Simple shear Simple shear is a special case of deformation of a fluid where only one component of velocity vectors has a non-zero value: And the gradient of velocity is perpendicular to it: , where is the shear rate and: The deformation gradient tensor for this... Jump to: navigation, search Figure 1. ... // Mathmatics In mathematics, the term torsion has several meanings, mostly unrelated to each other. ...


In the figure it can be seen that the compressive loading (indicated by the arrow) has caused deformation in the cylinder so that the original shape (dashed lines) has changed (deformed) into one with bulging sides. The sides bulge because the material, although strong enough to not crack or otherwise fail, is not strong enough to support the load without change, thus the material is forced out laterally. The word cylinder has several meanings. ...

Diagram showing the relationship between stress (force applied) and strain (deformation) of a ductile metal.
Enlarge
Diagram showing the relationship between stress (force applied) and strain (deformation) of a ductile metal.

The concept of a rigid body can be applied if the deformation is negligible. Generic stress-strain graph for a ductile material. ... Generic stress-strain graph for a ductile material. ... In physics, a rigid body is an idealisation of a solid body of finite dimension in which deformation is neglected. ...

Contents


Types of deformation

Depending on the material, size and geometry of the object, and the forces applied, various types of deformation may result.


Elastic deformation

This type of deformation is reversible. That is, once the forces are no longer applied, the object returns to it's original shape. As the name implies, elastic (rubber) has a rather large elastic deformation range. Soft thermoplastics and metals have moderate elastic deformation ranges while ceramics, crystals, and hard thermosetting plastics undergo almost no elastic deformation. Rubber is an elastic hydrocarbon polymer which occurs as a milky emulsion (known as latex) in the sap of a number of plants but can also be produced synthetically. ... A thermoplastic is a plastic that softens when heated and hardens again when cooled. ... For alternative meanings see metal (disambiguation). ... Jump to: navigation, search The word ceramic is derived from the Greek word Κεραμεικος (-keramos- the name of a suburb of Athens), and in its strictest sense refers to clay in all its forms. ... Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Thermosetting plastics (thermosets) refer to a range of polymer materials that cure, through the addition of energy, to a stronger form. ...


Metal fatigue

A phenomenon only discovered in modern times is metal fatigue. As the name implies, this occurs primarily in ductile metals. It was originally felt that a material deformed only within the elastic range completely returned to it's original state once the forces were removed. However, faults are introduced at the molecular level with each deformation. After many deformations, cracks will begin to appear, followed soon after by a fracture, with no apparent plastic deformation in between. Depending on the material, shape, and how close to the elastic limit it is deformed, failure may require thousands, millions, billions, or trillions of deformations. Metal fatigue has been a major cause of aircraft failure, such as the De Havilland Comet, especially before the process was well understood. There are two ways to determine when a part is in danger of metal fatigue; either predict when failure will occur due to the material/force/shape/iteration combo, and replace the vulnerable materials before this occurs, or perform inspections to detect the microscopic cracks and perform replacement once they occur. Selection of materials which are not likely to suffer from metal fatigue during the life of the product is the best solution, but not always possible. Avoiding shapes with sharp corners limits, but does not eliminate, metal fatigue, by reducing force concentrations. In materials science, fatigue is a process by which a material is weakened by cyclic loading. ... Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ... This article deals with the de Havilland Comet jet airliner. ...


Plastic deformation

This type of deformation is not reversible. However, an object in the plastic deformation range will first have undergone elastic deformation, which is reversible, so the object will return part way to it's original shape. Soft thermoplastics have a rather large plastic deformation range as do ductile metals such as copper, silver, and gold. Steel does, too, but not iron. Hard thermosetting plastics, rubber, crystals, and ceramics have minimal plastic deformation ranges. Perhaps the material with the largest plastic deformation range is wet chewing gum, which can be stretched dozens of times it's original length. A thermoplastic is a plastic that softens when heated and hardens again when cooled. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... Jump to: navigation, search General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Atomic mass 107. ... Jump to: navigation, search General Name, Symbol, Number gold, Au, 79 Chemical series transition metals Group, Period, Block 11, 6, d Appearance metallic yellow Atomic mass 196. ... Jump to: navigation, search The old steel cable of a colliery winding tower Steel is a metal alloy whose major component is iron, with carbon being the primary alloying material. ... Jump to: navigation, search General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... Chewing gum Chewing gum is a type of confectionery which is designed to be chewed, not swallowed. ...


Fracture

This type of deformation is also not reversible. A break occurs after the material has reached the end of the elastic, and then plastic, deformation ranges. At this point forces accumulate until they are sufficient to cause a fracture. All materials will eventually fracture, if sufficient forces are applied.


Misconceptions

A popular misconception is that all materials that bend are "weak" and all those which don't are "strong". In reality, many materials which undergo large elastic and plastic deformations, such as steel, are able to absorb stresses which would cause brittle materials, such as glass, with minimal elastic and plastic deformation ranges, to break. There is even a parable to describe this observation (paraphrased below):

"The mighty oak stands strong and firm before the wind, while the willow yields to the slightest breeze. However, in the strongest storm, the oak will break while willow will bend, and thus survive. So, in the end, which is the stronger of the two ?"

Note that some materials which bend are weak, however, such as wet chewing gum.


See also


  Results from FactBites:
 
Deformation (407 words)
Enormous stress is imposed on the crust at the boundaries of the lithospheric plates and where convection currents in the mantle tug and tear at the crust above.
The reaction of rock material to an imposed stress depends on the temperature and pressure conditions.
During plastic deformation mineral bonds adjust to the stress by breaking, moving about, and then reforming.
NationMaster - Encyclopedia: Plastic deformation (499 words)
In 1934, Egon Orowan, Michael Polanyi and Geoffrey Ingram Taylor, roughly simultaneously, realised that the plastic deformation of ductile materials could be explained in terms of the theory of dislocations.
One of the best-known examples of this is nitinol, which exhibits pseudoelasticity: deformations which are reversible in the context of mechanical design, but irreversible in terms of thermodynamics.
In reality, many materials which undergo large elastic and plastic deformations, such as steel, are able to absorb stresses which would cause brittle materials, such as glass, with minimal elastic and plastic deformation ranges, to break.
  More results at FactBites »

 
 

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