What Is Elasticity?
In physics and materials science, elasticity is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate loads are applied to them; if the material is elastic, the object will return to its initial shape and size after removal. This is in contrast to plasticity, in which the object fails to do so and instead remains in its deformed state.
The physical reasons for elastic behavior can be quite different for different materials. In metals, the atomic lattice changes size and shape when forces are applied (energy is added to the system). When forces are removed, the lattice goes back to the original lower energy state. For rubbers and other polymers, elasticity is caused by the stretching of polymer chains when forces are applied.
Hooke’s law states that the force required to deform elastic objects should be directly proportional to the distance of deformation, regardless of how large that distance becomes. This is known as perfect elasticity, in which a given object will return to its original shape no matter how strongly it is deformed.
This is an ideal concept only; most materials that possess elasticity in practice remain purely elastic only up to very small deformations, after which plastic (permanent) deformation occurs.
In engineering, the elasticity of a material is quantified by the elastic modulus such as Young’s modulus, bulk modulus, or shear modulus which measure the amount of stress needed to achieve a unit of strain; a higher modulus indicates that the material is harder to deform.
The SI unit of this modulus is the pascal (Pa). The material’s elastic limit or yield strength is the maximum stress that can arise before the onset of plastic deformation. Its SI unit is also the pascal (Pa).
Examples: Rubber bands and elastic and other stretchy materials display elasticity. Modeling clay, on the other hand, is relatively inelastic and retains a new shape even after the force that caused it to change is no longer being exerted.
How does elasticity work?
Elasticity is the ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed. A body with this ability is said to behave (or respond) elastically.
To a greater or lesser extent, most solid materials exhibit elastic behavior, but there is a limit to the magnitude of the force and the accompanying deformation within which elastic recovery is possible for any given material.
This limit, called the elastic limit, is the maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation. Stresses beyond the elastic limit cause material to yield or flow.
For such materials, the elastic limit marks the end of elastic behavior and the beginning of plastic behavior. For most brittle materials, stresses beyond the elastic limit result in fracture with almost no plastic deformation.
The elastic limit depends markedly on the type of solid considered; for example, a steel bar or wire can be extended elastically only about 1 percent of its original length, while for strips of certain rubberlike materials, elastic extensions of up to 1,000 percent can be achieved.
Steel is much stronger than rubber, however, because the tensile force required to affect the maximum elastic extension in rubber is less (by a factor of about 0.01) than that required for steel. The elastic properties of many solids in tension lie between these two extremes.
The different macroscopic elastic properties of steel and rubber result from their very different microscopic structures. The elasticity of steel and other metals arises from short-range interatomic forces that, when the material is unstressed, maintain the atoms in regular patterns.
Under stress, the atomic bonding can be broken at quite small deformations. By contrast, at the microscopic level, rubberlike materials and other polymers consist of long-chain molecules that uncoil as the material is extended and recoil in elastic recovery.
The mathematical theory of elasticity and its application to engineering mechanics is concerned with the macroscopic response of the material and not with the underlying mechanism that causes it.
In a simple tension test, the elastic response of materials such as steel and bone is typified by a linear relationship between the tensile stress (tension or stretching force per unit area of cross-section of the material), σ, and the extension ratio (difference between extended and initial lengths divided by the initial length), e.
In other words, σ is proportional to e; this is expressed σ = Ee, where E, the constant of proportionality, is called Young’s modulus. The value of E depends on the material; the ratio of its values for steel and rubber is about 100,000. The equation σ = Ee is known as Hooke’s law and is an example of a constitutive law.
Who discovered elasticity?
Well, we’ve always known that some materials are more flexible than others and that they behave in different ways when subjected to different types of force, but the key figure to remember when it comes to elasticity is Robert Hooke. Hooke was a contemporary of Isaac Newton, and he was the first person to properly quantify and analyses how elasticity works.
In 1660, Hooke discovered the Law of Elasticity, known as Hooke’s Law through lengthy experimentation with springs. The basic premise of the law is that for relatively small deformations of an object (by stretching or bending them, for example), the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions, the object returns to its original shape and size upon removal of the load.
The elastic behavior of solids according to Hooke’s law can be explained by the behavior we mentioned earlier. Materials are elastic if the particles that make them up are able to move within the material when they’re subjected to an external force, and Hooke’s Law states that this movement is directly proportional to the force that’s applied.
It’s not a perfect law – for larger amounts of force, the elastic limit is often surpassed, which means that the force creates more deformation than is strictly proportional, but when you’re getting started with exploring the topic, Hooke’s Law is the most important to know!
Why is elasticity useful?
Elasticity is a key property to understand whenever you need to make something – after all, there’s no point in building a building so rigid that it’ll break in a storm, or in making a ruler that’s so bendy you can’t use it to measure anything!
Because of this, being familiar with the elastic limit of a material is extremely useful for almost any task that requires working to make or repair an object, whether it’s as small as a spoon or as big as a skyscraper – and it’s especially important for things like forms of transport and buildings.
We need to be able to rely on these things to stay strong and not break even when they’re subjected to huge amounts of strain, which can come from a wide range of different sources. Elasticity can play a big part in making these things more able to weather damage, so it’s a vital field of study for engineers, in particular!