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Viscoelasticity explains elastic and viscous behavior of materials. All materials show some elastic and viscous effects when changing shape. Metals, woods, plastics, and biological tissues at high temperatures exhibit significant viscoelastic properties. James Clerk Maxwell devised a model to describe viscoelasticity using a spring and dashpot. Creep and stress relaxation are also important effects.
Viscoelasticity is the discipline that seeks to explain both the elastic and viscous behavior of materials. Elastic deformation can be seen in the way a rubber band behaves, although metals and other materials behave in a fundamentally similar way. Viscosity refers to how strongly fluids resist rapid changes in shape; honey, for example, is very viscous because it tends to deform slowly. All materials show some elastic and viscous effects when changing shape.
Viscoelasticity is basically a rearrangement of the molecules in a substance. For small deformations of metals, viscoelastic effects can often be ignored. Metals, woods, plastics and biological tissues at high temperatures generally exhibit significant viscoelastic properties which cannot be neglected.
In addition to rubber bands, the elastic behavior is also demonstrated in springs. The more a spring is compressed, the more force is required to hold it there. Springs are called linear if doubling the amount of compression will require twice the force. While it may not be apparent to the eye, metals are linearly compressed or stretched when forces are applied. Elastic materials quickly return to their original size when all forces are removed.
Purely viscous behavior can be understood in how honey responds to stresses due to gravity. Honey can be poured from a jar, but it moves very slowly. This results because the internal stresses between the molecules increase with the relative velocity between the molecules. Faster motion of molecules is met with greater resistance to that motion. Viscous materials exhibit a time-dependent response to strain.
James Clerk Maxwell, Scottish physicist and mathematician, has devised a model to describe the phenomenon of viscoelasticity. He uses a spring for springy effects and a dashpot, or device that resists motion based on its speed, for viscous effects. A car’s suspension system uses this same process using dashboard shock absorbers. Large strains in the system are resisted by springs, while rapid changes in strain are resisted by dashpots. Viscoelasticity is also commonly modeled using electrical circuits.
Other parts of viscoelasticity are the effects of creep and stress relaxation. Creep is when a material tends to slowly yield, or deform, when subjected to a force for a long time. Engineers must account for creep when designing buildings, as creep can cause materials to weaken to the point of failure. A related effect, the stress relaxation phenomenon, refers to a reduction in internal stress for a material held in a particular shape.
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