Viscoelasticity: Difference between revisions

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[[Image:Non-Newtonian fluid.svg|thumb|350px| Different types of responses {{nowrap|(<math>\sigma</math>)}} to a change in strain rate {{nowrap|(<math>d\varepsilon/dt</math>)}}]]

Depending on the change of strain rate versus stress inside a material, the viscosity can be categorized as having a linear, non-linear, or plastic response. When a material exhibits a linear response it is categorized as a [[Newtonian material]]. In this case the stress is linearly proportional to the strain rate. If the material exhibits a non-linear response to the strain rate, it is categorized as [[non-Newtonian fluid]]. There is also an interesting case where the viscosity decreases as the shear/strain rate remains constant. A material which exhibits this type of behavior is known as [[thixotropy|thixotropic]]. In addition, when the stress is independent of this strain rate, the material exhibits plastic deformation.<ref name=Meyers/> Many viscoelastic materials exhibit [[rubber]] like behavior explained by the thermodynamic theory of polymer elasticity.

Some examples of viscoelastic materials are amorphous polymers, semicrystalline polymers, biopolymers, metals at very high temperatures, and bitumen materials. Cracking occurs when the strain is applied quickly and outside of the elastic limit. [[Ligament]]s and [[tendon]]s are viscoelastic, so the extent of the potential damage to them depends on both the rate of the change of their length and the force applied.{{Citation needed|reason=maybe https://doi.org/10.1114/1.1408926| date=February 2017}}