Viscoelasticity - Current

A mechanical property that combines elastic and viscous properties. In a normal elastic body, when a certain strain is applied, a constant stress is uniquely determined, and in a viscous fluid, the stress is uniquely determined for a certain strain rate. However, some systems, especially those containing polymers, have a stress-strain relationship that cannot be expressed by either of these. For example, even if a constant strain is applied, the stress may decrease over time (stress relaxation), or the strain may increase (creep) even if a constant stress is applied. The Maxwell model is a model that represents stress relaxation properties, and the Voigt model represents creep properties. In addition, after a steady flow, even if the strain is stopped, the stress does not immediately become 0, but gradually decreases. These are typical viscoelastic phenomena. When the relationship between strain and stress is linear, it is called linear viscoelasticity. Linearity holds for small strains (stress), and phenomenological analysis methods have been established. On the other hand, large deformations such as rubber, non-Newtonian flow, and normal stress effects are nonlinear viscoelasticity. The treatment of stress-strain as a tensor quantity has been developed mainly in the analysis of nonlinear viscoelastic phenomena. The study of viscoelasticity is a major area of ​​rheology, and linear viscoelasticity is also used as a means of elucidating molecular motion. [See other terminology] Complex modulus

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

弾性的特性と粘性的特性を合わせもつ力学的特性．通常の弾性体では，あるひずみを与えると一義的に一定の応力が定まり，粘性流体ではあるひずみ速度に対して一義的に応力が定まる．しかし，ある種の系，とくに高分子を含む系ではこのどちらでも表せない応力-ひずみ関係をもつ．たとえば，一定のひずみを与えていても応力が経時的に減少(応力緩和)したり，一定の応力を与えてもひずみが増していく(クリープ)ことがある．応力緩和特性を表すモデルとして，マクスウェル模型があり，クリープ特性を表すフォークト模型がある．また，定常流動後，ひずみを止めても応力がただちには0にならず，徐々に応力が減少していく現象がみられる．これらは典型的な粘弾性現象である．ひずみと応力との間の関係式が線形であるとき線形粘弾性という．微小なひずみ(応力)では線形性が成り立ち，現象論的解析法が確立されている．一方，ゴムなどの大変形，非ニュートン流動，法線応力効果などは非線形粘弾性である．応力-ひずみをテンソル量とした扱いが，とくに非線形粘弾性現象の解析を中心に展開されている．粘弾性の研究はレオロジーの主要な分野であるとともに，線形粘弾性は分子運動解明の手段としても用いられている．[別用語参照]複素弾性率

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