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EDEV‐1

EDEV‐2

EDEV‐3

 EDEV‐1: Materials exhibiting “linear elastic, linear delayed elastic, and linear viscous” behavior. Ordinary soda‐lime–silica glass used as structural materials in buildings and cars belongs to this class.

 EDEV‐2: Materials exhibiting “linear elastic, linear delayed elastic, but nonlinear viscous” response. As an example, natural water ice (H2O) on Earth's surface belongs to this class.

 EDEV‐3: Materials exhibiting “linear elastic, nonlinear delayed elastic, and nonlinear viscous” response. Most metals and alloys belong to this class of materials.

It should be noted that, in this book, we will use the term “viscoelasticity” in a general sense to refer to time‐dependent mechanical response, irrespective of linear or nonlinear dependence of flow on stress.

There is confusion as to the use of the term “viscoelastic.” Traditionally, this term is often used without paying any critical attention to the details on the mechanisms involved in producing the inelastic (other than linear elastic) deformation. Consequently, terms such as “viscoplastic” appeared frequently in the engineering literature. The classical viscoelastic material (obeying linear elastic, linear delayed elastic, and linear viscous response) is equivalent to EDEV‐1 type of material. Naturally, the term “viscoelasticity” is loosely used without any clarifications to the stress dependence of delayed elastic and viscous components of deformation. Arguably, EDEV‐1, EDEV‐2, and EDEV‐3 materials can also be classified into terms such as “viscoelastic‐1,” “viscoelastic‐2,” and “viscoelastic‐3,” respectively; however, this may create confusion and it is better to avoid such uses.