Burgers material

A Burgers material is a viscoelastic material which consists of a Maxwell material and a Kelvin material in series. It is named after the Dutch physicist Johannes Martinus Burgers.

Given four rheological constants ${\displaystyle a_{1}}$, ${\displaystyle a_{2}}$, ${\displaystyle a_{3}}$, and ${\displaystyle a_{4}}$, the Burgers model has the constitutive equation

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