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Definition of Viscoelasticity
A viscoelastic material is characterized by possessing both viscous and elastic behavior. What this means exactly is best illustrated in figure below, which shows how various types of materials behave in the time domain. For a slab of material with a cross-sectional area, A, and a thickness, T, subject to cyclic loading, F(t), the corresponding response is given by the displacement function, x(t). The cyclic stress on the sample material is found by dividing the input load by the cross-sectional area, and the resulting cyclic strain on the material is found by dividing the displacement by the thickness.
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