Dynamic modulus is the ratio of stress to strain under vibratory conditions (calculated from data obtained from either free or forced vibration tests, in shear, compression, or elongation). It is a property of viscoelastic materials.
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Viscoelasticity is studied using dynamic mechanical analysis where an oscillatory force (stress) is applied to a material and the resulting displacement (strain) is measured. [1]
Stress and strain in a viscoelastic material can be represented using the following expressions:
where
The storage and loss modulus in viscoelastic solids measure the stored energy, representing the elastic portion, and the energy dissipated as heat, representing the viscous portion [1]. The tensile storage and loss moduli are defined as follows:
Similarly we also define shear storage and shear loss moduli, and .
Complex variables can be used to express the moduli and as follows:
where is the imaginary unit.