The phase angle of a material provides a useful insight into its viscoelastic properties: 8 = 0° for a perfectly elastic solid, 8 = 90° for a perfectly viscous fluid, and 0 < 8 < 90° for a viscoelastic material. The more elastic a material (at a particular frequency), the smaller the phase angle and the lower the amount of energy dissipated per cycle.
It is often more convenient to express the rheological properties of a viscoelastic material in terms of its modulus rather than its compliance (Whorlow 1992). The complex, storage, and loss moduli of a material can be calculated from the measured compliances using the following relationships:
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