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Fig. 2. Dynamic analysis of mechanical behavior quantifies the elastic and viscous
behavior of materials. (A) The phase lag (
) is the displacement of the
sinusoidal stress response (gray) to a tiny applied strain oscillation
(black). The degree to which the peak amplitude of the stress response curve
is in phase with that of the applied strain oscillation measures elasticity
while the viscosity is measured by the degree to which the stress response
90° out of phase with strain. (B) Vector relationship between dynamic
material properties are illustrated by the solid line vectors. Dynamic
stiffness (E*) is determined by the storage modulus
(E') and the loss modulus (E''). Tan (loss
tangent) defines the relative viscous and elastic behavior of the material.
E' and E'' can change independently of one
another and of tan. The dotted line vectors illustrate an example where
increases in both E' and E'' result in a decrease
in tan.
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