Question

Precisely explain the following subject.

Shear storage and shear loss moduli.

Answer 1

The storage and loss modulus tell you about the stress response for a visco-elastic fluid in oscillatory shear. If you impose a shear strain-rate that is cosine; a viscous fluid will have stress proportional to the shear strain-rate (Newtonian) an elastic solid will have stress proportional to the shear strain (sine - integral of cosine). A visco-elastic response will be a mixture of the two. The storage modulus is the elastic solid like behavior (G') and the loss modulus is the viscous response (G''). These will cross-over when the frequency is equal to the reciprocal relaxation time.