Generalised Viscous Models:
Maxwell and Kelvin models are too simple to represent the behaviour of real materials in an adequate way. These models allow a single time for relaxation or retardation. The real materials tend to behave as if they had several relaxation or retardation times due to the complexity of their structure.
Generalized Maxwell Model:
Several Maxwell elements in series generate the behaviour of the equivalent Maxwell model.
Several Maxwell elements in parallel represent instantaneous elasticity, elasticity slowed down with several retardation times and viscous flow.
Generalized Kelvin Model:
Like the Generalized Maxwell Models, these models arise from connecting several Kelvin models in series or parallel.
Standard Model:
It is made up by a spring in series with a Kelvin model. A spring, a dashpot and several Kelvin elements are disposed, so the total strain corresponds to the sum of each element strain. The spring produces an instantaneous strain, the Kelvin elements produce slowed down elasticity with multiple states of retardation.