These inputs are used to specify the mechanical properties of the material (matrix + fibers/filler in the case of composite material) according to the five standard coefficients used to describe a viscoelastic material.
A viscoelastic model must be used when stress relaxation data is required as a function of time and temperature. For example, a part under load and subject to a heating cycle can deform as a stress relaxation. This model will account for variation in properties in the flow direction and transverse to the direction of flow.