Maximum Loss Factor is a special damping model which can be used in frequency as well as in time domain studies. The model approximates a target loss factor, ηmax, when the material is loaded at a given reference frequency,
fref. The formulation of this damping model is very similar to the
Standard Linear Solid (SLS) viscoelastic model with both deviatoric and viscoelastic strains. The SLS model is often represented with a spring-dashpot analogy where an additional branch consisting of a spring and a dashpot are coupled in parallel to the parent material model (for instance a
Linear Elastic Material). The loss factor is defined as
where G'' and
K'' are the shear and bulk loss moduli, and
G' and
K' are the shear and bulk storage moduli, respectively. The parallel coupled SLS branch adds an inelastic stress,
Sq.
Here, the auxiliary viscous strain, εv, in the SLS branch follows the relation
Here G and
K are the equivalent shear and bulk moduli of the parent material model, for instance a
Linear Elastic Material. The loss factor is then defined from the frequency-dependent expression
and 
where 