= Boltzmann superposition
{c}
{title2=$\sigma(t)=\int_{-\infty}^tG(t-s)\dot\gamma(s)\,ds$}
In time-translation-invariant <linear response>, each infinitesimal past strain step contributes its amplitude times the elapsed-time <relaxation modulus>. Adding those causal contributions gives the displayed stress-history integral for shear. An equivalent formulation convolves the <creep compliance> with stress increments. This constitutive law assumes sufficiently small strains about a specified equilibrium or relaxed state; nonlinear deformation, aging and evolving material structure can invalidate that simple superposition.
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