Elastic Deformation
Viscoelastic property characterization governs how paperboard behaves under sustained mechanical loading during converting operations like creasing and die cutting. Board mills deploy the kelvin-voigt model to predict time dependent creep compliance in multilayer folding boxboard when stacks sit under heavy compression inside warehouse racking. Pure elastic response happens instantly upon stress application while viscous damping delays full strain development until internal polymer networks rearrange themselves fully.
Spring elements simulate instantaneous elastic deformation while dashpot components represent internal fluid friction within cellulose fibre bonds. Retarded elastic strain accumulates gradually because moisture plasticizes hemicellulose matrices and slows down dimensional stabilization across corrugated flutes.
Viscous Damping
Creep recovery rates dictate whether converted blanks warp or maintain flat geometries after leaving the printing nip. Engineers apply the kelvin-voigt model during finite element analysis to simulate stress relaxation profiles in high speed flexographic printing presses. Parallel coupling between elastic springs and viscous dashpots prevents infinite strain velocities when rollers apply transient loads onto moving webs.
Mathematical formulations balance applied traction against internal resistance forces by summing spring tension and dashpot velocity gradients into a single differential equation. Thermal fluctuations alter damping coefficients because higher ambient humidity decreases apparent viscosity inside cellulose structures and accelerates permanent deformation.
Relaxation Spectrum
Viscoelastic models fail to capture permanent plastic flow because the dashpot component lacks a yield stress threshold required for permanent set calculations. Packaging designers combine multiple kelvin-voigt units in series to simulate broad relaxation spectra observed across recycled linerboard containing mixed pulp grades. Creep testing protocols measure time dependent strain under constant tensile stress to calibrate retardation times for specific paper weights.
Material constants derived from these empirical curves allow converting lines to optimize tension control settings and prevent web breaks during high speed winding.
