Rheological Response
Viscoelastic constitutive equations represent time dependent stress strain behavior in polymeric and fibrous substrates under mechanical loading. The burgers model combines a Maxwell element and a Kelvin Voigt element in series to simulate immediate elastic deformation and delayed viscous flow in paperboard structures. Print convertors and board mills apply this four parameter formulation to predict container creep under prolonged compressive loads in warehouse storage.
Mathematical validity ceases when stress levels exceed the yield point where structural fiber fracture occurs.
Creep Mechanism
Mechanical deformation in paper structures under constant stress displays distinct instantaneous and time dependent strain components. When an external compression load impacts a corrugated board stack, the instantaneous elastic spring elements respond immediately without energy loss. Over extended storage periods, the Voigt dashpot retarder delays strain accumulation while the Maxwell dashpot permits steady irreversible creeping flow.
Higher relative humidity accelerates dashpot displacement within the cellulose matrix, multiplying overall strain rate. Structural failure occurs when cumulative creep strain degrades column stiffness below critical buckling thresholds.
Stacking Boundary
Storage performance calculations for heavy duty shipping cartons rely on accurate spring constant and viscosity parameters derived from creep testing protocols. Standard short term compression testing fails to isolate delayed viscous flow, making long term load predictions inaccurate without creep modeling parameters. Testing protocols determine transient compliance parameters by measuring board deflection over defined time intervals at controlled temperatures.
Converting plants adjust box compression safety factors based on calculated viscoelastic relaxation curves.
