Rheological Phase
Rheological phase identifies the first stage of time dependent deformation that occurs immediately after a constant load is applied to a material. Within a paper structure, primary creep involves the rapid but slowing movement of fibers as they settle into a new equilibrium. This initial response is largely recoverable if the load is removed quickly, though some permanent set usually remains.
It represents the transition from elastic behavior to the more stable secondary phase.
Stacking Behavior
When a corrugated box is placed at the bottom of a warehouse stack, the material undergoes primary creep as it adjusts to the weight of the containers above. The rate of deformation is high at first but decreases as the internal structure of the paperboard compacts and the fibers distribute the stress. Precise environmental control is necessary because high humidity accelerates this movement and leads to earlier failure.
This phase typically lasts from a few minutes to several hours depending on the magnitude of the stress.
Collapse Threshold
Collapse threshold is reached if the deformation during this early stage suggests that the material is underdesigned for the intended load. If the strain does not slow down, the structure will bypass the stable phase and move directly to a catastrophic collapse.
