Dynamic Strain Rate Modeling for Multi Ply Boxboard under Rapid Compression
Dynamic strain rate modeling predicts multi-ply boxboard Z-direction compression and interlayer shear collapse during high-speed converting and package drops.
Strain Hardening
Mechanical Resistance
Molecular reorganization within the crystalline lattice of a polymer or metallic substrate causes a permanent increase in yield strength after plastic deformation. This process, strain hardening, occurs when dislocations accumulate and interact within the material structure, creating internal barriers that hinder further movement of the atomic planes. Converting operations like high tension slitting or deep drawing utilize this effect to increase the final hardness of a stock beyond its initial factory state.
The phenomenon persists until the material reaches its ultimate tensile strength, at which point localized necking begins to compromise the structural integrity.
Deflection Limits
Engineering specifications for paperboard packaging account for this property during the scoring and folding phase of manufacturing. A carton blank experiences localized cold working at the fold lines, where the fibers undergo extreme deformation to allow for a permanent crease. Controlled hardening prevents the board from rebounding or tearing prematurely under the stress of rapid folder-gluer operation.
Designers calculate the necessary ductility to ensure the material accommodates this change without losing its primary function as a barrier or structural container.
Thermal Sensitivity
Higher temperatures during production accelerate the recovery of the crystalline lattice, effectively negating the gains in strength acquired through previous deformation. Annealing cycles intentionally reverse the effects of cold working to restore malleability for subsequent forming operations. High speed processing environments often generate sufficient heat through friction to induce localized softening, which reduces the effective load bearing capacity of the processed sheet.
Consistent control of machine speed relative to material heat dissipation remains the only method to maintain a stable temper throughout the entire batch.
Polymer Film Micro Fracture Mechanisms under High Strain Shear in Folding Boxboard Creases
High strain shear during boxboard creasing causes polymer film micro fractures when local elongation exceeds film yield capacity along the outer bend radius.