Dynamic Z Direction Tensile Stress Propagation in Recycled Fibers during High Speed Creasing
High speed creasing generates Z-direction tensile stress waves that fracture short recycled fibers unless matrix clearance absorbs elastic strain energy.
Dynamic Stress Propagation
Force Transmission
Transmission of a rapid mechanical impact or shock wave through the fiber network of a paperboard sheet occurs at speeds dictated by the elastic modulus and density of the material. This phenomenon of dynamic stress propagation governs how paper reacts to sudden loads during printing and converting operations. If the sheet cannot distribute this energy quickly, localized failures or web breaks occur.
High speed presses create severe tension spikes that require rapid energy dispersion.
Material Behavior
Determination of the wave velocity utilizes ultrasonic pulse technology to track the movement of mechanical energy across the sheet. Under these conditions, dynamic stress propagation depends on the orientation of the wood fibers, being faster in the machine direction than in the cross direction. This directional difference arises from the alignment of cellulose chains and fiber to fiber bonds.
Structural Integrity
Protection of packaged goods during transit relies on the ability of the outer paperboard carton to absorb and distribute external impacts. When a carton is dropped, dynamic stress propagation transfers the kinetic energy away from the point of impact toward the corners and edges of the structure. If the propagation occurs too slowly, the localized force can puncture the board and damage the contents.
Packaging engineers design fluting and linerboard combinations to damp these shock waves, ensuring that the package retains its shape under sudden compressive loads.