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.
Mechanical Anisotropy
Directional Variance
Paper and paperboard exhibit different physical strength values when measured along different geometric directions of the sheet. This property is known as mechanical anisotropy, and it is a fundamental characteristic of all machine-made papers. This variation must be managed to ensure consistent folding and printing results.
Fibre Alignment
During production on a paper machine, the flowing slurry of water and fibres is deposited onto a moving wire that aligns the fibres parallel to the direction of travel. This creates the machine direction, which has much higher tensile strength and stiffness than the cross direction. The mechanical anisotropy is quantified as the ratio of the strength in the machine direction to that in the cross direction.
A high ratio indicates that the board is highly oriented and will tear easily in one direction while resisting tears in the other. Controlling the speed of the slurry jet relative to the wire speed allows operators to adjust this ratio.
Converting Response
Package designers must align the creases and folds of a carton with the fiber orientation of the board to prevent cracking. The mechanical anisotropy dictates that creases made parallel to the machine direction are easier to fold than those made in the cross direction. If this alignment is ignored, the folding resistance can vary, which causes failures in high-speed packaging machines.
This directional sensitivity also influences how the finished box resists bulging under load.