Strain Concentration
Non-uniform distribution of internal forces leads to specific zones where the material is more likely to deform or fail. Shear stress localization describes the concentration of sliding forces within a narrow band of the fiber matrix or at an interface between layers. This phenomenon often precedes the development of a full thickness tear or a delamination event in the board.
Converting Stress
Die cutting and creasing operations are designed to create clean edges and predictable folds. Controlled shear stress localization at precise points allows the board to bend without rupturing the surface liners. Failure to manage this distribution results in messy folds or uneven carton dimensions.
Material Resilience
High quality boards are engineered to resist unintended localization by having a consistent fiber formation and uniform thickness. If shear stress localization occurs in the wrong place, it can cause a shipping container to buckle under a load that it should technically be able to support. This is particularly problematic in humid environments where the moisture weakens the fiber network and allows forces to concentrate more easily.
Using chemical sizing and mechanical refining helps to toughen the matrix and distribute the stress across a wider area of the sheet.
