The tensile mechanics of creped fiber networks: Effects of interfacial-delamination, buckling, and damage

Paper products, like tissue paper, are composed of bonded wood fiber networks. Dry creping is an industrial process used in tissue manufacturing. In this process, a wet paper sheet (web) is adhered to a high-speed metal dryer (substrate). The dried sheet is then scraped off against a stationary metal blade, leading to web–substrate debonding, sheet folding, and damage caused by the rupture of interfiber bonds. This process creates a microfolded structure, leading to a nonlinear tensile response and high failure strain, while sheet-damage results in sheet de-densification (through thickness explosion). Based on the visualized creped structures, creped sheets are classified as shaped-bulk (folding-dominated) or explosive-bulk (damage-dominated). While factors affecting sheet-folding have been studied extensively, the effects of sheet-damage on structural and tensile properties have not been previously studied. Using a Discrete Element Method (DEM) to model low grammage fiber networks, we simulate creping with a bilinear elastoplastic fiber model. We demonstrate that altering sheet–substrate bond (adhesive) properties relative to interfiber bonds shifts creping from shaped-bulk to explosive-bulk. Signatures of the above two creping modes are identified. Shaped-bulk sheets exhibit fewer interfiber bond ruptures, a higher degree-of-folding (waviness), and less through-thickness explosion, while explosive-bulk sheets show the opposite traits. During tensile deformation, bending dominates initially, followed by an increased axial deformation near failure as unfolding occurs. The transition from shaped-bulk to explosive-bulk creping shows an initial increase in stiffness followed by a decline, and a gradual then rapid, decrease in tensile strength.