A Computational Mechanics Model for the Delamination and Buckling of Paper during the Creping Process

The manufacture of low density paper such as tissue and towel utilizes the creping process that consists of adhesively bonding the paper in wet state onto the surface of a smooth drying cylinder and scraping it off with a blade once dried. This intricate failure and fracture process however is still not thoroughly understood and stands on the way of enhancing the production efficiency and reducing the development and testing costs before commercial production. The research on creping process by this dissertation has comprehensively reviewed the most relevant literature and ideas for this problem and has developed a capable method in understanding the relationship between control parameters and the creped paper's quality.;In this dissertation, a mechanics of materials description of the creping process is presented. Based upon previous experimental observations, the mechanism of this creping process is proposed as a periodic debonding with certain fracture and failure criteria applied and a repeating delamination buckling sequence of elastic thin film. The study has concluded the delamination and buckling as the basic fracture and failure aspects in creping process and uses them to create analytical creping model.;The stress analysis as the pre-investigation and foundation of fracture energy calculations later is described first. Data from experiments about creping length versus creping angle can be reproduced with the same behavior qualitatively by applying a reasonable set of values as input parameters to the stress criterion based calculation. Parametric study shows the adhesive shear strength and the sheet stiffness most affect the creping length and the force required to crepe or the creping force. The stress analysis provides some guidance in understanding the creping process primitively. Its limitations include the lack of a satisfactory way to measure the adhesive shear strength and inability to address the buckling and post-buckling behaviors in a continuous creping process.;By selectively using the solution of stresses in adhesive, a computational one-dimensional fracture mechanics model is developed for one creping length cycle. This fracture energy model, with fracture energy criteria applied, calculates strain energies and energy release rates of mixed-mode in different delamination buckling stages, and approaches to a desired creping length in an iteration manner. Buckling strain criterion is also employed to determine the buckling state of paper. Numerical calculations of the fracture model generate the delamination history in one creping length, showing the continuity and discontinuity phenomena in delamination procedure. Mode I and mode II effects are demonstrated: creping length decreases as the critical energy release rates increases; creping length decreases asymptotically with increase in critical energy release rates. The non-linear relation between the fracture criteria values and creping length indicates that creping length not only reduces its value to smaller one but also reduces its sensitivity to critical fracture energies, as the critical fracture energies increase; the creping length would become very large if critical fracture energy in any mode decreases to a very small value. In the parametric study, results show that the effects of creping blade angle, adhesive elastic modulus cause a decrease in creping length for increasing values of these parameters whereas the effects of paper thickness and paper elastic modulus show an increase with increase in the parameters.;The assumptions and results of fracture energy model are consistent with the previous research and approved by high speed camera video observations and prior experimental data. This fracture energy method developed in this dissertation has significantly extended the calculation's ability for creping problem and can satisfactorily and efficiently predict the paper's creping results which in turn could optimize the crepe paper production in complex practical conditions.