Debonding and buckling of a thin short-fiber nonwoven bonded to a rigid surface and its application to the creeping process

In this dissertation, debonding of a thin surface film from a rigid surface with debonded portion of the thin film undergoing buckling and postbuckling was studied both analytically and experimentally. The research is motivated from the creping process in tissue paper manufacturing, and it is turned out to be a general failure problem of thin surface films. The study is consisted of five parts: an experimental study with a laboratory creping simulator; a stress analysis of the thin film-adhesive-rigid surface structure; buckling and postbuckling analysis of the debonded film under unilateral constraint; an analytical model of debonding and buckling of a thin surface film; and a finite element simulation through ABAQUS.; The laboratory creping simulator described by Ramasubramanian et al (2000) was employed in the experimental study and was improved through introducing an adhesive coating mechanism. The Young's modulus and tensile strength of the creped paper, together the creping wavelength and creping force were examined to measure the creped paper qualities under different conditions.; A stress analysis was then presented in which the adhesive was modeled as an elastic layer. A simplified analytical model to the debonding problem was obtained by using the Euler buckling criterion of the debonded portion of film. Numerical study showed that the model could grasp most of the main features of the process, however ignoring the unilateral constraint for the film buckling brought about some unsatisfactory predictions. A buckling and postbuckling analysis was then conducted. Numerical results showed that the debonded film undergoes a contact and snap-through buckling sequence, and under the rigid unilateral constraint, the buckling force can be four times as large as the one when the constraint is released. Once the structure snaps through, the buckling force drops greatly, therefore cease of debonding propagation can be expected.; An improved analytical model of the thin film debonding with end shortening as the external load was then presented. Numerical analyses were carried out and the results agree well with experimental data. The effects of structural and process parameters, such as the film properties, the adhesive properties and the creping angle were discussed in detail.; A finite element analysis through ABAQUS was also conducted. The simulation results verified the observations from the experimental study and the assumptions used in the analytical study. FEA results and the analytical predictions were in satisfactory agreement. Stress intensity factors during the crack propagation were examined, which showed that under the compression of a blade, the thin film mainly undergoes a shear failure. The crack starts to propagate once KII reaches a certain value and then KII decreases greatly. The two crack surfaces typically are in closing mode before the debonded film buckles. After buckling, KI increases however is small and bounded. The results well explained the crack propagation and rest in this process.; The models and results presented in this dissertation research can be expected to have various applications.