Adhesive toughness and instability in bonded heterogeneous films

Abstract

Peeling of bonded films has applications to many engineering as well as biological systems. While significant prior research describes the mechanics of peeling of bonded homogeneous films, the studies on bonded heterogeneous films were relatively rare. Recently, bonded heterogeneous films have gained attention due to their potential for increasing the load required to propagate a debond without altering the adhesion characteristics of the interface. Although, it is known that the bending rigidity of a bonded heterogeneous film has significant influence on the adhesive toughness, the potential instability during the peeling process does not appear to be fully studied in the literature. In this paper, the heterogeneous film is simplified as a composite Euler-Bernoulli beam in a finite deformation framework. A semi-analytical model based on cohesive zone fracture description is developed, where both displacement-controlled and force-controlled loading conditions are considered. The semi-analytical solution is validated against experimental data in literature as well as finite element simulations. The study also addresses the transfer and distribution of energy in the film structure, and the variation of fracture process zone size with changing bending rigidity of the film. Additionally, comparisons are made between thickness enhancement and material enhancement to improve the peel performance of a heterogeneous film. The developed model provides insight into the mechanics of peeling, and it faithfully captures the instability often observed during debonding of heterogeneous films. The unstable load response to peeling can be leveraged to design systems where fracture toughness and overall reliability is improved without modifying the interface.