Peeling angle effect on soft adhesive: Mixed-mode CZM considering fibrillation

Soft adhesive has gained broad application in flexible electronics and biomedicine. Because the soft adhesive layer is frequently subjected to peeling load, it is critical to investigate the mixed-mode effect on the cohesive failure of the soft adhesive layer. In this paper, a mixed-mode CZM considering the fibrillation as well as the shear flow of the soft adhesive layer has been proposed, and shows a better agreement on the experimental data compared to the bilinear CZM. The complex evolution of the mode-mixity with the peeling angle, which is difficult to be experimentally investigated, can also be well characterized. The soft adhesive layer exhibits the mode-I dominating failure at the large peeling angle due to the significant fibrillation, indicating that its adhesive performance can be well correlated with that under the probe-tack test. The mixed-mode effect has a significant impact on the adhesive performance of the soft adhesive layer at the small peeling angles, and the mode-mixity varies dramatically with the peeling angle. The parametric study reveals that the failure mode of the soft adhesive layer can be changed with the material properties. When compared to the material property of the soft adhesive layer, decreasing the adherend stiffness results in a considerable change in the cohesive failure mode from mode-I failure to mixed-mode failure. The proposed CZM is a promising approach for describing the mixed-mode cohesive failure of the soft adhesive layer during the peeling test.