Impact-Induced Adhesion Degradation in Gecko-Inspired Fibrillar Adhesive Units

Gecko-inspired fibrillar adhesives are promising for impact-contact applications, yet the mechanism underlying adhesion degradation after a single impact event remains unclear. Existing studies have primarily focused on micropillar buckling as a possible degradation mechanism, whereas whether additional degradation pathways exist during impact remains unresolved. To address this issue, impact and quasi-static adhesion experiments were conducted on four fibrillar adhesive units (FAUs) with identical micropillar adhesive layers but different backing layers. Comparative analysis of mechanical responses and interfacial images indicates that, for the present short-pillar FAUs, tensile loading during post-impact rebound induces local interfacial fracture, which serves as the primary degradation pathway. Micropillar buckling alone cannot explain the observed degradation. Backing-layer-related compliance and dissipation suppress rebound and reduce the driving force for interfacial fracture, thereby mitigating adhesion degradation. A reduced-order rebound-stage model based on fracture mechanics qualitatively reproduces the adhesion-degradation trend and backing-dependent response, further supporting the fracture-based interpretation. Finally, transient buckling and fracture-activation analyses reveal that the applicability of this interpretation depends jointly on micropillar aspect ratio and intrinsic adhesion energy, with buckling emerging as a potential competing mechanism as the aspect ratio increases.