Experimental and modeling study on pull-off force of fibrillar adhesives

In recent years, the use of isotropic bionic fibrillar adhesives (BFA) in space non-cooperative target capture missions has become a research hotspot in the aerospace field. However, accurately evaluating the adhesion performance of these materials remains a critical challenge. To bridge this gap, we experimentally investigate the detachment behavior of two representative BFA types: mushroom-shaped fibrillar adhesives and flat-shaped fibrillar adhesives. The experimental results reveal that the critical detachment force (i.e. pull-off force) is significantly influenced by preload, detachment velocity, and detachment angle. Unlike the monotonic effects observed for preload and velocity, the detachment angle exhibits a non-monotonic relationship with the pull-off force. Specifically, as the detachment angle increases from 0° to 90°, the pull-off force first decreases and then increases. Further experimental validation and numerical simulations indicate that the equivalent bending moment induced by the pull-off force modulates the critical detachment angle-a phenomenon not reported in the existing literature. In addition, the fracture mode transitions from bilateral to unilateral crack propagation as the detachment angle decreases. Simulation results further demonstrate that the detachment angle alters the stress distribution at the adhesive interface, thereby affecting the crack propagation mode. Based on these findings, an approximate pull-off force model for BFA specimens is developed using linear elastic fracture mechanics, which incorporates the effects of preload, detachment velocity, and detachment angle. Following parameter identification, the proposed model accurately predicts the pull-off force for various loading conditions.