INVESTIGATION ON THE INTERFACIAL ADHESION OF A CYLINDRICAL FIBRILLAR ON A SUBSTRATE UNDER THE COUPLING EFFECT OF TENSION AND TORQUE

Inspired by the reversible adhesion of gecko seta, theoretical and numerical models of an elastic cylindrical fibrillar on a rigid substrate are established in the present paper, in which the coupling effect of tension and torque as well as the radius of the fibrillar on the interfacial adhesion is considered. It is found that when the fibrillar is subjected to the coupling effect of tension and torque, there also exists a critical radius of the fibrillar, below which the interfacial stress can reach the theoretical strength uniformly and the stress concentration at the contact edge vanishes, leading to the phenomenon of flaw insensitivity. When the radius of the fibrillar is larger than the critical value, the detachment of the interface between the fibrillar and substrate occurs in the form of crack propagation. The critical radius of the fibrillar under the coupling effect of tension and torque decreases with increasing the applied torque, but it is smaller than the case of pure tension and is larger than the case of pure torque. It can be concluded that if a fibrillar can reach the optimal theoretical adhesion strength under the pure tensile load, it could be easily detached under the coupling effect of tension and torque due to the different interface failure modes under different loading forms. The pull-off force decreases with the increase of the applied torsion load. The theoretical results are well consistent with the numerical ones. The obtained results in the present paper can be further applied to disclose the mechanical mechanism of the reversible adhesion of gecko seta through applying pure tension to achieve strong attachment and applying coupling effect of tension and torque to achieve easy detachment.