Abstract
Continuous approaching and detaching displacement usually occurs in an adhesion test. Here, we found a transient adhesion force at the end of a non-fully detached contact. This force occurred when the nominal detaching displacement was less than the traditional quasi-static theory predicted zero force point. The transient adhesion force was ascribed to interfacial adhesion hysteresis, which was caused by the cracking process of the contact and the deformation competition between the sphere and supporting spring. Results indicated that the testing of adhesion can be significantly affected by different combinations of stiffnesses of the contact objects and the supporting spring cantilever. This combination should be carefully designed in an adhesion test. All these results enabled increased understanding of the nature of adhesion and can guide the design of adhesive actuators.
Highlights
Adhesion widely exists in nature and greatly affects the activities of humans, creatures, and machines
When the first detaching displacement was larger than a certain value, F′ad in the two-step detachment (TSD)
We have presented that the value of the F′ad in TSD may appear as a positive transient force
Summary
Adhesion widely exists in nature and greatly affects the activities of humans, creatures, and machines. The two theories were subsequently integrated into the Maugis– Dugdale (MD) theory to incorporate the two extreme situations of material with compliant large radius and rigid small radius[6,7] For polymers, such as polydimethylsiloxane (PDMS) and polyurethane (PU), the adhesion was strongly related with the detaching velocity[8]. A typical adhesion test analysis usually only considers the deformation of the sphere. In a real adhesion test, the loading is usually conducted via a cantilever, whose deformation is generally not discussed. The phenomenon was ascribed to the interfacial viscoelasticity of the contact and the deformation compatibility between the sphere and the cantilever These results can provide additional insights on the comprehension of the tested adhesion, and can guide the selection of cantilever spring stiffness and a proper design of adhesion test procedure
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