Evolution of interfacial adhesion force in dynamic micromachines due to repetitive impact loading

A contact-mode surface micromachine was used to study the effect of repetitive impact loading on the evolution of the adhesion force at sidewall contact interfaces. Low and stable adhesion force was encountered during the initial stage of impact testing (run-in phase). A surface degradation phase occurred subsequently in which the adhesion force increased logarithmically with impact cycles. The experimental trend was used to derive a method for predicting micromachine failure due to excessive interfacial adhesion. High-magnification scanning electron microscopy did not reveal any modification of the surface topography even after 5.5×107 impact cycles, despite the significant enhancement of the adhesion force, attributed to the increase of the real contact area and the higher surface energy produced as a result of the removal of thin surface layers. The dominant surface degradation mechanisms are interpreted in the context of adhesion force measurements and microscopy images of the impacted surfaces.