Molecular dynamics study on quartz-indenter shape and depth effects in epoxy interfacial mechanics

Abstract

The interfacial mechanical behavior between epoxy and quartz at the microscale remains inadequately understood. The quartz-indenter shape and indentation depth (hc) effect on epoxy interfacial mechanical behavior has been investigated through molecular dynamics (MD) simulation of nanoindentation and nanoscratching. This work employs two Vickers-type and four spherical indenters with varying radii (R) under different hc conditions, revealing the fundamental deformation mechanisms at the microscale. The reduced modulus and Young's modulus of epoxy resin obtained from MD simulations align well with experimental results. Key findings include: (1) during MD nanoindentation, the elastic-plastic deformation of epoxy and the indentation force increased with rising R and hc, due to the enhanced interfacial interactions between epoxy and quartz. (2) A negative indentation force was observed during the unloading stage, attributed to adhesion effects. (3) In MD nanoscratching, the forces in the y- and z-directions increased with rising R and hc, which was due to a greater contact zone and elastic–plastic deformation. (4) The friction coefficient could increase with rising indentation depth, exceeding 1.0 at hc/R > 0.75. (5) The classic Coulomb's law of friction was not applicable at the microscale or nanoscale. These results provide a foundation for developing interfacial models at the macroscopic scale for engineering applications.