Molecular dynamics simulations of the interface friction behavior between fiber-reinforced polymer pile and sand

Abstract

The interfacial friction performance of the fiber-reinforced polymer (FRP) pile-sand interface plays an essential role in determining the load capacity of the foundation. It is necessary to identify its friction behavior in the marine environment due to the unique pile-soil interaction characteristics, which have not been well established at the nanoscale. The cross-linked epoxy resin and crystalline silica substrate are utilized to investigate the nanoscale friction characteristics at different normal stresses and sliding velocities in the dry, pure water, and salt water systems using the molecular dynamics (MD) simulation. The obtained coefficients of friction in three systems are ranked as dry > salt water > pure water systems. There is a tendency for the coefficient of friction to decrease with increasing normal stress, which is consistent with the experimental results. The interface roughness is validated by an analytical equation based on Archard’s elastic deformation friction theory. The increase in normal stress shortens the distance between the silica and the epoxy and increases the van der Waals force between the two layers, resulting in the increase of maximum friction force in three systems. The higher normal stress induces the more pronounced stick-slip motion of the silica substrate in the dry system, which can be reduced in the pure water system due to the lubrication effect of water, while the NaCl ions weaken the lubrication effect. On the other hand, the lubrication effect of the water molecules has more beneficial at lower sliding velocity because the diffusion of water molecules is more intense, which leads to the reduction of the amplitude of friction force in the stick-slip motion. By considering the effects of sliding velocity, normal stress, water, and NaCl ions, this study provides the fundamental insight for the friction process of FRP pile embedded in sand.