Investigation of soil-soil and soil-FRP interfacial mechanical behavior using molecular dynamics simulations

Abstract

The use of fiber-reinforced polymer (FRP) in civil engineering has garnered significant attention due to its durability and cost-effectiveness. A crucial aspect of employing FRP in geotechnical engineering is understanding the soil-FRP interface, which is pivotal for the stability of FRP-related structural systems. Material deformations originate at the atomic scale, making them difficult to detect with traditional experimental techniques and continuum theory. Consequently, despite numerous macroscale experiments on the FRP interface, the underlying mechanisms remain unclear. Molecular dynamics (MD) simulations offer a powerful method for examining materials at the nanoscale by simulating atomic interactions. This study utilizes MD simulations to investigate the mechanical behavior at the soil-FRP interface. Atomistic models are constructed for silica (representing sand), clay minerals (representing clay), water films (representing lubricated conditions), and cross-linked epoxy (representing FRP). The main work of this research are: (1) Investigation of sand-sand interfacial rate-dependent friction behavior under dry and lubricated conditions. (2) Examination of sand-FRP interfacial tribological and rheological properties through friction and creep simulations. (3) Validation of the mechanical behavior of three typical clay minerals and examination of their interactions with FRP. (4) Development and validation of a coarse-grained model of clay minerals, considering face and edge interactions. (5) Development and validation of a coarse-grained model of cross-linked epoxy, further exploring the friction and creep behavior at the soil-FRP interface through mesoscale simulations. The all-atom simulations reveal that friction force is linearly dependent on normal load, increases with sliding velocity, and decreases with higher water content. The modified Amontons’ law effectively describes the friction behavior at the soil-epoxy interface. Creep simulations show that shear stress level affects creep characteristics, displaying primary, secondary, and tertiary (rupture) creep modes. Coarse-graining techniques are applied to scale the interface model from the nanoscale to the mesoscale, significantly increasing the simulation size and timestep. The outcomes of this research provide a deeper understanding of the interfacial behavior between soil and FRP, offering insights that can refine contact laws in micromechanics-based modeling approaches for soil-FRP structures, potentially improving the design and performance of geotechnical systems incorporating FRP.