Studying effects of interface surface roughness, mean particle size, and particle shape on the shear behavior of sand-coated CFRP interface

Carbon fiber-reinforced polymer (CFRP) composites can be considered an ideal alternative for conventional structural elements due to their superior benefits, such as high durability, satisfactory strength, and cost-effectiveness. This study is focused on interface shear behavior between sand-coated CFRP [spark plasma sintering CFRP (SPSCFRP)] and different types of sand with varying mean particle sizes (D50), and particle shapes [well-rounded (glass beads or GB), well-angular (glass powder or GP), and sub-rounded to sub-angular (natural sand)] under two levels of initial relative density. Four types of SPSCFRP surfaces with different levels of surface roughness, ranging from very smooth (VS) to highly rough (HR) were selected to perform interface shear tests. Analysis of sand-SPSCFRP data highlights an increase in surface roughness, mean particle size, angularity, and initial relative density resulting in mobilization of higher peak and critical-state friction angles. Rough SPSCFRP shows the most effective performance of the tested configurations in interface shear response. A critical value for normalized roughness (Rn) is observed (0.2≤Rcr≤0.5), within which the highest value of peak and critical-state friction angles is obtained. A well-pronounced post-peak reduction in shear stress of interfaces with Rn≥ 0.3 is observed. The peak and critical-state friction angles of sand-rough SPSCFRP interfaces are 15–32% and 11–32% higher than those of sand-CFRP interfaces, respectively. Given the same surface roughness and mean particle size, smaller peak and critical-state interface friction angles are mobilized for well-rounded sand than for well-angular sand. For the sand-SPSCFRP and sand-CFRP interfaces, the sand-structure design ratio (D.R.) ranges between 1.04 and 1.16 and 0.79–0.96, respectively. The average efficiency factor (E.F.) of the sand-SPSCFRP surfaces are 1.02 and 1.06, respectively, for medium-dense and dense specimens, while this value is much lower for sand-uncoated CFRP (∼0.8).