Effect of SiO 2 Nanoparticles on the Mechanical and Tribological Properties of Chopped Carbon Fiber-Reinforced Epoxy Composites

This study examines how SiO2 nanoparticle loading (0–2.0 wt.%) affects the coupled mechanical and tribological response of chopped carbon fiber-reinforced epoxy (CF/EP) composites. A matched composition series was evaluated by SEM, FTIR, XRD, tensile, flexural, notched-impact, and dry-sliding tests, together with comparative molecular dynamics (MD) descriptors. The 0.8 wt.% SiO2 formulation gave the best overall performance: tensile strength of 191 ± 15 MPa, flexural strength of 326 ± 15 MPa, impact strength of 143 ± 8 kJ/m2, and minimum friction coefficients of 0.183 ± 0.012 at 200 N and 0.208 ± 0.015 at 220 N. At this loading, the rougher and more tortuous fracture morphology, coincident FTIR/XRD changes, strength maxima, and friction/wear minima are consistent with more effective local stress transfer and matrix restraint. The SiO2-containing MD interface likewise shows a larger absolute adhesion-energy descriptor and lower epoxy-chain mean-square displacement, indicating stronger local attraction and restricted segmental mobility in the idealized model. At 1.0–2.0 wt.%, reduced mixture flowability and shorter particle spacing are associated with greater local heterogeneity and defect sensitivity, reversing the property gains. Thus, 0.8 wt.% provides the most favorable balance among interfacial reinforcement, processability, mechanical strength, and sliding wear resistance under the investigated conditions.