CNF Effects in CFRP Under HCl/NaOH: Drilling Parameters, Delamination Maps, and Mechanical Performance

In this study, the tensile, three-point bending, and drilling behaviors of carbon/epoxy (CFRP) and CNF-reinforced carbon/epoxy composites were compared after exposure to HCl (acidic) and NaOH (basic) environments. Drilling used a 5 mm TiN-coated carbide drill at 2500–3500 rpm and 110–550 mm/min. Exit-side damage was quantified by delamination factor (Fd) and corrected delamination factor (Fda) via microscopy and image processing. Environmental conditioning clearly affected both mechanical load-carrying capacity and machinability within the tested conditions. NaOH caused the most severe degradation, while HCl had a more limited effect. In CFRP, tensile load dropped by ~7.3% (HCl) and ~14.3% (NaOH); CNF reduced these losses by ~5.7% and ~10.5%, respectively. During drilling, the lowest Fd/Fda occurred at 3500 rpm–110 mm/min, and the highest at 2500 rpm–550 mm/min. Under the critical NaOH condition (550 mm/min–2500 rpm), Fda decreased from 1.126 (CFRP) to 1.054 (CNF/CFRP), an absolute improvement of ~6%–7%. These gains reflect barrier/tortuosity and crack deflection/bridging mechanisms, and shift delamination to a more stable, less parameter-sensitive regime. The results provide practical, environment-specific process windows linking corrosion, microstructure, and drilling response.