Effect of Hygrothermal Aging on the Tensile Performance of GNP‐Modified Patch‐Repaired GFRP Composites

The combined effect of hygrothermal aging and graphene nanoparticle (GNP) modification of the adhesive layer on the tensile performance of patch‐repaired glass fiber reinforced polymer (GFRP) composites was experimentally investigated. Six configurations of specimen pristine, drilled, single and double‐sided patches with and without 0.5 wt% GNP modified adhesive were aged in seawater at 27°C, 50°C, and 60°C for up to 60 days and characterized under quasi‐static tensile loading with digital image correlation (DIC) and acoustic emission (AE) monitoring. Moisture absorption followed predominantly Fickian behavior; the double‐patch GNP (DPG) configuration absorbed the least, only 1.34% at 60°C after 60 days versus 2.20% for the drilled specimen (39% reduction). The pristine ultimate tensile strength fell by 40%–47% across the three aging temperatures after 60 days, retaining only about 53%–60% of its unaged value, with the steepest loss within the first 10 days. In the unaged condition, DPG performed best, sustaining a peak load about 19% above its unmodified counterpart; this advantage was substantially reduced by 60 days, indicating that GNP‐enhanced adhesives delay but do not prevent the moisture‐driven degradation of patch‐repaired GFRP composites under marine hygrothermal service.