Quasi-static penetration performance of balsa core sandwich composites with polypropylene face sheets under seawater and acid aging

Abstract This study evaluates the quasi-static penetration behavior of E-glass–reinforced polypropylene thermoplastic sandwich composites with balsa wood cores of 15 mm and 25 mm thicknesses, following aging in seawater and hydrochloric acid for periods up to 28 days. Sandwich panels were manufactured via hot pressing and subjected to quasi-static penetration tests to assess mechanical performance and energy absorption. Results indicate that initial exposure causes significant reductions in penetration strength, with day-1 decreases of 6.7–32.4 % for 15 mm panels and 3–3.4 % for 25 mm panels, most pronounced in acid-aged specimens. Maximum degradation occurred around day 14 (34.9–46.4 % loss in 15 mm cores), after which partial recovery and stabilization were observed, particularly in seawater-aged thicker panels retaining up to 83 % of unaged strength. Force–displacement and energy–displacement analyses reveal that thicker cores improve load-bearing capacity, buffer interface degradation, and enhance energy absorption through plasticization and hydraulic resistance of the balsa core. These findings provide quantitative insights into thickness-dependent aging effects, informing the design of durable, environmentally resistant balsa-core sandwich composites for marine and corrosive applications.