Closed-cell polyurethane in-situ foaming honeycomb for enhanced energy absorption and water intrusion resistance

To achieve novel core with high energy absorption and strong water intrusion resistance, a composite structure was created by employing in-situ foaming of closed-cell polyurethane (PU) in a honeycomb structure. Experimental, theoretical, and finite element analyses revealed that the in-situ foaming technique increased the honeycomb's energy absorption by 312.84 % and improved impact efficiency by 61.45 % while maintaining specific energy absorption (SEA). Remarkably, this composite structure surpassed the energy absorption capacity of individual honeycomb and foam. The coupling gain ratio introduced by the foam increases within a certain range as the honeycomb cell size decreases and wall thickness increases, with little influence from the foam's mechanical properties. Water intrusion, leading to ice formation at low temperatures, drastically reduced honeycomb SEA by 94.61 % and impaired mechanical properties significantly. Closed-cell PU in-situ foaming provided exceptional water intrusion resistance, preserving the honeycomb's mechanical performance, including energy absorption and SEA. • Designed a reinforced core HPU based on honeycomb structure. • Closed-cell PU in-situ foamed honeycomb increases energy absorption by 312.84 %. • Closed-cell PU foam enhances honeycomb's water intrusion resistance. • Explored coupling effects between foam and honeycomb of HPU. • Conducted theoretical and FE analysis of HPU.