Cryogenic compressive performance and multi-objective optimization of composite fluted-core sandwich structures

Composite sandwich structures possess excellent mechanical properties and multi-functional integration characteristics, suitable for cryogenic tanks of launch vehicles. This study investigated the cryogenic compressive performance and failure mechanisms of carbon fiber-reinforced plastic (CFRP) fluted-core sandwich structures, along with the multi-objective optimization to improve thermal insulation and load-bearing capacity. Uniaxial compressive experiments were conducted under cryogenic conditions. Theoretical models were established to predict the buckling and ultimate loads, explicitly incorporating the effect of temperature and the variation in failure modes. The structural parameters of foam-filled sandwich structures were optimized through NSGA-II algorithm to achieve optimal cryogenic insulation and load-bearing performance. The results showed an increase in compression modulus and strength of CFRP laminates by 18.5 % and 86.7 % as temperature dropped from 20 °C to −180 °C. The initial buckling and ultimate loads of sandwich panels rose by 17.89 % and 45.79 %, respectively. Low temperatures induced structures prone to brittle fracture, with carbon fiber facesheets exhibiting more pronounced delamination. Optimization of the structural design parameters resulted in foam-filled fluted-core sandwich panels achieving a 23.97 % weight cut, a 10.94 °C rise in bottom facesheet temperature, and a 25.92 % boost in failure load. The findings provide valuable insights into the structural design of cryogenic propellant tanks.