The sandwich materials used for composite sandwich structures mainly include: rigid foam, PMI foam, honeycomb and balsa wood. Rigid foams mainly include polyvinyl chloride, polyurethane, polyetherimide, acrylonitrile-styrene, polymethacrylimide, and foamed polyester. Honeycomb sandwich materials include glass cloth honeycomb, NOMEX honeycomb, cotton cloth honeycomb, aluminum honeycomb and so on.
The honeycomb sandwich structure has high strength and good rigidity, but the honeycomb is an open-cell structure, and the bonding area with the upper and lower panels is small, and the bonding effect is generally not as good as foam. Balsa sandwich material is a natural product. The common balsa sandwich cores on the market are mainly produced in plantations in South America. Due to climatic reasons, balsa wood grows very fast in the local area, so it is much lighter than ordinary wood, and its fiber With good strength and toughness, it is especially suitable for composite sandwich structures.
Sandwich material is one of the key materials for wind power blades. In order to increase structural rigidity, prevent local instability, and improve the load resistance of the entire blade, PMI foam is generally used at the leading edge, trailing edge and shear ribs of the blade. Sandwich structure. After proper high temperature treatment, PMI foam can withstand the high temperature composite material curing process requirements, so that PMI foam has been widely used in the aviation field.
Medium-density PMI foam has good compressive creep properties and can be autoclaved at a temperature of 120oC -180oC and a pressure of 0.3-0.5MPa. PMI foam can meet the creep performance requirements of the usual prepreg curing process, and can realize the co-curing of the sandwich structure. In order to avoid the core material collapse or side shift during the co-curing process, the curing pressure is usually 0.28-0.35 MPa instead of 0.69 MPa for laminates.
This will cause the porosity of the composite panel to be higher. In addition, because the pore diameter of the honeycomb structure is large, the skin is only supported at the honeycomb wall, which will cause the PMI foam fiber to bend and reduce the strength of the composite skin laminate.