NASA and European Airbus have recently proposed a foam- […]
NASA and European Airbus have recently proposed a foam-filled reinforced strip structure based on the use of sandwich structures and reinforced strip structures for many years, maximizing structural design and manufacturing processes, such as AIRBUS A380. The spherical frame of the airtight compartment.
PMI foam: PMI (Polymethacrylimide) foam can withstand high temperature composite curing process requirements after proper high temperature treatment, which makes PMI foam widely used in aviation. The medium density PMI foam has good compression creep properties and can be autoclaved at a temperature of 120oC - 180oC and a pressure of 0.3-0.5MPa. PMI foam meets the creep performance requirements of conventional prepreg curing processes and enables co-curing of sandwich structures. The PMI foam as aerospace material is a uniform rigid closed cell foam with substantially uniform pore size. PMI foam can also meet FST requirements. Another feature of the foam sandwich structure compared to the NOMEX® honeycomb sandwich structure is that it is much more hygroscopic. Since the foam is closed, moisture and moisture are difficult to enter the core. Although the NOMEX® Honeycomb Sandwich structure also enables co-curing, it reduces the strength of the composite panel. In order to avoid core crushing or side shifting of the honeycomb during the co-curing process, the curing pressure is usually 0.28-0.35 MPa instead of the usual laminate of 0.69 MPa. This can result in a high porosity of the composite panel. In addition, because the honeycomb structure has a large pore diameter, the skin is supported only at the position of the honeycomb wall, which causes the fiber to bend, resulting in a decrease in the strength of the composite skin laminate.
In combination with the comparison of the honeycomb and the foam core material, the foam material is generally selected as the core material of the A-shaped reinforced strip structure, and when used as the core mold, it serves as the structural core material of the A-type reinforced strip, which is a structural material. It is also a process aid.
PMI foam has been successfully used as a sandwich foam core in a variety of aircraft configurations. One of the most prominent applications is the engine intake side panels at the rear of the Boeing MD 11 aircraft. CNC precision machining and thermoforming of the foam greatly reduces the cost of the layup. The high-performance PMI foam core material has good compression and creep resistance during the curing process, which makes the panel compact and eliminates uneven surface. Compared with the honeycomb core, the isotropic pore structure of the PMI foam can also meet the dimensional stability requirements under the side pressure during the autoclave curing process. Unlike the honeycomb structure, it is not required to be filled with foam rubber. In addition, the foam can evenly transfer the pressure of the autoclave to the layup of the panel under the foam to compact it without surface defects such as indentation. The foam-filled Type A reinforced strip structure can be applied to, for example, a radar launching surface, a wall of an engine nacelle, a fuselage skin, a vertical stabilizer, and the like.