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PMI Foam for Sandwich Structure


After proper high temperature treatment, PMI foam can withstand the high temperature composite material curing process requirements, which makes PMI foam widely used in the aviation field. The medium-density PMI foam has good compressive creep properties and can be cured in an autoclave 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.

PMI foam as an aviation material is a uniform rigid closed-cell foam with basically the same pore size. PMI foam can also meet FST requirements. Another feature of the foam sandwich structure compared to the NOMEX® honeycomb sandwich structure is its much better resistance to moisture absorption. Since the foam is closed cell, it is difficult for moisture and moisture to enter the core. Although NOMEX® honeycomb sandwich structures can also be co-cured, this reduces the strength of the composite panel. 

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In order to avoid core collapse or side shift of the honeycomb during the co-curing process, the curing pressure is usually 0.28-0.35 MPa, instead of the usual 0.69 MPa for laminates. This results in a high porosity of the composite panel. In addition, because the pore diameter of the honeycomb structure is large, the skin is only supported at the position of the honeycomb wall, which will cause the fibers to bend and reduce the strength of the composite skin layer.

PMI foam has been used successfully in various aircraft structures as a core foam for sandwich structures, one of the most prominent applications being the engine air intake side panels at the tail of the Boeing MD 11 aircraft. The CNC precision machining and thermoforming of the foam greatly reduces the cost of layup. The high-performance PMI foam core has good resistance to compression creep during curing, compacting the panel and eliminating surface unevenness. 

Compared with the honeycomb core, the isotropic pore structure of the PMI foam can also meet the requirements of dimensional stability under lateral pressure during the curing process of the autoclave. Unlike the honeycomb structure, it does not need to be filled with foam glue. In addition, the foam can evenly transfer the pressure of the autoclave to the layup of the panel below the foam, so that it is compacted without surface defects such as indentation. The foam-filled A-rib structure can be applied to components such as radar emitting surfaces, nacelle panels, fuselage skins, and vertical stabilizers.


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