Truss Reinforced Foam Cores for Replacement of Aluminum Honeycomb Structures

Sandwich core structures represent a lightweight and structurally efficient approach for composite airframe fabrication. However, the use of sandwich core structures has also presented challenges, particularly in high humidity environments. In theseenvironments, any defect or damage to the sandwich facesheets allows moisture intrusion into the cells of the honeycomb. A simple approach to address moisture intrusion of conventional honeycomb materials would be to use closed-cell foam, however, thestrength properties of foam cores is limited at best. Aztex has developed a technology that utilizes lightweight, closed cell foam as a base. The foam is reinforced with very small diameter pultruded rods (typically carbon fiber/BMI or epoxy). The rods areused to create a truss network in the foam. This approach can be tailored to the specific applications. Shear and compression strengths can be adjusted as required (locally if necessary) to achieve the desired combination of core weight versus mechanicalproperties. The purpose of this program will be to develop preliminary design allowables and fabricate and test manufacturing demonstration hardware. We have discussed this program with Lockheed Martin Aerospace (Fort Worth, TX) who have agreed to supportthis Phase II program for application in the F-35 MLG doors. Aztex X-Cor and K-Cor technology represents a completely new class of core materials. These materials can be produced as completed parts, ready for incorporation into the structure without theadditional machining, potting and edge filling steps required with conventional honeycomb. X-Cor and K-Cor also can be designed with shear and compression strengths significantly greater than foam cores. Successful completion of this program will providepreliminary design allowables data for X-Cor/K-Cor and strcutural demonstration components as a first step for incorporation of these materials on F-35/JSF. These materials have essentially unlimited applications on DoD and commerical aerospace platforms,commerical aircraft, ground transportation, military shelters, etc. X-Cor and K-Cor can be used in any application where conventional core materials could be used, but without the moisture intrusion issues of honeycomb or the strength limitations of foamcores.