THERMAL-STABILITY OF ARAMID FIBER-REINFORCED HONEYCOMB CORE FOR THERMOPLASTIC FACESHEET APPLICATIONS

The effect of short term elevated temperature exposure on the mechanical performance of an aramid/phenolic honeycomb core was experimentally measured. This work was performed to evaluate the core material for use in sandwich structures with thermoplastic facesheets. At elevated temperatures, the data show that core strength gradually diminishes at an increasing rate with increasing temperature. Room temperature compression after exposure to the same elevated temperature indicates that the core retains 75-80 percent of its original strength and modulus for exposure temperatures at or below 260 degrees C. Residual compressive strength showed slight increases for long exposures at 200-220 degrees C, indicating that these exposures may provide a secondary cure of the aramid/phenolic core material. A progressive buckling model for the honeycomb cell was developed to show that the loss of material stiffness with increasing temperature is responsible for core compressive failure, not. a loss of inherent material strength. While the core material experienced a small degradation of mechanical properties under short-term elevated temperatures, the reduction of properties during the elevated temperature exposure may significantly limit the pressure that can be applied during bonding of thermoplastic facesheets.