The Development and Evaluation of Advanced Kevlar Sandwich Structure for Application to Rotorcraft Airframes

The results of an evaluation of Du.Pont Kevlar-based material systems in sandwich structure designed for rotorcraft primary airframe structure are presented in this report. The focus of this work has b􀀔en to evaluate the durability and compression strength of thin-gage Kevlar sandwich panels and investigate means of improvement. Furthermore, ensuring the long term durability of thin­skin sandwich primary structure has been a concern, especially preventing or accounting for manufacturing porosity, thermal cycling damage, and impact damage that results in strength reduction and could lead to water intrusion. It was found that sandwich panels made with Kevlar 149 fibers can be as strong as Kevlar 49 structures but have reduced compression stiffness properties at typical operating strain levels. Thermal cycling was found to affect permeability but not strength in thin facesheet sandwich structure. Any increased permeability can be prevented with the use of an interleaf or surfacing plies. The surfacing plies investigated also had a beneficial effect on sandwich strength due to their stabilizing effect on the facesheet in compression. Finally, a previously developed model was used to analyze the residual strength of a sandwich panel after impact damage.