TECHNOLOGY AREA(S): Materials/Processes

ACQUISITION PROGRAM: PMA261 H-53 Heavy Lift Helicopters

OBJECTIVE: Develop an out-of-autoclave processable, pre-impregnated carbon fiber fabric that has a room temperature shelf life, is curable at low temperatures, and performs equal to or better than the materials currently being used for repair on Navy platforms.

DESCRIPTION: The resin pre-impregnated fabrics (pre-pregs) the U.S. Navy currently uses require storage at or below freezing. This requirement drives up sustainment cost and limits the ability to perform certain types of Organizational level (O-level) repairs where freezer storage is not readily available. The fabrics also must be cured in an autoclave or through a Double Vacuum Debulk (DVD) procedure, which drives the need for expensive equipment to support repairs and also limits the location of where repairs can be performed. Only a few commercially available room temperature storage pre-pregs can be cured outside of an autoclave but these materials need to be cured at relatively high temperatures (>250�F) and frequently yield high porosity laminates. The required processing exposes the parent materials to conditions outside their operational temperature windows, which can result in degradation of material properties. Additionally, higher porosity causes poor laminate quality and can result in premature part failure.

The desire is to produce a pre-preg that reduces the use of cold storage and equipment needed for cure, while producing a laminate of sufficient quality. The pre-preg would be expected to meet the following requirements:

-  Can be produced as a plain woven and an unidirectional carbon fiber fabric

-  Minimum shelf life of 1 year when stored in a hangar (100�F), but longer is preferred

-  Reasonably tacky in order to perform repairs on part surfaces oriented vertically or horizontally

-  Reasonably drape-able to form over complex curvatures with as small as a 4 inch radius or less

-   Able to achieve a cure percentage of at least 95% when cured on aircraft

-  Can be cured in an uncontrolled environment, ideally but not limited to 45-65% humidity at 65-75�F.

-  Minimize the use of equipment needed to cure

-  Cure time of 2.5 hours or less

-  Cure cannot expose the part to temperatures greater than 200�F although as low as 150�F would be preferred.

-  Porosity of laminate less than 4% by volume

-  Wet glass transition temperature (Tg) of at least 230�F, but a higher wet Tg is desirable

-  Exposure to common aircraft fluids should not cause degradation of mechanical properties greater than 11% of the original strength. Common aircraft fluids include, but are not limited to anti-icing fluid, runway deicers, electronic equipment coolant, hydraulic fluid, lubricating oil, jet fuel, turbine fuel, aircraft cleaner, MEK, and acetone.

-Must be capable of being co-cured and bond with another epoxy-based adhesive system.

-   Ability to procure material in small quantities (by the roll) is desirable

Threshold Composite Laminate Mechanical Properties

-  0� tensile strength of 114 ksi (Room Temp), 109 ksi (180�F Wet)

-  0� compression strength of 69 ksi (Room Temp), 48 ksi (180�F Wet)

-  0� short beam shear strength of 8.9 ksi (Room Temp), 5.7 ksi (180�F Wet)