TECHNOLOGY AREA(S): Air Platform, Materials/Processes, Weapons

ACQUISITION PROGRAM: PMA265, JPO, Next Generation Air Dominance

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Demonstrate increased performance of polymer-matrix laminated composites using nanoscale additives resulting in a Phase II end product that is a nano-enhanced version of a commercially available fiber/resin system available and capability to produce at relevant scale for DoD programs.

DESCRIPTION: Polymer-matrix composites (PMCs) are used extensively in DoD systems due to their high specific strength and stiffness in-plane. While tensile properties are governed by fiber, many other properties are matrix-limited, including shear, fatigue, compression, impact, conductivity, and maximum service temperature. Polymers intended for high service temperature environments trade off mechanical properties for high Glass Transition Temperature (Tg), increasing the composite�s susceptibility to interfacial failures and narrowing their applicability to supplant metallic incumbent structures. For example, AFRPE-4 has a Tg of 371�C (compared with Hexcel 8552 at 200�C), but interlaminar shear with standard modulus fiber is only 73 MPa (vs 128 MPa for Hexcel 8552) [Ref 1].

State-of-the-art structural epoxy-matrix composites are toughened with thermoplastic particles to address interlaminar failure. However, their performance tends to suffer under hot/wet conditions, and epoxy prepregs are limited to Tg < 200 �C, below the range of interest for engine compressor and nozzle applications.

High-temperature polymers like Polybismaleimides (BMIs) and polyimides are in current use in Navy systems. Existing components comprising these materials make design trades to mitigate limitations in mechanical performance, for example interlaminar shear strength. The typical approach to reducing interlaminar stresses in corner radii, such as those that occur at the interface between airfoils and platform features on stator vane twin-packs, and up-turned flanges on fan ducts, is to increase the size of the radius and/or increase the laminate thickness. This approach may in turn produce other detrimental effects. A larger radius at the ends of an airfoil may reduce the aerodynamic efficiency of the airfoil. Furthermore, thicker laminates present material processing challenges for high-temperature PMCs, particularly for polyimides, that may lead to an increase in manufacturing defects such as wrinkles and porosity.

Use of high Tg polymer matrices composites could address an expanded range of applications for structural composites in high service temperature environments, if their mechanical properties can be bolstered.

Carbon nanotube (CNT) forests oriented through-thickness have been demonstrated as an effective interlaminar reinforcement for epoxy-matrix laminates, significantly increasing interfacial properties such as impact resistance, shear strength, compression and fatigue [Refs 2-6]. These effects are observed even at low loadings.� Furthermore, CNTs exhibit thermal stability comparable to carbon fiber, so they are intrinsically compatible with high Tg polymer matrices.

Increased interlaminar strength, toughness, and fatigue capability using aligned CNTs can relax current design constraints that drive increases in thickness and corner radii for high Tg polymer systems. Improving these key mechanical properties thus has the potential to reduce manufacturing defects and expand the design space. These compounded effects will enable future components with higher aerodynamic and structural efficiency. A higher-performing or lightened revision of an existing component using aligned CNT additives would effectively demonstrate these values: better performing existing systems and expanded design space for future components.

PHASE I: Develop an aligned CNT-based additive material that is compatible with one or more high temperature PMC prepregs in current Navy use. Identify current technical limitations (of the current PMC system) and improvement targets to enable wider adoption of high temperature PMCs, particularly in replacement of heavy or complex metallic components. Develop a process for controlled integration of the additive into the composite resulting in repeatable loading levels and morphology. Define and perform a test matrix to demonstrate relevant increases in performance, and verify property trades-off are minimized. Perform analyses to characterize the effect of the additive on damage modes. Develop a Phase II work plan including strategies for scaling, performance optimization and system targeting. Include a component-level technology demonstration in a Phase II work plan.

PHASE II: Identify one or more candidate components for high temperature PMCs where the current mechanical performance limits drive excess component weight or manufacturing complexity into the design; or preclude adoption altogether. Determine figures of merit and targets needed to improve the current component or modified component design. Refine additive material properties and integration methods to achieve stated targets repeatably, and demonstrate via coupon and/or subcomponent testing. Fabricate and test the candidate component(s) using the CNT-based additive to quantify increase in component performance under representative conditions. Quantify and demonstrate CNT synthesis manufacturing readiness level, and CNT-prepreg integration (�transfer�) manufacturing readiness level of 8+.

PHASE III DUAL USE APPLICATIONS: Evaluate and qualify the system for Navy use and procurement including approved manufacturing locations to ensure that Navy end-users have access to the system. Manufacture and make the system available for procurement by Navy end-users.

If an aligned CNT material and processing technology is successfully demonstrated, it could benefit commercial manufacturing industries which use DoD-relevant high-temperature prepreg systems for structural applications.

REFERENCES:

1. Whitley, Karen S. and. Collins, Timothy J. �Mechanical Properties of T650-35/AFR-PE-4 at Elevated Temperatures for Lightweight Aeroshell Designs.� 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; 1-4 May 2006; Newport, RI. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060013437.pdf

2. Guzm�n de Villoria, R., Ydrefors, L., Hallander, P., Ishiguro, K., Nordin, P., and Wardle, B.L. �Aligned carbon nanotube reinforcement of aerospace carbon fiber composites: substructural strength evaluation for aerostructure applications.� 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Honolulu, HI, USA, April 23-26 2012. https://dspace.mit.edu/bitstream/handle/1721.1/71233/rguzman_SDM2012_SAAB_rg_sw_blw_rg2_blw_rg2_blw4.pdf?sequence=1&isAllowed=y

3. Garcia, E.J., Wardle, B.L. and Hart, A.J. �Joining prepreg composite interfaces with aligned carbon nanotubes.� Composites: Part A, 39:1065�1070, 2008. https://www.deepdyve.com/lp/elsevier/joining-prepreg-composite-interfaces-with-aligned-carbon-nanotubes-WmPPRcFhOG

4. Gouldstone, C., Degtiarov, D. and Williams, R.D. �Reinforcing ply drop interfaces using vertically-aligned carbon nanotube forest.� SAMPE, Seattle, WA, 2014. https://www.researchgate.net/publication/288464534_Reinforcing_ply_drop_interfaces_using_vertically-aligned_carbon_nanotube_forests

5. Conway, H., Chebot, D., Gouldstone, C. and Williams, R. �Fatigue response of carbon fiber epoxy laminates with vertically-aligned carbon nanotube interfacial reinforcement.� SAMPE, Baltimore, MD, 2015. https://www.researchgate.net/publication/323640968_Fatigue_response_of_carbon_fiber_epoxy_laminates_with_vertically-aligned_carbon_nanotube_interfacial_reinforcement

6. Conway, H. et al. �Impact resistance and residual strength of carbon fiber epoxy laminates with vertically-aligned carbon nanotube interfacial reinforcement.� SAMPE, Seattle, WA, May 2017.� https://www.researchgate.net/publication/323641042_IMPACT_RESISTANCE_AND_RESIDUAL_STRENGTH_OF_CARBON_FIBER_EPOXY_LAMINATES_WITH_VERTICALLY-ALIGNED_CARBON_NANOTUBE_INTERFACIAL_REINFORCEMENT

KEYWORDS: Composites; Nanomaterials; CNTs; High Tg; Aircraft Engines; Polymer; PMC