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Carbon Fiber Thermoplastics with High Through Thickness Modulus

Description:

TECHNOLOGY AREA(S): Weapons 

OBJECTIVE: Increase the through thickness modulus of carbon fiber thermoplastic composites through the use of nano-additives. These composites are used on large caliber direct and indirect fire gun tubes. They use polyetheretherketone (PEEK) as the thermoplastic matrix and are processed via fiber placement. The increase in the through thickness modulus should not decrease the in-plane properties of the composite nor the ability to process it via fiber placement. 

DESCRIPTION: There is a need to increase the through thickness modulus in fiber placed thermoplastic composites. These materials are being used to overwrap gun tubes for both direct and indirect fire and the effectiveness of the composite wrap is limited by the through thickness modulus. Traditionally this modulus is only that of the matrix material which is an order of magnitude or more lower than that of the reinforcement. On previous efforts it was found that after about 0.5 - 0.75 inches of overwrap adding additional material doesn't help with limiting bore dilation due to the low modulus in the radial direction being solely a function of the matrix. This effort focuses on developing a process to increase the through thickness modulus by adding nano-materials to the matrix. The addition of these materials should not be detrimental to the in plane properties of the base composite and should still be processable via fiber placement. 

PHASE I: Develop a process to increase the through thickness modulus of carbon fiber reinforced thermoplastic by adding nano-materials to the system. For this effort the baseline material is the fully unidirectional carbon fiber / polyetheretherketone (PEEK) system commonly referred to as IM7/PEEK. This material is processed via fiber placement using either hot gas torches or lasers as the heating source. The material is processed as a fully consolidated tape of IM7/PEEK. A study should be conducted as to what type / loading amount of nano-material will give the highest increase in through thickness modulus without degrading in plane properties or processability. A suggested method for measuring the through thickness modulus is ASTM D695 with two to one size anisotropy though other methods are acceptable. The threshold is a 75% increase in through thickness modulus over the baseline of pure PEEK. The objective is a 200% increase. The material deliverable is the equivalent of one square meter (can be of any width) of the improved material for testing. The material deliverable does not have to be in a form processable by fiber placement but should be processable by heated platen press or autoclave. 

PHASE II: Refine the process and improve the modulus results over Phase I. Minimum expected improvement is 100% over pure PEEK with an objective of 200% or more increase. Material must be processable via fiber placement. The as processed interlaminar shear strength (D2344 -Standard Test Method for Short-Beam Strength of Polymer Matrix Composite Materials and Their Laminates), shall be equal to or greater than 9 ksi and any deviation from this value shall be reported and a plan to achieve 9 ksi shall be described. No degradation of the in-plane properties shall be verified by conducting at a minimum ASTM D3039 (Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials) in both longitudinal and transverse directions. Thermal conductivity shall also be measured to determine if there is any increase over the baseline material. The material deliverable is 25 lbs of 1/2" wide material capable of being processed via fiber placement. 

PHASE III: Finalize the development of a material based solution at production level quantities that can be readily implemented on existing manufacturing equipment. Non-DoD applications include down well piping, engine components, etc. 

REFERENCES: 

1: J. B. Root and A. G. Littlefield, Minimizing Rail Deflections in an EM Railgun, November 2006. http://handle.dtic.mil/100.2/ADA481582

2:  R. M. Erb, R. Libanori, N. Rothfuchs, A. R. Studart, "Composites Reinforced in Three Dimensions by Using Low Magnetic Fields," Science, Vol 335, 13 Jan 2012, pp 199-204

3:  L. Burton, R. Carter, V. Champagne, R. Emerson, M.l Audino, and E. Troiano, Army Targets Age Old Problems with New Gun Barrel Materials, AMPTIAC Quarterly, v8n4, 2004. http://ammtiac.alionscience.com/pdf/AMPQ8_4ART08.pdf

4:  A. Littlefield and E. Hyland, Prestressed Carbon Fiber Composite Overwrapped Gun Tube, November 2006. http://handle.dtic.mil/100.2/ADA481065

5:  S. Montgomery and R. L. Ellis, Large Caliber Gun Tube Materials Systems Design, 10th U.S. Army Gun Dynamics Symposium Proceedings, Austin, TX, April 2002. http://handle.dtic.mil/100.2/ADP012479

6:  U.S. Army Materiel Command, "Research and Development of Materiel, Engineering Design Handbook, Gun Series, Gun Tubes," AMCP 706-252, Washington DC (1964). http://handle.dtic.mil/100.2/AD830297

7:  Office of the Secretary of Defense (OSD) Manufacturing Technology Program, Manufacturing Readiness Level (MRL) Deskbook, Version 2.0, May 2011. http://www.dodmrl.com/MRL_Deskbook_V2.pdf

8:  J. B. Root, V. Olmstead, A. G. Littlefield, K. Truszkowska, "An Analysis of EM Railgun Cross Section Designs," ARDEC Technical Report ARWSB-TR-09017, Aug 2009, http://www.dtic.mil/docs/citations/ADA593788

9:  W. Zhang, J. Suhr, N. Koratkar, "Observation of High Buckling Stability in Carbon Nanotube Composites", Advanced Materials, Vol 18, 4, 2006, 452-456.

10:  M.A. Rafiee, J. Rafiee, Z. Wang, H. Song, Z.Z. Yu, N. Koratkar, "Enhanced Mechanical Properties of Nanocomposites at Low Graphene Content", ACS Nano, 3 (12), 2009, 2884-3890

11:  M.A. Rafiee, J. Rafiee, Z. Wang, H. Song, Z.Z. Yu, N. Koratkar, "Enhanced Mechanical Properties of Nanocomposites at Low Graphene Content", ACS Nano, 3 (12), 2009, 2884-3890

KEYWORDS: Advanced Composites, Nanomaterials, Fiber Placement, Thermoplastic Composites 

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