Center for Composite Materials - University of Delaware
University of Delaware

SAMPE 2019

Tuesday, May 21, 2019
1:00 pm – 2:00 pm
Room 208B
Advances in Composite Materials and Design Tools #FS 5
Featured Speaker: Dr. Jan Vandenbrande, DARPA Defense Sciences Office, Program Manager

Carbon fiber reinforced polymers (CFRP) composites have been the material of choice for decades in DoD systems where minimizing structural weight is critical. However, due to the limitations of manufacturing continuous carbon fiber and forming of the resulting feedstock, the cost of CFRP composites has limited its adoption to medium and large parts where manufacturing costs are on par or better than metal.

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DARPA’s Tailorable Feedstock and Forming (TFF) program aims to disrupt the trade space for small composite parts by developing a composite feedstock materiwal and reconfigurable forming methods that reduces manufacturing complexity and increase use of CFRPs for parts less than 20 pounds at finished costs competitive with metal. New architected materials such as those developed by TFF and advanced manufacturing processes including 3D Printing offer new possibilities to custom tailor material properties locally and fabricate dramatically differently shapes. Unfortunately, our design tools have not kept up with these advances and cannot handle the enormous number of design choices that they enable. DARPA’s Transformative Design (TRADES) program aims to address these shortcomings by developing new mathematics and computational tools to enable generation of designs that balance shape with material properties. This talk will provide a high level overview of both the TFF and the TRADES programs, their performers and highlight accomplishments to date.
Tuesday, May 21, 2019
2:00 pm – 2:25 pm
Room 208B
Tailorable Universal Feedstock for Forming (TUFF): Overview and Performance #TP19–1605
Speaker: Shridhar Yarlagadda, Asst. Director for Research, University of Delaware – Center for Composite Materials

Under the Defense Advanced Research Projects Agency (DARPA) Tailorable Feedstock for Forming (TFF) program, the University of Delaware – Center for Composite Materials (UD-CCM) led-team proposed to develop a manufacturing process and pilot facility to produce novel discontinuous carbon fiber composite feedstock for forming, with the potential to revolutionize the use of composite materials, as a cost-effective replacement for small complex geometry metal parts (<2 sq. m.).

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The TuFF (Tailored Universal Feedstock for Forming) feedstock consists of a highly aligned discontinuous carbon fiber preform in thin-ply format, which can be combined with thermoplastic or thermoset resins for prepreg, or used in dry form for infusion-based manufacturing processes. A patent-pending discontinuous fiber alignment and preforming process has been developed and implemented in a pilot facility at UD-CCM. The alignment process is fiber agnostic and TuFF preforms have been manufactured with aerospace grade fiber (IM7, T800), pitch carbon fiber, and recycled carbon fiber. Using discontinuous IM7 carbon fiber and Polyetherimide (PEI) thermoplastic resin, TuFF composites with aerospace quality requirements (<1% voids, up to 63% fiber volume fraction) have demonstrated 100% translation of fiber stiffness and strength in tension, and >40% bi-axial in-plane strain capability during forming. The in-plane stretchability of TuFF preforms enables conformability of simple planar preforms to complex geometries, eliminating the need for darting and complex ply patterns while minimizing associated scrap during composite layup. Closed-loop recycling and reuse strategies are possible for the first time with the ability to reuse fiber and preform scrap, prepreg scrap and recycled composite parts.
Tuesday, May 21, 2019
2:30 pm – 2:55 pm
Room 208B
Microstructural Evaluation of Aligned, Short Fiber TUFF Material #TP19–1609
Speaker: Dirk Heider, Asst. Director for Technology, University of Delaware – Center for Composite Materials

The Tailorable Universal Feedstock for Forming (TuFF) material is comprised of highly aligned discontinuous fibers that achieves a high level of mechanical properties with large in-plane extensibility for forming of complex geometries.

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The paper characterizes the TuFF microstructure in terms of areal weight and fiber volume fraction and statistical distributions of fiber length, fiber-fiber spacing and fiber alignment using microscopy and X-ray Computed-Tomography with custom developed algorithms for data reduction. The TuFF program has demonstrated full property translation of stiffness and strength compared to continuous prepreg (60% fiber volume fraction) when 95% of all fibers are aligned within 5° and have a minimum fiber aspect ratio (length over diameter) of 600.
Tuesday, May 21, 2019
3:00 pm – 3:25 pm
Room 208B
Formability of TUFF Composite Blanks #TP19–1606
Speaker: Shridhar Yarlagadda, Asst. Director for Research, University of Delaware – Center for Composite Materials

Under the Defense Advanced Research Projects Agency (DARPA) Tailorable Feedstock for Forming (TFF) program, the University of Delaware – Center for Composite Materials (UD-CCM) led-team proposed to develop a manufacturing process and pilot facility to produce novel discontinuous carbon fiber composite feedstock for forming, with the potential to revolutionize the use of composite materials in military platforms, as a cost-effective replacement for small complex geometry metal parts (<2 sq. m.).

View Abstract

The TuFF (Tailored Universal Feedstock for Forming) feedstock consists of a highly aligned discontinuous carbon fiber preform in thin-ply format, which can be converted to dry preforms for thermoset infusion, thermoset prepreg blanks or thermoplastic blanks for composite forming. Forming demonstrations have shown metal-like formability under vacuum forming conditions for complex geometries. In-plane as well as bi-axial stretch >40% has been demonstrated in both longitudinal (along fiber direction) and transverse (90 degrees to fiber direction) deformation modes for unidirectional and cross-ply composite blanks.
Tuesday, May 21, 2019
3:30 pm – 3:55 pm
Room 208B
Closed Loop Recycling of CFRP Into Highly Aligned High Performance Short Fiber Composites Using the TUFF Process #TP19–1607
Speaker: Dirk Heider, Asst. Director for Technology, University of Delaware – Center for Composite Materials

Current Carbon (CF) Fiber Reinforced Polymers (CFRP) recycling strategies reclaim continuous CF in powder or short fiber form. The material is added to molding compounds as a filler or short fiber reinforcement having random or semi-aligned orientation to produce composites with low fiber volume fraction and reduced mechanical properties (down cycling).

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Down cycling reduces the value chain limiting the recycling opportunities of CFRPs. This paper combines a short fiber alignment process (TuFF) with 1) the use of low-cost, short CFs obtained from recycled and waste stream, and 2) recycling of TuFF material using thermolysis to produce highly aligned short fiber composites with mechanical properties approaching continuous fiber levels. The closed-loop process recycles the CFRP, reclaims the fiber content, aligns the fibers using the TuFF process and produces new CFRP components with high property retention. The method reduces material and part cost and allows true recycling and reuse of CF components into high-performance parts.
Wednesday, May 22, 2019
1:00 pm – 1:25 pm
Room 208B
Surface Treatment of TUFF Pitch-Based Carbon Fiber for Adhesion Promotion in High TG Thermoplastic Composites #TP19–1613
Speaker: Joseph Deitzel, Senior Scientist, University of Delaware – Center for Composite Materials

Commercially available Pitch and PAN based carbon fibers undergo surface treatment to clean the surface of undesirable scale and to provide chemical functionality to promote resin wetting and adhesion in composites. Typically, these surface treatments are carried out in a continuous process that does not lend itself to the treatment of discontinuous fibers, like the mesophase pitch-based fibers being developed for the Tailorable Universal Feedstock for Forming (TuFF) alignment process.

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To address this challenge, we have developed a multiple-step batch process that oxidizes the fiber surface through ozone treatment at elevated temperature, followed by vapor deposition and/or solution coating to apply a coating package. Using this process, a series of coating formulations have been evaluated for thermal stability, coating uniformity, thickness and chemical composition on mesophase pitch-based carbon fiber. Single Fiber Fragmentation (SFF) testing of model polyether imide (PEI)/carbon fiber composites shows that the interfacial shear strength (IFSS) of as-spun carbon fibers can be increased from ~10 MPa to ~40 MPa with the right choice of coating chemistry. A discussion of the processing steps, and evaluation of the different fiber surface treatments with SFF, Energy Dispersive X-ray spectroscopy (EDAX), and X-ray Photoelectron Spectroscopy (XPS) measurements, as well as the potential for process scale up will be presented.

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