Publications by authors named "Clifton Bumgardner"

4 Publications

  • Page 1 of 1

Graphene reinforced carbon fibers.

Sci Adv 2020 Apr 24;6(17):eaaz4191. Epub 2020 Apr 24.

Department of Mechanical and Aerospace Engineering, University of Virginia, 122 Engineer's Way, Charlottesville, VA 22904, USA.

The superlative strength-to-weight ratio of carbon fibers (CFs) can substantially reduce vehicle weight and improve energy efficiency. However, most CFs are derived from costly polyacrylonitrile (PAN), which limits their widespread adoption in the automotive industry. Extensive efforts to produce CFs from low cost, alternative precursor materials have failed to yield a commercially viable product. Here, we revisit PAN to study its conversion chemistry and microstructure evolution, which might provide clues for the design of low-cost CFs. We demonstrate that a small amount of graphene can minimize porosity/defects and reinforce PAN-based CFs. Our experimental results show that 0.075 weight % graphene-reinforced PAN/graphene composite CFs exhibits 225% increase in strength and 184% enhancement in Young's modulus compared to PAN CFs. Atomistic ReaxFF and large-scale molecular dynamics simulations jointly elucidate the ability of graphene to modify the microstructure by promoting favorable edge chemistry and polymer chain alignment.
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http://dx.doi.org/10.1126/sciadv.aaz4191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182419PMC
April 2020

3D digital image correlation evaluation of arthrodesis implants.

Clin Biomech (Bristol, Avon) 2020 01 25;71:29-36. Epub 2019 Oct 25.

University of Virginia, Department of Mechanical and Aerospace Engineering, 122 Engineer's Way, Charlottesville, VA 22903, USA. Electronic address:

Background: Hallux valgus is a pathological condition that is typically treated via the Lapidus procedure. The purpose of this study was to understand the biomechanical characteristics of bone, implant devices and the bone-implant interface.

Methods: In-situ digital image correlation was performed on polyurethane foam, a known bone substitute in a modified three-point bend test frame. We introduced this modified rig as an enhanced methodology for characterizing bone and implant device mechanical performance. This new methodology was validated using aluminum rod specimens, in three and four-point bend setups followed by new configurations to reveal implications of load configurations on joint displacement and implant performance. Bone substitute specimens were constructed with nitinol staples or locking plate to minimize gapping at the 1 tarsometatarsal during testing.

Findings: Bone-implant interface characterization was enabled by digital image correlation, identifying maximum strain concentrations of 1.5% along the interfaces. Interfacial characteristics were analyzed in context with gap displacement allowed by the implant over cyclical loading. The locking plate implant and nitinol staples gapped an average of 2.2 mm and 3.2 mm respectively under 50 Newtons. Removing all load, the locking plate implant and nitinol staples averaged ~0.8 mm and ~0.3 mm of residual gapping respectively.

Interpretation: Our results demonstrate that locking plates provide more initial stability and resistance against gapping under load but are unable to recover compression throughout repetitive loading as seen with the nitinol staple technology. This could lead to a paradigm shift in materials used for early weight bearing protocols post-operation.
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http://dx.doi.org/10.1016/j.clinbiomech.2019.10.011DOI Listing
January 2020

Unveiling Carbon Ring Structure Formation Mechanisms in Polyacrylonitrile-Derived Carbon Fibers.

ACS Appl Mater Interfaces 2019 Nov 1;11(45):42288-42297. Epub 2019 Nov 1.

Department of Mechanical and Aerospace Engineering , University of Virginia , 122 Engineer's Way , Charlottesville , Virginia 22904 , United States.

As the demand for electric vehicles (EVs) and autonomous vehicles (AVs) rapidly grows, lower-cost, lighter, and stronger carbon fibers (CFs) are urgently needed to respond to consumers' call for greater EV traveling range and stronger safety structures for AVs. Converting polymeric precursors to CFs requires a complex set of thermochemical processes; a systematic understanding of each parameter in fiber conversion is still, to a large extent, lacking. Here, we demonstrate the effect of carbonization temperature on carbon ring structure formation by combining atomistic/microscale simulations and experimental validation. Experimental testing, as predicted by simulations, exhibited that the strength and ductility of PAN CFs decreased, whereas the Young's modulus increased with increasing carbonization temperature. Our simulations unveiled that high carbonization temperature accelerated the kinetics of graphitic phase nucleation and growth, leading to the decrease in strength and ductility but increase in modulus. The methodology presented herein using combined atomistic/microscale simulations and experimental validation lays a firm foundation for further innovation in CF manufacturing and low-cost alternative precursor development.
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http://dx.doi.org/10.1021/acsami.9b15833DOI Listing
November 2019

Cotton-textile-enabled flexible self-sustaining power packs via roll-to-roll fabrication.

Nat Commun 2016 05 18;7:11586. Epub 2016 May 18.

Department of Mechanical and Aerospace Engineering, University of Virginia, 122 Engineer's Way, Charlottesville, Virginia 22904-4746, USA.

With rising energy concerns, efficient energy conversion and storage devices are required to provide a sustainable, green energy supply. Solar cells hold promise as energy conversion devices due to their utilization of readily accessible solar energy; however, the output of solar cells can be non-continuous and unstable. Therefore, it is necessary to combine solar cells with compatible energy storage devices to realize a stable power supply. To this end, supercapacitors, highly efficient energy storage devices, can be integrated with solar cells to mitigate the power fluctuations. Here, we report on the development of a solar cell-supercapacitor hybrid device as a solution to this energy requirement. A high-performance, cotton-textile-enabled asymmetric supercapacitor is integrated with a flexible solar cell via a scalable roll-to-roll manufacturing approach to fabricate a self-sustaining power pack, demonstrating its potential to continuously power future electronic devices.
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http://dx.doi.org/10.1038/ncomms11586DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873971PMC
May 2016