AEROSPACE ENGINEERING

Abstract

This presentation describes several of my current research projects
within the topic area:

A) Length Scale Effect in Toughness Enhancement in Composites: Recent compact tension fracture experiments performed by my research group indicate that very significant increases in fracture toughness (~200%) can be achieved by dispersing only 0.5 weight percent of nanographene platelets within a thermoset epoxy polymer using high shear mixing. In order to model the actual compact tension experiment using atomistic simulation near the crack tip while maintaining computational tractability, concurrent coupling of partitioned domains between Generalized Interpolation Material Point Method (GIMPM) and Molecular Dynamics (MD) was carried out through the use of Embedded Statistical Coupling Method (ESCM). This numerically robust technique has proven to be very effective in coupling a local domain (continuum) to a nonlocal domain (MD) and mitigating high-frequency noise that emanates due to thermal motion in the MD region from being transmitted into the continuum domain.

As part of a three-year project funded by the NASA Aeronautical Sciences Project on structural light-weighting of aerospace vehicles, the concurrently coupled GIMPM/MD code was employed to study and understand the strength and fracture-toughness enhancement mechanisms at the nano-scale in nanographene reinforced thermoset polymer composites at elevated temperatures, using our novel atomistic J-Integral concept which includes polymer entropic effects. Recently, a breakthrough in our understanding of fracture mechanism at the nanoscale was achieved through the use of this approach, resulting in a unique “optimum nanoparticle size” based nano-carbon reinforced composite design guideline. Ideas for scaling up this novel nanoscale building-block approach to large-scale structures using nanoparticle alignment during manufacturing will be presented.

B) Scalable Nanomanufacturing of CNT Scrolled Carbon Fiber: One approach to improve properties of the fiber/matrix interface in a polymer matrix composite (PMC) is the so-called “fuzzy fiber” concept, where carbon nanotubes (CNT) are grown directly on the carbon fiber through CVD. However, the high temperatures typically required for CVD processing have been observed to degrade carbon fiber properties. In our manufacturing approach, we wrap (or scroll) a continuous CNT sheet on the carbon fiber at room temperature at a prescribed wrapping angle and then imbed the scrolled fibers in a resin matrix to build a composite. Consequently, our novel nano-fabrication technique has the potential to enhance the mechanical properties of the fiber/matrix interphase that directly influences the fiber/matrix debond strength and compressive strength of the composite, without degrading fiber properties.

The single-wall carbon nanotube (SWNT) or multiwall carbon nanotube (MWNT) sheets were prepared by pulling a well-aligned CNT forest from a substrate using a unique procedure pioneered by our multi-university team. The CNT sheets are then spiral-wrapped around a fiber, which is then embedded in a polymer matrix. Our preliminary test results indicate that a significant improvement (~80%) in interfacial shear strength and compressive properties is feasible using the proposed approach. Concepts for scaling up this nano-manufacturing process for large-scale scrolled fiber composite production will be discussed. In addition, future research directions regarding the Intelligent Self-healing Composites will be presented.

Speaker

Professor Samit Roy

He received his doctorate in engineering science and mechanics from Virginia Tech Institute. He is currently the William D. Jordan Endowed Professor in the Department of Aerospace Engineering and Mechanics at the University of Alabama. Roy’s research interest is directed toward out-of-autoclave manufacturing, multi-scale modeling, and failure prediction of fiber-reinforced polymer composites and structural adhesives subjected to aggressive environmental conditions. He is also actively involved in the application of nanostructured reinforcements in enhancing the performance of composite materials, and he has organized numerous sessions at the AIAA-SDM conference on this topic. He has developed structural health management concepts that include sensor placement optimization for structural weight and cost reduction, as well as smart materials for non-autonomous self-healing. He has been the PI on numerous projects, including several NASA-funded projects on the use of polymer matrix composites (PMC) for cryogenic storage as well as for high-temperature supersonic airframes. He was an invited panelist at the Fairbanks, Alaska, workshop on Composites for Extremely Cold Temperatures and Extraterrestrial Applications organized by the National Science Foundation in August 2004. He was invited as a plenary speaker at a Composites Durability Conference organized jointly by the NSF and Cambridge University in September 2007. Roy has authored one reference book on composite materials, more than 75 journal publications, 14 book chapters, and 80 conference papers. He was the recipient of Outstanding Teaching Award and a Faculty Excellence Award at UMR in 1999 and 2000, and Outstanding Ph.D. Mentoring award at Alabama in 2017. In December 2004, he was elected associate fellow of the American Institute of Aeronautics and Astronautics (AIAA), and elected fellow of ASME in 2010. He was elected chairman of the ASME NanoEngineering for Energy and Sustainability (NEES) steering committee in 2014, and division chair for the Emerging Composite Technologies Technical Division of the American Society for Composites in 2016. He is one of the contributing editors of the Polymer and Polymer Composites journal, Mechanics of Advanced Materials and Structures, and section editor of Applied Mechanics Review. He has also been invited to give plenary and keynote lectures at numerous conferences on composites and nanostructured materials.