MATERIALS KEYNOTE
Dr. Samit Roy
The University of Alabama
Presentation Title: Atomistic Simulation of Damage in Carbon-Carbon Composites from Impact with Water Droplets at Hypersonic Velocity
Abstract: Carbon-carbon (C-C) composites used in hypersonic airframes experience extreme thermo-mechanical stresses and environmental conditions that can lead to physical and chemical erosion of the material. The leading-edge of a hypersonic airframe may undergo erosion due to extreme aerodynamic heating and entrained moisture in the boundary layer. Such leading-edge erosion could adversely affect the accuracy of the terminal guidance to target of a hypersonic weapon. This study employs reactive molecular dynamics (RMD) to simulate the impact of water droplets on a novel C-C composite at hypersonic velocity transiting through a shockwave prior to impact. The composite consists of simulated carbon fibers embedded within a glassy carbon matrix derived from the pyrolysis of polyfurfuryl alcohol (PFA), modeled using ReaxFF potential. The polymerization and pyrolysis processes are precisely modeled using RMD simulations, closely matching experimental findings. To emulate the realistic flight environment, the simulation incorporates a pre-formed air shock-wave layer through which the water droplet travels before striking the heated composite surface at hypersonic velocity results in material degradation due to impact as well as chemical ablation due to high-temperature (2500 K) oxidation. This approach enables the evaluation of mechanical damage as well as chemical degradation in C-C composites, an aspect often neglected in purely mechanical simulations like finite element analysis or peridynamics. Figure 1 shows the RMD predicted damage on a simulated C-C composite due to water droplet impact normal to the surface and oblique to the surface. As shown in the figure, the depth of the crater due to oblique impact is less severe than the direct impact case. Furthermore, the flattening of the water droplet while transiting through the shock-wave region prior to impact on the C-C composite results in less severe cratering. The insights gained here are critical for advancing predictive models of erosion on C-C composites and guiding the design of next-generation thermal protection materials for hypersonic aerospace applications.
Biography: Dr. Samit Roy received his Ph.D. in Engineering Science & Mechanics from Virginia Tech in Blacksburg, Virginia. He is currently the William D. Jordan Endowed Professor in the Department of Aerospace Engineering and Mechanics at University of Alabama (UA). Dr. Roy's research interest is directed towards multi-scale modeling and life-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 performance of composite materials, and was awarded a patent for this work in 2023. He has developed structural health management concepts that include sensor placement optimization for structural weight and cost reduction, as well as smart materials for intelligent self-healing. This research has attracted keen interest from the US Air Force and NASA and he has filed for a provisional patent related to this work. He has authored over 200 peer-reviewed journal articles and book chapters, and has monitored more than 25 graduate students at UA. He was elected Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA) in 2004, elected Fellow of ASME in 2010, and Fellow of American Society for Composites (ASC) in 2022. He was elected Chairman of the ASME NanoEngineering for Energy and Sustainability (NEES) steering committee in 2014, and is the current Division Chair, Emerging Composite Technologies Technical Division, of the American Society for Composites since 2022. He is the recipient of the ASC Outstanding Researcher Award in Composites in 2019 and again in 2023.