About

David Ehrhardt is an Assistant Research Professor at The Grainger College of Engineering at the University of Illinois Urbana-Champaign. His academic background includes a BS and MS in Mechanical Engineering from Bradley University and a PhD in Engineering Mechanics from the University of Wisconsin-Madison. His research focuses on advanced material testing, structural dynamics, and experimental measurement techniques in extreme environments. Ehrhardt's work involves the development and application of novel optical measurement methods to study the static and dynamic responses of structures subjected to extreme mechanical, thermal, and fluid-thermal-structural loading conditions, including high-speed wind tunnel environments. His contributions include model calibration for predicting structural responses under extreme loads, designing structures with unique nonlinear behaviors, and investigating aeroelastic instabilities and fluid-structure interactions in supersonic flows. Ehrhardt has also worked on additive manufacturing of structural components, materials testing in extreme environments, and the use of finite element model updating and validation. His research has significant implications for aerospace structures, thermal post-buckling of panels, and the development of structures exhibiting nonlinear normal modes.

Research topics

• Computer Science
• Mechanics
• Physics
• Mathematics
• Engineering
• Materials science
• Structural engineering
• Optics
• Statistical physics

Selected publications

• Experiments on Aerothermal and Incident-Shock Effects on Fluid-Structure Interaction in Hypersonic Flow

  SSRN Electronic Journal · 2026-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Aerothermoelastic Behavior of Thermally Buckled Panels at Mach 6

  SSRN Electronic Journal · 2026-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Pressure-Sensitive Paint Investigation of Blunt Fin over a Compliant Panel in Supersonic Flow

  AIAA Journal · 2025-06-30

  article

  The fluid–structure interactions of a hemispherically rounded fin mounted over a compliant panel in Mach 2 flow were investigated as a continuation of a previous study that investigated the same fluid–structure interaction case. The main focus of this study was to investigate the pressure distribution across the surface of the fin using pressure-sensitive paint. The geometry for this study consisted of a thin, flexible panel fixed on all edges. A fin with a hemispherically rounded leading edge was mounted in a manner such that the leading edge of the fin overhung the panel. The fin was deflected to several angles of attack with respect to the oncoming flow. Both a rigid and compliant panel model were used in order to provide a comparison between the flow with and without the dynamics of the compliant panel. The time-averaged pressure distributions for the rigid panel visualized the flow features on the fin that are inherent to the fluid–structure interaction, without the impact of the compliant panel. Evaluation of the aerodynamic loading on the fin showed that at low fin angles of attack, the fin experienced higher loading compared to the rigid panel. Spectral analysis of the pressure distributions with the compliant panel revealed the oscillation of the flow structures on the surface of the fin. Spectral proper orthogonal decomposition verified that the flow structures found in the time-averaged pressure distributions also exhibited the same frequency content.

  PublisherDOI

• Sustainable Shape Memory Elastomers with Reduced Melt Viscosity and Enhanced Stiffness

  ACS Applied Polymer Materials · 2025-02-11 · 1 citations

  articleOpen access

  Melt reactive processing of lignin with nitrile rubber is a promising approach to synthesizing shape memory materials. The strong intramolecular interactions in lignin macromolecular structures, caused by π–π stacking in aromatic rings and hydrogen bonding, often result in large phase separation or low miscibility with rubbers. In this study, we investigated the chemical and molecular characteristics, as well as the stiffness and complex viscosity, of modified kraft lignin melt-reacted with an acrylonitrile/butadiene copolymer containing 41% acrylonitrile (NBR41). To enhance the macromolecular compatibility of kraft lignin with NBR41, kraft lignin was cross-linked with poly(propylene glycol) diglycidyl ether (PPDE) and trimethylolpropane triglycidyl ether (TTE), both rich in epoxy reactive groups capable of forming chemical bonds with hydroxyl and carboxyl groups. Our findings demonstrate that the modification of kraft lignin with PPDE and TTE resulted in significantly increased stiffness of the composites. The elastic modulus of NBR41-Kraft lignin-PPDE and NBR41-Kraft lignin-TTE increased by 82 and 162%, respectively. Both the yield strength and Young’s modulus of these two samples showed dramatic improvements. Specifically, the yield strength and Young’s modulus of NBR41-Kraft lignin-TTE increased nearly 4 and 3-fold, respectively, compared to the control sample. Interestingly, despite significant improvements in mechanical properties, the viscosity of NBR41-Kraft lignin-PPDE was substantially lower than that of the control sample. At 210 °C and an angular frequency of 1 rad/s, the complex viscosity of NBR41-Kraft lignin was approximately 100.25 ± 4.77 kPa·s, while that of NBR41-Kraft lignin-PPDE was significantly lower at 56 ± 0.93 kPa·s. These findings were validated through Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic mechanical analysis, thermal characterization, rheological tests, and quasi-elastic neutron scattering techniques.

  PublisherOA PDFDOI

• Experimental and Numerical Investigation of the Nonlinear Bending-Torsion Coupling of a Clamped-Clamped Beam with Centre Masses

  River Publishers eBooks · 2025-08-07

  book-chapter1st authorCorresponding

  The vibration characteristics of beams have been extensively studied due to their wide application across multiple fields (i.e. spacecraft antennae, aircraft wings, turbine blades, skyscrapers). Of particular interest, specific geometries of beams have been shown to induce coupling between the fundamental bending and torsion modes. This coupled motion can be observed in a beam’s linear normal modes can be avoided with the correct selection of geometric properties. This work investigates the coupled bending-torsion behaviour of a clamped-clamped beam that is coupled perpendicularly, mid-span to mid-span, to a second beam with tip masses within the nonlinear response regime. The first torsion mode of the beam system is tuned by modifying the mass distribution such that closely spaced bending and torsion linear normal modes can be realized. The nonlinear behaviour is presented using nonlinear normal mode backbone curves and forced responses in the vicinity of the modes of interest.

  PublisherDOI

• Flow-Induced Strain of Parachute Textiles With Multiscale Digital Image Correlation

  2025-01-03 · 1 citations

  article

  Micro- and macro-mechanics of parachute fabrics under a flow-induced pressure differential are studied using synchronous digital image correlation, microscopy, and permeability testing. Results are presented for a nylon textile commonly used in parachute systems, MIL-C-7020H Type III. The textile is subjected to a sequence of steady and stepwise incremental pressure differentials. Measurements resolve the pressure-dependent permeability and effective porosity of the textile, and the time and load-rate dependent response of sample deformation. It is shown that pore opening is negligible in the range of pressures studied.

  PublisherDOI

• PSP Investigation of a Hemispherically Rounded Blunt Fin over a Compliant Panel in Supersonic Flow

  2024-01-04

  article

  The fluid-structure interactions of a hemispherically rounded fin mounted over a compliant panel in Mach 2 flow were investigated as a continuation to a previous study which investigated the same fluid-structure interaction case. The main focus of this study was to investigate the pressure distribution across the surface of the fin using pressure-sensitive paint (PSP). The test geometry for this study consisted of a thin, flexible panel fixed on all edges. A fin with a hemispherically rounded leading edge was mounted in a manner that the leading edge of the fin overhung the panel. The fin was also deflected to several angles of attack with respect to the oncoming flow. Both a rigid and a compliant panel model were used in order to provide a comparison between the flow with and without the dynamics of the compliant panel. The time-averaged pressure distributions for the rigid panel visualized the flow features on the fin that are inherent to the fluid-structure interaction, without the impact of the compliant panel. Evaluation of the aerodynamic loading on the fin showed that at low angles of attack for the compliant panel, the fin experienced higher loading compared to the rigid panel. However, at high angles of attack, the aerodynamic load on the fin was found to be similar for both the rigid and compliant panels. Spectral analysis of the pressure distributions with the compliant panel revealed the oscillation of the flow structures on the surface of the fin. The frequencies of these oscillations agreed with the frequency content of the oscillations of the compliant panel found previously. Spectral proper orthogonal decomposition verified that the flow structures found in the time-averaged pressure distributions also exhibited the same frequency content.

  PublisherDOI

• Correction: PSP Investigation of a Hemispherically Rounded Blunt Fin over a Compliant Panel in Supersonic Flow

  2024-01-08

  article
  PublisherDOI

• Fluid-Structure Interactions of a Fin over a Compliant Panel in Supersonic Flow

  AIAA Journal · 2024-11-12 · 2 citations

  article

  The fluid-structure interactions of a blunt fin mounted over a compliant panel in Mach 2 flow were investigated. The test geometry consisted of a thin, flexible panel fixed on all edges with a blunt fin with a hemispherically rounded leading edge mounted in a manner that the leading edge of the fin overhung the panel. The blunt fin was also pivoted to several angles of attack with respect to the oncoming flow. This allowed for the study of the dynamic system created by the interactions between the compliant panel and the blunt fin geometries. Both rigid and compliant panel models were used in order to provide a comparison between the flow with and without the dynamics of the compliant panel. High-speed schlieren and surface oil flow visualizations showed that the time-averaged flow remained almost entirely unchanged between the rigid and compliant panels. The instantaneous flow fields, however, showed a highly dynamic system where the compliant panel induced oscillatory shock waves that were both stationary and freely moving. Simultaneous high-speed schlieren visualization and stereo digital-image correlation showed a strong linkage between the motion of the shock waves and the deformation of the panel. This was demonstrated through frequency analysis and modal decomposition of the panel deformation and shock motions.

  PublisherDOI

• Fluid-Structure Interactions of a Hemispherically Rounded Blunt Fin over a Compliant Panel in Mach 2 Flow

  2023-06-08

  article

  View Video Presentation: https://doi.org/10.2514/6.2023-3882.vid The fluid-structure interactions of a blunt fin mounted over a compliant panel in Mach 2 flow were investigated. The test geometry consisted of a thin, flexible panel fixed on all edges with a blunt fin with a hemispherically rounded leading edge mounted in a manner that the leading edge of the fin overhung the panel. The blunt fin was also pivoted to several angles of attack to the oncoming flow. This allowed for the study of the dynamic system created by the interactions between the flexible panel and the blunt fin geometries. Both rigid and compliant panel models were also used in order to provide a comparison between the flow with and without the dynamics of the compliant panel. High-speed schlieren and oil flow visualizations showed that the time-averaged flow remained almost entirely unchanged between the rigid and compliant panels. The instantaneous flow fields, however, showed a highly dynamic system where the compliant panel induced oscillatory shock waves that were both stationary and freely moving. Simultaneous high-speed schlieren visualization and stereo digital-image correlation showed a strong linkage between the motion of the shock waves and the deformation of the panel. This was demonstrated through frequency analysis and modal decomposition of the panel deformation and shock motions.

  PublisherDOI

Frequent coauthors

• Timothy J. Beberniss

  United States Air Force Research Laboratory

  23 shared

• Ricardo Pérez

  United States Air Force Research Laboratory

  12 shared

• Matthew S. Allen

  12 shared

• Simon A. Neild

  11 shared

• S. Michael Spottswood

  United States Air Force Research Laboratory

  11 shared

• Zachary B. Riley

  11 shared

• Thomas Hill

  University of Bristol

  5 shared

• Ludovic Renson

  5 shared