Research

Dynamic Characterization of Avian Muscle Tissue

Airplanes are not the only things in the sky- aerospace engineers must also consider the possibility of bird strikes affecting their aircraft. Designing safe aircraft requires engineers to accurately simulate and design components to withstand vehicle-animal collisions. This research combines knowledge across many engineering disciplines such as materials, aerospace, and even biomedical engineering to mechanically characterize avian muscle tissue at quasi-static and dynamic rates to better inform bird-vehicle collision simulations.

Studying the mechanical properties of biological materials is notoriously difficult, even more so with the added complexities of testing at dynamic strain rates. In this research, we quantify the strain rate dependent and anisotropic mechanical behaviors of avian skeletal muscle under compression, tension, and ballistic impact experiments. This is accomplished by designing and implementing a variety of experimental setups that incorporate hydraulic load frames, Split-Hopkinson Pressure Bars, drop-towers, and more. The knowledge and experimental techniques generated from this research have opened pathways to explore more difficult-to-test materials in the future.

(Left) Histology Scan of Typical Avian Muscle Compression Specimen. (Right) Dynamic Compression  Stress-strain data of Avian Skeletal Muscle Highlighting Anisotropic Stress-Strain Response

In-Situ Visualization of Dynamic Processes using High-Energy Synchrotron X-rays

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Dynamic Four-Point Bend Fracture Using Kolsky Bar

Our lab specializes in conducting high strain rate experiments using our in-lab setup of Kolsky Bar (Split Hopkinson Pressure Bar), traditionally used for compression and tension experiments. This project introduces four-point bending with modified Kolsky Bar and explores the methodology and deformation of widely used aerospace materials as it is important to understand their performance under extreme loading conditions. Pulse shaping techniques are implemented to ensure dynamic equilibrium and minimize inertial effects. Fracture is observed with high-speed imaging cameras and strain analysis is done using Digital Image Correlation (DIC) to measure local strain fields. Computationally, Finite Element Analysis (FEA) is done to extract further values.

In-situ Visualization of Dynamic Loading on Energetic Materials

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Past Research

Dynamic Response of Textile Materials

The focus of this Army-sponsored research program is on the mechanical behavior and the rate effects of single high-performance fibers. New experimental methods are developed to measure the axial tension, transverse compression and torsion behavior of transversely isotropic high-performance fibers with diameters in the order of 10 micrometers. The effects of the damage caused by transverse deformation on the load-bearing capabilities of the fiber have been fully investigated. Phenomenon similar to the Mullins effect observed in rubber materials also exists in the transverse response of Kevlar KM2 and other fibers.

Dynamic Behavior of Biological Tissues

This Collaborative Program with Army Research Laboratory aims to the determination of mechanical behavior and the associated rate effects of biological tissues. The dynamic mechanical response of biological tissues to impact loading has been an important aspect in effective design of personnel protection systems. However, the rate effects on the mechanical response of soft tissues have not been well studied. Furthermore, the effects of the tissue status (temperature, aging, freezing, etc.) on the high-rate mechanical response are not understood.

In this research, the tensile and compressive stress-stain behavior of soft tissues is investigated experimentally, at quasi-static strain rates (0.04/s~4.0/s) with a conventional material testing system and at dynamic strain rates (400/s~1500/s) with modified Kolsky tension and compression bars. The experimental results reveal a significant dependence of the stress-strain behavior on strain rates.

Dynamic Response of Steel

This research program, supported by Sandia National Laboratories, is designed to determine the dynamic fracture toughness of high-strength steels as a function of loading rates. When a structure, such as the fracture specimen and the associated loading fixtures, is under high-rate loading, special attention is needed to minimize the inertia effects on the experimental records for material behavior. We use pulse shaping techniques to achieve dynamic load equilibrium, as well as constant loading rates.

Dynamic Interfacial Fracture in Composites

The goal of this ARO-supported research program is to determine the interfacial delamination behavior of composite laminates under impact loading conditions. In particular, the effects of through-thickness pin density on the dynamic fracture behavior are studied systematically.

Impact Damage in Aircraft Composites

This Marines-supported research program aims to determine the damage to the aircraft composite by the impact from a variety of conditions ranging from tool box drop to bird strike to ballistic impact. The experimental results and the microstructural observations will lead to the development of practical damage criteria to determine the aircraft structural integrity after impact.

Dynamic Compressive Behavior of Geo-Materials

In this research program, supported by the Sandia National Laboratories and DTRA, we develop new experimental capabilities that enable the characterization of dynamic compressive response of particulate geo-materials with systematic  variations in initial density, moisture level, strain rate, and hydrostatic confinement.

Dynamic Response and Failure Behavior of Materials at Small Scales

This research program, initially supported by the Sandia National Laboratories with current support from DTRA, explores the fundamental mechanisms of deformation and failure of materials used in MEMS/NEMS structures under impact loading conditions. Controlled acceleration/deceleration conditions are generated to subject the micro-machined specimens and devices to desired loading conditions. The functions of these structures are monitored during shock events. The small structures are then examined under optical and electron microscopes to reveal the mechanisms of high-rate deformation and failure.

High-strain Flow Behavior of Ductile Materials

When the cylindrical specimen of a ductile material is under compression for stress-strain response, the cylinder typically barrels at larger strains due to the effects of end friction. In this research project, we aim to examine approaches to subject the specimen to uniaxial stress loading even at very large axial strains using both experimental and numerical approaches. Effects of loading rates are also investigated.

Dynamic Damage Isolation by Interfaces in Layered Structures

Impact-induced damage has been observed to be contained in the front layer of a multi-layered structural system. In this program, we aim to examine the dynamic crack propagation within the front layer and the crack arrest at the interface. The focus is on a single crack such that fundamental understandings are developed that lead to critical conditions for damage isolation.

Penetration through MEMS sensor embedded Granular Earth Materials

Supported by DTRA, this project is to investigate the behavior of granular earth material such as sand, soil and concrete under penetration by high speed projectiles. The behavior of particle, wave propagation and failure procedure of those material have not been revealed yet. RF-communicated MEMS sensors are embedded in the target to measure the history of temperature and pressure. Flash X-ray is employed to monitor the motion of the particles during the process of penetration.