Our Current Research Projects
  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 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 Fracture of High-strength Steels
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 plates under impact loading conditions. In particular, the effects of cross pin densities on the dynamic fracture behavior are studied systematically.
  Impact Damage in Aircraft Composites
The Marines-supported research program aims to determine the damage to the aircraft composite by the impact of 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 the Air Force Research Laboratory, 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.
  Dynamic Behavior of Brittle Materials
This research program, supported by US Army and DARPA, examines the dynamic mechanical response and failure behavior of brittle materials such as glass, glass ceramic, and high-strength ceramic. The materials are subject to a variety of loading conditions including uniaxial compression, compression/shear, multi-axial compression, four-point bending, dynamic fracture, and dynamic ring-on-ring. The effects of loading conditions and material composition are systematically investigated.
  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 Separation 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 separation.