RESEARCH

Mechanical Behavior of Open Cellular Materials at Ambient and Elevated
Temperatures:
The goal of the present research is to develop a better understanding of the tensile
response of open-cellular aluminum 6061 - T6 alloy. Both tensile and compression
samples of this metallic foam were tested under constant strain rate conditions at 293,
423, and 523 K. Scanning electron microscopy was performed on individual struts to
assess the modes and mechanisms associated with fracture. Theoretical models are being
evaluated and developed which predict the behavior of the open cell structure from the
mechanical properties of the fully dense alloy. Funded by a grant from the Department of
Energy in collaboration with Lawrence Livermore National Laboratory.

Mechanisms of Corrosion Fatigue Damage in Implant Materials:
This research is aimed at investigating the characteristics of the surface damage processes
that lead to fatigue cracking in a titanium alloy, cobalt-base superalloy and polymer
specimens used in biomedical implants. The research utilizes a recently developed
scattered light scanning system to monitor crack formation and coalescence in-situ. The
present methodology takes both microcrack length and density into account. The present
approach promises to provide improved predictions of corrosion fatigue failure over
those based on conventional crack detection techniques. Funded by Gifts for Research
from Baxter Healthcare – Cardiovascular Division.

Fatigue Deformation and Damage Mechanisms in Bimetal Fasteners:
Riveted joint assemblies are common sites for the early onset of fatigue damage in
aircraft structures. Fatigue and corrosion-fatigue damage at these sites is often
complicated by the fact that multiaxial stresses are inherent to joint structures. Fatigue
specimens consisting of a plates joined together with several bimetal rivets are currently
being tested in the present research program. An computer-controlled servo-hydraulic
testing machine is being used to test rivet joint samples under carefully controlled fatigue
loading conditions. State of the art diagnostic instruments are also being investigated in
an effort to develop better methods of monitoring fatigue crack initiation and growth in
the joint structures. Finite element models are also being developed to better understand
the nature of the fatigue stresses generated in these structures. The goal of the research is
to develop a better understanding of fatigue mechanisms in riveted joints with fatigue life
that will lead to increased fatigue life. Supported by Textron Fasteners, Inc. in Irvine,
CA.

COLLABORATIVE RESEARCH

Role of Impurities on Superplastic Flow and Cavitation:
The primary objective of the investigation is to develop a better understanding of the
ways in which impurity segregation at interfaces influences the characteristics of
superplastic flow at low stresses. The experimental approach involves a detailed
examination of the effect of selected impurity elements on dislocation motion, plastic
instability, interfacial sliding, microstructure, and cavitation processes. In particular,
cavity nucleation and the relationships between deformation and cavity growth are
closely investigated. Funded by NSF. [Role: Co-PI, PI: Professor F. A. Mohamed]

Energy Dissipation in Dental Implant Materials and Structures:
Recent clinical findings indicate that an optimum amount energy dissipation is a critical
to maintain the proper positioning of teeth integrated into dental implant structures. The
amount of energy dissipated is determined by the design of the implant structure and the
mechanical properties of the materials used. As a result of both aesthetic and medical
constraints, the freedom to alter the design of dental implants is limited. However, the
proper selection of materials makes it possible to achieve the desired energy dissipation
by the implant structure. The activities of the present work are threefold. First, I invented
a new materials testing technique for this work that performs quantitative determinations
of energy dissipation under typical occlusal conditions. A patent has been issued for this
novel instrumentation (Patent No. 6,120,466). Second, optimum energy dissipation is
determined by measuring the mechanical response of the natural tooth complex. Third,
the mechanical response of dental implant structures is assessed and the energy
dissipation is being characterized. Finally, new implant materials are being selected and
assessed based on the experimental results to achieve the optimum mechanical response.
Funded by Gifts for Research from Steri-Oss Inc. [Role: PI, Associate Researcher: C. G.
Sheets, DDS]

Biological Methods for Controlling Corrosion in Service Water Systems:
The primary objectives of the present research are twofold:
(1) to evaluate and develop biological methods that prevent, or significantly reduce,
abiotic corrosion and microbiologically influenced corrosion (MIC) in power plant
service water systems, and (2) to develop a simple diagnostic kit that will identify the
bacteria present in the biofilm before and after the biological treatment. Sidestream
systems have been developed that are capable of combined testing approaches involving
microbiology, electrochemistry, and surface chemistry, which are being used to provide
insight into complex interactions between biofilms and metal surfaces in service cooling
water. One of these systems is stationed at the UCI Central Generating Facility.
Multimedia microbiological cultures, biochemical assays and genetic probes are being
used to investigate the presence of specific types of bacteria. Electrochemical techniques,
including electrochemical impedance spectroscopy (EIS), linear polarization resistance
(LPR), electrochemical noise analysis (ENA) and DC techniques are being used to
investigate the corrosion behavior of various engineering alloys under service water
conditions. News articles describing our research have appeared in several periodicals
including Scientific American. Funded by EPRI. [Role: PI, Co-PI: Dr. P. J. Arps]