SIZE ANALYSIS AND THE USE OF PARTICULATES IN ADVANCED MATERIALS
Professor Don Rasmussen
has published extensively in the areas of nucleation and growth
of new phases and on techniques to study nucleation and particle
growth processes. Currently his research is focused on the study
of characterizing concentrated colloidal systems, depositing thin
films and modifying binder systems for high temperature ceramics.
His ongoing experimental projects include (1) measurement of the
dynamic light power spectrum from concentrated colloidal systems
using a fiber optic probe (being developed to study particle breakdown,
aggregation or growth in concentrated systems.), (2) determination
of the particle size from the shape of the power spectrum and the
particle concentration from the integrated power spectral density,
(3) controlled precipitation of nanoscale alumina from bauxite liquors,
(4) nucleation and growth of particles in supersaturated systems
( both aerosols in vapors and particles in supersaturated liquors
), and (5) the characterization of the hardness and surface properties
of CMP polishing pads by surface energy determination and measurement
of hardness using nanoindentation resistance.
Flows and Materials
Professor Hayley Shen, of Clarkson University's Department
of Civil and Environmental Engineering, is investigating granular
flows in terms of constitutive relations, flow rate effects, particle
size and shape effects. She is also interested in two-phase flows.
Professor Shen submitted two proposals about granular flows to NASA.
("Transitional Granular Flows" was submitted to the NASA Space Station
Program on Jan. 12, 2001. "Constitutive Relation in Transitional
Granular Flows" was submitted to the NASA Microgravity Complex Fluids
Program on May 12, 2001.) These proposals involve collaborations
with Tohoku University and Saitama University
(Japan), and the University of Florida and Clarkson University.
Professor Shen recently made the following conference
presentations. ("Plastic to Nonlinear Viscous Transition of Constitutive
Relations for Granular Materials - Sample Size Effect," presented
at the Powders and Grains 2001, Sendai, Japan, May 2001. "Random
Voids and Constitutive Relations for Two-Dimensional Dense Granular
Materials," presented at the ASCE-ASME-SES Joint conference on Mechanics
and Materials 2001 (MMC2001), San Diego, June 2001.) Her paper "Sample
Size Effects on Constitutive Relations of Granular Materials" appears
in the October 2001 issue of the Journal of Engineering Mechanics.
AND CYCLIC PLASTICITY
Reverse magnetostriction has been identified as a
deformation mechanism in the low plastic strain amplitude fatigue
behavior of nickel. Professors David Morrison
and John Moosbrugger,
working with graduate student Yan Jia, have been studying the links
between dislocation substructure evolution and the mechanical behavior
of nickel during fatigue type loading at low plastic strain amplitude.
They have recently found that anomolies in the shapes of the stress-
plastic strain hysteresis loops can be explained on the basis of
the magnetostriction of nickel. All ferromagnetic materials exhibit
strain due to an applied magnetic field, the so-called Joule magnetostriction.
In reverse magnetostriction, the imposition of a normal stress induces
magnetization along with an accompanying magnetostriction. In nickel,
a tensile stress causes net domain magnetization perpendicular to
the stress axis, while a compressive stress causes domain magnetization
parallel to the stress axis. The result is that at low plastic strain
amplitudes, hysteresis loops are constricted due to the magnetic
component of inelastic strain that is not dislocation-based. Experiments
performed on specimens in the presence of a magnetic field strong
enough to maintain nearly fixed domain magnetization under tension-compression
cycling showed that these constrictions could be eliminated.. In
this case nickel will behave much like copper, which produces analogous
dislocation substructure in fatigue type loading and which is diamagnetic
at room temperature.