Seminar Series - 2000-2001

Antiplane Piezoelectricity With Initial Fields
Dynamical Methods of Atomic Force Microscopy
Manufacturing, Characterization, and Applications of Carbon Nanofibers

Date:  Tuesday, March 6, 2001
Time:  3:30 p.m.
Place:  W128 Nebraska Hall

Antiplane Piezoelectricity With Initial Fields

Fenghong Liu
Department of Engineering Mechanics
University of Nebraska, Lincoln, NE    68588-0526
Advisor:  Dr. Eveline Baesu

The effects of pre-existing stress and electric field on stress concentrations in piezoelectric materials under antiplane state deformation are studied. The objectives are to obtain an analytic solution in terms of complex potentials and to conduct a parametric study of these effects on stress and electric fields. The formulation of the problem of an infinite piezoelectric plane with a circular hole is presented. The problem of finding the solution is reduced to identifying the coefficients of Laurent’s series for the unknown complex potentials involved. This will be done by enforcing the boundary, and the far field conditions.

Dynamical Methods of Atomic Force Microscopy

Roshanak Nilchiani
Department of Engineering Mechanics
University of Nebraska, Lincoln, NE    68588-0526
Advisor:  Dr. Joseph Turner

Atomic force microscopy (AFM) has become the leading method for obtaining surface topographies in the last decade. Recently, interest has shifted towards obtaining material stiffness data by modification of the AFM to an Atomic Force Acoustic Microscope (AFAM). This is achieved by implementing an ultrasonic excitation source, which is used to vibrate the sample. The contact with the sample causes shifting of the natural frequencies of the cantilever. Using appropriate contact theories, it is then possible to relate the frequency shifts to changes in surface stiffness. In this talk, the experimental setup of the AFAM and its application to different materials, including polysilicon Micro Electromechanical Systems (MEMS) is discussed. Using this methodology, it is possible to determine the stiffness difference of the individual grains with nanometer resolution, in addition to obtaining the surface characteristics provided by topographical data.

Manufacturing, Characterization, and Applications of Carbon Nanofibers

Yongkui Wen
Department of Engineering Mechanics
University of Nebraska, Lincoln, NE    68588-0526
Advisor:  Dr. Yuris Dzenis

Carbon nanofibers were manufactured using electrospinning technique. The as-spun polyacrylonitrile (PAN) nanofibers were stabilized and carbonized to convert them into carbon nanofibers. The diameters of typical carbon nanofibers were in the range from 100 - 500 manometers. The carbon nanofibers were observed by scanning electron microscopy, transmission electron microscopy, and atom force microscopy. Electron diffraction patterns were obtained from individual carbon nanofibers. Carbon nanofibers have very high ratio of surface area to mass. They are also expected to retain many good properties of regular carbon fibers such as high modulus and strength, good fatigue durability, and excellent corrosion resistance. Therefore, carbon nanofibers can be used in composites to improve mechanical properties. Reinforcement of interfaces with carbon nanofibers as a means to improve interlaminar fracture toughness and suppress delamination is being currently explored.


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