RESEARCH PROJECTS

On-Going Project

• Nondestructive Evaluation of Composite Sandwich Panels, 2000-present, sponsored by ONR (Office of Naval Research).
  
  Develope quantitative thermographic and ultrasonic NDE techniques to characterize various types of defects in polymeric composite sandwich panels.

Past Projects

• Full Scale Simulation of Multiple Scattering of Elastic Waves in Composite Materials, 1992-2000, MIT, sponsored by ONR (Office of Naval Research).
  
  This is the project on which my Ph.D. thesis is based. This project is mainly a theoretical study of multiple scattering phenomenon of elastic waves in an elastic medium embedded with an arbitrary number of scatterers, a micromechanical model for fiber-reinforced composite materials. The scatterers under consideration consists of a fiber core and a surrounding layer which can either be the model for the interphase, a thin layer which is chemically or/and physically generated between fiber and its surrounding polymeric matrix medium, or be part of the fiber structure commonly fond in many types ceramic fibers. The study would lay the theoretical foundation for the development and application of the ultrasonic and acousto-ultrasonic nondestructive evaluation and characterization techniques for composite materials, with an emphasis in characterization of the mechanical properties of the interphase. Publications under preparation.

  Moisture Effects in Composite Materials, 1990-1992, University of Tennessee Knoxville, sponsored by US ONR (Office of Naval Research).
  

  Study the sea-water absorption process, which is typically nonlinear (non-Fickian), and its effects on the mechanical properties of carbon-fiber composite materials in both macro and micro scales. Built a pressure vessel to simulation the deep see immersion; devised a computational methodology to predict the moisture distribution profile inside the composites from the mere knowledge of the total moisture weight gain due to the non-linear (non-Fickian) moisture absorption process; analyzed the residual stresses within the composite materials due to the moisture intake. Performed standardized test on material strength, modulus, fatigue life with comparison with virgin materials, and some SEM observations of microscopic damages due to moisture. 1 Publication.

  Design of Loading Tab for Composite Specimens, 1992, University of Tennessee Knoxville.

  Loading tabs are usually made of aluminum adherer to the ends of a composite specimen. The tabs serve two purposes: to improve the gripping interface with the testing machine and to distribute the load evenly. However, the down side of a poorly designed tab is that it may cause stress concentrations in the specimen around the ends of the tabs, leading to measurement inaccuracy and specimen inmaturely break up. In this project, FEM was used to study the elastic-plastic deformation of a tabbed composite specimen for various configurations of the loading tab and the mechanical properties of the glue. An optimal design of is thus drawn.

  Nonlinear Viscoelastic Fracture/Damage Behaviors of Composite Materials, 1989-1991, Chinese Academy of Sciences, sponsored by Chinese National Science Foundation.

  Viscoelasticity and damage (in the continuum mechanics sense) are the two most prominent mechanical properties of polymeric composite materials, and in general, their phenomenological characteristics are similar in that, when the load level is held steady, the deformations by these effects continue. The project investigated the constitutive relations of the two, and devised experimental methods to distinguish, and in turn, characterize them. This project was an extension of the research works of my Master thesis. I was listed as one of the two principal investigators.

  Prediction of the Strength and Mixed-Mode Crack Propagation Direction in Composite Materials, 1987-1990, Chinese Academy of Sciences & Beijing University of Science and Technology, sponsored by Chinese Academy of Sciences.

  Early in 1987, I, along with my Master thesis advisor, Prof. S. Y. Zhang, proposed a criterion to predict the cracking direction of the composite materials. This project extended the scope of the criterion to the prediction of the failure strength of composites. Extensive experimental works were done to verify the criteria. A few publications, and 1 award.

  Computer Simulation of Damage Evolution Process of Notched Composite Materials Under Creep Loading, 1986-1988, Chinese Academy of Sciences.

  This is the project for my Master thesis. The work include modified a nonlinear anisotropic viscoelasticity theory to make it experimentally deterministic, and in turn, developed a recursive form for computation needs; developed an experimental procedure and the associated data processing procedure to determine the nonlinear viscoelastic constitutive relation; developed a process of fabricating random short fiber reinforced composite specimens by hand-layup; developed a continuum damage mechanics model for the damage evolution process; developed of a complete finite element package that couples nonlinear viscoelastic and the damage effects. This is the exploratory study upon which a 3-year project (1989-1991, see above) funded by Chinese National Science Foundation was based. The publication of the works was halted due to my departure from the academic circle to take a government administrative. Only 2 conference papers were generated.

  On the Dynamic Response of Offshore Structures Due to Wave Loadings, University of Science and Technology of China, 1985.

  Project for my Bachelor thesis. Modal and spectrual analysis of the dynamic response of offshore structures under the loadings induced by ocean waves using a simple finite element model.