Seminar Series - 2001-2002

Polycrystal Modeling and Analysis of Ceramics
Micromechanical Analysis of Polycrystalline Ceramics
Transmission of Electric Energy Through an Elastic Wall by Acoustic Waves

Date: Tuesday, April 23, 2002
Time: 2:30 p.m.
Place: W183 Nebraska Hall

Polycrystal Modeling and Analysis of Ceramics

Shengqiang Xue
Advisor:  Dr. Ruqiang Feng

A computational method has been developed for analyzing the microstructural effects on the response of polycrystalline ceramics subjected to high-confinement loading. The material structure modeling is based on the simulated Voronoi polycrystal, which is a Voronoi tessellation with randomly selected crystallography orientation for each cell. The finite element (FE) analysis using the ABAQUS codes is employed for stress calculation. In order to incorporate the material structure model in the FE analysis, an algorithm has been worked out to generate special meshes that preserve the simulated polycrystalline structure. Numerical simulations have been carried out to investigate the influences of grain size and orientation on the stress distributions in the materials. Results will be presented for simulated polycrystalline silicon carbide undergoing highly confined elastic deformation. The significance of the results and future work will be discussed.

Micromechanical Analysis of Polycrystalline Ceramics

Dongmei Zhang
Advisors:  Drs. Ruqiang Feng and Mao S. Wu

An analytical and numerical study has been carried out to develop a computational method for analyzing crystal-crystal interactions and microplasticity in polycrystalline ceramics deformed under high confining stress. In this method, the micromechanical response at a point of interest is analyzed using an aggregation of simulated Voronoi crystals embedded in a homogenous and isotropic matrix. The microscopic heterogeneities due to both anisotropic crystal elasticity and in-grain plasticity are transformed into “eigenstrain” with the generalized Eshelby method. Closed-form fundamental solutions for the residual stress field resulted from the eigenstrains are formulated for generalized plane strain condition. An algorithm to implement the method for numerical analysis has been developed. Results will be presented for a series of calculations on polycrystalline silicon carbide under elastic uniaxial-strain compression, and future work will be discussed.

Transmission of Electric Energy Through an Elastic Wall by Acoustic Waves

Xuesong Zhang
Advisor:  Dr. Jiashi Yang

Electronic devices operating in a sealed armor have certain military and civilian applications like powering robots inside envelopes that should not be penetrated, process control devices operating in explosive-gas environments, and even medical devices implanted in human bodies. These sealed devices are usually powered by batteries that are also enclosed in the armor. After a period of time the batteries need to be recharged without opening the armor. The possibility of using acoustic waves to send energy through the elastic armor and charge the batteries inside has been suggested. A piezoelectric transducer exterior to the armor is used to convert electric energy into acoustic waves that propagate through the armor. Another piezoelectric transducer inside the armor is used to pick up the acoustic waves and convert the acoustic energy back into electric energy that is then used to charge the battery. In this work we perform a theoretical analysis of the processbased on the linear theory of piezoelectricity. Solutions for transmitted voltage, current, power and efficiency are obtained and their dependence on various parameters are examined.
 

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