Mechanical Effects of the Polarization Switching on Electrically Excited Vibration of a Ferroelectric Bar
Acoustic Emission and Acousto-Ultrasonic Damage Analysis of Composites

Date:  Tuesday, April 29, 1997
Time:  3:30 p.m.
Place:  306 Bancroft Hall
 

Mechanical Effects of the Polarization Switching on Electrically Excited Vibration of a Ferroelectric Bar

Huiyu Fang
Department of Engineering Mechanics 
University of Nebraska 
Lincoln, NE    68588-0526 
Ph.D. Advisor:  Dr. Qing Jiang

When an alternating electric field is imposed along the length of a ferroelectric bar with the magnitude exceeding a certain value -- the coercive field, the response of the dielectric displacement to the applied electric field, exhibits a hysteresis loop. The shape of the loop is determined by the ferroelectric characteristics of the material. A mathematical model has been developed to simulate the hysteretic response, and the analysis is carried out using the finite difference method. A comparison of the present analysis with previous work available in the literature and an interpretation of the present results are included. 
 
 

Acoustic Emission and Acousto-Ultrasonic Damage Analysis of Composites

Jie Qian
Department of Engineering Mechanics 
University of Nebraska 
Lincoln, NE   68588-0526 
M.S. Advisor:  Dr. Yuris Dzenis

As a consequence of the heterogeneity of composites, different modes of damage occur in these materials under loading, such as matrix cracking, delamination, fiber/matrix debonding, and fiber failure. Accumulation and evolution of damage in composites under fatigue is the general topic of this research. In the first stage of the research, damage evolution in a cross-ply graphite/epoxy composite under tensile loading has been studied by means of acoustic emission (AE) and acousto-ultrasonic (AU) analysis. Wide band sensors have been used in the AE and AU monitoring for the first time. In the AE analysis, both parametric and transient data were investigated. History plots, distribution plots, correlation plots, and cluster analysis were used to understand the damage evolution in the composite. In future work, damage analysis under fatigue will be studied. New techniques, such as pattern recognition, will be introduced in the transient AE data analysis.