Seminar Series - 1997-1998

Acoustic Emission Study of Damage Evolution in CFRP Laminates Based on Waveform Analysis
Direct Analysis of Interface Problems Using Virtual Dislocation Models and Integral Equations
Polycrystal Generation and Analysis

Date:  Tuesday, April 7, 1998
Time:  3:30 p.m.
Place:  W128 Nebraska Hall

Acoustic Emission Study of Damage Evolution in CFRP Laminates Based on Waveform Analysis

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

Due to heterogeneity of composites, damage modes in these materials are extremely complex.  Acoustic emission (AE) was employed in this work for nondestructive evaluation of damage accumulation and evolution in CFRP laminates.   Both AE parameters and transient waveforms were analyzed with special emphasis on the full waveform classification.  Three typical AE waveforms (A,B, and C) were extracted.  Based on their analysis, the rise time, amplitude, and duration of the AE events were chosen as the key parameters to classify the damage modes.  Parameter ranges for different damage modes were obtained and used to separate the overall AE history into the evolution histories for different damage mechanisms.  Capabilities of the method are illustrated on examples.

Direct Analysis of Interface Problems Using Virtual Dislocation Models and Integral Equations

Haitao Zhang, Ph.D.
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE   68588-0526
Advisor:  Dr. M.S. Wu

A model for investigating heterogeneous material interfaces is derived by using the virtual-dislocation method.  For the bimaterial interface, governing integral equations are obtained.  Through proper treatment of the  Causchy and logarithmic kernels, these integral equations are solved numerically using the piecewise quadratic technique.  The effect of the collocation number on the numerical convergence is discussed in detail.  Future investigations and expected results are also outlined.

Polycrystal Generation and Analysis

Jingchun Guo
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE   68588-0526
Advisor:  Dr. M.S. Wu

A statistical description of the properties of a cellular microstructure generated by a three-dimensional Voronoi tessellation has been obtained by a rigorous computer simulation involving more than one thousand crystals.  The algorithm is proved to be effective if several thousand crystals are involved.  The distributions of the number of faces and the number of edges of the crystals are obtained.  Results are also obtained for the stress distributions on the crystal faces when a remote stress is applied to the polycrystal.


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