Thermomechanical Fatigue Analysis of Polymer Composites
Diffusion of Ultrasound in Concrete
Date: Tuesday, April 6, 1999
Time: 3:30 p.m.
Place: W128 Nebraska Hall
Thermomechanical Fatigue Analysis of Polymer Composites
Di Wu
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE 68588-0526
Advisor: Dr. Yuris Dzenis
Thermomechanical fatigue behavior of unidirectional [0]8 and [90]8 and cross-ply [+/-45]2s graphite-epoxy
laminates was studied. A new thermomechanical fatigue testing apparatus
designed at UNL was used in the tests. The test results are presented and
analyzed. Some problems encountered in the experiments and their possible
solutions are discussed.
Diffusion of Ultrasound in Concrete
Phanidhar Anugonda
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE 68588-0526
Advisor: Dr. Joseph Turner
[Work supported by the Nebraska Research Initiative]
The propagation and scattering of ultrasound in concrete is discussed. The heterogeneous composition of concrete causes the ultrasound to scatter considerably. In the limit of many scattering events, the ultrasonic energy density in bars of concrete is shown to evolve in accordance with a one-dimensional diffusion equation. The ultrasonic diffusivity and dissipation are measured experimentally over the frequency range of 100-500 kHz. Such frequencies are well above typical frequencies used for concrete inspection. The diffusivity, which is a measure of themicrostructure, is shown to correlate with concrete damage. This technique also allows the true dissipation from viscoelastic effects in the cement to be assessed directly. It is anticipated that the use of these higher frequencies will result in new techniques for characterizing material properties and damage in concrete structures.
