Two topics, i.e., the scale effects and the geodesics of random heterogeneous materials will be discussed in this work. / When the separation of scales in random media does not hold, the representative volume element (RVE) of deterministic continuum mechanics does not exist in the conventional sense, and new concepts and approaches are needed. This subject is discussed here in the context of microstructures of two types - planar random chessboards, and planar random inclusion-matrix composites -- with microscale behavior being elastic-plastic-hardening (power-law). The microstructure is assumed to be spatially homogeneous and ergodic. Principal issues under consideration are those of yield and incipient plastic flow of statistical volume elements (SVE) on mesoscales, and the scaling trend of SVE to the RVE response on macroscale. Indeed, the SVE responses under uniform displacement (or traction) boundary conditions bound from above (respectively, below) the RVE response, and we show via extensive simulations in plane stress that the larger is the mesoscale, the tighter are both bounds. However, the mesoscale flows under both kinds of loading do not, in general, display normality. Also, with the limitation imposed by currently available computational resources, we do not recover normality (or even a trend towards it) when studying the largest possible SVE domains. / The second topic is the geodesic (i.e., shortest path) character of strain fields occurring in elasto-plastic response of planar inclusion-matrix composites. The composites' spatially random morphology is created by generating the disk centers through a sequential inhibition process based on a poisson point field in plane. Both phases (inclusions and matrix) are elastic-plastic-hardening with the matrix being more compliant and weaker than the inclusions, and perfect bonding everywhere. A quantitative comparison of a response pattern obtained by computational micromechanics with that found only by mathematical morphology indicates that (i) the regions of plastic flow are very close to geodesics, and (ii) a purely geometric, and orders of magnitude more rapid than by computational mechanics assessment of these regions is possible.

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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Dionisios G. Vlachos, Dept. of Chemical Engineering. Includes bibliographical references.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

An effective way to describe changes in the microstructure of a material or to assess fatigue damage at an early stage in fatigue life is by measuring the acoustic nonlinearity parameter beta. The nonlinearity parameter is defined for harmonic longitudinal plane waves and it depends on the ratio of the amplitudes of the first harmonic of the exciting signal and the second harmonic. A reliable measurement of the amplitudes of these harmonics is crucial since their amplitude of the second (higher) harmonic is much smaller than the amplitude of the first harmonic. This research investigates the influence of the apparent nonlinearity that can occur due to the signal processing and shows how this influence can be quantified and minimized to enable a more accurate evaluation of the acoustic nonlinearity parameter. Furthermore the concept of the nonlinear parameter is extended to Rayleigh surface waves by developing a connection between the harmonic amplitudes and the third order elastic constants, using the approximate model by Zabolotskaya. Finally the problem of modeling the influence of fatigue damage on the nonlinear parameter and the elastic constants is discussed. The reduction of the processing nonlinearity combined with Rayleigh surface waves - Rayleigh surface waves are more efficient in the detection of fatigue damage initiated and concentrated at the surface - helps improve the prediction of fatigue damage and the remaining life of a sample.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 208-232).

This master thesis is concerns the preparation of Alkali Activated Materials, specifically Alkali Activated Slag (AAS), with the addition of fiber reinforcement. Alkali Activated Materials have great potential for use in construction practice. However, their use is limited by certain undesirable properties, which can be diminished by adding fiber reinforcement. This thesis deals with the influence of carbon fibers (2 % by weight of the binder) and carbon nanotubes (0,2 % by weigh of the binder) on the mechanical properties, microstructure and shrinkage of AAS. The results of the experiments which were carried out correspond with the literary research. Conclusions of this thesis agree with research published in original scientific papers.

Mechanical properties of widely applicable thin nanocrystalline films have been a sub- ject of interest for some time due to deviation of their properties from the properties of bulk and micro sized grain materials. The deformation mechanisms in these materials are altered by restricted size of the material and high ratio of surface and grain boundary areas. Recent advances in transmission electron microscopy (TEM) allow direct obser- vations of the deformation mechanisms during nanoindentation or tensile deformation of the specimen. Thin Al films prepared by DC magnetron sputtering were deformed in situ in TEM and bright field TEM. High resolution TEM and automated crystallographic orientation mapping (ASTAR) were implemented to observe the ongoing deformation mechanisms. Molecular dynamic simulation designed to approach the conditions of per- formed experiment were used to visualize the deformation mechanisms on atomic scale and the reliability of both methods was discussed. 1