This dissertation explores structural damage identification of civil infrastructure by an image-based approach. The underlying basis for the research is that optical images of structures or structural components provide pixels that can be viewed as spatially high- resolution s̀ensors', which convey the topographical appearance characteristics of structural integrity in a highly collaborative manner. With images captured at different times, the temporal variations of the images can capture the changes of structural integrity, i.e. structural damage. Two scales of structural damage are addressed in this dissertation, namely, the geospatial scale of structural damage in urban areas and the local scale of structural damage in structural components. Accordingly, satellite imagery and digital camera imagery are used in the two scales of damage identification. The methodology in this dissertation for solving the identification problem do not fall into the traditional photogrammetric category. Instead, modern computer vision and machine learning methods are relied upon. For the urban structural damage identification, the task is formulated as a damage extraction and classification problem. Accordingly, two sets of solution frameworks, each of which includes a damage feature extraction method and a multi-level structural damage classification method, are proposed. For the image-based local structural damage identification, two problems are studied; one is the geometric quantification of damage in images, the other is the monitoring of the inception or propagation of damage using multi-temporal images. Two different model-based solutions are proposed to solve these problems. The methods proposed in the study of urban damage identification using satellite imagery can be used to perform urban damage classification for individual urban buildings or urban sub-areas in the immediate aftermath of a large-scale disaster that strikes a built urban area. Therefore, a preliminary damage assessment can be quickly produced, which may facilitate rapid disaster response. Based on the study of image-based local damage identification, the resulting damage-related information may be integrated into mechanics-based predicative modeling or vibration-based structural health monitoring, and the proposed methods can be extended to analyze images from different types of non-destructive imaging devices

Augmentation of the peak bone mass (PBM) may be one of the most effective interventions to reduce the risk of developing osteoporosis later in life; however treatments to augment PBM are currently limited. Our study evaluated whether a greater PBM could be achieved either in the progesterone nuclear receptor knockout mice (PRKO) or by using a nuclear progesterone receptor (nPR) antagonist, RU486 in mice. Compared to their wild type (WT) littermates the female PRKO mice developed significantly higher cancellous and cortical mass in the distal femurs, and this was associated with increased bone formation. The high bone mass phenotype was partially reproduced by administering RU486 in female WT mice from 1-3 months of age. Our results suggest that the inhibition of the nPR during the rapid bone growth period (1-3 months) increases osteogenesis, which results in acquisition of higher bone mass. Our findings suggest a crucial role for progesterone signaling in bone acquisition and inhibition of the nPR as a novel approach to augment bone mass, which may have the potential to reduce the burden of osteoporosis.

In BaTiO3 single crystals, we observed a strain-driven phase transition from the tetragonal phase to the tetragonal-orthorhombic phase boundary which can be introduced by slow cycling compressions (a loading of up to 0.5 GPa, strain rate of 10-4 s-1, and 100 cycles) at room temperature. Different from the well-known tetragonal to cubic phase transition under stress (∼2 GPa), it only takes place locally around bent 90° domain walls. The inhomogeneous local stress and electrical fields as well as the mobile point defect pinning effect contribute to the phase re-entrance. Through comparison experiments by in situ synchrotron x-ray diffraction, Raman scattering, and (scanning) transmission electron microscopy, we explored the phase transition mechanism. Based on that, we developed a mechanical method to obtain well-stabilized high-density thermotropic phase boundary structures (with tetragonal, orthorhombic, and bridging monoclinic phases) in BaTiO3 for potential applications.

Large superelastic deformation in ferroelastic-ferroelectrics (FMs) is a complex phenomenon involving multiple mechanisms operating simultaneously. Understanding how these mechanisms contribute corporately is critical to apply this useful property to the intrinsically brittle FMs, which can therefore display both excellent functional and mechanical performance. Here, we have directly observed and quantitatively analyzed in situ in a transmission electron microscope the three main mechanisms of twinning domain, phase transformation and mobile point defect contributing to extremely large superelastic deformation in single-crystal BaTiO3 (5.0% strain) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (10.1% strain). Our results reveal the hierarchical origin of large recoverable strain in “brittle” FMs.

Ceramics are strong but brittle. According to the classical theories, ceramics are brittle mainly because dislocations are suppressed by cracks. Here, the authors report the combined elastic and plastic deformation measurements of nanoceramics, in which dislocation-mediated stiff and ductile behaviors were detected at room temperature. In the synchrotron-based deformation experiments, a marked slope change is observed in the stress-strain relationship of MgAl2O4 nanoceramics at high pressures, indicating that a deformation mechanism shift occurs in the compression and that the nanoceramics sample is elastically stiffer than its bulk counterpart. The bulk-sized MgAl2O4 shows no texturing at pressures up to 37 GPa, which is compatible with the brittle behaviors of ceramics. Surprisingly, substantial texturing is seen in nanoceramic MgAl2O4 at pressures above 4 GPa. The observed stiffening and texturing indicate that dislocation-mediated mechanisms, usually suppressed in bulk-sized ceramics at low temperature, become operative in nanoceramics. This makes nanoceramics stiff and ductile.

The operating conditions of functional materials usually involve varying stress fields, resulting in structural changes, whether intentional or undesirable. Complex multiscale microstructures including defects, domains, and new phases, can be induced by mechanical loading in functional materials, providing fundamental insight into the deformation process of the involved materials. On the other hand, these microstructures, if induced in a controllable fashion, can be used to tune the functional properties or to enhance certain performance. In situ nanomechanical tests conducted in scanning/transmission electron microscopes (STEM/TEM) provide a critical tool for understanding the microstructural evolution in functional materials. Here, select results on a variety of functional material systems in the field are presented, with a brief introduction into some newly developed multichannel experimental capabilities to demonstrate the impact of these techniques.