Bioinspired Materials Design: A Text Mining Approach to Determining Design Principles of Biological Materials

Biological materials are often more efficient and tend to have a wider range and combination of properties than present-day engineered materials. Despite the limited set of components, biological materials are able to achieve great diversity in their material properties by the arrangements of the material components, which form unique structures. The structure-property relationships are known as structural design principles. With the utilization of these design principles, materials designers can develop bioinspired engineered materials with similarly improved effectiveness. While considerable research has been conducted on biological materials, identifying beneficial structural design principles can be time-intensive. To aid materials designers, the research in this dissertation focuses on the development of a text mining algorithm that can quickly identify potential structural design principles of biological materials with respect to a chosen material property or combination of properties. The development of the text mining tool involves four separate stages. The first stage centers on the creation of a basic information retrieval algorithm to extract passages describing property-specific structural design principles from a corpus of materials journal articles. Although the Stage 1 tool identifies over 90% of the principles (recall), only 32% of the returned passages are relevant (precision). The second stage investigates text classification techniques to refine the program in order to improve precision. The classic techniques of machine learning classifiers, statistical features, and part-of-speech analyses, are evaluated for effectiveness in sorting passages into relevant and irrelevant classes. In the third stage, manual identification of patterns in the returned passages is employed to create a rule-based method. The resulting Stage 3 algorithm’s precision values increase to 45%. In the final stage of algorithm development, the manual rule-based classification method is revisited to identify stricter rules to further emphasize precision. The Stage 4 algorithm successfully improves overall precision to 65% and reduces the number of returned passages by 74%, which allows a materials designer to more quickly identify useful principles. Finally, the research concludes with a validation that the text mining tool effectively identifies structural design principles and that the principles can be used in the development of bioinspired materials

Thermal-elastic stresses and the criticality of the continental crust

Heating or cooling can lead to high stresses in rocks due to the different thermal-elastic properties of minerals. In the upper 4 km of the crust, such internal stresses might cause fracturing. Yet it is unclear if thermal elasticity contributes significantly to critical stresses and failure deeper in Earth's continental crust, where ductile creep causes stress relaxation. We combined a heating experiment conducted in a Synchrotron microtomograph (Advanced Photon Source, USA) with numerical simulations to calculate the grain-scale stress field in granite generated by slow burial. We find that deviatoric stresses >100 MPa can be stored during burial, with relaxation times from 100's to 1000's ka, even in the ductile crust. Hence, grain-scale thermal-elastic stresses may serve as nuclei for instabilities, thus rendering the continental crust close to criticality

Tectonic inheritance and continental rift architecture: Numerical and analogue models of the East African Rift System.

The western branch of the East African Rift is composed of an arcuate succession of elongate asymmetric basins, which differ in terms of interaction geometry, fault architecture and kinematics, and patterns of uplift/subsidence and erosion/sedimentation. The basins are located within Proterozoic mobile belts at the edge of the strong Tanzanian craton; surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture, although other processes have been proposed. In this study, we use lithosphere-scale numerical models and crustal-scale analogue experiments to shed light on the relations between preexisting structures and rift architecture. Results illustrate that on a regional scale, rift localization within the mobile belts at the curved craton's western border results in an arcuate rift system, which implies that under a constant extensional stress field, part of the western branch experienced orthogonal extension and part oblique extension. Largest depocenters are predicted to form mostly orthogonal to the extension direction, and smaller depocenters will form along the oblique parts of the rift. The varying extension direction along the rift zone furthermore results in lengthwise varying rift asymmetry, segmentation characteristics, and border fault architecture (trend, length, and kinematics). Analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of extension-related faults at a local scale. Models support that fabric reactivation is responsible for the oblique-slip kinematics on faults and for the development of Z-shaped or arcuate normal faults typically documented in nature. Copyright 2007 by the American Geophysical Union

A Physics‐Based Rock Friction Constitutive Law: Steady State Friction

Experiments measuring friction over a wide range of sliding velocities find that the value of the friction coefficient varies widely: friction is high and behaves according to the rate and state constitutive law during slow sliding, yet markedly weakens as the sliding velocity approaches seismic slip speeds. We introduce a physics‐based theory to explain this behavior. Using conventional microphysics of creep, we calculate the velocity and temperature dependence of contact stresses during sliding, including the thermal effects of shear heating. Contacts are assumed to reach a coupled thermal and mechanical steady state, and friction is calculated for steady sliding. Results from theory provide good quantitative agreement with reported experimental results for quartz and granite friction over 11 orders of magnitude in velocity. The new model elucidates the physics of friction and predicts the connection between friction laws to independently determined material parameters. It predicts four frictional regimes as function of slip rate: at slow velocity friction is either velocity strengthening or weakening, depending on material parameters, and follows the rate and state friction law. Differences between surface and volume activation energies are the main control on velocity dependence. At intermediate velocity, for some material parameters, a distinct velocity strengthening regime emerges. At fast sliding, shear heating produces thermal softening of friction. At the fastest sliding, melting causes further weakening. This theory, with its four frictional regimes, fits well previously published experimental results under low temperature and normal stress