A thermo-chemo-electro-mechanical framework of unsaturated expansive clays

To investigate the soil structure and mechanical behavior of an unsaturated expansive clay soil, triaxial and mercury intrusion tests have been performed and are presented in this paper. Also an optical test system was developed for studying the internal structure evolution of the unsaturated expansive soil during shear-loading tests. The research results show a linear relationship between the cohesion intercept and the degree of saturation of the unsaturated clay for the test data. For the tested soil, the pore-size distribution curves were found to be bimodal. The measurement results from mercury intrusion tests confirm that the micropores of Guangxi expansive soils of this study remain constant, and that the macropores vary with the dry density of soil samples. Comparing the volumetric strain curves with the soil particle area curves, some correlation and dependence on the macropore variation of soil samples during shear-loading tests can be shown to exist.Key words: soil structure, mechanical behavior, unsaturated soil, mercury intrusion, expansive clay.

A model considering solid-fluid interactions stemming from capillarity and adsorption mechanisms in unsaturated expansive clays

A mechanical approach for unsaturated expansive soils considering double porosity has been developed based on the porous media theory. In this approach, the adsorbed and the capillary water, as well as the micropores and macropores, are two distinct phases. An interaggregate stress considered as the work-conjugate of the macrostructural strain increment has been defined. Both physicochemical and capillary effects of the pore water have been introduced at the macroscopic level. Other work-conjugate variables relevant for the constitutive modeling of double-porosity unsaturated media have also been identified, consisting of the modified suction as conjugate of the increment of the macrostructural degree of saturation and the microstructural effective stress as conjugate of the microstructural volumetric strain increment. A hydromechanical model for unsaturated expansive clays taking into account the interaction between the micro- and the macrostructures in expansive clays can thus be built. Based on the bounding surface concept, an anisotropic loading – collapse yield surface has been introduced to reproduce the three-dimensional mechanical behavior. To analyze the model capabilities, two series of laboratory tests consisting of multiple wetting and drying cycle tests on Boom clay and triaxial tests on Zaoyang (ZY) expansive clay were simulated. The comparisons between numerical and experimental results show that the model can reproduce with reasonable accuracy the mechanical behavior and the water retention characteristic of unsaturated expansive clays.

Thermodynamically consistent, maximum dissipation, time-dependent models for non-equilibrium behavior

A framework for deformation, generalized diffusion, mass transfer and growth in multi-species multi-phase biological tissues

It is currently necessary to build the structural foundation in expansive and sensitive soil in India because of rapid population growth leading to shortage of suitable land. Research has thus been done over the decades to modify the various properties of different soils in the presence of different additives to qualify these for appropriate usage in geotechnical field. This study investigates shrinking potential of highly expansive bentonite clay (BC) in presence of extremely alkaline red mud (RM). The study analysed the results of four distinct mixtures of BC and RM in the proportions of 20:1, 20:2, 20:3, and 20:4. The study indicates the gradual fall in plasticity index, shrinkage index, shrinkage ratio, volumetric shrinkage, and linear shrinkage when RM rises. The study advocates that RM is effective in reducing the volumetric shrinkage potential of the BC by possibly changing its molecular polarity and physicochemical properties.

Experimental and modeling investigations of hydrate phase equilibria in natural clayey-silty sediments

Energy usage in the United States is predicted to increase exponentially over the foreseeable future. However, data from the Energy Information Administration (EIA) indicates that 56-57% of all energy produced each year in the US is still rejected as waste heat. For example, a major portion of the energy generated by burning gasoline in automobiles (approximately 70%) is lost either in the engine coolant or through the exhaust. Therefore, a possible pathway for meeting the ever-increasing demand for energy is through the recovery of waste heat. Solid-state thermoelectric modules are useful for this purpose. The lack of any moving parts, portability, very long operational lifetimes, and minimal maintenance requirements of these solid-state thermoelectric modules make them very attractive for waste heat recovery. Current state-of-the-art thermoelectric modules are not highly efficient. This limits their use to specialty application (e.g., for powering up satellites). The lack of a pathway for precisely and independently tuning the thermal and electrical transport through materials employed in the fabrication of thermoelectrics is the primary reason for their low efficiencies. Recent theoretical and experimental studies have indicated that nanostructuring of materials serves as a route for independently tuning the thermal and electrical transport through them, and further enhance their heat-to-electricity conversion efficiencies. Of all the forms of nanomaterials, nanowires hold the most promise for the fabrication of efficient thermoelectric modules. The two different dimensions of the nanowires, namely the diameter and the length, offer a convenient pathway for independently tuning the electrical and thermal transport through them. This fact is supported by a few recent experimental studies on individual nanowires that indicated that nanowire form of materials exhibit enhanced thermoelectric performance, compared to their bulk counterparts. As the large-scale deployment of thermoelectrics for terrestrial use is a bulk application, it is required to ensure that enhanced thermoelectric performance observed in individual nanowires is also extendable to assemblies composed of a multitude of nanowires. This further requires strategies for the synthesis and assembly of nanowire powders on an industrial scale. Furthermore, any assembly strategy developed should offer the ability to tune the thermal and electrical transport through the interfaces between the nanowires. In short, the fabrication of next-generation, highly-efficient thermoelectrics requires the large-scale synthesis and interface-engineered assembly of nanowires (1-3). The aim of this presentation is to showcase the progress that has been made in this research area by our group. More specifically, the strategies useful for the bulk production of nanowire powders and their in-situ functionalization with organic molecules (1), together with the strategies useful for assembling them in an interface-engineered manner on a large-scale into functional thermoelectric devices (2,3), will be addressed in this talk (Figure 1). Example illustrations of how the interface-engineered assembly affords thermal and electrical transport control of the interface between the nanowires in the assembly will be presented. Novel strategies for imparting the nanowires resistance against air-, moisture- and acid-assisted degradation will also be presented. Specific examples that will be addressed include the fabrication and characterization thermoelectric devices based on bulk assembled Zn3P2 and ZnO nanowire powders (2,3). In addition, use of phase transformation as a strategy for the simultaneous synthesis (4) and assembly via welding of metal silicide nanowire powders will also be presented. The thermoelectric performance of metal silicide nanowire assemblies will be discussed.ACKNOWLEDGEMENTS Financial support from NSF/DOE thermoelectrics Partnership (NSF CBET # 1048702) is gratefully acknowledged. REFERENCESL. Brockway, M. Van Laer, Y. Kang, S. Vaddiraju, Physical Chemistry Chemical Physics, 15, 6260-6267, (2013).L. Brockway, V. Vasiraju, S. Vaddiraju, Nanotechnology, 25, 125402 (2014).L. Brockway, V. Vasiraju, H. Asayesh-Ardakani, R. Shahbazian-Yassar, S. Vaddiraju, Nanotechnology, 25, 145401 (2014).Y. Kang, L. Brockway, S. Vaddiraju, Materials Letters, 100, 106-110 (2013).

A multiscale analysis of growth and diffusion dynamics in biological materials

Comparative studies on the performances of implicit and explicit integration schemes are conducted for a double structure hydro-mechanical coupling model of unsaturated expansive clays at an integration point level. The published constitutive model is built on the basis of two pore levels in expansive clay. In this paper, firstly, the implicit and explicit schemes based on the Euler backward and forward integration algorithms are proposed. These schemes can deal with multi-plastic mechanisms defined in the model and distinguish various cases in relation to the number of plastic mechanism active. Secondly, the performances of the integration schemes are demonstrated by comparisons of calculation results of a control-strain test with different strain increment sizes.

The nucleus pulposus of the intervertebral disc is a gelatinous viscous hydrogel that has an essential role in the mechanics of the intervertebral disc joint. The viscoelastic properties of the nucleus pulposus significantly change in the course of time and particularly at the outset of disc degeneration. Viscoelasticity is the result of production and may be characterized by hysteresis when the tissue undergoes cyclic mechanical loading. Nature never undertakes any change unless her interests are served by an increase in entropy once commented Max Planck. In the context of mechanobiology, we present an original concept wich is referred to the hysteresis theory and states that for a given range of frequency and biological tissue, the maximum mechanotransduction signal coincides with maximum hysteresis. If verified, this statement would introduce a relevant variable in the study of pathophysiological conditions such as degeneration of the nucleus pulposus and serve as a reliable variable to define optimized mechanical load settings for the culture of tissue engineered materials. This doctoral work deals with the proposition of this theory and defines the experimental and theoretical framework to verify this hypothesis in following studies. Hysteresis is not specific to a single process, but is the result of many internal processes that can happen simultaneously. Deformation may imply entropic and/or elastic changes in the tissue which from a phenomenolgical point of view is equivalent, and yet are fundamentally different in nature. Deformation may also be accompanied by reversible and irreversible processes that result in mechanical hysteresis. A clear knowledge on the thermomechanical processes involved during the deformation of biological tissues enables the experimenter to overcome perhaps too restrictive assumptions and may lead to new insights. In this work, we provide a prototype of a deformation calorimeter that is specifically designed for biological hydrogel tissues, thereby refocusing the theory of biological materials on solid experimental thermodynamic grounds. This prototype produced satisfactory results with a measurement precision of 3% and a characteristic time constant of 40 seconds. The thermal stability of the deformation calorimeter was, however, not suficient to experimentally investigate the thermomechanical properties of very soft tissue (kPa scale) such as the nucleus pulposus, but acceptable for stiffer materials ranging in the MPa scale. In conjunction, a theoretical framework is proposed to recover the information that is hidden in hysteresis. Based on continuum mechanics and, in particular, mixture and normal dissipation theories, the governing nonlinear heat equation for thermomechanical porous materials was derived. This equation is general and valid for finite perturbations in temperature and deformations. A particular model for hydrogels was also proposed. Finally, hysteresis and damping properties of the nucleus pulposus was measured at large physiological deformations and for frequencies ranging between 0.01 and 10 Hz. The proposed method relies on the introduction of a small testing device, called hydrogel encapsulation device, which addresses several issues when dealing with mechanical testing on soft tissues such as synthetic and biological hydrogels.

In this talk we discuss simulations of the mass and thermal transport in oxide nuclear fuels. Redistribution of fission gases such as Xe is closely coupled to nuclear fuel performance. Most fission gases have low solubility in the fuel matrix, specifically the insolubility is most pronounced for large fission gas atoms such as Xe, and as a result there is a significant driving force for segregation of gas atoms to grain boundaries or dislocations and subsequently for nucleation of gas bubbles at these sinks. The first step of the fission gas redistribution is diffusion of individual gas atoms through the fuel matrix to existing sinks, which is governed by the activation energy for bulk diffusion. Fission gas bubbles are then formed by either separate nucleation events or by filling voids that were nucleated at a prior stage; in both cases their formation and latter growth is coupled to vacancy dynamics and thus linked to the production of vacancies via irradiation or thermal events. In order to better understand bulk Xe behavior (diffusion mechanisms) in UO{sub 2{+-}x} we first calculate the relevant activation energies using density functional theory (DFT) techniques. By analyzing a combination of Xe solution thermodynamics, migration barriers and the interaction of dissolved Xe atoms with U, we demonstrate that Xe diffusion predominantly occurs via a vacancy-mediated mechanism, though other alternatives may exist in high irradiation fields. Since Xe transport is closely related to diffusion of U vacancies, we have also studied the activation energy for this process. In order to explain the low value of 2.4 eV found for U migration from independent damage experiments (not thermal equilibrium) the presence of vacancy clusters must be included in the analysis. Next a continuum transport model for Xe and U is formulated based on the diffusion mechanisms established from DFT. After combining this model with descriptions of the interaction between Xe and grain boundaries derived from separate atomistic calculations, we simulate Xe redistribution for a few simple microstructures using finite element methods (FEM), as implemented in the MOOSE framework from Idaho National Laboratory. Thermal transport together with the power distribution determines the temperature distribution in the fuel rod and it is thus one of the most influential properties on nuclear fuel performance. The fuel thermal conductivity changes as function of time due to microstructure evolution (e.g. fission gas redistribution) and compositional changes. Using molecular dynamics simulations we have studied the impact of different types of grain boundaries and fission gas bubbles on UO{sub 2} thermal conductivity.

ABSTRACTThe study of heat and mass transport in non‐Newtonian fluid flow over a stretching surface accompanying relevant characteristics is important in several engineering and industrial processes like annealing and thinning of copper wires, aerodynamic extrusion of plastic and rubber sheet, glass fiber, and so forth. Based on significant practical applications, the objective of this investigation is to assess the time‐dependent flow of Williamson fluid influenced by porous sheet stretching in exponential manner accompanied by thermal and mass transport and entropy generation. Various factors affecting fluid flow, thermal and mass transport (viscous dissipation, non‐linear radiation, porous media, chemical reaction, and heat source) are considered. The regulating PDEs are turned into ODEs in nondimensional form utilizing adequate similarity transformation relations. The problem is solved numerically on MATLAB adopting the Keller‐Box scheme. On fluid flow, temperature, and concentration distribution the effects of relevant parameters are depicted by drawing sketches and discussed. Besides, second law analysis is also evoked in the study in terms of entropy generation accompanying the Bejan number. Moreover, quantities of physical significance such as skin friction coefficient, Sherwood number, and Nusselt number are computed, compared with prior research and found in excellent agreement. It is concluded that temperature profile magnifies due to radiation and heat generation effects. The reaction coefficient and order of the reaction exhibited opposite effects on concentration profile. It is also concluded that entropy production reduces with increasing slips and temperature difference parameter, while opposite effect is observed due to Brinkman number. Furthermore, it is observed that skin‐friction coefficient at the surface decreases with velocity slip and non‐Newtonian parameter however, trend is reversed due to unsteadiness parameter. The results of the study may find applications of practical importance in engineering fields such as designing heat exchangers, cooling processes, improving energy storage systems, and so forth.

A numerical model incorporating the microscale heat and mass transport in biological tissue during freezing is developed. The heat transfer problem is formulated in a general one-dimensional coordinate system (cartesian, cylindrical or spherical), and a finite control volume discretization is used. The latent heat release for each control volume in the domain is determined by the cellular water transport and intracellular ice formation processes occurring there (a coupled thermal/biophysical approach). The coupled model is applied to two cryobiological freezing problems, with different geometry and boundary conditions. The temperature dependent thermal properties of water and the biophysical properties of two biological tissues, normal rat liver and Dunning AT-1 rat prostate tumor tissue are used to simulate both the micro and macroscale freezing processes. A major advantage of the coupled thermal/biophysical model is its unique ability to predict both the macroscale thermal response and the microscale biophysical response at various locations within the tissue domain during a freezing process, simultaneously. Thermal histories predicted by the coupled model are compared to predictions of a standard enthalpy-method model in which the temperature dependence of the latent heat release, Λ(T) is an explicit function adapted from the water-NaCl phase diagram, and phase change is not rate-limited by microscale biophysical processes (i.e., an uncoupled approach). The results for both models are very similar; this suggests that the microscale biophysical processes which occur in the chosen biological tissues during freezing do little to limit the rate at which phase change occurs. Additional simulations suggest that the predicted macroscale thermal history results are not significantly affected (<2 percent variation) even with significantly altered biophysical parameters (i.e., a factor of 100 times lower or higher), as long as the magnitude of the latent heat is constant.

The chapter is concerned with new developments over the last two decades of familiar experimental techniques for the measurment of thermal conductivity and related transport properties, as well as a variety of diffusion coefficients. It begins with an historical review of the transient hot-wire instrument for accurate thermal conductivity measurement; it has widespread applicability over a wide range of thermodynamic states and a variety of materials. The second section explores a family of measurement techniques that exploit the disturbance of materials caused by absorbtion of light in photoacoustic and photothermal techniques to study thermal transport processes. In Section 5.3, solutions of the diffusive transport equations in simple geometries are derived and simplified to offer new methods for the study of thermal and mass transport in materials of industrial importance. Finally, in Section 5.4, recent work to develop established experimental techniques for the study of both mutual and self-diffusion coefficients in extremes circumstances, such as high pressures and/or high temperatures and special thermodynamic states, are considered.