Multi-scale modeling of biomaterials and tissues

Constitutive modeling of jugular vein-derived venous valve leaflet tissues.

Abstract. Salt, crystalline and clay formations are under discussion as potential host rocks for storage of heat-generating radioactive waste. Each of these rocks has a different structure and composition, and consequently a different material behavior. The latter needs to be studied and evaluated with respect to the main aim: to find a place to store the waste in a safe and sustainable manner. Several requirements in the context of the safety of a repository need to be fulfilled, concerning the long-term as well as the operational phase. One key point in this matter is the integrity, which refers to retention of the isolating rock zone's containment capabilities. With the focus on some experimental and numerical investigations on the excavation influenced near-field behavior of Opalinus clay (OPA), this contribution aims to illustrate an example for the role of numerical modeling in safety assessment. Once, e.g. anthropogenic action such as excavation starts, the natural state of equilibrium in the formation is disturbed. Trying to restore it, the rock deforms (convergence) and/or releases energy in other ways such as cracking. This could lead to loss of integrity since crack nucleation and propagation can affect the mechanical stability and create paths to transport contaminants. During operation in the excavated rock, environmental changes, e.g. temperature and humidity, further affect its behavior. The understanding of these dynamic phenomena ideally needs to occur at the in situ scale; however, performing an experiment in the spatial and time scales of interest is not always possible. For this reason, the in situ problem needs to be formulated, abstracted and mathematically modeled. The interpretation of the results must take place with simplifying assumptions and complementary laboratory scale experiments can be used to improve understanding of the system. The real problem is approached stepwise, each step associated to the size of the model and its complexity. The gradually obtained knowledge is necessary to achieve a better understanding of the process and to evaluate the capacities and limitations of the models. This contribution aims at showing the basic practical steps for numerical modeling with particular focus on the preparation and interpretation of the models and results, e.g. model calibration, verification and validation. As an example, the OPA at the Mont Terri site is chosen. The material parameters are obtained either experimentally or from the literature. We choose and perform laboratory scale simulations that are related to nearly the same mechanism as in the in situ scale. To have a first impression on the latter, a simplified, large-scale numerical model is prepared. The mechanism in study is drying and wetting, which is associated with shrinkage and swelling. We analyze the pore pressure and stress development in both scales. Thus, hydraulic mechanically coupled approaches are essential. The concept of effective stress is used, which combines the contributions of the solid and fluid phases (gas and liquid). In the current modeling approach, the gas pressure remains constant (atmospheric pressure) and during drying, the liquid pressure induces capillary pressure development and decrease of saturation. The laboratory scale simulation is important to evaluate the model of choice and to assess potential numerical problems. Furthermore, it can be used to perform a sensitivity study of material and numerical parameters. This step is necessary during the development or extension of numerical models as well as to evaluate their applicability on new research questions. The simplified in situ scale numerical model is then extended. In this phase the numerical model is evaluated once again, especially with respect to its complexity. Furthermore, specific questions related to this scale are posed: overall behavior of the rock, influence of the excavation, seasonal and long-term effects. In this contribution we deal with the long-term cyclic deformation (CD-A) experiment. The CD-A experiment has been taking place in the Mont Terri Rock Laboratory since October 2019. It consists of twin niches, a closed and an open niche, subjected to either high air humidity or seasonal humidity changes leading to saturation/desaturation during summer/winter in the OPA, respectively. Several parameters are periodically or continuously measured, including relative air humidity, convergence and crack development. We attempt to transfer the knowledge and numerical models developed in the small scale to the large scale and to evaluate the possibilities and limitations of the chosen approaches by comparing the numerical and experimental results.

As deputy assistant secretary for research, development, and simulation in the US Department of Energy Office of Defense Programs, Gil Weigand provides programmatic and policy direction for the DoE's nuclear weapons research, development, and simulation work. In partnership with the national labs, he leads the effort to preserve the technology base and develop programs for the surety, reliability, military effectiveness, and credibility of the nation's nuclear-weapons stockpile.Prior to this job, Weigand was deputy assistant secretary for strategic computing and simulation and a senior information officer for the DoE Office of Defense Programs, where he led advanced initiatives in high-performance computer simulation, computation, and communications. In particular, he was responsible for directing the Accelerated Strategic Computing Initiative, which has created leading-edge computational modeling and simulation tools necessary to move from test-based to simulation-based assessment and certification. The ASCI initiative is based on the Comprehensive Test Ban Treaty, an international treaty to move toward no nuclear testing announced by President Bill Clinton on 11 August 1995.Paul Messina now manages ASCI as DoE deputy assistant secretary for advanced simulation and computing for defense programs. He is on a two-year leave from the California Institute of Technology, where he is assistant vice president for scientific computing, a faculty associate in scientific computing, and director of the Center for Advanced Computing Research. He has a joint appointment at the Jet Propulsion Laboratory as manager of high-performance computing. Messina is also on leave from the position of chief architect for the National Partnership for Advanced Computational Infrastructure, where he established and led the Scalable I/O Initiative.Editor-in-chief George Cybenko recently talked to Weigand and Messina about their roles in ASCI and the Alliance Program, and their thoughts about where the high end of computational performance is headed.

Reinforced concrete slabs supported on columns fail by punching when a conical plug of concrete perforates the slab above the column. This failure has been mostly investigated experimentally, so what can numerical simulation contribute to understand this phenomenon? To answer this question, a computational simulation tool based on the finite element method is developed. This numerical model is implemented into a computer code in applying the object-oriented programming concept. The requirements that the numerical model should fulfill are derived from a review of the experimental results published in the literature and obtained in our laboratory. The numerical model reproduces the non-linear material behavior characterizing reinforced concrete structures by decoupling the actions of steel reinforcement and concrete. The steel reinforcement is represented by uniaxial truss elements which follow a bi-linear stress-strain response. The concrete is modeled with continuum elements which are described at the constitutive level within the framework of the incremental flow theory of plasticity. The concrete triaxial strength is delimitated with a new failure criterion. A plastic flow rule is derived so as to reproduce the evolution of the plastic strain observed experimentally. Cracking induces strain-softening which refers to a gradual decrease in tensile strength with increasing deformations. The reduction of the tensile strength is controlled by an isotropic decohesion process which is monitored by constant fracture energy. The stiffness degradation due to cracking is reproduced with an isotropic elastic damage model. A perfect bond between concrete and steel is assumed. The capabilities of the numerical model are illustrated by simulating the localized shear failure in soil under a footing, the uniaxial tensile, and the confined compressive tests in plain and reinforced concrete specimens. The simulation of punching failure is investigated for three circular reinforced concrete slabs. The comparison with experimental results indicates that: (1) the punching failure mechanism –characterized by a localized inclined punching crack– is generated, (2) the value of the punching load is predicted, (3) the cracking sequence is reproduced, (4) the global response is slightly too stiff. For slabs with orthogonal reinforcement, the perfect bond hypothesis does not allow to capture the punching failure mechanism and the numerical model is improved by relaxing this hypothesis. The developed computational simulation tool reproduces the punching failure observed experimentally and is consequently used to investigate the failure mechanism. First, it is shown that the punching crack results from a crack coalescence phenomenon at the top of the slab followed by a crack propagation in the direction of the corner slab-column. Second, a condition for punching failure to occur is determined. Third, it is illustrated that the size-effect observed experimentally is reproduced and is reflected by a modification of the tensile stress distribution along the punching crack. Finally, a parametric study of the punching failure is performed revealing that punching failure is governed by the tensile strength of concrete. It is also shown that increasing the percentage of reinforcement raises the punching load and reduces the ductility of failure. Lastly, the computational simulation tool allows to demonstrate that in a circular slab, the applied bending moment is not determinant for the value of the punching load.

Additive Manufacturing of polymers is transitioning from rapid prototyping to a true industrial production technique. While it brings valuable opportunities to the industry, such as drastically decreasing the time-to-market of new products or enabling lightweight, multi-material and multi-functional designs, it also comes with a series of challenges for the engineers. The reliability of the mechanical properties of the final part still has some uncertainty and is not fully supported by standard engineering tools. Dimensional accuracy is not always met and cannot be predicted prior to printing. To cope with these issues, the engineering workflow which is daily applied for traditional manufacturing processes needs to be replicated and adapted to the Additive Manufacturing. Specifically, Additive Manufacturing of polymers and composites shows a very strong influence of the manufacturing on the material and global component behavior and its modeling constitutes a true multi-scale challenge. In this paper, insights on how the process simulation of FDM/FFF or SLS method can be solved via coupled thermo-mechanical models are presented. The numerical simulation follows the real printing workflow, takes into account the process setup and the material behavior, allows to predict the deformed shape of the part and residual stresses and offers warpage compensation techniques. An industrial application of process simulation is shown to demonstrate the validity of warpage predictions. Finally, a strongly coupled process-structure methodology is presented that predicts the as-printed mechanical behavior. This approach links the material anisotropy and the process-induced microstructure to the as-printed part performance. The part strength sensitivity to the build direction is also highlighted. This integrative workflow, which accounts for the full manufacturing history of the part, enables the design validation and the optimization of the performance of AM designs, as demonstrated on an automotive engine air manifold.

The complex problems in mechanical subjects for experimental studies still exist, this is why it is necessary to resort to numerical modeling which develops exponentially and follows the evolution of the computer tool. Modeling carried out by simulating a physical phenomenon by mathematical equations which will be integrated into a computer tool to give good results to an analytically persistent problem. This modeling is presented in this article to study the mechanical behaviors of a composite material, and we are talking about the addition of a bio-filler in the form of chicken feathers according to different percentages 5, 10 and 15% on flexible Polyvinyl chloride (PVC) already aged. The numerical modeling of this article intervenes in the validation of the experimental result, since a preliminary experimental study has already been carried out. We use a numerical processing model well known for its relevance and the accuracy of the results, which is the finite element calculation model. This model is used on three samples of bio-loaded PVC with three different percentages of chicken feathers. The results obtained are integrated into a comparative study to find the appropriate percentage that improves the mechanical characteristics, with the aim of increasing the number of recyclability of this material.KeywordsNumerical modelingFlexible PVCChicken feathers

A systematic procedure for multi-scale computational modeling is presented to simulate polycrystalline material behaviors for structural application. The modeling procedure bridged different length scales, from macro-scale to nano-scale, by proper flow of information from one scale to the next scale. The multi-scale model could include material characteristics at different length scales like nano-, micro-, meso-, and macro-scale. Both finite element analysis and molecular dynamics were used in the multi-scale analysis. An example of a large plate with a center hole is given to demonstrate the multi-scale modeling procedure.

Physical scale modeling (PSM) is an experimental technology that has been used to evaluate and design shipboard impressed current cathodic protection (ICCP) systems by various researchers and designers. PSM is also a preferred tool for validating ICCP numerical modeling results, owing to the well-controlled conditions in PSM experiments. However, one issue in using PSM for the validation of numerical modeling results is the lack of information on the actual polarization behavior of the cathodes on a model hull during PSM experiments. Consequently, the polarization curve data used as boundary conditions in numerical modeling trials is usually different from the polarization behavior of the cathodes in PSM experiments. This difference can result in a discrepancy between the numerical modeling and the PSM results, which is difficult to separate from other numerical errors. A discrete area current control (DACC) technique was developed in a previous ICCP PSM study to simulate the polarization behavior of a propeller material under various conditions. The present study extended the DACC technique to simulate the polarization curve behavior of four discrete cathodes representing one nickel aluminum bronze (NAB) propeller and three discrete steel patches. This study also demonstrated that use of the DACC technique can ensure that both PSM and numerical modeling studies use identical polarization curve relationships as boundary conditions. The technique facilitates the use of the PSM results for comparison with numerical modeling results. The comparison study showed good agreement between the PSM results and numerical modeling results, in both simulated static and dynamic flow conditions.

The development of a sustainable energy economy based on renewable, carbon-neutral energy is a necessary and urgent task. Photo-electrochemical (PEC) approaches to solar fuels and materials are interesting, provided they can be efficiently, stably, scalably, and sustainably implemented.While significant progress on the development of earth abundant materials and on high-efficiency demonstrations has been achieved, there is relatively little known about the behavior of materials and devices under more realistic, varying conditions and on the implication of degradation on the performance and lifetime.Here, I will first discuss multi-scale numerical modeling approaches to investigate and quantify the effect of photocorrosion on the performance evolution. I will show how important the local reaction environment is for the stability of a component, and how heterogeneity in the operating variables (current density, species concentration, temperature, etc.) affect degradation. Furthermore, I will comment on the importance of device design on device stability.Second, I will then transition towards discussing material, device and system performance as a function of varying, non-design-point operation. I will show how these dynamics can affect the performance, show how multi-physical transport can help in controlling and smoothing some of the observed variations, and generally highlight synergistic effects. I will end with providing general guidelines on operating materials, devices and systems under more realistic conditions.

Experimental and numerical study on the thermal behavior of phase change material infiltrated in low porosity metal foam

ABSTRACTThis study focuses on the mechanical behavior and design of membrane filters that are used in water and wastewater treatment. The aim of this study is, after characterizing the mechanical behavior of the membrane materials, to find a better shape in terms of mechanical parameters. As the first step, uniaxial tensile testing is applied to the produced polymeric membranes with certain contents of poly(ether imide), poly(vinylpyrrolidone), and N‐methyl‐2‐pyrrolidone to get an understanding of the mechanical behavior of the membrane materials. The material data obtained from this experimental process are used as input to software where a finite element model of the membrane is built. Each geometry has the same boundary conditions and the same area, and the same pressure is applied to each geometry. Using these numerical models, the selected geometries are analyzed in terms of displacement, equivalent stress, and equivalent strain. The results are discussed based on these parameters. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47073.

This research aims at studying the shear behavior of homogeneous and heterogeneous granular materials by the triaxial test. The research work is performed on glass beads both in laboratory tests and by numerical simulations in DEM. The experimental tests are firstly performed on mono-disperses beads, then expanded to heterogeneous cases like bi-disperses mixtures. For numerical simulations, a cylindrical rigid wall boundary condition, based on Lame formula is implemented, and a series of procedures is proposed to simulate the conventional triaxial test in similar conditions to experimental tests. The numerical and experimental results are compared for both mono-disperses and bi-disperses cases. The numerical model can reproduce deviatoric curves satisfactorily in all experimental conditions.

La fibrilación auricular es una de las arritmias cardíacas más comunes observadas en la práctica clínica. Por lo tanto, es de vital importancia desarrollar nuevas tecnologías destinadas a diagnosticar y acabar con este tipo de arritmia, para mejorar la calidad de vida de los pacientes y reducir los costes de los sistemas nacionales de salud.\nEn los últimos años ha aumentado el uso de las nuevas técnicas de mapeo auricular, basadas en sistemas multi-electrodo para mapear la actividad eléctrica en humanos. Dichas técnicas permiten localizar y ablacionar los impulsores de la fibrilación auricular, como son las fuentes focales o los rotores. Sin embargo, todavía existe incertidumbre sobre su precisión y los procedimientos experimentales para su análisis están limitados debido a su carácter invasivo. Por lo tanto, las simulaciones computacionales son una herramienta muy útil para superar estas limitaciones, al permitir reproducir con fidelidad las observaciones experimentales, dividir el problema bajo estudio en sub-estudios más simples, y realizar investigaciones preliminares imposibles de llevar a cabo en el práctica clínica.\nEsta tesis doctoral se centra en el análisis de la precisión de los sistemas de mapeo multi-electrodo a través de modelos y simulaciones computacionales. Para ello, desarrollamos modelos realistas multi-escala con el objetivo de simular actividad eléctrica auricular reentrante, en primer lugar en una lámina de tejido auricular, y en segundo lugar en las aurículas completas. Posteriormente, analizamos los efectos de las configuraciones geométricas multi-electrodo en la precisión de la localización de los rotores, mediante el uso de agrupaciones multi-electrodo con distancias inter-electrodo equidistantes, así como a través de catéteres de tipo basket con distancias inter-electrodo no equidistantes. Después de calcular los electrogramas unipolares intracavitarios, realizamos mapas de fase, detecciones de singularidad de fase para rastrear los rotores, y mapas de frecuencia dominantes. Finalmente, descubrimos que la precisión de los sistemas de mapeo multi-electrodo depende de su posición dentro de la cavidad auricular, de la distancia entre los electrodos y el tejido, de la distancia inter-electrodo, y de la contribución de las fuentes de campo lejano. Además, como consecuencia de estos factores que pueden afectar a la precisión de los sistemas de mapeo multi-electrodo, observamos la aparición de rotores falsos que podrían contribuir al fracaso de los procesos de ablación de la fibrilación auricular.

Concrete is a porous medium gaining its strength and stiffness in the course of the hydration process, i.e., the chemical reaction between anhydrous cement and water. Multiscale models enable the modeling of the hydration process [1] by consideration of finer scales of observation and the respective physical/chemical processes at these scales. In this paper, the spectrum of multiscale modeling of cement-based materials, starting from material characterization by state-of-the-art experimental methods, development of homogenization schemes for determination of macroscopic material behavior, and finally the incorporation of the multiscale model into the design process of concrete structures is presented. Unlike material models formulated at the macroscopic scale of observation, multiscale models allow the explicit link of complex macroscopic behavior to its respective origin at finer scales of observation with a sound physical/ chemical basis of the employed constitutive laws at these scales. Recently developed experimental methods for material characterization at finer scales of observation, e.g., nanoindentation, are combined with analytical and numerical methods for (i) interpretation of experimental data [4] and (ii) upscaling towards the macroscopic scale. Whereas an upscaling scheme for elastic properties of early-age cement-based materials has recently been proposed in [1], a homogenization scheme for autogenous shrinkage [3], and viscoelastic properties of early-age cement-based materials is presented in this paper. Classical homogenization schemes, e.g. the Mori-Tanaka scheme [2], for upscaling of elastic properties are specialized in order to account for the loading of the microstructure comprising the effect of capillary depression in the liquid material phase and swelling phenomena resulting from crystallization pressure and viscoelastic material behavior of calcium-silicate-hydrates (CSH).

Large scale/mega projects are lengthy complex endeavors that require significant planning by management, engineers and construction personnel to ensure the success of the project. When we examine the state of mega projects today, we are faced with a real crisis. Companies, both client and contractor, are reporting significant cost and schedule overruns. Lack of project scope definition and planning are the primary characteristics of this problem. Computer simulation is a powerful tool for analyzing complex and dynamic scenarios. It provides an appealing approach for the analysis of repetitive processes. Simulation helps decision makers identify different possible options by analyzing enormous amounts of data. Hence, computer simulation can be used effectively to analyze the resource loading and manpower requirements needed to complete a task in a given time frame, based on current progress levels. This paper discusses a special- purpose simulation (SPS) tool for optimization of manpower forecast loading and resource leveling. The simulation model is capable of optimizing resource requirements for a petrochemical project, based on standard discipline requirements and involvements. Tests of this simulation tool have produced exceptional results; currently, the system is being modified to incorporate historical data within the simulation.