Mesoscopic Model Research Articles

A Meso-scale study to predict high-temperature behavior of concrete structures in a hygral-thermal-chemical-mechanical framework

Fire has become one of the common hazards that a concrete structure faces in today’s world. Considering the heterogeneity of concrete and the contrasting nature of the constituents at high temperatures (cement paste dehydrates and shrinks while aggregate expands in volume), the use of a homogeneous macroscopic model to predict concrete's thermo-mechanical performance is questionable. Therefore, a more realistic description of concrete (in terms of explicit consideration of coarse aggregate and cement mortar rather than homogenized concrete medium) is needed to characterize the behavior of a concrete structure under such severe loading conditions (e.g., fire). In fact, the performance of a macro-scale (meter size or higher) concrete structure is the coupled effect of the various physico-chemical processes that occur within its constituents at meso-scale, a scale (mm-cm scale size) where coarse aggregates are randomly distributed in a mortar paste medium. Therefore, it is required to develop a model that explicitly considers the constituents' contrasting nature and the different thermo-hygral-mechanical processes at the scale of occurrence of these processes. Hence, in this contribution, a meso-scale based model is developed in a coupled hygro-thermo-chemo-mechanical (HTCM) framework to investigate the effect of high temperature on the thermo-mechanical performance numerically (e.g., in terms of spalling, deformation, residual capacity, etc.) of fire-exposed plain and reinforced concrete structural elements (e.g., slab, beam, etc.). Simulated results and validation with experimental data (taken from the literature) highlight several crucial aspects related to obtaining a more precise residual capacity of a concrete structure, which is impossible to reproduce with a homogenized macroscopic model. The study highlights that the failing of random concrete parts at different times during high-temperature exposure can not be simulated with a homogenized assumption. Further, a mesoscopic model does not require transient creep strain to be specified explicitly. The primary influencing factors behind this transient creep strain, such as the different thermo-chemical and thermo-mechanical damage of the concrete constituents (cement paste, aggregate), thermal-incompatibility of the components and associated damages, etc., are implicitly taken into account in a meso-scale model.

A new educational approach to surface tension and Young-Laplace law by using computer-based simulations

Here we present a pedagogical approach to surface tension phenomena based on a novel mesoscopic fluid model. We show that computer simulations based on this model can provide quantitative results that are consistent with experimental results. We simulate the formation of a two-dimensional liquid droplet without gravity and obtain its surface tension as a result by also verifying Young-Laplace’s law. By controlling some simulation parameters, students can understand step by step how some physical quantities (e.g., the intensity of the interaction between two fluid particles) can affect the behaviour of fluids. This approach will provide students with an explicative model of surface phenomena.

Experimental and mesoscopic modeling numerical researches on steel fiber reinforced concrete slabs under contact explosion

This paper presents experimental research on the damage characteristics of steel fiber reinforced concrete slabs (SCS), steel fiber reinforced concrete slabs mixed with fly ash (CFS), and steel fiber reinforced concrete slabs mixed with fly ash and slag (CFSS) under contact explosion loads. The findings reveal that SCS and CFS exhibit crater damage on the top surface, spalling failure on the bottom surface, and certain damage cracks under the same contact explosion load. Additionally, the CFSS displays crater and spalling damage along with a through-hole at the center. Comparative analysis demonstrates that CFS offers the best explosion resistance properties. A reliable three-dimensional mesoscopic modeling using PYTHON and ABAQUS is established to analyze the dynamic response of the CFS, emphasizing its dependence on fiber volume. Furthermore, the study evaluates energy changes in the matrix and steel fiber to understand their impact on the slab's damage dimensions under contact explosion. Results indicate that the mesoscopic modeling effectively reflects structure damage and failure behavior under explosive super dynamic loads. Specifically, for CFS, with a steel fiber volume of 1.3%, the internal energy and stress generated by steel fiber are maximized, resulting in the smallest damage dimension under contact explosion and the best explosion-resistant effect. This research provides valuable insights for guiding the design of explosion-resistant structures and their deployment in concrete engineering applications.

FEATURES OF USING CRUSHED CONCRETE AS A COARSE AGGREGATE FOR CONCRETE

Problem statement. According to the results of a study by the Kyiv School of Economics as of June 2023 the total amount of direct documented damage to residential and non-residential infrastructure due to destruction and damage as a result of military actions exceeded $150.5 billion. During the post-war reconstruction Ukraine will face the problem of a large number of buildings and structures that will be subject to partial dismantling and demolition. This process will be accompanied by the generation of a significant amount of construction waste, which traditionally in Ukraine is taken to landfills without recycling. On the other hand, there will be a need for a large quantity of construction materials, the share of which in the construction cost may reach 50 %. To reduce the cost of objects, it is advisable to reuse materials from waste generated after dismantling. Such materials are called recycling. The most obvious option is the use of crushed concrete waste as a coarse aggregate for the production of new concrete. The purpose of the article. Identification of the features of recycled coarse aggregates from concrete waste and concrete with their use, determination of the influence of source concrete on the properties of recycled aggregates. Conclusions. The mesoscopic model of concrete with recycled coarse aggregate has been examined. The analysis of the current research results on both recycled concrete aggregates and concrete with their use showed that, in general, with correct calculations of concrete mix compositions that consider the actual physical and mechanical properties of recycled aggregates, the production of structural concrete is possible. At the same time, crushing methods and the grain composition of such aggregates have a significant influence. In order to standardize the approaches to the research of recycled aggregates, it is necessary to create an appropriate methodology or regulatory framework.

Rate-dependent damage sequence interaction model for predicting the mechanical property of in-service aluminum alloy 6005A-T6

Engineering structures and materials will undergo fatigue, aging, and other degradation behaviors during long-term service under the combined influence of complex boundary conditions. These service damages make the materials and structures no longer meet the initial design requirements and pose a potential risk to the service system. This study proposes a material mesoscopic model to decouple the microstructure into a system composed of matrix and void phases. The matrix phase has an invariant constitutive relationship as an ideally undamaged material, and the different evolutionary behaviors of the void phase are described as damage evolution functions and lead to different stress–strain behaviors of the actual material. First, the damage described by different definitions is proposed, and a nonlinear function of damage evolution consistent with the Weibull distribution characteristic of microstructural continuity is derived. Then, an experimental–numerical method is improved to accurately identify the accelerated damage evolution behavior under various strain rates. Finally, the ideally undamaged constitutive of the matrix phase and the damage evolution function of the void phase are established, which can cover the void nucleation, growth, and aggregation process. Besides, the damage sequence interaction model is established in conjunction with the mesoscopic physical mechanism, and the total damage evolution function for materials containing prior service damage in subsequent ductile deformation is achieved by measuring the apparent elastic modulus of the material only. Finally, the ideally undamaged constitutive and damage evolution function are calibrated for aluminum alloy 6005A-T6, commonly used in the car body structure of rail vehicles, and verified with damaged specimens that experienced certain service loads. The material's damage sequence interaction mode is determined, and the rate-dependent residual strength is predicted.

Conformational Space of the Translocation Domain of Botulinum Toxin: Atomistic Modeling and Mesoscopic Description of the Coiled-Coil Helix Bundle.

The toxicity of botulinum multi-domain neurotoxins (BoNTs) arises from a sequence of molecular events, in which the translocation of the catalytic domain through the membrane of a neurotransmitter vesicle plays a key role. A recent structural study of the translocation domain of BoNTs suggests that the interaction with the membrane is driven by the transition of an α helical switch towards a β hairpin. Atomistic simulations in conjunction with the mesoscopic Twister model are used to investigate the consequences of this proposition for the toxin-membrane interaction. The conformational mobilities of the domain, as well as the effect of the membrane, implicitly examined by comparing water and water-ethanol solvents, lead to the conclusion that the transition of the switch modifies the internal dynamics and the effect of membrane hydrophobicity on the whole protein. The central two α helices, helix 1 and helix 2, forming two coiled-coil motifs, are analyzed using the Twister model, in which the initial deformation of the membrane by the protein is caused by the presence of local torques arising from asymmetric positions of hydrophobic residues. Different torque distributions are observed depending on the switch conformations and permit an origin for the mechanism opening the membrane to be proposed.

Drops on Polymer Brushes: Advances in Thin-Film Modeling of Adaptive Substrates.

We briefly review recent advances in the hydrodynamic modeling of the dynamics of droplets on adaptive substrates, in particular, solids that are covered by polymer brushes. Thereby, the focus is on long-wave and full-curvature variants of mesoscopic hydrodynamic models in gradient dynamics form. After introducing the approach for films/drops of nonvolatile simple liquids on a rigid smooth solid substrate, it is first expanded to an arbitrary number of coupled degrees of freedom before considering the specific case of drops of volatile liquids on brush-covered solids. After presenting the model, its usage is illustrated by briefly considering the natural and forced spreading of drops of nonvolatile liquids on a horizontal brush-covered substrate, stick-slip motion of advancing contact lines as well as drops sliding down a brush-covered incline. Finally, volatile liquids are also considered.

A mesoscopic model for inter-yarn friction

Friction between yarns is a crucial phenomenon in fabric manufacturing processes, and it becomes more complex when using lubrication agents to improve processing. This work presents an experimental investigation of the frictional behaviour of different combinations of yarns under dry and wet conditions, as occurring in overbraiding processes. The experiments were designed to maintain a constant yarn tension, and subsequently also a constant normal force and contact area during the test. Both the inter-yarn angle and the normal force significantly influence the friction coefficient. The additional contribution of the capillary force results in consistently higher friction coefficients for the water-lubricated yarns compared to the dry yarns. An anisotropic friction model is proposed to capture the influence of the inter-yarn angle, normal force, and capillary effects observed during the experiments. The model shows that the friction follows Amontons’ friction at high external normal forces and Howell’s friction at moderate normal forces.

Engineering Mesoscopic 3D Tumor Models with a Self‐Organizing Vascularized Matrix (Adv. Mater. 5/2024)

Engineering Mesoscopic 3D Tumor Models with a Self‐Organizing Vascularized Matrix (Adv. Mater. 5/2024)

Retracted: Explosion Resistance of Three-Dimensional Mesoscopic Model of Complex Closed-Cell Aluminum Foam Sandwich Structure Based on Random Generation Algorithm

Retracted: Explosion Resistance of Three-Dimensional Mesoscopic Model of Complex Closed-Cell Aluminum Foam Sandwich Structure Based on Random Generation Algorithm

Mechanical properties and acoustic emission characteristics of two dissimilar layers of rock-like specimens with prefabricated parallel fissures

AbstractThrough the uniaxial compression test of double parallel fissured layered rock mass, the mechanical properties of layered rock mass with different fissure dip angle, and the characteristics of acoustic emission (AE) parameters in the process of fracture are studied. The influence of fissure dip angle on the progressive damage, and macroscopic fracture of layered rock mass is explored. The fracture mode, local stress variation characteristics, and stress field evolution law of fissured layered rock mass are analyzed from a mesoscopic point of view. The results show that with the increase of the fissure dip angle α, the peak strength and the elastic modulus of the layered rock mass decrease first and then increase. The low frequency-high amplitude (LF-HA) signals of AE all appear in the crack propagation stage. With the increase of fissure dip angle α, the LF-HA signal ratio increases first, then decreases and then increases, and shows significant stage characteristics. The cracks are mainly generated around the relatively low strength A rock and prefabricated fissures, and all pass through the interface between A rock and B rock. Eight types mesoscopic displacement field models are found, and the final failure mode of the model is tensile-shear mixed failure. The upper and lower regions of the fissure are tensile stress areas, while the left and right regions are compressive shear stress areas, which are distributed in a “butterfly” type. The stress difference at the fissure tip is negatively correlated with the mechanical parameters of the layered rock mass.

Towards an efficient multi-scale numerical model of the impact behavior of woven materials with global/local approach

This paper presents the global/local approach in the multi-scale modeling of woven material impact behavior. This approach optimally considers important microscopic mechanisms to accurately predict outcomes and reduce computational time. The inspiration for this approach stems from the specific behavior exhibited by woven materials under ballistic impact:(1) Zone 1 (Local) is a small square around the impact position, requiring comprehensive microscopic modeling to describe complex physical phenomena accurately.(2) Zone 2 (Global) represents the remaining fabric outside of Zone 1, exhibiting more global behavior and modeled with a mesoscopic model.Building upon a previous work's joining technique, an interface between these two zones is implemented and validated through numerical tensile testing. The proposed approach is then compared to the complete mesoscopic model already validated in the case of a 2D Kevlar KM2 woven fabric submitted to ballistic impact. The global/local approach demonstrates slightly greater flexibility due to the presence of microscopic yarns. It successfully predicts all microscopic phenomena while significantly reducing the degrees of freedom compared to full microscopic modeling along the entire yarn length.

A mathematical model for predicting crystallization fouling in narrow rectangle channel incorporating crystal growth effect

Crystallization fouling is an ongoing concern for many heat transfer systems, and simulating fouling formation under various flow and heat transfer conditions is crucial for predicting fouling resistance and improving energy efficiency. This paper proposes a mesoscopic model for predicting crystallization fouling in narrow rectangle channels accounting for the realistic crystal growth. A hybrid lattice Boltzmann and finite difference model is established to predict the coupled process of fluid flow, heat transfer, concentration diffusion and crystallization fouling. The second-order mass deposition rate is solved and transformed to the surface-reaction boundary condition in lattice Boltzmann (LB) scheme, and the volume of pixel (VOP) method is employed to simulate the dynamic crystal growth. The scheme and the sub-models are verified systematically by the analytical solution of a linear diffusion-reaction problem, the semi-theoretical fouling models, and the experimental data. The results indicate that the present model can effectively predict the crystallization fouling controlled by either surface integration or mass transfer, and show its capability to simulate the non-uniform fouling growth process in heat transfer channels, providing insight towards full understanding and mitigation design of crystallization fouling.

Mesoscopic Model of Extrusion during Solvent‐Free Lithium‐ion Battery Electrode Manufacturing**

AbstractSolvent‐free (SF) manufacturing of lithium‐ion battery (LIB) electrodes is safer and more environmentally friendly than the traditional slurry casting approach. However, as a young technique, SF manufacturing is under development of its pathways and operation conditions. In different SF processes reported in literature, extrusion is a common step. A detailed model of this process would be extremely computationally demanding. This work proposes a novel simplified discrete element model at the mesoscopic scale for the extrusion during SF manufacturing of LIB electrodes. In addition to active material particles, we consider fluid‐like solid particles to approximate the molten polymer and the carbon additive phases. The formulation and other process parameters are taken from our experimental facility that uses extrusion to fabricate filaments for 3D printing of LIB cells. The extrusion is carried out in a conical twin screw extruder. Our approach allows to obtain representative electrode microstructures after extrusion, where electrical conductivity, ionic effective diffusivity, tortuosity factor and porosity are calculated. The model is a proof of concept that is employed to investigate the influence of the extruder speed and the cohesion level on the resulting electrode properties.

Ion effects on co-existing pseudo-phases in aqueous surfactant solutions: cryo-TEM, rheometry, and quantification

HypothesisSpecific alkaline cation effects control the area per headgroup of alkylester sulphates, which modifies the spontaneous packing of the surfactants. The resulting effective packing minimizes the total bending energy frustration and results in a Boltzmann distribution of coexisting pseudo-phases. These pseudo-phases constitute of micelles and other structures of complex morphology: cylindrical sections, end-caps, branching points, and bilayers, all in dynamic equilibrium. According to our model, excess of end-caps or excess of branching points lead to low viscosity, whereas comparable amounts of both structures lead to viscosity maxima. Relative occurrence of branching points and end-caps is the molecular mechanism at the origin of the salt-sensitive viscosity peak in the “salt-curve” (viscosity against salt concentration at fixed surfactant concentration). Up to now, and as indicated in former papers, this has been a pure model without microscopic verification. ExperimentsIn this work, we introduce explicit counting of the number of coexisting pseudo-phases as observed by state-of-the-art cryogenic transmission electron microscopy (cryo-TEM). The model system used, i.e., sodium laurylethersulfate (SLES)/salt/water, is very common as part of cosmetic formulations. As added salts, we used Li+, Na+, K+, and Cs+ chlorides. In parallel to imaging, we measured the macroscopic viscosities of the different solutions. FindingsWith cryogenic transmission electron microscopy (cryo-TEM), we imaged a variety of morphologies (pseudo-phases) in the different aqueous surfactant/salt solutions: cylindrical micelles with end-caps, discs surrounded by “rims”, entangled thread-like micelles with branching points, networks with gliding branching points, and bilayers. The relative chemical potentials of these morphologies could be approximated simply by counting the relative proportion of their occurrence. This simple multi-scale approach avoids any ad-hoc “specificity” assumption of ions, and is based on the bending energy model in an extended version of the Benedek “ladder model”. It is capable of explaining and even quantifying the location of all viscosity peaks in the “salt-curves” for the different cations investigated, thus confirming the previously proposed model experimentally, and – thanks to cryo-TEM – for the first time on a microscopic scale. Moreover, this approach can also be applied when the added cations lead to newly observed pseudo-phases, such as discs and vesicles. To the best of our knowledge, this is the first time that cryo-TEM is used, together with a mesoscopic model, to describe a macroscopic property such as viscosity and specific ion effects on it, without any a priori assumption about these effects. So, in total, we could a) confirm the predictions of the previously developed model, b) use cryo-TEM imaging and viscosity measurements to predict and find unusual morphologies when varying the cations of the added salt, and c) count the pseudo-phases in cryo-TEM micrographs to quantitatively explain the different nanostructures.

Modelling the piezoelectric effect in a composite polymer film filled with disperse piezoelectric

Mesoscopic modelling of a composite material constituted by an electroneutral polymer (matrix) film filled with micropowder of piezoelectric ceramics (filler) is presented. The calculation scheme resembles that of the RVE (Representative Volume Element) method. The representative element (cell) is a right-angle prism with square cross-section, the height of which is equal to the film thickness. Around the midsection of the prism, there are a few (from 2 to 4) spherical piezoelectric particles positioned close to one another. The length of the base side of the prism is determined from the assumed solid phase content of the composite. To simulate the film, the cells are arranged in a continuous flat layer, inside which they are coupled by means of periodic boundary conditions imposed on their lateral surfaces. To reduce the artifacts of the model, the position of the center of each particle is chosen randomly within the area of the prism cross-section. In the framework of this approach, a low-density polyethylene film with embedded barium titanate particles is considered as an example. One of the surfaces of the film is fixed (no displacements), and the other one is left free. For the characteristics of the particles close to those used in the experiment and the typical matrix material parameters (elasticity moduli, Poisson coefficients, dielectric permittivity), the voltage output (piezoeffect) induced in the film in response to the uniform pressure applied to its free surface is evaluated. It is shown that the electric potential along the thickness of the film is nonuniform: it grows inside the particles and falls down in the interparticle gap. In order to present the results in the form applicative for comparison with the experimental data, for each variant of the system (number of the particles, weight fraction of the solid phase), the calculated values are averaged over a few tens of realizations of the particle positions inside the element.

Road network free flow speed estimation using microscopic simulation and point-to-point travel times

Roads in mesoscopic traffic simulation models are often parametrized by a free speed attribute, which describes the speed at which a vehicle can traverse a road in the absence of congestion. Unlike microscopic models, mesoscopic models do not typically simulate traffic lights, individual driver behavior or acceleration and deceleration of vehicles. In consequence, the free speed parameter of each road must account for all the aforementioned effects. Modeling free speed accurately is important, as it determines the travel time, which in turn affects the decision-making of agents in the simulation.This paper introduces an approach combining microscopic simulation with machine learning models to estimate road segment free speeds. Using the microscopic simulator SUMO, we generate training data for a model search employing Bayesian optimization. Subsequently, these models undergo fine-tuning via gradient-based optimization using real-world point-to-point travel times. A significant advantage is the adaptability of this approach to diverse road networks, including those from OpenStreetMap, and the ability to incorporate routing data from various online providers independently.Our evaluation illustrates a notable decrease in prediction error between 30% and 60% compared to baseline models that assume a uniform free speed reduction for all urban roads. The fine-tuned models are able to generalize well to unseen regions and are therefore applicable to case studies where data for new or altered roads is unavailable.

Investigating the effect of particle size distribution and complex exchange dynamics on NMR spectra of ions diffusing in disordered porous carbons through a mesoscopic model.

Ion adsorption and dynamics in porous carbons are crucial for many technologies, such as energy storage and desalination. Nuclear magnetic resonance (NMR) spectroscopy is a key method to investigate such systems thanks to the possibility of distinguishing adsorbed (in-pore) and bulk (ex-pore) species in the spectra. However, the large variety of magnetic environments experienced by the ions adsorbed in the particles and the existence of dynamic exchange between the inside of the particles and the bulk renders the interpretation of the NMR experiments very complex. In this work, we optimise and apply a mesoscopic model to simulate NMR spectra of ions in systems where carbon particles of different sizes can be considered. We demonstrate that even for monodisperse systems, complex NMR spectra, with broad and narrow peaks, can be observed. We then show that the inclusion of polydispersity is essential to recover some experimentally observed features, such as the co-existence of peaks assigned to in-pore, exchange and bulk species. Indeed, the variety of exchange rates between in-pore and ex-pore environments, present in experiments but not taken into account in analytical models, is necessary to reproduce the complexity of experimental NMR spectra.

Power law creep and delayed failure of gels and fibrous materials under stress.

Motivated by recent experiments studying the creep and breakup of a protein gel under stress, we introduce a simple mesoscopic model for the irreversible failure of gels and fibrous materials, and demonstrate it to capture much of the phenomenology seen experimentally. This includes a primary creep regime in which the shear rate decreases as a power law over several decades of time, a secondary crossover regime in which the shear rate attains a minimum, and a tertiary regime in which the shear rate increases dramatically up to a finite time singularity, signifying irreversible material failure. The model also captures a linear Monkman-Grant scaling of the failure time with the earlier time at which the shear rate attained its minimum, and a Basquin-like power law scaling of the failure time with imposed stress, as seen experimentally. The model furthermore predicts a slow accumulation of low levels of material damage during primary creep, followed by the growth of fractures leading to sudden material failure, as seen experimentally.

Mesoscopic conductivity and trap distribution characteristics in the interfacial region of polypropylene/MgO nanocomposites with high energy storage density

Polymer dielectric materials are crucial for storage devices in power and electronic systems, as well as electric vehicles, due to their high energy density and fast discharge rates. Polymer nanocomposites (PNCs) possess superb electrical and energy storage properties, making them highly promising as next-generation thin-film dielectrics for energy storage. The excellent performance of PNCs derive from the interfacial region introduced by nano-doping. However, the current measurement equipment and technology make it difficult to accurately obtain the mesoscopic scale distribution characteristics of the conductivity of the interfacial region, and are also impossible to clarify the formation mechanism of deep traps in the interfacial region. We employed high-throughput simulation and experiment to investigate the mesoscopic conductivity and trap distribution properties of the interfacial region in PNCs. Furthermore, we developed a three-dimensional mesoscopic conductivity distribution simulation model of PNCs containing polymer matrix, nanoparticles, and interfacial region. The interfacial region size and conductivity distribution of the PNCs were determined by comparing with the experimental results, and the mesoscopic distribution characteristics of the interfacial traps in PNCs were obtained. It is proved that the nanofillers form a condensed structure with high order and compactness by restraining the movement of molecular chains, which deepens the trap energy in the interfacial region and restricts the free volume expansion. This results in the formation of interfacial regions with low conductivity, contributing to enhancing energy storage performance.