Multiscale Theoretical Model Research Articles

Characteristic frequencies of localized stress relaxation in scaling-law rheology of living cells

Living cells are known to exhibit power-law viscoelastic responses and localized stress relaxation behaviors in the frequency spectrum. However, the precise interplay between molecular-scale cytoskeletal dynamics and macroscale dynamical rheological responses remains elusive. Here, we propose a mechanism-based general theoretical model showing that cytoskeleton dissociation generates a peak in the loss modulus as a function of frequency, while the cytoplasmic viscosity promotes its recovery, producing a subsequent trough. We define two characteristic frequencies (ωc1 and ωc2) related to the dissociation rate of crosslinkers and the viscosity of the cytoplasm, where the loss modulus 1) exhibits peak and trough values for ωc1<ωc2 and 2) monotonically increases with frequency for ωc1>ωc2. Furthermore, the characteristic frequency ωc1 exhibits a biphasic stress-dependent behavior, with a local minimum at sufficiently high stress due to the stress-dependent dissociation rate. Moreover, the characteristic frequency ωc2 evolves with age, following a power-law relationship. The predictions of the dissociation-based multiscale theoretical mechanical model align well with experimental observations. Our model provides a comprehensive description of the dynamical viscoelastic behaviors of cells and cell-like materials.

A Review of the Efficient and Thermal Utilization of Biomass Waste

As a new type of energy that can meet the requirements of carbon neutrality, biomass has received wide attention in recent years, and its rational and efficient thermal utilization can help reduce greenhouse gas emissions and establish an energy-saving, low-carbon energy system to promote sustainable development. In this paper, the current utilization and research status of plant-based biomass waste is comprehensively summarized from four aspects, namely component properties, industrial thermal utilization means, experiments and theoretical calculations. In addition, this paper summarizes the research progress in several aspects, such as microscopic experimental studies, macroscopic pyrolysis characterization, and multiscale theoretical model construction of biomass waste. However, due to the diversity and heterogeneity of biomass, there are still some challenges to extending the laboratory research results to large-scale industrial production, for which we also provide an outlook on future technological innovations and development directions in this research area.

A multiscale fracture model to reveal the toughening mechanism in bioinspired Bouligand structures

The Bouligand structure has been observed in a variety of biological materials, such as lamellar bone and exoskeleton of lobsters. It is a hierarchical and non-homogeneous architecture that exhibits excellent damage-resistant performance. This paper presents a multiscale fracture model considering the material inhomogeneity, the multiscale property, and the anisotropy to reveal the toughening mechanisms in the Bouligand structure. Firstly, the macro and micro constitutive properties of this composite are derived. Then, a multiscale fracture model is developed to characterize the local stress intensity factors and the energy release rates at the crack front of twisted cracks. Our results demonstrate that the decrease in the local energy release rate can be attributed to two-step mechanisms. The first mechanism is that the multiscale structure and the material inhomogeneity cause a release of stress near the initial crack tip. The second mechanism is that the twisted crack leads to the transformation from single-mode loading to mixed-mode loading, which enhances the fracture toughness. These results can not only reveal the toughening mechanism of the Bouligand structure but also provide guidelines for the design of high-performance composites. Statement of significanceBiological materials in nature often possess excellent mechanical properties that have not been achieved by synthetic materials. Bioinspired Bouligand structures provide prototypes for designing high-performance materials. In this study, we propose a multiscale theoretical fracture model to investigate the fracture properties of Bouligand structures with twisted cracks. We systematically consider the roles of material inhomogeneity, anisotropy, and multiscale properties. Our analysis demonstrates that the remarkable toughness of Bouligand structures results from the combined effects of material inhomogeneity and twisted cracks. This research contributes to unveiling the secret behind the outstanding toughness of Bouligand structures and provides inspiration for the development of novel designs for man-made composites.

Multi-scale modeling and simulation of bidirectional coupled moisture and heat transfer in concrete

The change of humidity and temperature field of concrete is closely related to its long-term time-varying performance of shrinkage and creep. Therefore, accurate prediction of temperature and humidity in concrete plays an important role in studying the service performance of concrete structures. In the study, the mechanism of coupled moisture and heat (M&H) transfer in concrete is systematically analyzed from three scales: micro-nano scale, mesoscale, and macroscale; meanwhile, a multi-scale theoretical model of coupled M&H transfer in concrete is established. In addition, a novel simulation method of bidirectional coupled of M&H is proposed and the corresponding ABAQUS subroutine is compiled. Based on the existing experiments, the concrete temperature and humidity data for 180 days were further monitored, which verified the feasibility of the proposed method. Finally, the prediction results of M&H transfer are analyzed and compared in three cases: uncoupling, unidirectional coupling, and bidirectional coupling. For the temperature prediction, the early hydration temperature rise is underestimated under the uncoupled model and the unidirectional coupled model that only considering the influence of temperature on humidity, and the prediction error of unidirectional coupled model that only considering the influence of humidity on temperature is relatively small. For the humidity prediction, both uncoupled and unidirectional coupled models underestimate the water consumption, and the closer to the surface of the concrete, the greater the error. Through experiments and numerical simulation analysis, it is suggested that the bidirectional coupled effect should be considered in the analysis of wet-heat field of concrete. This study provides a new way for the modeling and simulation of coupled M&H of concrete, and lays the foundation for the long-term performance research of infrastructure.

Multiscale theoretical model shows that aging-related mechanical degradation of cortical bone is driven by microstructural changes in addition to porosity

This study aims to gain mechanistic understanding of how aging-related changes in the microstructure of cortical bone drive mechanical consequences at the macroscale. To that end, cortical bone was modeled as a bundle of elastic–plastic, parallel fibers, which represented osteons and interstitial tissue, loaded in uniaxial tension. Distinct material properties were assigned to each fiber in either the osteon or interstitial fiber “families.” Models representative of mature (20–60 yrs.) bone, and elderly (60+) bone were created by modeling aging via the following changes to the input parameters: (i) increasing porosity from 5% to 15%, (ii) increasing the ratio of the number of osteon fibers relative to interstitial fibers from 40% to 50%, and (iii) changing the fiber material properties from representing mature bone samples to representing elderly bone samples (i.e., increased strength and decreased toughness of interstitial fibers together with decreased toughness of osteon fibers). To understand the respective contributions of these changes, additional models isolating one or two of each of these were also created. From the computed stress–strain curve for the fiber bundle, the yield point (ϵy, σy), ultimate point (ϵu, σu), and toughness (UT) for the bundle as a whole were measured. We found that changes to all three input parameters were required for the model to capture the aging-related decline in cortical bone mechanical properties consistent with those previously reported in the literature. In both mature and elderly bundles, rupture of the interstitial fibers drove the initial loss of strength following the ultimate point. Plasticity and more gradual rupture of the osteons drove the remainder of the response. Both the onset and completion of interstitial fiber rupture occurred at lower strains in the elderly vs. mature case. These findings point to the importance of studying microstructural changes beyond porosity, such as the area fraction of osteons and the material properties of osteon and interstitial tissue, in order to further understanding of aging-related changes in bone.

Multi-scale modeling and simulation of additive manufacturing based on fused deposition technique

The issue of multi-scale modeling of the filament-based material extrusion has received considerable critical attention for three-dimensional (3D) printing, which involves complex physicochemical phase transitions and thermodynamic behavior. The lack of a multi-scale theoretical model poses significant challenges for prediction in 3D printing processes driven by the rapidly evolving temperature field, including the nonuniformity of tracks, the spheroidization effect of materials, and inter-track voids. Few studies have systematically investigated the mapping relationship and established the numerical modeling between the physical environment and the virtual environment. In this paper, we develop a multi-scale system to describe the fused deposition process in the 3D printing process, which is coupled with the conductive heat transfer model and the dendritic solidification model. The simulation requires a computational framework with high performance because of the cumulative effect of heat transfer between different filament layers. The proposed system is capable of simulating the material state with the proper parameter at the macro- and micro-scale and is directly used to capture multiple physical phenomena. The main contribution of this paper is that we have established a totally integrated simulation system by considering multi-scale and multi-physical properties. We carry out several numerical tests to verify the robustness and efficiency of the proposed model.

Multiscale Theoretical Model of Thermal Conductivity of Concrete and the Mesoscale Simulation of Its Temperature Field

Temperature field analysis is the precondition of studying the heat and mass transfer and durability of a concrete building; thermal conductivity is a key parameter that affects the distribution of the temperature field of concrete. Through reasonable assumptions and simplifications, the relationship between the micro-microscopic composition of concrete and its macroscopic thermal conductivity is established, and a multiscale theoretical model of thermal conductivity considering the influence of interface transition zone (ITZ) is proposed. The model can predict the thermal conductivities of concrete and its components at an arbitrary saturation. Subsequently, the influence of saturation, water-cement ratio, volume fraction and type of coarse aggregate, and sand ratio is researched. Moreover, according to the prediction results of the proposed model, a mesoscale simulation of the concrete temperature field is carried out. The results demonstrate that the presence of aggregate and ITZ leads to the isotherm deflection and abruption at the junction of the phases. Meanwhile, the heat flux density at the corners of the polygonal aggregate is significantly higher than at other positions; the phenomenon, first named the “corner effect” in the research, causes the temperature field distribution of concrete containing polygonal aggregates to be more uneven than that of circular and elliptical aggregates, and it is more likely to produce temperature-induced cracks. The research helps explain the influence mechanism of material components on the thermal conductivity of concrete and the distribution of its temperature field and provides a basis for the fine simulation of concrete thermal crack growth and creep at variable temperatures.

Development and theoretical analysis of novel surface adaptive polishing process for high-efficiency polishing of optical freeform surface

A novel surface adaptive polishing (SAP) process is initially proposed to efficiently improve the surface accuracy of optical freeform surfaces while suppressing their surface and subsurface damage. A multiscale theoretical model is developed to predict the generation of surface microtopography. This model captures considerable fundamental physics of the SAP process, such as the variable curvature characteristics of the workpiece surface, the surface topography of pad, the brittle-ductile removal effect of materials, and the trochoidal motion trajectories of polishing tool. The feasibility and accuracy of the model were quantitatively analyzed through a series of experiments. Moreover, the influence mechanism of process parameters on surface morphology and subsurface damage was studied. The simulated results by the theoretical model agree well with the experimental data, and maximum relative errors of material removal rate (MRR) and surface roughness Sa are 3.91 % and 1.38 %, respectively. Results indicated that the SAP process can produce axisymmetric Gaussian removal functions, significantly remove the damage layer, and improve the surface quality while avoiding the generation of periodic surface textures. The increase in the tool offset changes the material removal mode from ductile to brittle mode, resulting in a higher MRR and Sa. In addition, the Taguchi simulation experiments are conducted to quantitatively evaluate the significance of the process parameters.

Sound absorption of porous materials perforated with holes having gradually varying radii

A multiscale theoretical model and a finite element (FE) model are established to investigate the sound absorption of porous materials perforated with holes having gradually varying radii. Experimental measurements are carried out to favorably validate the theoretical and numerical models. In the theoretical model, the double porosity material is divided into multiple thin layers and each layer is modeled by adopting the double porosity theory; the transfer matrix method is further applied to establish the relationship of the sound pressure and velocities between the connected layers. The FE simulations give a more detailed explanation for the sound absorption mechanism of the double porosity materials through the distributions of sound pressure, particle vibration velocities, sound energy flow and sound energy dissipation in the material. The influences of the static airflow resistivity of the micro-pore matrix, perforation hole dimensions and hole shapes on the sound absorption of the double porosity materials are analyzed. Results show that the radius gradually varying perforation holes can substantially improve the impedance match between the material and air, and thus enhance sound absorption. Also, the perforation hole shapes have a significant effect on the sound absorption of the double porosity materials. This work provides a helpful guidance to improve the sound absorption of the microporous materials by employing the multiscale design approach.

A multiscale magneto-thermo-mechanically coupled model for ultra-low-field induced magneto-elastocaloric effect in magnetostrictive-shape memory alloy composite system

Recent experimental results show that apparent magneto-elastocaloric effect can be induced in the magnetostrictive-shape memory alloy composite system under an ultra-low magnetic field. In this paper, a multiscale theoretical model is constructed to predict the magneto-thermo-mechanically coupled response of such a composite system by considering the multi-field interactions among the heterogeneous constituent elements in the grain, polycrystalline aggregate and macroscopic scales. In the grain scale, for the magnetostrictive alloy (MEA), the fluctuations of stress and magnetic fields caused by the interactions among the domains are addressed by the self-consistent homogenization scheme. Adopting a probabilistic domain switching criterion based energetic analysis, a constitutive model of MEA is established. For the shape memory alloy (SMA), a crystal plasticity based thermo-mechanically coupled constitutive model is constructed in the framework of irreversible thermodynamics. The interactions among austenite phase and martensite variants are considered by the Mori-Tanaka's homogenization scheme. Thermodynamic driving force for martensite transformation and the internal heat production originated from transformation latent heat and inelastic deformation dissipation are derived from the dissipative inequality and the conservation of energy, respectively. In the polycrystalline aggregate scale, to estimate the interactions among the grains and predict the overall responses of the polycrystalline aggregates of MEA and SMA, a unified incremental magneto-thermo-mechanically coupled self-consistent homogenization scheme is developed. In the macroscopic scale, the magneto-thermo-mechanical interaction equations among the MEA rod, SMA cuboid and Al alloy frame in the composite system are derived by considering the conditions of deformation compatibility, force balance and thermodynamic equilibrium. The capability of the proposed multiscale model to describe the magneto-elastocaloric effect of MEA-SMA composite system is validated by comparing the predictions with the existing experimental data. Moreover, the influences of geometric dimension, pre-load, frame's stiffness and crystallographic orientation on the magneto-elastocaloric effect of the composite system are discussed. The proposed model provides a theoretical guidance for the optimization design of solid-state refrigeration devices in both the microscopic and macroscopic scales.

Timely spread characteristics of micro- and meso-scale fractures based on SEM experiment

Macroscale fracture of rocks is a progressive process consisting of the initiation, propagation and coalescence of numerous microcracks, but the micro- and meso-crack propagation process and the accuracy parameters of multiscale crack evolution timely have not been studied systematically. This study investigates the micro- and meso-damage evolution characteristics based on in-situ scanning electron microscopy (SEM) tests of marble specimens under compression. The propagation and evolution characteristics of microcracks at different locations in marble specimen under load are analyzed in detail. The qualitative analysis of micro- and meso-crack propagation of marble specimen under different loading is performed. The results show that during the compression process of marble from a microscopic point of view, there are mainly three types of microcracks between mineral crystals and mineral crystals: through-grain cracks, transgranular cracks and intragranular cracks. The microcracks that dominate the failure of marble samples are intergranular cracks, and intragranular cracks do not play a significant role. The initiation and evolution of micro-fractures are carried out in zones. Unlike the macro-scale, which is basically a single-wing crack initiation, multiple micro-wing cracks initiate from the end of a prefabricated crack, and some micro-cracks close successively during the loading process, the main wing cracks also undergo a slow or even non-propagating stage. Distribution rules of different micro-parameters are obtained, the transformation from micro-scale to meso-scale is realized. Besides the study provides parameters for the study of a multi-scale theoretical model of rock deformation and failure. Different samples have different characteristics of damage expansion, and the warning before instability is different. This study will provide a warning for possible larger fractures in engineering under different conditions.

Influence of the hydrophobic domain on the self-assembly and hydrogen bonding of hydroxy-amphiphiles.

The amphiphiles 1-octadecanol (octadecyl (stearyl) alcohol, ODA) and 1,2-dioleoylglycerol (DOG) were studied by IR spectroscopy and X-ray diffraction combined with multiscale theoretical modeling. The computations allowed us to rationalize the experimental findings and deduce the supramolecular structure of the formed assemblies while providing a fairly detailed insight into their hydrogen-bonding patterns. IR spectra revealed that the amphiphilic assemblies dramatically differ in structural order and hydrogen-bond strength, both being high in ODA and low in DOG. On the other hand, both compounds demonstrated common features, namely a splitting of the IR bands arising from O-H stretching vibrations (νOH) as well as complete hydrophobicity. However, the observed phenomena have different origins in the two amphiphiles. While the νOH split in ODA occurs due to a vibrational coupling along the string of inter-layer O-HO hydrogen bonds, in DOG it arises from different types of hydrogen bonds (intra- and intermolecular). The hydrophobicity of ODA stems from the very tight O-HO hydrogen bonding network connecting the opposite monolayers in a densely packed tilted crystalline phase (Lc'), whereas in DOG it occurs because the polar sites are locked inside reverted micellar-like assemblies. ODA and DOG illustrate that, in the assemblies of amphiphilic hydroxyl compounds, hydrogen bonds can be formed in a wide structural latitude, which is primarily governed by the chemical nature of apolar chains. Such a wide structural variability of OH-involving hydrogen bonds can be essential for the biological functioning of relevant molecules, such as glycolipids, acylglycerols, and, potentially, glycoproteins and carbohydrates.

A novel multiscale theoretical model for droplet coalescence in turbulent dispersions

A novel multiscale theoretical model for droplet coalescence in turbulent dispersions

A novel multiscale theoretical model for droplet coalescence induced by turbulence in the framework of entire energy spectrum

This work mainly focused on the droplet coalescence induced by turbulence. Two kinds of interaction mechanisms between turbulent eddies and droplets were proposed, and the corresponding coalescence model for each mechanism has also been proposed by counting the number of collisions that can lead to coalescence directly. Most of previous coalescence models only considered the contribution of the turbulent eddies of size equal to the size of droplets since the droplet velocity was assumed to be equal to the velocity of turbulent eddies of same size. In contrast, the contribution of multiscale turbulent eddies (i.e. turbulent eddies with various sizes, not just the turbulent eddies of size equal to the size of droplets) to the coalescence of droplets of given sizes was considered in the proposed model. This work also simulated the coalescence in the framework of entire energy spectrum. Simultaneously, the influences of the average collision free path between droplets and turbulent eddies as well as the lifetime of turbulent eddies on the coalescence were considered. Furthermore, this work proposed a novel second-order longitudinal structure function, which showed a good agreement with the results of direct numerical simulation. Finally, the predicted droplet size distributions of the proposed model were in agreement with experimental data.

Effect of gas composition on morphological properties of graphene nanosheet

A multiscale theoretical model to study the effect of different gas mixtures on the nucleation and growth kinetics of a graphene nanosheet in the reactive low-temperature plasma environment has been developed. The model includes the plasma sheath formalization, kinetics of all the plasma species, charging of the graphene sheet, plasma-surface interaction, clusters and graphene islands nucleation, and vertical growth of a graphene nanosheet. The three different gas mixtures, i.e., C2H2, CH4, and CF4 with hydrogen and argon, are considered in the present investigation to examine the variations in the number densities of carbon and hydrogen species generated on the catalyst surface and their consecutive effects on the dimensions (i.e., height and thickness) and number density profiles of the graphene nanosheet. It is found that the thickness and height of the graphene sheet are maximum for C2H2 gas mixtures and least for CH4 and CF4, respectively. On the basis of the results obtained, the field emission characteristics of the graphene sheet have been analyzed, and it is estimated that C2H2 contained gas mixture enhances the field emission characteristics of the graphene sheet followed by CH4 and CF4. The presented results are in good agreement with the existing experimental observations.

Fatigue Hysteresis Behavior of 2.5D Woven C/SiC Composites: Theory and Experiments

This paper presents an intriguing fatigue hysteresis behavior of 2.5 dimensional woven C/SiC composites via the integration tool of advanced experimental techniques with a multiscale theoretical model. Tension-tension fatigue experiment has been carried out to predict the fatigue hysteresis properties of 2.5D woven C/SiC composite at room temperature, accompanied with the fracture of specimens to investigate the mechanism of fatigue damage. Meanwhile, a multiscale fatigue model of 2.5D woven C/SiC composites, which encompasses a micro-scale model of fiber/matrix/porosity in fiber tows and a macro-scale model of unit-cell, has been proposed to provide a reliable validation of the experimental results based on fiber damages resulting from relative slip motion with respect to matrix at interfaces and the architecture of 2.5D woven C/SiC composites. The predicted hysteresis loop from theoretical model at room temperature holds great agreement with that from tension-tension fatigue experiments. Also, effects of fatigue load, braided structural parameters and material properties at micro scale on fatigue hysteresis behavior have been investigated.

Multi-scale simulations of metamagnetic martensite transition in NiCoMnIn

A multi-scale theoretical model is performed to investigate magnetic field-induced metamagnetic martensite transition in NiCoMnIn alloys. First, the total energy is calculated to demonstrate antiferromagnetic-ferromagnetic transition from first principle calculation. Second, the transition temperature from antiferromagnetic to ferromagnetic can be tuned by the external magnetic field and hydrostatic pressure in thermodynamic calculation, which is consistent with experimental results. Third, phase field simulation found that martensite variant boundaries are superposed with the 90° antiferromagnetic magnetic domain walls, revealing magneto-structural coupling between structural and magnetic domain structures. It is demonstrated that this multi-scale model is very effective for describing antiferromagnetic-ferromagnetic accompanied with martensite-austenite transitions with magnetostructural coupling.

Multi-scale modeling and simulation of material removal characteristics in computer-controlled bonnet polishing

Computer-controlled Bonnet Polishing (CCBP) is an enabling technology which is capable of fabricating ultra-precision freeform surfaces with sub-micrometer form accuracy and surface roughness in the nanometer range, especially for difficult-to-machine and ferrous materials. However, the material removal mechanism of computer controlled bonnet polishing (CCBP) usually exhibits multidisciplinary and multi-scale complexity and hence our understanding of the material removal characteristics is still far from complete. As a result, this paper presents a multi-scale theoretical model for the prediction and simulation of the material removal characteristics in the CCBP process. The model is established based on the study of contact mechanics, kinematics theory and wear mechanisms. A series of spot polishing tests as well as simulation experiments by the theoretical model were conducted. The predicted results agree well with the experimental data. The successful development of the theoretical model helps to make the CCBP process more predictive, and so that optimizing the manufacturing process, and forms the theoretical basis for explaining some material removal mechanisms in CCUP, such as the critical polishing depth for minimizing pad scratching.

Materials for sustainable energy production, storage, and conversion.

Materials for sustainable energy production, storage, and conversion.

The role of roughness-induced damping in the oscillatory motion of bilayer graphene

A multi-scale theoretical model is presented that is the first to offer quantitative agreement with experimental measurements of self-retraction and oscillation of bilayer graphene. The model integrates density-functional theory calculations of the energetics driving flake retraction and molecular-dynamics simulations capturing the dynamic response of laterally-offset rough surfaces. We demonstrate that nanoscale roughness explains self-retraction motion and propose a recipe for tuning that motion by controlling friction.