Mesoscopic Field Research Articles

Strain-softening model for granite and sandstone based on experimental and discrete element methods

Combing macroscopic experimental method and mesoscopic numerical method, this study analyses the strain-softening behaviours of granite and sandstone. From the macroscopic perspective, the stress–strain curves of granite and sandstone under different confining pressures are studied by laboratory triaxial compression test. Variations of post-peak reduction modulus and critical plastic shear strain versus confining stress are obtained. Evolution of strength parameters at peak, residual and strain-softening stage are proposed. Then a method to develop the strain-softening model of hard and soft rocks is presented. From the mesoscopic perspective, based on the laboratory test results, the parameters of discrete element method PFC for the samples of the granite and sandstone are calibrated. Comparing the basically consistent results of laboratory experiment and numerical simulation, the feasibility of discrete element method is verified. Evolutions of mesoscopic crack propagation and mesoscopic particle displacement field in the complete failure process are analysed. Typical stresses of granite sample and sandstone sample in the failure stage are investigated. Above combined macroscopic experimental method and mesoscopic numerical method systematically analyse the characteristics of hard rock and soft rock in the strain-softening stage. Failure process and mechanical property of hard rock and soft rock are revealed at the macroscopic and mesoscopic levels. The initiation and propagation process of micro-cracks in rock are thoroughly investigated. The research results provide a scientific foundation for the analyse of strain-softening behaviour of hard rock and soft rock. The result shows that both the mesoscopic numerical method and macroscopic experimental method indicate that the failure pattern of sandstone is influenced by both confining pressure and axial stress, while granite is mainly affected by axial stress.

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.

Quantum nonlocality evolution for two entangled mesoscopic fields under decoherence

Investigation of the nonlocality evolution of entangled mesoscopic fields under decoherence not only is important for understanding the quantum–classical transition, but also has relevance to quantum communication and quantum computation protocols based on continuous variables. According to previous formulations of Bell inequalities, the system loses nonlocal features far before the disappearance of entanglement. We here construct a new version of Bell signal based on rotated and displaced on–off correlations, with which the Bell inequality is violated as long as there remains entanglement and the field state components keep quasiorthogonal. Consequently, the nonlocal character revealed by our formulation decays much slower compared with those based on previous ones. More importantly, there exists a wide regime where the Bell inequality is restored with previous formulations but remains to be violated based on our correlation operators.

A Coupled Machine Learning and Lattice Boltzmann Method Approach for Immiscible Two-Phase Flows

An innovative coupling numerical algorithm is proposed in the current paper, the front-tracking method–lattice Boltzmann method–machine learning (FTM-LBM-ML) method, to precisely capture fluid flow phase interfaces at the mesoscale and accurately simulate dynamic processes. This method combines the distinctive abilities of the FTM to accurately capture phase interfaces and the advantages of the LBM for easy handling of mesoscopic multi-component flow fields. Taking a single vacuole rising as an example, the input and output sets of the machine learning model are constructed using the FTM’s flow field, such as the velocity and position data from phase interface markers. Such datasets are used to train the Bayesian-Regularized Back Propagation Neural Network (BRBPNN) machine learning model to establish the corresponding relationship between the phase interface velocity and the position. Finally, the trained BRBPNN neural network is utilized within the multi-relaxation LBM pseudo potential model flow field to predict the phase interface position, which is compared with the FTM simulation. It was observed that the BRBPNN-predicted interface within the LBM exhibits a high degree of consistency with the FTM-predicted interface position, showing that the BRBPNN model is feasible and satisfies the accuracy requirements of the FT-LB coupling model.

Mesoscopic thermal field reconstruction and parametrical studies of heterogeneous rock-filled concrete at early age

Rock-filled concrete (RFC) is a highly heterogeneous material composed of rock blocks and self-compacting concrete (SCC). There is still limited literature regarding the non-uniform thermal behavior of early-age RFC, making it difficult to predict equivalent homogeneous parameters. In this study, a novel mesoscopic FEM model was developed to simulate the full-scale heterogeneous RFC, both considering the pre-placement of stochastic rocks and layered filling process of SCC into rock voids. Based on on-site experiments of an integrally-poured RFC arch dam, the mesoscopic simulation results were validated and showed good accordance with the monitoring data. The results show that: (1) Spatial heterogeneity in RFC is most pronounced within the first 4 h after SCC pouring, and the RFC temperature typically reaches its peak within about 3 days. (2) The maximum temperature rise observed for SCC is only around 6∼7 °C, whereas the presence of the rockfill skeleton aids in the absorption of hydration heat, leading to a maximum temperature rise of 12.9 °C. (3) With a 5 % increase in the rock-fill ratio, the overall temperature level of the RFC model decreased by approximately 1 °C. (4) Increasing the adiabatic temperature rise of SCC by 10 °C, will lead to an approximate 3 °C rise in the highest temperature observed in RFC. These findings offer valuable insights for effective thermal control strategies in practical engineering applications.

Efficient nonlinear homogenization of bones using a cluster-based model order reduction technique.

We present a reduced order model for efficient nonlinear homogenization of bones, accounting for strength difference effects and containing some well-known plasticity models (like von Mises or Drucker-Prager) as special cases. The reduced order homogenization is done by using a cluster-based model order reduction technique, called cluster-based nonuniform transformation field analysis. For an offline phase, a space-time decomposition is performed on the mesoscopic plastic strain fields, while a clustering analysis is employed for a spatial decomposition of the mesoscale RVE model. A volumetric-deviatoric split is additionally introduced to capture the enriched characteristics of the mesoscopic plastic strain fields. For an online analysis, the reduced order model is formulated in a unified minimization problem, which is compatible with a large variety of material models. Both cortical and trabecular bones are considered for numerical experiments. Compared to conventional FE-based RVE computations, the developed reduced order model renders a considerable acceleration rate beyond , while maintaining a sufficient accuracy level.

An extended two-scale random field model for stochastic response analysis and its application to RC Short-leg shear wall structure

For the stochastic response analysis of concrete structures, it is necessary to model the heterogeneous concrete with significant spatial variability by random fields. In practical applications, multiple material parameters are typically required to characterize the nonlinear constitutive relationship of concrete. As a result, the material parameters of concrete will be represented by a multivariate random field in the nonlinear stochastic response analysis. Nevertheless, a vast number of random variables are frequently involved in representing the multivariate random field, and it is difficult to quantify the probabilistic dependence among the material parameters. To address the preceding issues, this paper proposes an extended two-scale random field model (ETSRF) to quantify the spatial variability of the constitutive relationship of concrete. The model can accurately depict the fluctuation of material properties at the micro-meso scale and the spatial correlation at the macro scale. Besides, it is proved that there is a linear relationship between the mesoscopic random field and ETSRF. Furthermore, a new framework of stochastic response analysis is proposed, where the probability density evolution method (PDEM) is applied to obtain the probabilistic information of the structural responses, and ETSRF is adopted to describe the spatial variability of the material properties. Finally, the proposed model is validated by two illustrative examples, one of which simulates the random fields of compressive and tensile strength of a plain concrete slab, and the other of which deals with the stochastic response analysis of a RC short-leg shear wall structure. The results indicate that the proposed model can depict the spatial variability of the nonlinear constitutive relationship of concrete effectively.

Effect of horizontal stress on the mesoscopic deformation and failure mechanism of layered surrounding rock masses in tunnels

The deformation and failure behaviors of layered surrounding rocks under high in-situ stress are important indicators for tunnel stability evaluation. The attitude of bedding planes is too complex, which impedes the understanding of the rock deformation mechanism under different horizontal stress, especially from the microscopic perspective. In this study, high-precision and easy-to-prepare 3D printing materials are used to simulate layered rock masses. The biaxial loading test system is adopted to explore the creep properties of layered rocks during tunnel excavation in the case of different horizontal stress. The mesoscopic deformation field and failure evolution mechanism of the layered surrounding rocks are revealed using digital image correlation technology. The test results are verified with the numerical simulation method. The shear displacement and plastic strain zone of surrounding rocks in the case of different layer dip angles are studied, and the plastic failure region is given. This paper provides significant experimental and theoretical guidance for the excavation and support of layered soft rock tunnels.

MesoTIRF: A prism-based Total Internal Reflection Fluorescence illuminator for high resolution, high contrast imaging of large cell populations

Total Internal Reflection Fluorescence (TIRF) illumination bypasses the axial diffraction limit of light by using an evanescent field to excite fluorophores close to a sample substrate. However, standard TIRF imaging through the objective requires a high numerical aperture (NA) to generate the evanescent wave. Available lenses have a high magnification with a correspondingly small field of view—ranging from ∼50 μm to 1 mm in diameter. Switching to the older prism-TIRF configuration introduced by Axelrod in the 1980s might seem to remove the requirement for high objective NA and allow the use of existing large-field objectives. Unfortunately, these lenses are unsuitable because their throughput of light is too low for TIRF imaging. As such, high sensitivity TIRF imaging over a much larger mesoscopic field has yet to be demonstrated. We have developed a prism-based TIRF illuminator for the Mesolens—a highly corrected objective lens with an unparalleled ratio of NA to magnification. The imaging field of the Mesolens is 204 times larger than that of the TIRF objectives previously described, increasing the optical throughput of the optical system by a factor of 25 compared to an off-the-shelf microscope objective of the same magnification. We demonstrate MesoTIRF imaging of cell specimens and show the multi-wavelength capability of the modality across more than 700 cells in a single image.

Intelligent dissipative particle dynamics: Bridging mesoscopic models from microscopic simulations via deep neural networks

We develop a bottom-up coarse graining framework to construct mesoscopic force fields directly from microscopic dynamics by a machine learning technique. This scheme, called the intelligent dissipative particle dynamics (IDPD), holds various consistencies, including configuration, phase, static and dynamic consistencies that are incorporated into a deep neural network. The network is trained with full atomic data in a special way for preserving the natural symmetries of the system, and generates both the conservative and non-conservative force fields in the mesoscopic system. Subsequently, the force fields are used in the dissipative particle dynamics (DPD) that is considered as the effective mesoscopic dynamics resulting from the Mori–Zwanzig projection of the underlying atomic dynamics. To show the validity and applicability of IDPD, we coarse grain star polymer and methane fluids respectively, from full molecular dynamics (MD) simulations. Quantitative comparisons between the MD and IDPD indicate that the IDPD is able to reproduce both the static and dynamic properties of underlying MD system, with the aids of a pressure correction and a diffusion rescaling, even when coarse graining multiple molecules into a particle. It follows that the IDPD is competent for preserving the dynamic properties and coarse graining non-bonded molecules, which are common challenges for most of coarse graining methods.

Experimental and numerical study on fracture characteristics and constitutive model of sandstone under freeze-thaw-fatigue

The present paper proposes a whole-process constitutive model of rock mass under freeze-thaw-fatigue based on the Drucker-Prager criterion and the Lemaitre strain equivalence hypothesis and by using a Weibull distribution. The fracture characteristics of rock mass under freeze-thaw-fatigue are studied from a macro and mesoscopic perspective, by using the discrete element method and acoustic emission technology. The results show that as the number of freeze-thaw treatments increases, the b value fluctuation amplitude of the rock mass at fatigue failure decreases, the shear crack increases, the anisotropy of the mesoscopic force field enhances, and the required energy decreases, and the rock burst tendency weakens.

Onset of non-Gaussian quantum physics in pulsed squeezing with mesoscopic fields

We study the emergence of non-Gaussian quantum features in pulsed squeezed light generation with a mesoscopic number (i.e., dozens to hundreds) of pump photons. Due to the strong optical nonlinearities necessarily involved in this regime, squeezing occurs alongside significant pump depletion, compromising the predictions made by conventional semiclassical models for squeezing. Furthermore, nonlinear interactions among multiple frequency modes render the system dynamics exponentially intractable in naïve quantum models, requiring a more sophisticated modeling framework. To this end, we construct a nonlinear Gaussian approximation to the squeezing dynamics, defining a “Gaussian interaction frame” in which non-Gaussian quantum dynamics can be isolated and concisely described using a few dominant (i.e., principal) supermodes. Numerical simulations of our model reveal non-Gaussian distortions of squeezing in the mesoscopic regime, largely associated with signal-pump entanglement. We argue that state of the art in nonlinear nanophotonics is quickly approaching this regime, providing an all-optical platform for experimental studies of the semiclassical-to-quantum transition in a rich paradigm of coherent, multimode nonlinear dynamics. Mesoscopic pulsed squeezing, thus, provides an intriguing case study of the rapid rise in dynamic complexity associated with semiclassical-to-quantum crossover, which we view as a correlate of the emergence of new information processing capacities in the quantum regime.

Laser Melting Deposition Additive Manufacturing of Ti6Al4V Biomedical Alloy: Mesoscopic In-Situ Flow Field Mapping via Computational Fluid Dynamics and Analytical Modelling with Empirical Testing.

Laser melting deposition (LMD) has recently gained attention from the industrial sectors due to producing near-net-shape parts and repairing worn-out components. However, LMD remained unexplored concerning the melt pool dynamics and fluid flow analysis. In this study, computational fluid dynamics (CFD) and analytical models have been developed. The concepts of the volume of fluid and discrete element modeling were used for computational fluid dynamics (CFD) simulations. Furthermore, a simplified mathematical model was devised for single-layer deposition with a laser beam attenuation ratio inherent to the LMD process. Both models were validated with the experimental results of Ti6Al4V alloy single track depositions on Ti6Al4V substrate. A close correlation has been found between experiments and modelling with a few deviations. In addition, a mechanism for tracking the melt flow and involved forces was devised. It was simulated that the LMD involves conduction-mode melt flow only due to the coaxial addition of powder particles. In front of the laser beam, the melt pool showed a clockwise vortex, while at the back of the laser spot location, it adopted an anti-clockwise vortex. During printing, a few partially melted particles tried to enter into the molten pool, causing splashing within the melt material. The melting regime, mushy area (solid + liquid mixture) and solidified region were determined after layer deposition. This research gives an in-depth insight into the melt flow dynamics in the context of LMD printing.

A new finite element approach to model microscale strain localization within olivine aggregates

Abstract. This paper presents a new mesoscopic full field approach for the modeling of microstructural evolutions and mechanical behavior of olivine aggregates. The mechanical framework is based on a reduced crystal plasticity (CP) formulation which is adapted to account for non-dislocation glide strain-accommodating mechanisms in olivine polycrystals. This mechanical description is coupled with a mixed velocity–pressure finite element (FE) formulation through a classical crystal plasticity finite element method (CPFEM) approach. The microstructural evolutions, such as grain boundary migration and dynamic recrystallization, are also computed within a FE framework using an implicit description of the polycrystal through the level-set approach. This numerical framework is used to study the strain localization, at the polycrystal scale, on different types of pre-existing shear zones for thermomechanical conditions relevant to laboratory experiments. We show that both fine-grained and crystallographic textured pre-existing bands favor strain localization at the sample scale. The combination of both processes has a large effect on strain localization, which emphasizes the importance of these two microstructural characteristics (texture and grain size) on the mechanical behavior of the aggregate. Table 1 summarizes the list of the acronyms used in the following.

Mesoscopic Optical Imaging of Whole Mouse Heart.

Both genetic and non-genetic cardiac diseases can cause severe remodeling processes in the heart. Structural remodeling, such as collagen deposition (fibrosis) and cellular misalignment, can affect electrical conduction, introduce electromechanical dysfunctions and, eventually, lead to arrhythmia. Current predictive models of these functional alterations are based on non-integrated and low-resolution structural information. Placing this framework on a different order of magnitude is challenging due to the inefficacy of standard imaging methods in performing high-resolution imaging in massive tissue. In this work, we describe a methodological framework that allows imaging of whole mouse hearts with micrometric resolution. The achievement of this goal has required a technological effort where advances in tissue transformation and imaging methods have been combined. First, we describe an optimized CLARITY protocol capable of transforming an intact heart into a nanoporous, hydrogel-hybridized, lipid-free form that allows high transparency and deep staining. Then, a fluorescence light-sheet microscope able to rapidly acquire images of a mesoscopic field of view (mm-scale) with the micron-scale resolution is described. Following the mesoSPIM project, the conceived microscope allows the reconstruction of the whole mouse heart with micrometric resolution in a single tomographic scan. We believe that this methodological framework will allow clarifying the involvement of the cytoarchitecture disarray in the electrical dysfunctions and pave the way for a comprehensive model that considers both the functional and structural data, thus enabling a unified investigation of the structural causes that lead to electrical and mechanical alterations after the tissue remodeling.

Contraction and exhumation of the western Central Andes induced by basin inversion: New evidence from “Pampean” subduction segment

AbstractIn this study, we conducted an integrated analysis supported by previous regional and mesoscopic field observations, new U–Pb chronological data of synorogenic deposits and thermochronological data from syncontractional granitic rocks. The objective is understanding the main mechanism and timing of crustal uplift of the western Central Andes on the modern flat‐slab segment of northern Chile. The first‐order structural styles identified in several basins of northern Chile consisted mostly of large reverse‐reactivated Mesozoic normal faults, which formed large kilometer‐scale inverted anticlines and localized doubly verging basement reverse faults depending on the degree of tectonic inversion. The observations indicate that crustal shortening experienced in the region was distributed along with the pre‐orogenic half‐graben structures of the Triassic to Jurassic basement. The wide distribution of Upper Cretaceous–Paleocene synorogenic deposits over the syn‐rift Mesozoic deposits along inverted structures in both the Coastal and Frontal cordilleras indicate that the Andean orogenesis in the region was initiated during this period. Our field and geochronological interpretations suggest that basin inversion of the ancient Mesozoic half‐graben structures was frequently accompanied by the emplacement of Upper Cretaceous and Paleocene intrusive granitic bodies hosted in the core of the anticline and syncline folds. Their crystallization ages correlated with those reported by the synorogenic deposits, thereby suggesting that both basin inversion and magmatism occurred simultaneously. The thermal history of the intrusives also indicates that they were rapidly exhumed at 53‒57 Ma, possibly during the final episodes of the basin inversion.

Two-scale random field model for quasi-brittle materials

A new idea of two-scale random field is presented by taking the mechanical behaviors of quasi-brittle materials as an example. In this way, the random fluctuation of material damage at the micro-meso-scale and the spatial correlation of mechanical properties at the macro-scale are both well described by the random distribution of fracture strain. Moreover, it is proved that by introducing a transform matrix, the mesoscopic random fields can be described by a two-scale random field. Based on this, a two-step numerical implementation of the two-scale random field is proposed, and the mechanical behaviors of quasi-brittle materials can be analyzed by incorporating the probability density evolution theory. Finally, an experimental example is presented to demonstrate the capability of the proposed model. Ideal agreements are achieved against the experimental results. Particularly, the randomness of material properties at both scales can be well reproduced.

A multi-scale method for predicting the properties of 3D braided composite under three-point bending load

A more versatile and efficient multi-scale coupling finite element method for researching the mechanical response of 3D braided composites under three-point bending load is represented in this paper. In the mesoscale, the multiphase representative unit-cell models are established to describe the mesoscopic structure which consists of braiding yarns and matrix. In the macroscale, the unit-cells are regarded as homogeneous material, and the load and constraint conditions are applied on the macroscopic structure model. The multi-scale homogenization theory is introduced to calculate the equivalent stiffness matrixes of mesoscopic unit-cells and build the mathematical relationships between the mesoscopic stress fields and the macroscopic strain fields. According to the element damage criterion, the bending modulus and ultimate load-bearing ability of 3D braided composites are predicted by simulating the progressive damage process of unit-cells Comparing with the experimental result, the predicted result satisfies the required precision for engineering.

The meso-failure mechanism of lightweight concrete simulated by the phase field method

PurposeA mesoscopic phase field (PF) model is proposed to simulate the meso-failure process of lightweight concrete.Design/methodology/approachThe PF damage model is applied to the meso-failure process of lightweight concrete through the ABAQUS subroutine user-defined element (UEL). And the improved staggered iteration scheme with a one-pass procedure is used to alternately solve the coupling equations.FindingsThese examples clearly show that the crack initiation of the lightweight concrete specimens mainly occurs in the ceramsite aggregates with weak strength, especially in the larger aggregates. The crack propagation paths of the specimens with the same volume fraction of light aggregates are completely different, but the crack propagation paths all pass through the ceramsite aggregates near the cracks. The results also showed that with the increase in the volume fractions of the aggregates, the slope and the peak loads of the force-deflection (F-d) curves gradually decrease, the load-bearing capacity of the lightweight concrete specimens decreases, and crack branching and coalescence are less likely during crack propagation.Originality/valueThe mesostructures with a mortar matrix, aggregates and an interfacial transition zone (ITZ) are generated by an automatic generation and placement program, thus incorporating the typical three-phase characteristics of lightweight concrete into the PF model.

Measuring coarse grain deformation by digital image correlation

AbstractThis work presents results from oedometric compression of coarse granular material. Coarse granular media exhibit significant deformations making it complicated to predict the settlement of structures. In this paper, a measurement technique was developed for the analysis of two‐dimensional (2‐D) images of a deforming coarse granular medium to investigate its deformation. This was achieved by realising grain‐based image correlation to measure the grain transformation in gravel with the use of a digital image correlation technique. The 2‐D displacement fields enable us to explore the behaviour of granular media at different scales: microscopic, mesoscopic and macroscopic scales. The mesoscopic scale is defined from branches that connect the centres of three neighbouring grains, using a Delaunay triangulation to account for an equivalent continuum media. Whereas the consistency of the macroscopic strain and the average mesoscopic strain is assessed, it is shown that a deviation from the normalised microscopic vertical displacement is an indicator of the heterogeneity of the mesoscopic strain field. The proposed mesoscopic analysis allows us to investigate these heterogeneities. Another important result is that even if the amplitude of the microscopic strain is small (approximately 100 times smaller) compared with the other strain measures, it confirms that the grains are not rigid and that their ultimate strain can be estimated using the proposed approach.