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We present a novel formalism to characterize elastic heterogeneities in amorphous solids. In particular, we derive high-order strain-energy expansions for pairwise energies under athermal quasistatic dynamics. We then use the presented formalism to study the statistical properties of pairwise expansion coefficients and their link with the statistics of soft, quasilocalized modes, for a wide range of formation histories in both two- and three-dimensional systems. We further exploit the presented framework to access local yield stress maps by performing a non-linear stress–strain expansion within a cavity embedded in a frozen matrix. We show that our "bond micromechanics" compare well with the original "frozen matrix" method, with the caveat of overestimating large stress activations. We additionally show how local yield rules can be used as an input for a scalar elasto-plastic model (EPM) to predict the stress response of materials ranging from ductile to brittle. Finally, we highlight some of the limits of simple mesoscale models in capturing the aging dynamics of post-yielding systems. Intriguingly, we observe subdiffusive and diffusive shear band growths for particle-based simulations and EPMs, respectively. [ABSTRACT FROM AUTHOR]

Despite the wide existence of vesicles in living cells as well as their important applications like drug delivery, the underlying mechanism of vesicle fusion/fission remains under debate. Classical models cannot fully explain recent observations in experiments and simulations. Here, we develop a constrained self-consistent field theory that allows tracking the shape evolution and free energy as a function of center-of-mass separation distance. Fusion and fission are described in a unified framework. Both the kinetic pathway and the mechanical response can be simultaneously captured. By taking vesicles formed by polyelectrolytes as a model system, we predict discontinuous transitions between the three morphologies: parent vesicle with a single cavity, hemifission/hemifusion, and two separated child vesicles, as a result of breaking topological isomorphism. With the increase in inter-vesicle repulsion, we observe a great reduction in the cleavage energy, indicating that vesicle fission can be achieved without hemifission, in good agreement with simulation results. The force–extension relationship elucidates typical plasticity for separating two vesicles. The super extensibility in the mechanical response of vesicle is in stark contrast to soft particles with other morphologies, such as cylinder and sphere. Our work elucidates the fundamental physical chemistry based on intrinsic topological features of vesicle fusion/fission, which provides insights into various phenomena observed in experiments and simulations. [ABSTRACT FROM AUTHOR]

A multiscale micromechanics-based progressive damage model is developed to investigate the overall mechanical behavior and the interfacial microcrack evolutions of the cementitious composites featuring superabsorbent polymer (SAP) under uniaxial tension. Elastic properties, progressive damage process, and homogenization procedure of cementitious composites are systematically integrated in this model. The effective elastic moduli of the composites are determined based on a multiscale micromechanical framework. According to the small strain assumption, the total strain tensor and the elastic-damage compliance tensor are additively decomposed into elastic and damage-induced components. The damage-induced strains and compliances are then deduced from micromechanics. To characterize the progressive elastic-damage induced by microcracks, stages of microcrack propagation are identified from the interface contact stress and the matrix cleavage stress. The complex potentials and stress intensity factors for kinked interface cracks are derived from the distributed dislocations method. By implementing the homogenization process, the macroscopic mechanical behavior is obtained from the micro/mesoscale. The results indicate that the material parameters have clear mechanical significance. Different parameters, such as the SAP addition ratio, aggregate content, initial interfacial crack size, and initial interfacial crack location, are revealed to be influential in the overall mechanical behavior of the composites. The proposed model can be generalized to other particle-reinforced composites with different constituent properties, which can potentially contribute to the design and optimization of durable composites.

Highlights The demand for natural fiber‐reinforced polymer composites is increasing in the automotive industry, and Mexican blue‐gave fiber (AF) is getting attention from automakers. Quantitative characterization of the tensile behavior of AF allows for a better ascertain of fiber performance. This work developed a model to study the elastoplastic behavior of AF prior and after its incorporation within a thermoplastic matrix. Finite element predictions showed excellent agreement with both theoretical and experimental values from literature. It was revealed that the increase in the fiber aspect ratio hastens the interaction between nearby defects within the fiber with earlier coalescence of voids, and ultimately fosters the loss of both fiber ductility and load carrying capacity. Moreover, the preponderant character of the damage in AF is controlled by nucleation and growth of voids. On the other hand, AF reinforced thermoplastic composites exhibit a microfailure based essentially on the matrix failure, and the composites become more damage tolerant with the increase in fiber aspect ratio. Stiffer AF leads to a more uniform interfacial shear stress distribution, with higher stiffness of the composite. Therefore, the effectiveness of AF to reinforce polymeric matrixes depends strongly on the elastic mismatch of the coupled materials. Local stress state in AF is correlated to macroscopic stress. AF may be recognized as a von Mises material. Ductile fracture in AF is controlled by nucleation and growth of voids. Increasing the fiber aspect ratio leads to more damage tolerant composites. Stiffer AF led to a more uniform interfacial shear stress distribution. [ABSTRACT FROM AUTHOR]

The anisotropic microstructure of granular materials has a profound effect on their macroscopic behaviour and can be characterised using a fabric tensor. To include of fabric in the critical state theory (CST), anisotropic critical state theory (ACST) was proposed by modifying the state parameter (ψ) of CST to a fabric-dependent dilatancy state parameter (ζ) . Noteworthy that ψ showed a very strong correlation with characteristic features (e.g. instability, phase transformation and characteristic state) of macroscopic behaviour and, as a result, it has been adopted in many constitutive models. While ζ aided the inclusion of fabric in ACST models, the correlation between ζ and characteristic features has not been evaluated in detail yet, although a large number of works are found on micromechanics and fabric only. In this study, a large number of discrete element method simulations for drained and undrained triaxial were conducted to evaluate the correlation between ζ and characteristic features. To this purpose, the correlation between stress ratio and both classic and dilatancy state parameter (ψ and ζ ) were studied in important characteristic features (e.g. instability, phase transformation and characteristic state). It was found that this correlation was improved using ζ which might be due to the inclusion of fabric in our model. This observation is new and significant for inclusion of fabric evolution in constitutive modelling. [ABSTRACT FROM AUTHOR]

Enhancing the understanding of the behavior, optimizing the design, and improving the predictability and reliability of manufactured unidirectional (UD) FRP plies, which serve as primary building blocks for structural FRP laminates and components, are crucial to achieving a safe and cost-effective design. This research investigated the influence of fiber volume fraction ( v f ) on the predictability and reliability of the homogenized elastic properties and damage initiation strengths of two different types of UD FRP plies using validated micromechanical virtual testing for representative volume element (RVE) models. Several sources of uncertainties were included in the RVE models. This study also proposed a modified algorithm for microstructure generation and explored the effect of v f on the optimal sizes of the RVE in terms of fiber number. Virtual tests were systematically conducted using full factorial DOE coupled with Monte Carlo simulation. The modified algorithm demonstrated exceptional performance in terms of convergence speed and jamming limit, significantly reducing the time required to generate microstructures. The developed RVE models accurately predicted failure modes, loci, homogenized elastic properties, and damage initiation strengths with a mean error of less than 5 % . Also, it was found that increasing v f led to a concurrent increase in the optimal size of the RVE. While it was found that the v f had a direct influence on homogenized elastic properties and damage initiation strengths, it did not significantly affect the reliability and predictability of these properties, as indicated by low correlation coefficients and fluctuations in the coefficient of variation of normalized properties. [ABSTRACT FROM AUTHOR]

To decipher the mechanical response mechanisms of coal seams with multi-scale porefracture structure to supercritical CO2 (ScCO2) injection, two coal samples from different mines of the Ordos Basin, North China, were first selected for conducting ScCO2-watercoal reaction experiments. Subsequently, the pore-fracture structure, macroscopic and microscopic mechanical behaviors of samples with different reaction times were analyzed, and the evolution patterns of pore-fracture parameters and relationships between the macroscopic and microscopic mechanical parameters were finally elucidated. The results showed that the ScCO2-water-coal reaction modifies the pore-fracture structure in coal. Originally filled fractures re-open, original micro-fractures expand, new fractures form, and pores evolve from small- to large-sized. After the ScCO2-water-coal reaction, the evolution of the compaction stage, the macroscopic mechanical parameters and the energy dissipation during loading corroborate the weakening effect of the ScCO2-water-coal reaction on coal. The changes observed in the microscopic mechanical parameters align with those in the macroscopic mechanical parameters; however, due to the strong heterogeneity of coal and the inability of microscopic parameters to reflect the component and porefracture distribution, certain characteristics of the change amplitude of macroscopic and microscopic mechanical parameters of coal are inconsistent. The ScCO2 extraction effect, the chemical dissolution, the different-sized pore-fracture evolution, the coupling effect of geostress, reservoir pressure, and swelling stress are the main factors to consider during the process of ScCO2 sequestration in deep coal seams at the micro-, meso- and macro-scales, as they are responsible for potential safety issues. [ABSTRACT FROM AUTHOR]

The high source stability and brightness of field emission gun equipped scanning electron microscopes (SEM) makes them ideal for high‐resolution digital image correlation (HRDIC). However, their high initial capital cost can be prohibitive for research organisations and groups. Conventional thermionic SEMs using either a tungsten hairpin or LaB6 filament are far more widespread due to their lower cost. Whilst it is understood that overall performance and ultimate resolution are lower than field emission SEMs, we propose that there is no fundamental reason why these instruments are unsuitable for HRDIC. We investigate the use of a LaB6 SEM as a viable tool for HRDIC. We detail the subtleties of performing HRDIC using a LaB6 thermionic source SEM, providing technical recommendations for best practices in using these instruments for strain mapping. The effects of instrument parameters on strain measurement noise are examined, with a focus on parameters of key relevance to in situ and ex situ mechanical testing. Errors in focus and image pixel size are found to be the primary contributors to the strain noise floor values, with stage accuracy being of secondary importance. We present a case study in oxygen‐free high‐conductivity copper, OFHC‐Cu, which is used in the designs of nuclear fusion components as a heat sink interlayer. Heterogeneous strain patterns are observed in this material, with high levels of strain localisation at grain boundaries. Active slip systems are identified using the relative displacement ratio method, demonstrating the quality of these data and the suitability of LaB6 instruments for HRDIC strain mapping, achieving performance approaching that expected of a field emission SEM. [ABSTRACT FROM AUTHOR]

A large amount of waste clay is generated in shield tunnel engineering. Although the physical properties such as the unconfined compressive strength of the clay have been improved through lime modification, some still fail to meet the specifications for road embankment materials. In this study, a indoor carbonation device was used to carbonize lime-modified clay samples with different lime contents. The changes in water content (ω), plasticity index (IP), undrained compressive strength (qu), and softening coefficient (Kr) of the samples were analyzed. Microscopic mechanisms were investigated through tests such as Scanning electron microscope (SEM) and Diffraction of x-rays (XRD). The results showed that with increasing carbonation period, the ω and IP of soil samples with different lime contents gradually decreased and stabilized. After 2 hours of carbonation, the qu, elastic modulus (E50), and Kr of the soil samples significantly increased. After 1 hour of carbonation and 7 days of curing, the modified clay with lime content greater than 7% met the subgrade strength standards for secondary and lower-grade highways (IP ≤ 26; qu ≥ 500 kPa). The carbonation reaction resulted in the formation of CaCO3 crystals on the surface of soil particles and Ca(OH)2. With carbonation further developed, a CaCO3—Ca(OH)2—C-S-H hybrid material was generated, which filled the pore space in clay reinforcing the structure and improving the strength of lime-modified clay. [ABSTRACT FROM AUTHOR]

A multi-scale framework is constructed for the computation of the stiffness tensors of an elastic strain-gradient continuum endowed with an anisotropic microstructure of arbitrarily-shaped particles. The influence of microstructural features on the macroscopic stiffness tensors is demonstrated by comparing the fourth-order, fifth-order and sixth-order stiffness tensors obtained from macro-scale symmetry considerations to the stiffness tensors deduced from homogenizing the elastic response of the granular microstructure. Special attention is paid to systematically relating the particle properties to the probability density function describing their directional distribution, which allows to explicitly connect the level of anisotropy of the particle assembly to local variations in particle stiffness and morphology. The applicability of the multi-scale framework is exemplified by computing the stiffness tensors for various anisotropic granular media composed of equal-sized spheres. The number of independent coefficients of the homogenized stiffness tensors appears to be determined by the number of independent microstructural parameters, which is equal to, or less than, the number of independent stiffness coefficients following from macro-scale symmetry considerations. Since the modelling framework has a general character, it can be applied to different higher-order granular continua and arbitrary types of material anisotropy. [ABSTRACT FROM AUTHOR]

Reduced order models (ROMs) are often coupled with concurrent multiscale simulations to mitigate the computational cost of nonlinear computational homogenization methods. Construction (or training) of ROMs typically requires evaluation of a series of linear or nonlinear equilibrium problems, which itself could be a computationally very expensive process. In the eigenstrain‐based reduced order homogenization method (EHM), a series of linear elastic microscale equilibrium problems are solved to compute the localization and interaction tensors that are in turn used in the evaluation of the reduced order multiscale system. These microscale equilibrium problems are typically solved using either the finite element method or semi‐analytical methods. In the present study, a reduced order variational spectral method is developed for efficient computation of the localization and interaction tensors. The proposed method leads to a small stiffness matrix that scales with the order of the reduced basis rather than the number of degrees of freedom in the finite element mesh. The reduced order variational spectral method maintains high accuracy in the computed response fields. A speedup higher than an order of magnitude can be achieved compared to the finite element method in polycrystalline microstructures. The accuracy and scalability of the method for large polycrystals and increasing phase property contrast are investigated. [ABSTRACT FROM AUTHOR]

Glenoid implants used in anatomic total shoulder arthroplasties typically incorporate peripheral pegs as a design feature to support eccentric loads. These peripheral pegs and the implant‐cement‐bone interface undergo substantial cyclic tensile‐compressive loads during normal activity. Therefore, these pegs are of interest in translating the micromechanics of local implant fixation failure to the biomechanics of gross anatomic failure of the glenoid implant after total shoulder arthroplasty. This study used an in vitro peg‐cement‐bone construct which incorporated bone tissue acquired from osteoarthritic patients undergoing total shoulder arthroplasty. Strain distributions in the peripheral peg‐cement‐bone interfaces were analyzed under loading conditions emulating glenoid implant edge displacements. It was found that tensile strains in the interfaces were highest near the backside‐peg junction and were greater in magnitude than compressive strains. Notably, strains near the peg's fixation channels were relatively low. These results suggest that cracks may initiate around the peg near the backside and travel downward to cause broader fixation failure. [ABSTRACT FROM AUTHOR]

We consider a static linear bond–based peridynamic (proposed by Silling, see J. Mech. Phys. Solids 2000; 48:175–209) composite materials (CMs) of a periodic structure. In the framework of the second background of micromechanics (also called computational analytical micromechanics), one proved that local micromechanics (LM) and peridynamic micromechanics (PM) are formally analogous to each other for CM of both random and periodic structures. It allows a straightforward generalization of LM methods (including fast Fourier transform, FFT) to their PM counterparts. So, in the PM counterpart of the implicit periodic Lippmann–Schwinger (L-S) equation in LM, we have three convolution kernels corresponding to the properties of the matrix, inclusions, and interactive interface. Eshelby tensor in LM, depending on the inclusion shape, is replaced by PM counterparts depending on the shapes of inclusions, and the interaction interface (although the Eshelby concept of homogeneous eigenfields does not work in PM). The mentioned tensors are estimated once (as in LM) in a frequency domain (also by the FFT method). The possible incorrectness of FFT applications to PM is analyzed and corrected. The polarization schemes of the solution of the L-S equation in the Fourier space have one primary unknown variable (polarization), whereas the PM counterpart contains three primary ones estimated at each step, which are formally similar to the LM case. A description of the generalized basic scheme and the Krylov approach is presented. Computational complexities O(N log2 N) of the FFT methods are the same in both LM and PM. [ABSTRACT FROM AUTHOR]

Brittle to ductile transition with the increase of confining pressure is a common behavior of porous geomaterial. In the present work, a micromechanics-based multiscale constitutive model is constructed to describe the macroscopic mechanical behavior of porous chalk. At the microscopic scale, the Drucker–Prager criterion is adopted to describe the plastic behavior of the solid matrix with dissymmetric responses between tensile and compressive loading. Based on the macroscopic yield criterion derived in Shen et al. (Int J Plast 126:102609, 2020), an effective damage parameter is introduced and then a complete multiscale constitutive model is constructed and implemented with a plastic hardening law and a macroscopic plastic potential to describe the overall mechanical behavior of porous geomaterial. Through the evolution of microstructure of the studied porous materials, the proposed micromechanics-based multiscale model well describes the transition from brittle behavior to ductile one with the increase of confining pressure. The proposed constitutive model is then applied to porous chalk and validated by the comparisons between its numerical predictions and experimental results under different confining pressures. The main features of porous materials are captured by the proposed model which improves significantly the phenomenological ones. Highlights: A novel elastoplastic damage constitutive model is established for porous material. The model considered explicitly the effects of porosity and matrix properties. The brittle-ductile transition in porous material is well taken into account. The variation of material microstructure during the loading is considered. The new model is general and can be applied to a large range of geomaterials [ABSTRACT FROM AUTHOR]

Multiphase heterogeneity significantly affects mechanical and micro-cracking properties of geomaterials. Heterogeneity representations of geomaterials, however, can bring out fatal errors for cracking behavior investigations due to inaccurate characterizations of multiphase matrixes. This work aims to deeply characterize microscopic heterogeneity in rocks represented by digital multiphase matrixes, and to study their effects on cracking properties of geomaterials. X-ray μ-Computed Tomography (μCT) imaging under the same physical field of view is employed to obtain multiphase microstructures of sandstone with different resolutions. Digital colour difference segmentation (DCDS) and the coupling multiple point statistics-marching cube (MPS-MC) algorithms are applied to accurately characterize three-dimensional (3D) multiphase heterogeneity of rocks. Digital simulations coupled with uniaxial compression are conducted to study multiphase heterogeneity effects on micromechanics and cracking behaviors. Results show that with increasing resolution and voxel scale, heterogeneity index increases. Peak stress and crack ratio increase with increasing heterogeneity index, and the relative errors between experimental and numerical stresses are all less than 5% when the voxel is larger than 3003. Micro-pores extremely improve damage of multiphase microstructures, and the transgranular cracks initiate first, and then intergranular cracks initiate due to large heterogeneity of microscopic elements between micro-pores and microscopic interfacial transition zones (ITZs) and similar strength heterogeneity of microscopic elements in micro-grains. The proposed digital-analysis framework is effective to evaluate multiphase heterogeneity effects on mechanical and cracking responses in various engineering projects. Highlights: Complete microscopic multiphase element heterogeneity is established to characterize heterogeneous geomaterials. Voxel scale and imaging resolution effects on characterizing microscopic multiphase heterogeneity are analyzed. Microscopic cracking and micromechanical responses of geomaterials are studied. [ABSTRACT FROM AUTHOR]

The homogenized and local behavior of wavy brick-and-mortar structures accounting for the piezoelectric multiphysics effect was studied in a systematic manner. The information on the connection between composite microstructure and their macro-properties serves as the directives for devising and crafting engineered materials that align with specific target performance criteria. Secondly, we scrutinized the potential of the multiphysics finite-volume direct averaging micromechanics (MFVDAM) method and compared it with finite element techniques in simulating the effective and local piezoelectric response within wavy brick-and-mortar architectures. The numerical findings demonstrated robust agreement between the two methods, underscoring that the MFVDAM stands as a convincing alternative to the finite element approach for examining multiphysics challenges encompassing various microstructures and scales. This establishes a benchmark for comparison against conventional micromechanics techniques. [ABSTRACT FROM AUTHOR]

The mechanical response of granular materials, exemplified by frictional grain interactions, is characterized by a critical state in which deformation occurs without change of material volume or stresses when subjected to large shear deformation. In this work, a granular micromechanics approach (GMA) based continuum model is used to investigate the emergence of such a critical state. The continuum description is constructed through mechanical concepts based upon elastic and dissipation energies defined for a generic grain‐pair interaction. A hemivariational principle provides the basis for considering the evolution of damage and plasticity phenomena comprising grain‐pair contact loss and irreversible deformation. As a consequence, the Karush–Kuhn–Tucker (KKT)‐type conditions are derived, which give the evolution equations for the irreversible phenomena. Notably, in this derivation there is no invocation of flow rules and other similar assumptions of classical phenomenological continuum damage and plasticity. Further, Piola's ansatz is elaborated to kinematically connect granular micromechanics of grain‐pair to the continuum description. While the concept of critical state analysis has been handled with either phenomenological approaches or discrete numerical frameworks, in the present paper this concept is examined within a micromechanics‐based continuum description. The constitutive model is established and the coupled damage and plastic irreversible quantities are assessed. The critical state is shown to emerge as grain‐pair related damage and plastic evolution in a competitive/collaborative manner during the imposed loading path. [ABSTRACT FROM AUTHOR]

Dental enamels of different species exhibit a wide variety of microstructural patterns that are attractive to mimic in bioinspired composites to simultaneously achieve high stiffness and superior toughness. Non-human enamel types, however, have not yet received the deserved attention and their mechanical behaviour is largely unknown. Using nanoindentation tests and finite element modelling, we investigate the mechanical behaviour of Macropus rufogriseus enamel, revealing a dominating influence of the microstructure on the effective mechanical behaviour and allowing insight into structural dependencies. We find a shallow gradient in stiffness and low degree of anisotropy over the enamel thickness that is attributed to the orientation and size of microstructural features. Most notably, M. rufogriseus 's modified radial enamel has a far simpler structural pattern than other species', but achieves great property amplification. It is therefore a very promising template for biomimetic design. The diversity of dental enamel structures in different species is well documented, but the mechanical behaviour of non-human enamel types is largely unknown. In this work, we investigate the microstructure and structure-dependent mechanical properties of marsupial enamel by nanoindentation and finite element simulations. Combining these methods gives valuable insights into the performance of modified radial enamel structures. Their stiffness and toughness stems from a unique structural design that is far less complex than well-studied human enamel types, which makes it a uniquely suitable template for biomimetic design. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, the effective behavior of viscoelastic composites with ellipsoidal reinforcements and imperfect interface or degraded interphase is investigated through the inclusion replacement concept. The concentration equations have been reformulated as to define the equivalent inclusion's behavior with imperfect interface or thin coating allowing to evaluate the effective behavior through different homogenization schemes. The correlation between interface and interphase descriptions is formulated in the context of anisotropic behavior of the inclusion and the matrix and for ellipsoidal inclusion shape. In the case of isotropic elasticity, the exact analytical solutions agree with the literature references for spherical and cylindrical inclusion morphologies and linear spring interface model. The replacement procedure was extended to viscoelastic behavior of the components with imperfect interface and/or interphase. Alternative descriptions of the interface behavior are proposed through Maxwell and Kelvin–Voigt models. The combined influence of shape of inclusions and interface parameters is analyzed on the effective relaxation modulus. [ABSTRACT FROM AUTHOR]

Asphalt, a widely utilized binder material in pavement construction, brings notable environmental and economic advantages through its efficient and high-utilization technique of multiple recycling. Nevertheless, the microscale mechanical mechanisms and laws governing the damage evolution in asphalt during repeated aging and recycling processes remain unclear, posing challenges in determining the optimal reclamation method and timing for binder maintenance. This study seeks to bridge this gap by employing microstructural numerical simulation and viscoelastic computational methods to elucidate the fundamental changes in microstructural mechanics and relaxation spectra of asphalt binders during multiple aging and regeneration processes, ultimately enhancing the design efficiency of multiple regeneration pavements. The study's key findings revealed that aging decelerates the relaxation capacity and increases the modulus of asphalt, while regeneration reduces the modulus and enhances relaxation capacity. The initial two aging and regeneration processes significantly influenced the stress distribution in the microscopic phase of the asphalt. Following the third aging and rejuvenation, the stress threshold and area of stress concentration remained relatively unchanged. Aging and regeneration primarily alter the mechanical properties of the microscopic phase, affecting the stress relaxation capacity and complex modulus of asphalt. The present study provides a certain research basis for the micro-mechanism of multiple regeneration asphalt. [ABSTRACT FROM AUTHOR]

Highlights In this study, a micromechanics model, based on a hierarchical/gradient interface design, for predicting randomly hybrid carbon nanotube (CNT)/aramid pulp (AP) micro/nano‐fibers interleaved in a laminar unidirectional carbon fiber‐reinforced polymer (UD‐CFRP) is proposed. The model emphasizes the gradient interfaces that are formed in situ because of the graded penetration mechanisms of the CNT and AP. Additionally, via an experimental study, it is analytically verified that CNT/AP‐interleaving enhances the transverse tensile strength and modulus of the UD‐CFRP. The modeling and experimental results show a strong correlation. The increase in transverse tensile strength and modulus of the UD‐CFRP with CNT/AP hybrid interleaving and the associated hierarchical toughening mechanism are confirmed theoretically and experimentally. Furthermore, new insights into the multiscale toughening mechanisms of transverse tensile properties are obtained via systematic analysis. The hierarchical gradient interfacial structure formed by the penetration of CNT/AP‐interleaving and multiscale fiber‐bridging results in a transformation of the failure mechanism. Finally, the effects of the failure mechanism on model predictions and the applicability of micromechanical models are further discussed. A micromechanics modeling of UD‐CFRP with CNT/AP‐interleaving is proposed. The enhancements of CNT and AP are confirmed theoretically and experimentally. The contribution of CNT and AP to the properties of CFRP is theoretically verified. The effect of the hierarchical fiber‐bridging toughening mechanism is revealed. [ABSTRACT FROM AUTHOR]

The structured sand presents significant interparticle bonding and anisotropy, resulting in significant differences in the physical and mechanical properties from the pure sand. This study proposes a new surrogate model based on the concept of multi‐fidelity residual neural network (MR‐NN) as an alternative to DEM simulation for predicting the mechanical behaviours of structured sand with different initial anisotropy and saving largely computational costs. The model is initially trained using low‐fidelity (LF) data to focus on capturing the main underpinning correlations between macroscopic mechanical parameters with inter‐particle properties and anisotropic state variables (i.e., microscopic fabric and tilting angle of sand), where the LF data are generated from previously proposed anisotropic macro‐micro quantitative correlation. Subsequent training on sparser high‐fidelity (HF) data is used to calibrate and refine the model with HF data generated from DEM simulations for anisotropic structured sand. Feedforward neural network (FNN) is adopted as the baseline algorithm for training models. The macroscopic anisotropic parameters of structured sand predicted by the surrogate model are compared with DEM simulations to examine its feasibility and generalization ability. Furthermore, the robustness of the surrogate model is examined by discussing the effect of LF data on the performance of MR‐NN. The superiority of the MR‐NN is further verified by comparing the performance of the trained MR‐NN with the one‐shot trained FNN based on the same HF data. All results demonstrate that the proposed surrogate model can provide a fast and accurate simulation of the anisotropic parameters of structured sand. [ABSTRACT FROM AUTHOR]

The aim of the current study is to provide evidence regarding the influence of particle size on the dynamic properties in granular materials. Experiments using a resonant column (RC) device were conducted on glass beads having similar coefficient of uniformity, but four different mean grain sizes to describe the tendencies in the magnitude of Gmax and Emax. It can be clearly seen that for similar particle gradation the influence of particle size is significant, in particular for larger mean grain sizes d50 exceeding 1·5 mm. The experimental data were fitted using existing empirical relationships with corresponding fitting parameters. The fitting parameters describing the void ratio and pressure dependence to estimate maximum stiffness were found to depend on grain size to a certain extent. This influence was diminished for the materials with a d50 < 1·5 mm. It was therefore possible to use a unique set of fitting parameters for these materials with a satisfying degree of accuracy. The results were compared with some previous studies to highlight the size dependency of Gmax and Emax for materials with mean size greater than 2 mm, but also the relatively small influence on materials with lower mean particle sizes (d50 < 2 mm) is acknowledged. The results are furthermore discussed through a micromechanical interpretation highlighting why larger grain sizes influence stiffness values. [ABSTRACT FROM AUTHOR]

Torsional vibration response of a circular nanoshaft, which is restrained by the means of elastic springs at both ends, is a matter of great concern in the field of nano-/micromechanics. Hence, the complexities arising from the deformable boundary conditions present a formidable obstacle to the attainment of closed-form solutions. In this study, a general method is presented to calculate the torsional vibration frequencies of functionally graded porous tube nanoshafts under both deformable and rigid boundary conditions. Classical continuum theory, upgraded with nonlocal strain gradient elasticity theory, is employed to reformulate the partial differential equation of the nanoshaft. First, torsional vibration equation based on the nonlocal strain gradient theory is derived for functionally graded porous nanoshaft embedded in an elastic media via Hamilton's principle. The ordinary differential equation is found by discretizing the partial differential equation with the separation of variables method. Then, Fourier sine series is used as the rotation function. The necessary Stokes' transformation is applied to establish the general eigenvalue problem including the different parameters. For the first time in the literature, a solution that can analyze the torsional vibration frequencies of functionally graded porous tube shafts embedded in an elastic media under general (elastic and rigid) boundary conditions on the basis of nonlocal strain gradient theory is presented in this study. The results obtained show that while the increase in the material length scale parameter, elastic media and spring stiffnesses increase the frequencies of nanoshafts, the increase in the nonlocal parameter and functionally grading index values decreases the frequencies of nanoshafts. The detailed effects of these parameters are discussed in the article. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) and particle flow code (PFC3D) are utilized to characterize microcracking nature in mode-I fracture of coal with strong bursting liability. The microcracks are represented by AE moment tensor (MT), which corresponds to displacement discontinuities involving opening/closing and sliding motions. The microcracking source parameters, including shear/tensile type, volume, orientation, motion, and magnitude, are calculated by minimizing the errors between the analytical and measured displacements, with an imposed constraint. Then, the detailed fracture processes, including microcracking source mechanisms and energy dissipation during coal tensile failure, are analyzed using both experimental and numerical approaches. The results show that the time-varying of crack mode angle and decomposed crack volume suggest a mixed-mode mechanisms locally with both normal and tangential displacements for microcracks. However, the orientations of microcracks with bigger magnitude are almost parallel to the direction of the crack propagation path, and their movement directions are mainly along the direction of the maximum principal stress, which is compatible with the expected fracture mechanism of mode-I opening globally. The dissipated energy and crack opening displacement obtained from AE inversion are approximately consistent with results calculated from energy release rate G and opening displacement measured using DIC, respectively. A new AE MT simulation method, based on particle motion, is developed using PFC3D to verify the reliability of the above-mentioned microcracking characterization results. The mechanical properties as well as AE responses (including AE rate, magnitude distribution, spatial location, and MT) from PFC3D numerical simulation are in good agreement with the experimental results, which reinforces the reliability the microcracking characterization results from AE inversion and simulation. Due to the tortuous crack propagation path and the inhomogeneity between grains, the maximum principal stress and resultant displacement coexists both on the normal and tangential of the inclined crack surface. Under the combined action of tensile and shear stress, the normal and tangential motion displacement components along the crack plane are generated, respectively, resulting in mixed-mode microcrack. This research provides a new approach for characterizing the microcracks in loaded rock/coal, which can deepen the understanding of meso-process and mechanism during rock/coal fracture. Highlights: Microcracks are represented by acoustic emission moment tensor subjected to displacement discontinuity. A new method for acoustic emission simulation is developed using particle flow code to verify test results. Time–space–energy evolution process and focal-mechanism of microcracks are analyzed. Meso-mechanism of mixed-mode microcracks during coal tensile failure is explained. [ABSTRACT FROM AUTHOR]

This study investigated the effects of intercalation and exfoliation of the graphite flake particles on the mechanical properties of elastomeric composites using analytical, computational, and experimental techniques. Relying on the modified Eshelby and incremental Mori–Tanaka approach, a new micromechanics model was proposed to estimate Young's modulus and develop a constitutive model for expanded graphite (EG)-filled elastomer in finite strain deformation. It was found that when the initial graphite flakes expanded, the actual volume fraction and ultimate aspect ratio of the dispersed particles significantly affected the mechanical properties of the EG-reinforced composites. The present model and subsequent predictions reflect the initial flake diameter, actual volume fraction, ultimate aspect ratio of the particles, and other convenient physical properties of the composite constituents. In addition, molecular dynamics simulations were performed to evaluate the elastic properties of the EG-Matrix interphase region using the COMPASS force field function. The MD results showed that Young's modulus of the interphase region increased significantly as the quantity of the graphene layer increased. The micromechanics-constitutive model results were validated using the experimentally determined stress–strain relation of the composites. EG- and CB-elastomer nanocomposite specimens were fabricated and tested in the experimental program. Field emission scanning electron microscopy (FESEM) analysis of the cryo-fractured surfaces of the elastomer compounds showed good interactions between the constituents. Numerical computations indicated that the proposed model incorporating the new parameters could accurately predict the experiment at a small particle concentration. [ABSTRACT FROM AUTHOR]

This study evaluated two fundamental assumptions about the geometry of the wood cell wall to develop a mechanistic characterization of wood behavior at the scale of wood structural components. This paper used a three-step homogenization scheme implemented through homogenization techniques and finite-element analyses to evaluate a multilayered cell wall and a simplified single-layer method. Both earlywood and latewood geometries were considered. A three-part sensitivity analysis assessed the influence of wood constituent proportions, microfibril angle, and cellulose crystallinity on cell wall stiffness. Sensitivity to constituent ratios was evaluated through a Monte Carlo simulation of 1,000 sampled points and correlation analysis. Sensitivity to microfibril angle and cellulose crystallinity was evaluated through parametric characterization. The investigation found that both methods provided an accurate assessment of wood stiffness when compared with experimentally determined values. Care should be taken when modeling higher densities of wood, and use of either method in higher order models should be determined by the resolution of input data and computational needs. [ABSTRACT FROM AUTHOR]

The tunnel face stability is closely related to the migration behavior and clogging mechanism of the slurry particles in granular soils, which is not yet fully understood. In this study, the coupled computational fluid dynamics–discrete element method (CFD–DEM) is adopted to investigate the infiltration behavior of slurry at the particle scale. The full Johnson–Kendall–Roberts (JKR) contact model describing interparticle behavior that accounts for cohesion present even when particles are microseparated after collisions is adopted for clay‐clay or clay‐sand particles and the Hertz–Mindlin model is used for sand‐sand particles. Through simulations, the mechanism of the slurry particle's blockage is identified as physical, frictional and cohesive modes, and slurry particle migration usually undergoes the process of aggregation‐destruction‐migration‐reassembly. Meanwhile, the influences of pressure, cohesive force, and particle shape on infiltration are also analyzed. The results indicate that high pressure lengthens the infiltration path and increases the infiltration rate. The increase in cohesion enhances the effective clogging of the sand column by the slurry, and particles with smaller sphericity are more likely to clog in the sand column. These findings may enhance our understanding of the slurry infiltration mechanism and its practical application in TBM tunneling. [ABSTRACT FROM AUTHOR]

The increasing use of rock‐socketed piles highlights the importance of developing a suitable design method for their bearing capacity. This study quantifies the shear behavior of the rock–pile interface, which generally dominates the bearing capacity of rock‐socketed piles under service load. A micromechanics‐based rock–pile interface model with idealized nonuniform profile is proposed with two enhancements: (1) the slip line method together with nonlinear Hoek–Brown failure criteria is integrated to identify the critical shear displacement of rock asperity; and (2) the residual stage of shear behavior is properly considered with the rounding progress of sheared rubbles. The enhanced interface model is first validated by the direct shear test results under constant normal stiffness. Then, the interface model is implemented via user‐defined FRIC into the finite element code ABAQUS without the need of explicitly building the rock–pile interface profile. Accordingly, the model is applied to simulate and analyze two field cases involving rock‐socketed piles. Comparison between the predictions and field observed results shows this method can well capture the axial load transfer behavior of pile socket into weak rock. [ABSTRACT FROM AUTHOR]

A fine -macroscopic scale computational model was constructed based on the numerical analysis of the fracture phase field method to simulate the internal temperature field and microscopic stress field in the case of a sudden cooling of the exterior wall surface after being subjected to hot sunshine. An evaluation model of heat and humidity progressive micro-damage was established, which was verified by the bonded mortar pull-out test. The results indicate that when the external surface of the external wall system is subjected to a temperature increase of 88.6 °C, in summer and then a sudden decrease to 20 °C, by hail and heavy rainfall, the maximum principal stress value of fine aggregate and net mortar subjected to 15 MPa, respectively. Cracks with a depth of 5 mm and a width of 100 microns in the direction of the thickness were developed, which means that this kind of extreme climate change has caused substantial damages to the structural integrity of the heat preservation system, and the structural integrity of the heat preservation system is substantially damaged by this kind of extreme climate change. The risk of "high fall" of the external wall system increases rapidly. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the influence of flexoelectricity on the coupled electromechanical behavior of MXene/graphene-based hybrid piezocomposite (MGHPC) plates. We developed an analytical model based on Navier’s solution and Kirchhoff’s plate theory, as well as an approximate model based on the Ritz method for validation purposes. A three-phase micromechanical modeling is developed for determining the effective properties of MGHPC composed of 2D MXene and graphene nano-reinforcements embedded in an epoxy matrix. These micromechanical models were implemented to predict the static and dynamic electromechanical response of MGHPC plates subject to various edge support and loading conditions. Both the analytical and approximate solutions provided unequivocal evidence of the profound impact of the flexoelectric effect on the bending and modal analysis of MGHPC nanoplates. The flexoelectric effect enhanced the stiffness of the nanoplate, irrespective of the support condition. This implies that MGHPC plates can be tailored for precise resonance frequencies and static deflection within nanoelectromechanical systems. This can be achieved by manipulating parameters such as boundary conditions and geometric attributes, including plate thickness/aspect ratio and graphene/MXene nano-reinforcements volume fractions.

Using instrumented indentation testing, we explore the measurement of surface residual stress in H-section steel beams produced through the quenching and self-tempering (QST) process. We establish a significant correlation between the plastic pile-up behavior observed during indentation and the magnitude of surface residual stress. We thoroughly clarify the distribution of plastic pile-up and residual stress, linking their variations to non-uniform phase transformation and changes in mechanical properties resulting from the QST process. Moreover, we employ an indentation curve analysis to evaluate surface residual stress, obviating the need for direct measurements of pile-up height. These findings facilitate the measurement of non-uniform surface residual stress in H-section beams, crucial for ensuring structural integrity, yet challenging to measure in situ.

The complex mechanical and damage mechanisms of rocks are intricately tied to their diverse mineral compositions and the formation of pores and cracks under external loads. Numerous rock tests reveal a complex interplay between the closure of porous defects and the propagation of induced cracks, presenting challenges in accurately representing their mechanical properties, especially under true triaxial stress conditions. This paper proposes a conceptualization of rock at the mesoscopic level as a two-phase composite, consisting of a bonded medium matrix and frictional medium inclusions. The bonded medium is characterized as a mesoscopic elastic material, encompassing various minerals surrounding porous defects. Its mechanical properties are determined using the mixed multi-inclusion method. Transformation of the bonded medium into the frictional medium occurs through crack extension, with its elastoplastic properties defined by the Drucker–Prager yield criterion, accounting for hardening, softening, and extension. Mori–Tanaka and Eshelby’s equivalent inclusion methods are applied to the bonded and frictional media, respectively. The macroscopic mechanical properties of the rock are derived from these mesoscopic media. Consequently, a True Triaxial Macro-Mesoscopic (TTMM) constitutive model is developed. This model effectively captures the competitive effect and accurately describes the stress-deformation characteristics of granite. Utilizing the TTMM model, the strains resulting from porous defect closure and induced crack extension are differentiated, enabling quantitative determination of the associated damage evolution.

Objective: Anterior disc displacement (ADD) has been used to establish temporomandibular joint disorder (TMD) models. Based on whether preserve of the retrodiscal attachment, the modelling methodologies include ADD with dissecting the retrodiscal attachment (ADDwd) and ADD without dissecting the retrodiscal attachment (ADDwod). This article aims to determine which model better matches the micromechanical and microstructural progression of TMD. Methods: Through meticulous microscopic observations, the microstructure and micromechanical deformation of the TMJ discs in ADDwd and ADDwod rabbit models were compared at 2 and 20 weeks. Result: Scanning electron microscopy and transmission electron microscopy showed that collagen fibres became slenderized and straightened, collagen fibrils lost diameter and arrangement in the ADDwd group at 2 weeks. Meanwhile, nanoindentation and atomic electron microscopy showed that the micro‐ and nano‐ mechanical properties decreased dramatically. However, the ADDwod group exhibited no significant microstructure and micromechanical deformations at 2 weeks. Dissection of the retrodiscal attachment contribute in the acceleration of disease progression at the early stage, the devastating discal phenotype remained fundamentally the same within the two models at 20 weeks. Conclusion: ADDwod models, induced stable and persistent disc deformation, therefore, can better match the progression of TMD. While ADDwd models can be considered for experiments which aim to obtain advanced phenotype in a short time. [ABSTRACT FROM AUTHOR]

Fabric anisotropy is a sought-after micro index to correlate macro mechanical responses of granular materials. In this work, the discrete-element method is utilised to simulate multi-directional bender element tests in granular soils to obtain the evolution of wave velocities during drained conventional triaxial (CT) and true triaxial (TT) tests; the contact normal-based fabric is simultaneously monitored for bridging the fabric anisotropy and wave velocity anisotropy. The results show that stress-normalised wave velocities and microscopic fabric, including contact normal distribution and coordination number, remain nearly constant until a stress ratio threshold is reached. After the threshold value is reached, stress-normalised wave velocities start to decrease, especially in the minor principal stress direction, accompanied by significant adjustment of coordination number and fabric anisotropy. The results also reveal that the normalised wave velocity depends on the contact normal densities in the wave propagation and particle oscillation directions. With the contact normal distribution represented by a density function, a good linear relationship between the microscopic fabric anisotropy and macroscopic wave velocity anisotropy is obtained for both CT and TT tests. [ABSTRACT FROM AUTHOR]

Snow melting and deicing of pavement has long been a subject that has attracted researchers from a diverse range of fields. In this paper, graphite modified asphalt concrete was used to melt snow and ice on pavement. The micromechanics theory of composites was used to establish the effective electrical conductivity model of graphite modified asphalt concrete. Flake graphite was used as the conductive phase. Considering the hexagonal inclusion of graphite particles, the Eshelby tensor was calculated. The modified self-consistent (MSC) model was based on the self-consistent theory and percolation theory considering the polygonal inclusion of Eshelby tensor. By comparison, the predicted values of the MSC model were in good agreement with the experimental values. The conductivity of graphite modified asphalt concrete was studied by the finite element (FE) simulation according to the prediction model. The predicted conductivity value of 0.13 S/m at 18Vol% of graphite volume fraction was applied to proceed the finite element analysis (FEA). The temperature field distribution and the ice-melting performance of graphite modified asphalt concrete were calculated by the influence of different input power, environment temperature and wind speed. Through analysis and research, the input power reaching between 600 W to 1000 W was more reasonable. Wind speed had a greater effect on ice melting time when the wind scale exceeded 3 scale at lower input power. The application of MSC model and FEA can play an important role in the design and application of deicing or snow melting systems.

Abstract Palm leaf manuscripts (PLMs), venerable historical artefacts containing Buddhist scriptures, history, mathematics and literature, which are carried by palm leaves (Corypha umbraculifera) and are highly susceptible to microbial degradation during prolonged storage. This degradation results in significant alterations to both the appearance and material properties of PLMs, but the precise mechanism underlying this deterioration remains a mystery. To this end, the present study focused on ancient PLMs from Xishuangbanna Dai Autonomous Prefecture in Yunnan Province, China. The objective of present study was to isolate, culture and identify the microorganisms typically found in these manuscripts and to use them to biodegrade the carriers of PLMs. Detailed observations of the biodegradation behavior of these microorganisms on the carriers of PLMs were carried out, together with characterizations of the hierarchical structure and mechanical properties of the leaf fiber cell walls. This comprehensive analysis provided insights into the deterioration mechanisms of the carriers of PLMs. The study revealed the presence of the common fungus Aspergillus niger on ancient PLMs. Aspergillus niger can secrete cellulase, lipase, and acidic substances after colonizing on the carriers of PLMs. These substances sequentially damage the carrier's epidermal cells, mesophyll cells, and leaf fibers, leading to the separation of different tissue structures. At the molecular level, the lipids on the surface of the leaves were degraded initially, and sequential depolymerization of hemicellulose, amorphous cellulose, and crystalline cellulose occurred. Additionally, this study firstly applied nanoindentation technology in the research of PLMs. The mechanical properties of the cell walls underwent notable alterations due to the modifications in chemical and crystalline structure of the carriers of PLMs upon the biodegradation of Aspergillus niger. Specifically, the hardness and elastic modulus of leaf fiber cell walls showed an initial increasing and then decreasing trend, consistent with the trend of cellulose crystallinity, which also provided a new reference for assessing the degree of deterioration of PLMs.

Abstract Blade cut-out is a common complication when using proximal femoral nail anti-rotation (PFNA) for the treatment of intertrochanteric fractures. Although cement augmentation has been introduced to overcome the cut-out effect, the micromechanics of this approach remain to be clarified. While previous studies have developed finite element (FE) models based on lab-prepared or cadaveric samples to study the cement-trabeculae interface, their demanding nature and inherent disadvantages limit their application. The aim of this study was to develop a novel 'one-step forming' method for creating a cement-trabeculae interface FE model to investigate its micromechanics in relation to PFNA with cement augmentation. A human femoral head was scanned using micro-computed tomography, and four volume of interest (VOI) trabeculae were segmented. The VOI trabeculae were enclosed within a box to represent the encapsulated region of bone cement using ANSYS software. Tetrahedral meshing was performed with Hypermesh software based on Boolean operation. Finally, four cement-trabeculae interface FE models comprising four interdigitated depths and five FE models comprising different volume fraction were established after element removal. The effects of friction contact, frictionless contact, and bond contact properties between the bone and cement were identified. The maximum micromotion and stress in the interdigitated and loading bones were quantified and compared between the pre- and post-augmentation situations. The differences in micromotion and stress with the three contact methods were minimal. Micromotion and stress decreased as the interdigitation depth increased. Stress in the proximal interdigitated bone showed a correlation with the bone volume fraction (R2 = 0.70); both micromotion (R2 = 0.61) and stress (R2 = 0.93) at the most proximal loading region exhibited a similar correlation tendency. When comparing the post- and pre-augmentation situations, micromotion reduction in the interdigitated bone was more effective than stress reduction, particularly near the cement border. The cementation resulted in a significant reduction in micromotion within the loading bone, while the decrease in stress was minimal. Noticeable gradients of displacement and stress reduction can be observed in models with lower bone volume fraction (BV/TV). In summary, cement augmentation is more effective at reducing micromotion rather than stress. Furthermore, the reinforcing impact of bone cement is particularly prominent in cases with a low BV/TV. The utilization of bone cement may contribute to the stabilization of trabecular bone and PFNA primarily by constraining micromotion and partially shielding stress.

Despite β-type Ti alloys achieving a low elastic modulus, metallic implants generally exhibit poor wear resistance. To address this issue, in-situ Ti-based matrix composites (TMCs) are considered due to their strong bonding at the matrix/reinforcement interface. While TiC particles and TiB whiskers are common reinforcements for in-situ TMCs, limited research combines their effects with the low elastic modulus of Ti alloys. Here, we present a novel approach using arc-melting on Ti–40Nb alloy with 5 vol% additions of NbC, NbB2, and B4C. Respectively, three TMCs were obtained with the β-type Ti–Nb matrices reinforced individually with TiC particles, TiB whiskers, and hybridized with both. The produced TMCs exhibited the same passive behavior of the unreinforced Ti–40Nb alloy. However, tribocorrosion resistances were improved, as TMCs achieved nobler potentials during sliding than the unreinforced alloy (−0.5 and −0.9 V, respectively). Notably, the TiB-reinforced and the hybrid reinforced TMCs displayed minimal wear damage, while the TiC-reinforced TMC achieved a remarkable low elastic modulus of approximately 73 GPa. This study introduces promising alternatives for wear-resistant load-bearing implant applications.

The properties of unidirectional (UD) composites has been investigated by analyzing their elastic and strength characteristics under shear loading. The UD fiber‐reinforced polymer (FRP) composites usually consist of fibers randomly dispersed throughout the cross‐section in the transverse direction which is generally not accounted for. A micromechanical model based on finite element analysis (FEA) approach is utilized here to examine these properties. The study begins by identifying micro scale unit cells or repetitive unit cells (RUCs) at the micro scale, as well as representative volume elements (RVEs). The distribution of fiber volume fraction (Vf) varies among various micro scale unit cells positioned in the transverse cross‐section. The elastic properties and strength are estimated by considering the properties of the matrix and fibers, and the configuration of micro scale unit cells, which feature a fiber arrangement which is categorized as hexagonal and varying Vf at different locations (from 0.35 to 0.75). However, the overall Vf for the UD composite remains constant at 0.65. Studies are also carried out with the random distribution of fibers at micro scale unit cells. The findings reveal that the random distribution of fibers significantly impacts the shear behavior of the composite. This investigation provides valuable insights into how the mechanical properties of the UD composite are subjective by the distribution of fiber, thereby contributing to the design and development of this light weight high‐performance material. Highlights: Elastic and strength analysis of UD composites is presented.Emphasis is on fiber dispersion in transverse plane.Microscale unit cells, RUCs and RVE are identified.Studies are carried out based on micromechanical model.Influence of fiber distribution on shear behavior is investigated. [ABSTRACT FROM AUTHOR]

In this paper, we develop a nonlinear mixed finite element method for flexoelectric semiconductors and analyze the mechanically tuned redistributions of free carriers and electric currents through flexoelectric polarization in typical structures. We first present a macroscopic theory for flexoelectric semiconductors by combining flexoelectricity and nonlinear drift-diffusion theory. To use C0 continuous elements, we derive an incremental constrained weak form by introducing Langrage multipliers, in which the kinematic constraints between the displacement and its gradient are guaranteed. Based on the weak form, we established a mixed C0 continuous nine-node quadrilateral finite element as well as an iterative process for solving nonlinear boundary-value problems. The accuracy and convergence of the proposed element are validated by comparing linear finite element method results against analytical solutions for the bending of a beam. Finally, the nonlinear element method is applied to more complex problems, such as a circular ring, a plate with a hole, and an isosceles trapezoid. Results indicate that mechanical loads and doping levels have distinct influences on electric properties. [ABSTRACT FROM AUTHOR]

Temperature serves as a critical yet elusive factor impacting the mechanical properties of deep rocks. In this work, we shall develop a new micro‐thermomechanical model for rocks based on the Mori‐Tanaka homogenization scheme. Free energy and thermodynamic forces are deduced within the framework of irreversible thermodynamics, including the local stress applied on the mesocracks, damage driving force, macroscopic stress, and entropy. The salient innovation of this study lies in formulating subtle physically based temperature‐dependent friction and damage laws, considering the influence of ambient temperature on the mesocracking in rocks. Through a coupled friction‐damage analysis, a temperature‐dependent quasi‐static strength criterion and analytical stress‐strain‐damage relations are then derived. Physical implications and calibration methods of each parameter in the proposed model are meticulously presented. Furthermore, a semi‐implicit plasticity damage decoupled procedure (SIPDDC) integration algorithm is employed for the numerical implementation of the proposed model. Subsequently, numerical simulations are conducted to obtain the mechanical response of Jinping marble, Beibei sandstone, and Gongjue granite under various real‐time temperature‐confining pressure coupling conventional triaxial compression tests (TP‐CTC). The congruence of stress‐strain curves between model predictions and experimental data validates the robust performance and potential applicability of the proposed model. Plain Language Summary: High ground temperatures have a crucial influence on the stability of deep rocks. Establishing a robust calculation model is paramount for the feasibility and reliability analysis of deep rock engineering. However, incorporating mesocracking mechanisms into such models remains challenging. This paper presents an advanced micro‐thermomechanical model based on homogenization theory, aiming to investigate the macro‐ and micromechanical behaviors of rocks under different ambient temperature conditions. The model innovatively considers the temperature‐dependent characteristics of mesocracking. The model demonstrates satisfactory numerical performance and can effectively capture temperature‐dependent mechanical behaviors of three typical rocks, that is, marble, sandstone, and granite. This work provides a new perspective from a micromechanical standpoint for the theoretical and engineering analysis of deep rock mechanics under high‐temperature and high‐pressure conditions. Key Points: A homogenization‐based micro‐thermomechanical constitutive model is established considering temperature‐dependent friction and damage lawsA temperature‐dependent strength criterion and analytical damage‐stress‐strain relations are derived through cross‐scaling analysisThe model possesses robust numerical performance and shows a promising application prospect in deep rock engineering analysis [ABSTRACT FROM AUTHOR]

Highlights: Estimation of rock uniaxial compressive strength and elastic modulus from mineral micromehanical properties. Upscaling techniques for predicting rock mass mechanical properties from mineral properties. [ABSTRACT FROM AUTHOR]

We report on experiments and discrete element simulations of homogeneous, simple, normal stress-controlled, shear flows of model unsaturated granular materials: assemblies of frictional spherical particles bonded by a small quantity of a wetting liquid. The rheology of such unsaturated granular materials in the dense flow regime was characterized in recent publications of our group, in terms of internal friction coefficient μ ∗ and solid fraction Φ , depending on the reduced pressure P ∗ comparing capillary forces to controlled normal stress, and on inertial number I. The present study extends this description to the influence of the liquid viscosity on material rheology in the low saturation regime. The quantitative agreement of simulations with experiments is confirmed for the quasistatic limit, and our numerical results, despite some quantitative differences, capture the correct trends in the regime dominated by viscous forces. Rheological properties are then determined, to a large extent, by the same viscous number I v as used to formulate constitutive laws in saturated, dense suspensions. More precisely, a visco-inertial number J , combining I v with inertial number I as J = I v + 2 I 2 , appears apt to describe the rheological laws, as expressed by the internal friction coefficient and the solid fraction, measured in the laboratory or in the simulations, as well as the numerically investigated internal state of the flowing material. Simulations provide insight into the role of viscous forces: predominantly tensile, they contribute to the increase with shear rate of the macroscopic friction coefficient μ ∗ through a direct positive contribution to shear stress, a negative contribution to normal stresses (enhancing the strength of the contact network), and microstructural changes affecting the network of contacts and liquid bridges. [ABSTRACT FROM AUTHOR]

The load-carrying capacity of rock-socketed piles depends on the shaft resistance at the pile-rock interface which is governed by the interactions between the pile, rock, and soft interface materials (smear or infill). Despite recent advancements in 3D experimental pile testing of smeared interfaces, the knowledge in this field still remains quite limited primarily due to the experimental limitations, and high costs and fabrication challenges associated with extensive laboratory tests. This study presents a comprehensive numerical investigation to simulate 3D rock-socketed piles with smear using the discrete element method (DEM). By correlating the observations with the experimental x-ray CT images, the interactions between the pile, rock and smear are investigated for various smear area proportions in terms of the micromechanics at the asperity level. The movements of smear and rock debris in the socket and their influence on the various asperity failure modes in relation to the shaft resistance development are evaluated by monitoring the force and damage evolution in DEM. Finally, the calibrated DEM model is utilized to examine the influence of the various smear fabric parameters on the shaft response. Based on the observations, it was inferred that the shear failure mode primarily dictates the interface damage evolution, with a significant contribution from mixed-mode failure involving both tensile and shear damages. Insights from the results indicated that the effect of smear placement on the load-bearing capacity of the pile is found to be minimal compared to the other smear fabric parameters (thickness and area proportion). Moreover, the critical smear thickness to asperity height ratio was determined to be 1.75 beyond which the smear controls the load-bearing capacity of the pile. The discussions presented in this study provide a novel understanding into the smear fabric effect and act as a foundation for further research aimed at improving the reliability and efficiency of rock-socketed pile construction in soft rocks. [ABSTRACT FROM AUTHOR]

In this article, the predictive abilities of two prevalent homogenization formulations, two-step Mori–Tanaka (MT–MT) and MT–Voigt are benchmarked using virtual representative volume element (RVE) involving full FE models and real RVE using prior published experimental data. MT–MT and MT–Voigt are interpreted as involving "pseudodiscretization" and "pseudograin discretization," respectively. A comprehensive test campaign involving all possible permutations and combinations of modulus of inclusions and matrix (inclusions stiffer than the matrix and vice versa) and different loading types are conducted. The comparisons are done at three length scales: effective modulus, stresses in individual inclusions, stress distribution in the interphase, and strain at the onset of interphase debonding. Overall, both schemes have similar predictive capabilities for the effective modulus and phase average stress. The predictions of the stresses in the individual inclusions for complex RVEs with inclusions length and orientation distribution are correct as average trends but do not represent the full details of the FE-revealed strain scatter. Depending on the modulus mismatch, or loading direction, better predictions can be achieved by either MT–MT or MT–Voigt, even if the microstructure considered remains the same. The relative difference in the strain at the onset of debonding, predicted by MT–MT and MT–Voigt formulations, is about 10%. Two-step MT–MT and MT–Voigt are benchmarked against virtual and real RVEs Comparisons are done for all permutations of modulus mismatch and loading types Predictions are compared at three length scales: RVE, inclusions, and interphase [ABSTRACT FROM AUTHOR]

A micromechanics based analytical model under combined loading for unidirectional composites has been developed. The peak compressive load predicted from the combined loading analytical model is compared with the experimental results of carbon epoxy pultruded rod having a volume fraction 60%. The specimens were subjected to torsional load under rotational control and longitudinal compressive load using displacement control. The model captures the compressive strength of the composite subjected to remotely applied shear stress. It is observed that the peak compressive strength of the composite decreases linearly with an increase in shear stress. The analytical modeling results are in good agreement with the experiment data. The analytical model and the experimental results are used to find the effect of shear stress on longitudinal compressive loading. The peak compressive strength caused in the presence of applied shear stress and compressive load and the effect of shear on the compressive strength are predicted using a 2D analytical model in this study. The model results are confirmed using experimental data from combined loading. [ABSTRACT FROM AUTHOR]

We consider a dense aggregate of elastic, frictional particles isotropically compressed and next uniaxial strained at constant pressure. We show how failure can be predicted if fluctuations in the kinematics of contacting particles are introduced. We focus on the second order work and the possibility that at some stressed states it becomes negative under proper perturbations. Our analysis involves both a theoretical model and numerical simulations based upon the distinct element method (DEM). The theoretical model deals with contacting particles with incremental relative displacements that deviate from the average deformation in order to ensure their equilibrium. Because of this, the macroscopic stiffness tensor of the aggregate, that relates increments in stress with increments in strain, does not have the major symmetry. Consequently, in the hardening regime, we predict stressed states in which the second order work vanishes. The model seems transparent, and it makes clear and illustrative the role played by the fluctuations introduced in the kinematics of contacting particles in relation to the vanishing of second order work in an aggregate of compressed particles. The comparison with numerical simulations data supports the model. Statistical representation of the aggregate: conditional average. [ABSTRACT FROM AUTHOR]

Structural damage in heterogeneousmaterials typically originates frommicrostructures where stress concentration occurs. Therefore, evaluating the magnitude and location of localized stress distributions within microstructures under external loading is crucial. Repeating unit cells (RUCs) are commonly used to represent microstructural details and homogenize the effective response of composites. This work develops a machine learning-based micromechanics tool to accurately predict the stress distributions of extracted RUCs. The locally exact homogenization theory efficiently generates the microstructural stresses of RUCs with a wide range of parameters, including volume fraction, fiber/matrix property ratio, fiber shapes, and loading direction. Subsequently, the conditional generative adversarial network (cGAN) is employed and constructed as a surrogate model to establish the statistical correlation between these parameters and the corresponding localized stresses. The stresses predicted by cGAN are validated against the remaining true data not used for training, showing good agreement. This work demonstrates that the cGAN-based micromechanics tool effectively captures the local responses of composite RUCs. It can be used for predicting potential crack initiations starting from microstructures and evaluating the effective behavior of periodic composites. [ABSTRACT FROM AUTHOR]