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• A novel time-dependent micromechanical model is proposed to consider the glass fiber dissolution phenomenon. • The dissolution phenomenon is linked to the mechanical properties of the glass-reinforced composite. • The governing equations of conveying fluid composite pipe systems with fiber dissolution defects are presented. • Natural frequencies, divergence and flutter critical flow velocities of the composite pipe are investigated. The motivation for the present study comes from the appearance of fiber dissolution in industrial applications of composite pipes under different flowing fluids and operating conditions. To mitigate the consequences of glass fiber dissolution in glass fiber reinforced plastics (GRP) pipes, it is essential to investigate the dynamic characteristics of the pipes under internal fluid flow. This paper presents a novel time-dependent micromechanical model and examines the effects of glass fiber dissolution on the instability and vibrational behavior of a composite pipe conveying fluid. The Hamiltonian principle obtains the governing equations of the conveying fluid composite pipe system with fiber dissolution defects. The Finite Element Method (FEM) is then used to solve the eigenvalue problem for the natural frequencies, divergence, and flutter critical velocities of the composite pipe conveying fluid. The effects of different parameters, such as span and amount of dissolution, as well as the quality of the dissolved portion of the fibers, are highlighted on the instability and vibration characteristics of composite pipes. The results show that fiber dissolution significantly affects the behavior of composite pipes conveying fluid. This work also provides a better understanding of the above-mentioned "environmental aging" type in fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

This study employed magnetic field induction and steel fiber hybridization methods to prepare Hybrid Aligned Steel Fiber-Reinforced Cementitious Composites (HASFRCCs). The direct tensile performance of specimens with aligned and randomly dispersed steel fibers was compared under different hybrid coarse-to-fine fiber ratios (3:1, 2:1, 1:1, 1:2, and 1:3). The fiber pullout tests were conducted to determine the bond-stress-slip relationship between steel fibers and matrix for both coarse and fine steel fibers. Based on these results, an analytical model for the tensile behavior of HASFRCC was then developed based on the composite mechanics theory and modified according to the hybrid fiber effect. The results demonstrated a significant increase in the fiber orientation coefficient η θ of the HASFRCC by 21.1–26.9 % compared with the random specimens. Additionally, the tensile strength and energy absorption capacity substantially improved by 43.8–64.1 % and 58.5–71.4 %, respectively, compared to the specimens with random steel fiber. In addition, the modified model of HASFRCC quantitatively reveals the role of the two kinds of fibers in the tensile process, and the difference between the model-predicted and experimental results was less than 10 %. • The utilization efficiency of steel fibers has been significantly increased by utilizing a method that combines the magnetic field induction. • The interaction and hybrid effect between two types of steel fibers has been quantified using hybrid effect coefficients. • An analytical model was developed using micromechanical model and weighted superposition to simulate the tensile behavior of HASFRCC. [ABSTRACT FROM AUTHOR]

Graphene reinforced cement composites (GRCCs) have attracted great attention due to their excellent mechanical and physical properties. Instead of uniform distribution, the functionally graded distribution of graphene fillers can effectively utilize the mechanical and physical properties of the reinforcements while reducing cost. This paper is the first attempt to combine experimental analysis and theoretical modelling to investigate the thermomechanical properties of functionally graded graphene nanoplatelet (GNP) reinforced cement composites (FG-GNPRCCs). Samples with uniform (profile H) and functionally graded (profiles X, O and A) distribution of GNPs were prepared and tested. Among all the FG distribution patterns as involved, profile X exhibited the most pronounced enhancement. Compared to the uniform distribution at room temperature, the loss factor and storage modulus of profile X increased by 19.3 % and 19.5 %, respectively. Based on the effective medium theory (EMT) and Mori-Tanaka (MT) model, a parallel triple-inclusion model was developed to predict the thermal conductivity of GNPRCCs. The effects of coated GNP, agglomeration and the attributes of pores (i.e., size, shape and porosity) on the thermomechanical properties of the composites were considered. Dynamic mechanical analysis revealed that profile X had the best energy dissipation and the extent of inelastic deformation within the temperature range from −50 °C to 70 °C. In contrast, profile A is beneficial for scenarios that desire a gradual transition and controlled stress along a certain direction. [ABSTRACT FROM AUTHOR]

The mechanical properties of BaTiO 3 filled HDPE nanocomposites are studied by experimental and numerical approaches. First, the viscoelastic behavior of neat HDPE is highlighted experimentally in tensile and relaxation tests. A method is then proposed to define a constitutive viscoelastic law representative of this behavior at different tensile crosshead speeds at room temperature. Afterward, this law is implemented in a finite-element-based micromechanical model representing the BaTiO 3 filled HDPE nanocomposites with different filler amounts. The experimental and numerical results are further compared. Both the experiments and numerical simulations confirm the viscoelastic behavior of the polymer nanocomposite. For nanocomposites with filler concentrations up to 20 %, the error between the experimental and numerical findings remains less than 8 %, confirming that the model represents well the composite behavior for low and moderate filler amounts. The proposed strategy can be applied to other polymer composites in order to predict the complete mechanical behavior of viscoelastic composite materials. [Display omitted] • The viscoelasticity of polymer nanocomposites is highlighted. • The master curve of HDPE relaxation modulus is experimentally obtained. • A constitutive law based on the generalized Maxwell model is established for HDPE. • Mechanical properties of nanocomposites are predicted using a micromechanical model. [ABSTRACT FROM AUTHOR]

The longitudinal extensional viscosity of a highly aligned discontinuous fiber (ADF) thermoplastic matrix composite is investigated to develop a model and validate microstructural evolutionary mechanisms. Samples stretched at constant temperature and strain rate are shown to exhibit a strain softening behavior. X-ray CT analysis and optical micrographs show that the composite microstructure deconsolidates before forming and evolves with deformation. The conventional unit cell micromechanical model includes the effects of matrix viscosity, fiber aspect ratio and fiber volume fraction. This model is modified to include the stiffening effect of fiber spacing variability, and the softening effects of porosity and decreasing fiber overlap length with elongation. Calibration of the model reveals that matrix shear strain rate is an order of magnitude higher than previously predicted due to local fiber spacing. This effect is captured by a fiber spacing variability parameter which scales average spacing down by an order of magnitude. The observed strain softening behavior is described and a combinations of fiber overlap length reduction and local fiber spacing increase. [Display omitted] [ABSTRACT FROM AUTHOR]

It is a long-standing puzzle that whether the micromechanical theory is still valid to CNTs-reinforced polymer nanocomposites and why these nanocomposites always show inferior mechanical properties. Herein, we introduced the concept of the real volume fraction for CNT, based on the hypothesis that only the tube walls having direct contact with the polymer matrix carry the external loading. A new micromechanical model on the modulus of nanocomposites was then developed based on this concept. Through a joint study of molecular dynamics (MD) simulations and experimental tests, the correctness and applicability of the proposed micromechanical model were verified, which strongly demonstrate that the micromechanical theory is still applicable to nanocomposites when it sufficiently considers the unique nature of CNTs, such as the real volume fraction, orientations, and aspect ratio. Moreover, the low real volume fraction of multi-walled CNTs is the key reason for the inferior mechanical properties of nanocomposites with uniformly dispersed fillers. [Display omitted] • Micromechanical theory is still applied to CNTs/epoxy nanocomposites. • Low real volume fraction of MWCNTs is the key reason for the inferior nanocomposite stiffness. • CNTs in an agglomeration maintain their aspect ratio although the real volume fraction is dramatically reduced. [ABSTRACT FROM AUTHOR]

In this study, the elastic response and residual stress of the ceramic matrix composites were simulated in multiscale view for exploring the elastic modulus of the two-phase composites reinforced with ceramic particles by diffraction method. Combined with the macroscopic stress-strain relationship of two-phase composites, the effective elastic response model under uniaxial loading was theoretically predicted by introducing the effective representative volume element (RVE). Subsequently, the effective elastic properties of the material and its constituents were calculated, along with comparison with the experimental values reported in the literature. On the basis of Eshelby's inclusion theory, a micromechanical elastic response model for the two-phase composites was established, and a series of micromechanical field equations related to the crystal planes diffraction elastic constants were derived. A comparison with the different micromechanical models for predicting the crystal planes diffraction elastic constants of the ceramic matrix and particle reinforcement was carried out, so as to qualitatively and quantitatively analyze the residual stress. It was revealed that the effective elastic parameters of the ZrB 2 matrix and SiC particle reinforcement were very close to the experimental values reported in literature, and the calculated values of the elastic modulus in seven crystallographic diffraction directions were similar to the experimental values. In addition, the average residual stress of the SiC reinforcement and the ZrB 2 ceramic matrix predicted by the developed model were consistent with the measured, which proved the reliability and accuracy of the theoretical model for multiscale simulation of the residual stress of two-phase composites. [ABSTRACT FROM AUTHOR]

Phenomenological models are commonly used to model void nucleation from second phase particles in ductile fracture simulations. Parameters in these continuum models are typically estimated using indirect methods, by comparison with experimental fracture data. In this paper, a novel approach based on acoustic emission (AE) measurements in smooth and notched bar tension tests is proposed to estimate void nucleation model parameters such as the mean and standard deviation of the nucleation strains. Tensile tests on AA 7075-T651 specimens combined with AE data establish a robust correlation between AE amplitude and the average void nucleation rate. The nucleation parameters are calibrated using a dog-bone tensile specimen. Simulations using these calibrated parameters accurately reproduces AE amplitude trends in other specimen geometries. This approach provides a promising alternative to traditional calibration methods, enhancing the reliability and adaptability of void growth based ductile fracture models. [Display omitted] • A correlation exists between void nucleation and acoustic emission (AE) amplitude for AA 7075-T651. • The Chu and Needleman void nucleation parameters can be calibrated using acoustic emission. • With calibrated parameters, the model reproduces AE amplitude characteristics in various geometries. [ABSTRACT FROM AUTHOR]

• A novel multiscale analysis is developed to assess the buckling behavior of MWCNT-reinforced laminated composites. • Integration of microstructural factors like MWCNT clustering, alignment, and curvature in evaluating composite material performance. • Comprehensive assessment of the influence of moisture and temperature on the buckling performance of MWCNT composites. • Results successfully compared and validated with existing experimental and theoretical data. • Offers significant insights for the design and optimization of MWCNT-reinforced composites. This study introduces a detailed method for analyzing the buckling behavior of laminated composite structures strengthened with multi-walled carbon nanotubes (MWCNTs). We propose a multi-scale analysis that combines analytical and computational techniques to assess the mechanical performance of MWCNT-reinforced composites under combined moisture, temperature, and mechanical stress conditions. The Halpin-Tsai equations are used to calculate the overall stiffness properties of the nano-enhanced matrix, considering factors like MWCNT clustering, alignment, and curvature. Additionally, we incorporate the nanoscopic, size-dependent features of MWCNTs into our model. The Chamis micromechanical formulas are applied to determine the individual elastic properties of the nanocomposite layers, considering the impacts of temperature and moisture. We then explore how variables such as MWCNT content and size, along with temperature and moisture levels, influence the critical buckling load of MWCNT-based laminated composite beams and plates using our multi-scale model. Our results are successfully compared with existing experimental and theoretical data to validate our approach. The developed method offers significant insights for the design and optimization of MWCNT-reinforced composites, potentially benefiting various engineering fields, including aerospace and automotive industries. [ABSTRACT FROM AUTHOR]

Most of the concrete structures in service are unsaturated, estimating the ionic diffusion coefficient of unsaturated cement-based material is of paramount significance to assessment of corrosion of reinforced concrete. Taking account of the contributions from different water configurations at multi-scale (water films, interlayer water, large gel pore (LGP) water and capillary pore water) and the corresponding diffusion mechanisms of each type of water, a micromechanical model for estimating the ionic diffusion coefficient of unsaturated hardened cement paste (UHCP), is developed in this study. Model results show that the interconnectivity of the spheroidal capillary pore water is closely related to the aspect ratio of spheroidal capillary pore, the slender the prolate pore, the higher the interconnectivity of the capillary pore water; when the capillary pore water is totally drained, water films and interlayer water within C-S-H governs the ionic diffusion, the higher the water to cement ratio (w/c), the less the contribution of interlayer water, and the greater the contribution of water film, to ionic diffusion within UHCP. Application on saturated hardened cement paste and UHCP shows the capability of the model to accurately reproduce the experimental results. [ABSTRACT FROM AUTHOR]

The microscopic damage initiation characteristic in welded joint greatly determines the subsequent damage evolution and fracture behavior of aluminum alloy tailor-welded blank (TWB) during plastic forming. In this study, the interactive dependence of void nucleation on microstructure and stress state in the welded joint of a 2219 aluminum alloy TWB was quantitatively explored by in-situ SEM testing. Moreover, a micromechanical model based on actual microstructure was adopted to reveal the underlying mechanisms from the perspective of microscopic heterogeneous deformation. The results showed that three void nucleation mechanisms, including particle-cracking, interface-debonding and matrix-cracking, coexisted in the deformation at different microstructure regions and stress states. The nucleation strain of each mechanism mainly depended on the particle volume fraction, grain size and stress triaxiality. Besides, the proportions of particle-cracking and interface-debonding greatly varied with the grain size and particle volume fraction, and the variation law changed with the stress state. The proportion of matrix-cracking had a weak dependence on the microstructure, while increased with the stress triaxiality decreasing. It made the damage initiation in aluminum alloy welded joint transit from particle-cracking dominance to matrix-cracking dominance with the stress triaxiality decreasing. The micromechanical modeling results suggested that the changes of evolutions and distributions of Mises stress in particle, hydrostatic stress at interface and plastic strain in matrix with microstructure and stress state were responsible for the above effects. [Display omitted] • Interactive dependence of void nucleation on microstructure and stress state in welded Al-alloy blank was revealed. • Nucleation strain and proportions of voids depend on the particle volume fraction, grain size and stress triaxiality. • The dependence of proportions on microstructure varies with the stress triaxiality. • Void nucleation changes from matrix-cracking to particle-cracking dominance with stress triaxiality increasing. • Nucleation features are explained by the microscopic heterogeneous deformation characteristics. [ABSTRACT FROM AUTHOR]

This paper presents a micromechanical model to predict the time-dependent damage and deformation behavior of an orthogonal 3-D woven SiC fiber/BN interface/SiC matrix composite under constant tensile loading at elevated temperature in vacuum. In-situ observation under monotonic tensile loading at room temperature, load–unload tensile testing at 1200 °C in argon, and constant load tensile testing at 1200 °C in vacuum were conducted to investigate the effects of microscopic damage on deformation behavior. The experimentally obtained results led to production of a time-dependent nonlinear stress–strain response model for the orthogonal 3-D woven SiC/SiC. It was established using the linear viscoelastic model, micro-damage propagation model, and a shear-lag model. The predicted creep deformation was found to agree well with the experimentally obtained results. [ABSTRACT FROM AUTHOR]

The change of the mechanical properties of granular materials with pressure is an important topic associated with many industrial applications. In this paper we investigate the influence of hydrostatic pressure (P e) on the effective bulk compressibility (C eff) of a granular material by applying two modified theoretical approaches that are based on contact mechanics and micromechanics, respectively. For a granular material composed of rough grains, an extended contact model is developed to elucidate the effect of roughness of grain surfaces on bulk compressibility. At relatively low pressures, the model predicts that the decrease of bulk compressibility with pressure may be described by a power law with an exponent of -1/2 (i.e., C eff ∝ P e −1/2), but deviates at intermediate pressures. At elevated pressures beyond full contact, bulk compressibility remains almost unchanged, which may be roughly evaluated by continuum contact mechanics. As an alternative explanation of pressure-dependent bulk compressibility, we suggest a micromechanical model that accounts for effects of different types of pore space present in granular materials. Narrow and compliant inter-granular cracks are approximated by three-dimensional oblate spheroidal cracks with rough surfaces, whereas the equant and stiff pores surrounded by three and four neighboring grains are modeled as tubular pores with cross sections of three and four cusp-like corners, respectively. In this model, bulk compressibility is strongly reduced with increasing pressure by progressive closure of rough-walled cracks. At pressures exceeding crack closure pressure, deformation of the remaining equant pores is largely insensitive to pressure, with almost no further change in bulk compressibility. To validate these models, we performed hydrostatic compression tests on Bentheim sandstone (a granular rock consisting of quartz with high porosity) under a wide range of pressure. The relation between observed microstructures and measured pressure-dependent bulk compressibility is well explained by both suggested models. Image, graphical abstract [ABSTRACT FROM AUTHOR]

High temperature creep and fatigue properties are important characteristics of SiC/SiC composites. In this work, dwell-fatigue tests were conducted at 1300 °C for 3D-braided SiC/SiC with and without coatings, and experimental results of dwell-fatigue tests were analyzed together with results of fatigue and creep tests. Then, general quantitative method was adopted to explain the deformation and rupture behaviors of SiC/SiC in creep, fatigue and dwell-fatigue tests. Micromechanical creep model could effectively simulate deformation behavior when the maximum load was under matrix cracking stress. Stress transfer behavior of constituents during creep and fatigue tests provided insights into the difference in macro time/cycle dependent deformation. Next, by incorporating damage evolution model which represents oxidation assisted unbridged crack growth, deformation acceleration in tertiary stage of creep was successfully simulated. Finally, SiC/SiC lifetimes under all fatigue, creep, and dwell-fatigue loads were predicted considering matrix crack propagation and fiber strength degradation. Simulated results correlated well with experimental data, verifying the effectiveness of micromechanical model to predict the creep and fatigue behaviors of SiC/SiC composites at high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, micromechanical models are used to predict the 3D viscoelastic behaviour of asphalt mixtures (with volume fraction of aggregate particles up to 87%) from the mechanical properties of their constituents. To fulfil the objective of study, complex modulus tests are conducted on bituminous materials at three different scales: bitumen, asphalt mastics and asphalt mixtures. The volume fraction of particles varies from 0% (bitumen) to 15%, 25%, 35% (asphalt mastic) and up to 87% (asphalt mixture). In the experimental program, complex modulus of bitumen, asphalt mastic and asphalt mixtures at different temperatures, frequencies are measured. For asphalt mixtures, measurements of complex Poisson's ratio are also performed. The rheological model 2S2P1D is used to simulate the 3D viscoelastic behaviour of tested bituminous materials. From the experimental results and simulations, two micromechanical models (self-consistent and generalized self-consistent model) are used to predict the complex modulus and complex Poisson's ratio of asphalt mixtures. The obtained results show that both micromechanical models give the good prediction of complex modulus for asphalt mastic where the volume fraction of aggregate particles is lower than 35%. At asphalt mixture scale where the volume fraction of particles is up to 87%, only simulation using the generalized self-consistent model can show good results. The prediction using the generalized self-consistent model at the mixture scale can be applied for both complex modulus and complex Poisson's ratio. In addition, the prediction of complex modulus and complex Poisson's ratio of asphalt mixtures becomes better when the asphalt mastic instead of bitumen is considered as viscous matrix. ● Relationships between 3D LVE properties of asphaltic materials are built. ● Large volume fraction of filler/aggregate is considered (from 0 up to 87%). ● Rheological model parameters are linked with volume fraction of filler/aggregates. ● Complex modulus/complex Poisson's ratio is predicted using micromechanical models. ● Asphalt mastic instead of bitumen is considered as the matrix phase of mixture. [ABSTRACT FROM AUTHOR]

• Effective thermoelectric properties considering interfacial resistance are reached. • Effective thermoelectric properties under large temperature difference are derived. • Effect of inclusion's shapes on effective thermoelectric properties is discussed. • Effect of inclusion's sizes on effective thermoelectric properties is discussed. • Theoretical model is well validated by finite element analysis. The effective design of thermoelectric composites is of great significance in improving performance of thermoelectric composites. Herein, we develop a homogenization theory to predict the effective thermoelectric properties of thermoelectric composite containing ellipsoidal inclusions whereby interfacial thermal and electrical resistances are considered. Firstly, the closed-form representations of the effective thermoelectric properties are derived under the assumption of a small temperature difference. Then the effective properties of the thermoelectric composite subjecting to a large temperature difference are obtained by cutting the composite to a serial connection of pieces with a small temperature difference. The relationship between the interfacial resistances and the effective properties of thermoelectric composites is discussed systematically under the different conditions of the aspect ratio, volume fraction, size of inclusion and temperature difference in the composite. Our theoretical predictions well match the effective properties obtained from finite element analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • This improved micromechanical model can consider contributions of microstructure, multiscale fibers, thermal cracking, and interfacial thermal resistance between sands and the matrix. • The proposed model confirms that thermal cracking beyond 400 °C can significantly influence the thermal conductivity. • The addition of multi-scale fibers can increase the thermal conductivity of high performance concrete by around 10% An improved micromechanical model to estimate the thermal conductivity of multi-scale fiber reinforced ultra-high performance concrete (MSFUHPC) subjected to elevated temperatures is formulated in this study. This model considers the contributions of microstructure, multiscale fibers, water/cement ratio, thermal dehydration of hydrates, thermal cracking, interfacial thermal resistance, heating rate and temperature dependent thermal conductivity of each phase. To verify the proposed model, comparisons with experimental data on MSFUHPC specimens are carried out. Accordingly, factors affecting the thermal conductivity of MSFUHPC are discussed through the proposed model. Results suggest that blending multi-scale fibers and increasing the sand content can significantly enhance the thermal conductivity of MSFUHPC. While adding cenosphere particles can reduce the thermal conductivity. Overall, the thermal conductivity of MSFUHPC exhibits a decreasing trend with temperature. Meanwhile, thermal cracking occurs beyond 400 °C can remarkably decrease the thermal conductivity of MSFUHPC. A higher interfacial thermal resistance between sands and the matrix can result in a lower thermal conductivity. It is also found that thermal conductivity mainly depends on the maximum temperature experienced rather than the heating rate. [ABSTRACT FROM AUTHOR]

• Three micromechanical models was selected to predict the asphalt mastic behavior. • GSCG gave the most accuracy modulus prediction of mastic with low filler fraction. • J-C model cannot predict modulus of mastic with high filler fraction. • Phy-C gave a good modulus prediction for mastic with moderate filler fraction. • Prediction accuracy deteriorated severely with the increase of filler fraction. Micromechanical models have been used since the 1990s to predict the properties of asphalt mastic. However, most of these models are found to be unsatisfactory in predicting the mastic's properties because the models were derived from the research of particle-filled composites that did not take into account the asphalt-filler physico-chemical interactions and particle interactions. In this paper, three micro-mechanical models for predicting the complex shear modulus master curve of asphalt mastic are evaluated: the generalized self-consistent scheme model, the four-phase micro-mechanical model, and the particle interaction model. All three micro-mechanical models are based on the mechanical properties of their constituent materials as well as the filler-asphalt physiochemical interactions and the particle interactions. Two virgin asphalt binders and two polymer modified asphalt binders were selected to fabricate 16 mastics of four different filler volume fractions. The accuracy of prediction was evaluated by comparing the relative differences between the experimental complex shear modulus master curves and that predicted by the models. The results suggest that (1) the generalized self-consistent scheme model have a satisfactory prediction at a low filler volume fraction, but their accuracy is significantly affected by frequency; (2) the particle interaction model cannot calculate the complex shear modulus of mastic with a filler volume fraction of more than 0.53; (3) the four-phase model shows a precise forecast of complex shear modulus for mastic with moderate and high filler volume fractions; and (4) for all of the three models, the deviations increase severely with the increase of the filler volume fraction. [ABSTRACT FROM AUTHOR]

• This work deals with biaxial low-cycle fatigue (LCF) response of a micromechanical model. • The damage activation/deactivation phenomenon was formulated at the macroscale. • A new hybrid cycle jump approach was proposed to minimize the computation costs through. • The proposed development is able, for example, the concept of new hybrid cycle jump. • The model response highlights that the greater, the number of cycles, the greater, the gain in computation time but the less, the accuracy. In this work, a new hybrid cycle jump approach was proposed to predict the low-cycle fatigue (LCF) response using a well-established micromechanical model. The damage activation/deactivation phenomenon was formulated at the macroscale. Using the concept of rate independent plasticity with the small strains assumption, the damage deactivation effect on the LCF response and its lifetime was accurately described by the model under simple and complex cyclic loading paths. Three algorithms namely, Taylor 1st and 2nd order and predictor-corrector were utilized for estimating the model response after each cycle jump. An optimum precision factor (ρ) value was defined and then tested via a suitable compromise between computation times and accuracy. In order to numerically determine the cyclic jump length (ΔN), a new hybrid approach was developed based on the overall von Mises stress and the overall damage together with monitoring the accumulated slip. Then, a comparative study revealed that the predictor-corrector algorithm was opted due to its robustness compared to the other algorithms. The numerical study was carried out using two different cyclic loading configurations. One was under simple tension-compression and the other under complex tension-torsion with 90° out-of-phase angle. The model response was described under two distinct states: (i) cycle-by-cycle and (ii) cycle jump concept. For each numerical state, the overall and local responses were recorded. With the new hybrid cycle jump approach, the model response highlights that the greater, the number of cycles, the greater, the gain in computation time but the less, the accuracy. For example, in TC for N f = 10,000 cycles, a recorded gain in computation time was attained 77% (against 95% by means of cycles number) with a relative error of 4%; whereas in TT90 of N f = 2124, the computation gain became 43.4% (and 73.4% with respect to number of jumped cycles) with a relative error of 3%. [ABSTRACT FROM AUTHOR]

In this paper, a micromechanical model is proposed to study the elastoplastic behavior of the Callovo-Oxfordian (COx) argillite. Three scales (i.e., macroscopic, mesoscopic and microscopic) are considered. At the mesoscopic scale, the COx argillite is regarded as a three-phase composite with clay as matrix and calcite and quartz as reinforcements. At the microscale, the clay matrix is a porous medium constituted by clay minerals and interparticle pores. The porous clay is described with an extended Gurson-Tvergaard-Needelman (EGTN) model while the calcite and quartz reinforcements are described with the linear isotropic elastic model. The macroscopic behavior of the COx argillite is determined by adopting the Hill's incremental formulation. All the numerical aspects including: (1) the integration of the EGTN model with the backward Euler method; (2) the derivation of the corresponding consistent tangent moduli from a new point of view; (3) the realization of the homogenization process, are fully described. The proposed micromechanical model is validated from two aspects. The first aspect is the numerical predictions against the finite element (FE) computations performed on a two-phase unit cell, where the key steps related to the modelling are presented. The second aspect is the comparisons between the numerical predictions and experimental data. [ABSTRACT FROM AUTHOR]

Highlights • A multiscale micromechanical homogenization framework is proposed for fluid-filled porous materials. • The overall elastic properties of the fluid-filled porous materials are determined in the framework. • The effects of pore distribution and fluid pressure on the effective elastic properties are quantified. • By considering the fluid diffusion from macro- to micro-scale pores, evolution of the effective properties is predicted. Abstract Fluid-filled porous materials are widely encountered in natural and artificial systems. A comprehensive understanding of the elastic behavior of such materials and its dependence on fluid diffusion is therefore of fundamental importance. In this work, a multiscale framework is developed to model the overall elastic response of fluid-filled porous materials. By utilizing a two-dimensional micromechanical model with porosity at two scales, the effects of fluid diffusion and the geometric arrangement of pores on the evolution of effective properties in fluid-filled porous materials are investigated. Initially, for a single-porosity model the effective elastic properties of the dry and fluid-filled porous materials with ordered pores are obtained theoretically by considering a geometrical factor, which is related to the distribution of pores in the matrix. Model predictions are validated by finite element simulations. By employing a double-porosity model, fluid diffusion from macro- to micro-scale pores driven by a pressure gradient is investigated, and the resulting time-dependent effective elastic properties are obtained for both constant pressure and constant injection rate conditions. It is found that the presence and diffusion of pressurized pore fluid significantly affect the elastic response of porous materials, and this must be considered when modeling such materials. It is expected that the proposed theoretical model will advance the understanding of the fluid-governed elastic response of porous materials with implications towards the analysis of geophysical, biological and artificial fluid-filled porous systems. Graphic abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Evidences of both sluggish eutectoid and active eutectoid (not suppressible under rapid cooling) transformations have been found for the first time in a single hyper-eutectoid Ti-Cu alloy. Both of these types of eutectoid reactions have been investigated in detail, at different length scales, by coupling scanning electron microscopy (SEM),transmission electron microscopy (TEM) and atom probe tomography (APT). The unique three phase crystallographic relationship between the parent β (bcc) and the two product phases, α (hcp) and Ti 2 Cu, has been established. The extent of partitioning of the solute (Cu) between the two product phases has been determined by APT and is rationalised in terms of thermodynamic considerations. Based on the observed lattice site correspondence and the extent of solute partitioning, a possible mechanism of active eutectoid transformation is proposed. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract The metals with gradient nanostructures possess exceptionally superior mechanical properties. Here, the gradient-nanotwinned 304 stainless steel wires are fabricated by surface mechanical attrition treatment (SMAT) with a range of process time. The quasi-static tensile tests and dynamic compressive tests are conducted to examine the constitutive response of gradient-nanotwinned 304 stainless steels under different loadings. The experimental measurements show that under static and dynamic loadings, their mechanical properties are closely related to the SMAT process time. With an increase in the process time, their yield strength is improved, while their ductility is weakened. Furthermore, a theoretical model is proposed to describe the static and dynamic constitutive relation of gradient nanotwinned 304 stainless steels. The micromechanical model of nanotwinned composite is developed to characterize the constitutive relation of the material with nanograins embedded in nanotwinned matrix in depth. For the constitutive relations of each phase in nanotwinned composite structure, the athermal behaviors of dislocations are only considered in describing the flow stress under the static loadings. The size-dependent athermal flow stress and rate-dependent thermal flow stress are both involved under the dynamic loadings. The theoretical simulations demonstrated that the mechanical response of gradient-nanotwinned 304 stainless steels under different loadings can be successfully characterized by the presented model. A good agreement is obtained between the numerical results and experimental measurements. Furthermore, the mechanical properties of gradient-nanotwinned 304 stainless steels are forecasted for the various distribution of twin spacing along the depth. The results in this work are helpful for optimizing the static and dynamic mechanical performance of the gradient-nanostructured metallic materials through controlling microstructural size and distribution. Highlights • Gradient-nanotwinned 304SS are prepared by the surface mechanical attrition treatment. • Static and dynamic mechanical properties of gradient-nanotwinned 304SS are measured. • A mechanism-based theoretical model for static and dynamic mechanical behaviors is developed. • The constitutive relations of gradient-nanotwinned 304SS are completely described. • The simulations show good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Abstract A new three-dimensional (3D) micromechanical model is proposed to simulate the arbitrary multidirectional carbon fiber reinforced polymer (CFRP) composite laminates. Carbon fiber is assumed as transversely isotropic and linear elastic, matrix is assumed as isotropic and elastic–plastic. Maximum strain criterion is used to describe the failure of fiber and matrix. The stresses, strains and damage are described in the fiber and matrix levels, but the debonding between the fiber and matrix and the delamination between two plies are not modeled in the present analysis. Numerical analyses of nonlinear mechanical behavior of angle-ply [±θ] 2s under tension are conducted to verify the validity of the present micromechanical model. Numerical results of nonlinear mechanical behavior, negative Poisson's ratio through the thickness direction, and stress distribution on the free edge show good agreement with previous experimental and analytical results. [ABSTRACT FROM AUTHOR]

Abstract This paper calibrates micromechanical fracture models for duplex stainless steel in order to study its fracture behaviour under seismic loading, characterized by large strain ultra low cyclic conditions. In this investigation, smooth round bars and notched round bars were subject to monotonic and cyclic loading. Monotonic and cyclic loading constitutive models were calibrated against smooth round bar test tests. The fracture toughness parameters of the void growth model (VGM), the stress modified critical strain (SMCS) model and the cyclic void growth model (CVGM) were calibrated against the notched round bar tests. Furthermore, the skeleton curve, hysteresis loop and characteristic length of duplex stainless steel were also investigated. The test results indicate that duplex stainless steel exhibits cyclic hardening behaviour under cyclic loading, and the subsequent numerical simulation successfully captured this behaviour. The toughness parameters of duplex stainless steel are generally higher than those for carbon steel grades Q345B and Q460, which demonstrates that duplex stainless steel has better toughness. All the experimental results provide useful data for the prediction of ultra low cycle fatigue (ULCF) fracture of duplex stainless steel. Highlights • We establish the constitutive model of duplex stainless steel under cyclic loading. • We calibrate the fracture toughness parameters of microscopic mechanism model. • The fracture toughness parameters are related to the material itself. • Duplex stainless steel has better ductility than Q345 and Q460. • Duplex stainless steel is more sensitive to ULCF than Q345 and Q460. [ABSTRACT FROM AUTHOR]

• A micromechanical model for bioinspired nanocomposites was established with the interphase explicitly considered. • A compact formula of the effective modulus was derived, showing a load sustain dominant term and a term reflecting the load transfer. • The significance of the interphase influence was revealed to be dependent and tuned by a non-dimensional parameter β II. The stagger-aligned structures including "brick-and-mortar" are well-known as a generic feature in biological tough and strong nanocomposites, leading to bioinspired high-performance composites. Experimental observations have shown that the region between the stiff reinforcements and the soft matrices is not an interface of zero thickness but a nanoscale interphase. The interphases are believed to play an important role in the overall mechanical achievements; however, related theoretical models are still yet to be developed for decoding the interphase-related mechanisms. Based on the shear-lag theory, this work establishes a theoretical model for the staggered nanocomposites explicitly considering the interphase. In particular, a compact formula of the nanocomposites' effective modulus (E c) is derived, clearly showing the relations to a load-sustain dominant term (E R) and a term (E S) reflecting the load-transfer through shear deformation, as well as other microstructural and material parameters. With comparison to results by the finite element analysis and other existing relevant models, our model exhibits superior accuracy and simplicity, as well as general applicability. Furthermore, our model reveals an interesting working mechanism of the interphase: E c is sensitive to the interphase properties for the shear transfer parameter (β II ) being around 1.5–7.5, as the interphase undertakes both stress-transfer and stress-sustaining roles. The model and findings shed light on the role of the interphase in enhancing load-bearing biological composites and provide new insights in optimizing bioinspired nanocomposites through modulating the interphase properties. [ABSTRACT FROM AUTHOR]

• The combination of GO and steel fiber makes UHPC have the best fracture property. • GO improves the pull-out property of steel fiber by reinforcing the UHPC matrix. • The prediction model of UHPC fracture energy based on micromechanics is established. This paper aims to achieve multi-scale crack control of concrete by using graphene oxide (GO) and macroscopic steel fiber in combination, and to reveal the multi-scale collaborative reinforcement mechanism of GO and steel fiber. A three-point bending fracture mechanics test was employed to analyze the macroscopic fracture properties of ultra-high performance concrete (UHPC) reinforced by GO, and a single fiber pull-out test was utilized to assess the impact of GO on the fiber–matrix interface properties. The results showed that 0.04% GO reinforced UHPC had the best fracture property, and steel fiber and GO showed good synergistic crack control effect. GO directly acted on controlling the cracking of concrete matrix at the nanoscale, thus improving the fracture energy of UHPC matrix by 14% from 73.08 N/mm to 83.39 N/mm. This micro-scale matrix reinforcement provided by GO further improved the pull-out property of steel fibers, and the pull-out energy dissipation of straight steel fibers and hook-end fibers was increased by 43.7% and 31.5%. A micromechanical prediction model for fracture energy of straight steel fiber UHPC was established, which could construct the quantitative relationship between UHPC fracture energy and micromechanical parameters. The model showed that the initial fiber–matrix bond strength (τ 0) and slip hardening coefficient (k 0) had a powerful influence on the UHPC fracture energy. [ABSTRACT FROM AUTHOR]

Highlights • A micromechanics based model is proposed for the CTE of HFRC. • Model is validated level by level from the cement paste level to HFRC level. • The micromechanical model can provide reasonable predictions on the CTE of HFRC. • Water/cement ratio, hydration degree, aggregate type and fiber type are taken into consideration. Abstract This study is involved with presenting a multi-level micromechanical model for predicting the coefficients of thermal expansion (CTE) of randomly distributed and oriented short hybrid fiber reinforced concrete (HFRC), which includes the cement paste level, concrete level, and HFRC level. In this micromechanical model, the inner products (IP), outer products (OP), calcium hydroxide (CH), unhydrated clinker, sands, aggregates and hybrid fibers are comprehensively considered. A substepping homogenization framework is presented to realize the upscaling from the microstructure to macro HFRC, based on which the overall CTE of HFRC is determined. In addition, the volume fractions of phases at each level are also presented to facilitate the prediction of CTE. Comparisons with experimental data from previous studies are implemented level by level. Subsequently, the influences of the water-cement ratio, the hydration degree, the aggregate property and the fiber property on the CTE are discussed carefully. [ABSTRACT FROM AUTHOR]

Abstract This article investigates the history of long-term radial and circumferential creep strains and radial displacement for a three-phase nano-composite exposed to an internal pressure and placed uniform temperature and magnetic field. Three-phase nano-composite made of single-walled carbon. The results in this paper were achieved by presuming a non-linear viscoelasticity, based on Shapery's integral model, classical laminate theory, Prandtl-Reuss's relation and Mendelson's approximation method. The distribution of the radial creep strain, circumferential creep strain and radial displacement in two states of with and without magnetic field and three temperature conditions for two lay-ups [0/45/0/45] and [0/90/0/90] described for 10 years. It has been found that the values of creep strain and radial displacement in magnetic field are lower than without a magnetic field, for two lay-ups. [ABSTRACT FROM AUTHOR]

The response of NiTi shape memory alloy (SMA) changes drastically with the loading rate. This paper presents a three-dimensional thermomechanically coupled constitutive model to describe the rate dependent cyclic performance of superelastic NiTi SMA. Two inelastic mechanisms, i.e. martensitic transformation and transformation-induced plasticity, are taken into account. The fully coupled heat equilibrium equation is deduced from the first law of thermodynamics. The thermodynamic driving forces of the internal variables are derived from the second law of thermodynamics (Clausius-Duhem inequality). The constitutive model is extended from single crystal scale to polycrystalline version via finite element approach. The validity of the model is verified through simulating thermomechanical response of cyclically tensioned superelastic NiTi SMA at various deformation rates. Moreover, the robustness of the model is checked by simulating the thermomechanical behavior of superelastic NiTi cantilever tube subjected to cyclic bending. The simulation results match with the experimental observation reasonably. [ABSTRACT FROM AUTHOR]

In this paper a micromechanical model considering PyC interphase thermal conductance and manufacture-induced voids is proposed to predict the thermal conductivities of plain woven C/SiC composite. This model is based upon the analysis of the representative volume element (RVE) models of composite. The modeling strategy starts with a geometrical description and finite element discretization on two scales consisting of the fiber yarn modeling (fiber-scale) followed by a woven fabric modeling (yarn-scale). The PyC interphase is introduced in the fiber-scale modeling while the large voids at the intersection of orthogonal yarns are included in the yarn-scale modeling. Experiments are conducted to measure the thermal conductivities of plain woven C/SiC samples from room temperature to 800 °C temperature. The satisfied agreement with experimental data has highlighted the predictive capability of the proposed micromechanical model. Finally, a parametric study is performed using the presented model to investigate the effects of PyC interphase thermal conductance and manufacture-induced voids on the thermal conductivities of composite. [ABSTRACT FROM AUTHOR]

This study focuses on the poroelastic behaviour and permeability of tight sandstones, which are characterized by a low porosity, a low gas permeability and a strong sensitivity to in-situ stress. Experimentally the Biot coefficient takes a value close to 1 at low confinement and decreases with increasing confining pressure; the permeability shows an important reduction with increasing confining pressure. This behaviour can be attributed to pore entrapment and to the closure of cracks and joints. Micromechanical models, considering low permeable sandstones as made up of an assemblage of grains with interfaces and pores, reproduce well the observed trends of Biot coefficient and permeability. [ABSTRACT FROM AUTHOR]

Microcracks can affect the mechanical properties of rocks, such as their stiffness and strength. To provide a link between the microstructural parameters and the mechanical behaviour of rock, micromechanical models use parameters that represent a quantitative description of the microcrack population. However, these parameters are difficult to constrain. With the aim of better constraining micromechanical models for rock strength and stiffness, we provide here robust measurements of microcrack characteristics. We developed an algorithm to process optical micrographs of rock, automatically creating binary images of the microcrack network. We applied this procedure to optical micrographs of fine-grained granite samples that have undergone varying degrees of thermal microcrack damage. From these processed images, we calculate the mean microcrack length and the number of microcracks per unit area (and therefore the 2D microcrack density). We also create heat maps showing the spatial distribution of microcracks and their lengths. The results of our automated image analysis are in very good agreement with those of widely-used stereological techniques, and we show that our method can be applied to other rock types (sandstone and andesite) that contain microcracks. Using the measured microcrack characteristics as inputs for Ashby and Sammis’ (1990) 2D micromechanical sliding wing crack model, we predict the uniaxial compressive strength of the granite and compare the predictions with strength measurements made in the laboratory. We find good agreement between the model and the experimental data for granite heated to temperatures below the alpha-beta transition of quartz (~573 °C). Rock strength is overestimated above this threshold, possibly due to variations in fracture toughness, which is considered constant in our modelling. Finally, we use the 2D sliding crack model of David et al. (2012) to infer microcrack density and aspect ratio from the mechanical response of the thermally microcracked samples to cyclic stressing. We show a good agreement between inferred and measured crack densities if a scaling factor is introduced. [ABSTRACT FROM AUTHOR]

The topic of this work is assessment of ductile fracture initiation and development in different zones of welded joint of a high strength low alloyed (HSLA) steel. A combined experimental-numerical procedure is applied for determination of properties of the weld metal and the heat affected zone - HAZ. One tensile specimen with rectangular cross-section is tested, and the surface strains are determined using stereometric 3D measurement (measurement system Gom Aramis with two cameras and software solution). This methodology enabled formation of the stress-strain curves for micromechanical analysis of fracture of specimens with initial fatigue pre-cracks. Two different geometries are considered: standard single-edge notched bend (SENB) specimens and surface-cracked tensile specimens. The cracks were positioned either in weld metal or in HAZ - within the fine-grained part. Micromechanical model (complete Gurson model, by Z.L. Zhang) is applied for assessment of crack growth onset and stable growth. Higher resistance to ductile fracture initiation and crack growth in HAZ is successfully predicted, as well as constraint effect caused by different crack shapes. [ABSTRACT FROM AUTHOR]

Nano-reinforced composites have a wide range of useful applications thanks to their exceptional all-encompassing characteristics. Understanding the micromechanical model and the reinforcing process in nano-composites is crucial for a quantitative assessment of the reinforcement impact of nano-fillers and performance optimization. The original micromechanical model for common composite materials is no longer applicable since mechanical modeling of composite materials takes into consideration variables like multi-scale, multi-phase, and multi-morphology. The multi-scale parameter equivalent modeling theory of nano-reinforced composites is examined in this work. It is suggested to use a generalized modified Halpin-Tsai micromechanical model, which may accommodate any reinforcement form, size, or orientation, after theoretical and experimental comparison and verification. A tiny sample of the nano-reinforced composite material's mechanical tensile characteristics was examined, and its microscopic. • By examining the multi-scale parameter equivalent model and technique of nano reinforced composite materials, a generalized modified Halpin Tsai model that can be used for any form, size, and orientation was developed. • Using the mixed solution approach, nano reinforced composite material samples were created, their mechanical tensile properties were examined, their microscopic features were observed, and the distribution and reinforcing process of nano reinforced materials were researched. • Experimental evidence shows that GPL in epoxy resin/GPL nanocomposites made using the mixed solution approach is randomly oriented in the same section, making the micromechanical concept of random orientation distribution more applicable. [ABSTRACT FROM AUTHOR]

• A new strategy is proposed to generate regional random fiber-reinforced polymer composites. • Theoretically, this method can produce FRP composites with a volume fraction of up to 90.7%. • The numerical model accurately predicts the mechanical properties of the composite. • The method alleviates the trend of decreasing tensile strength as volume fraction increases. This paper proposes a novel method of random fiber distribution inspired by the finite element mesh technique. It solves the problem of fiber interference when generating the Representative Volume Element (RVE) with a high volume fraction and prevents fiber cluster formation at low volume fractions. Theoretically, the method can produce Fiber-Reinforced Polymer (FRP) composites with volume fractions up to 90.7%. The mechanical properties of FRP composites are then predicted using a progressive damage model that considers the failure of the matrix and interface. The experimental results in the literature verify the rationality of the numerical model. Finally, the effect of varying volume fractions and cell-cutting methods on the mechanical characteristics of unidirectional FRP composites under transverse loading was studied. The results show that the elastic modulus increases with increasing fiber volume fraction, while the tensile strength shows an opposite trend. The hexagonal cell-cutting method can alleviate the adverse effect of the decrease in tensile strength with the increase in fiber volume fraction. Meanwhile, the hexagonal cell-cutting method is reliably reproducible, and the coefficient of variation for the 30 renditions is only 0.05%. It illustrates that the hexagonal cell-cutting method can generate composites with higher tensile strength compared to other methods. [Display omitted] [ABSTRACT FROM AUTHOR]

Hyperelastic rubber-like materials are described by their nonlinear elastic behavior subjected to large deformations. The one-dimensional strain energy function for polymeric material was introduced in Mahnken and Mirzapour (2022). This follow-up contribution presents a three-dimensional statistical micro-mechanical-based constitutive model incorporating the topological constraint's effects. The micro strain energy corresponding to the stored energy in a single polymer chain is mainly entropic and calculated from the entropic part of the Helmholtz free energy based on the Boltzmann equation. Then, the macro strain energy corresponding to the polymer networks is obtained by homogenizing the micro strain energy over the unit volume. At the same time, it can be decomposed into cross-linked and entangled strain energies. The current model is developed on the different angles of the polymer chain. The random nature of the polymer chain's angles is defined by proper probability distribution functions (PDFs) representing different angles' distribution. I incorporate the entangled chains based on the statistical degree of freedom introduced as polymer angles. Numerical examples to calibrate and verify the proposed model illustrate the capability of the current proposed model to reproduce the highly nonlinear behavior of rubber-like materials under different loading conditions. • An extension of one-dimensional strain energy to three-dimensional. • Incorporating the effects of the entangled chains. • Physically-based evolution of different angles of the polymer chain. • Considering the tension and compression phases of the polymer chain. [ABSTRACT FROM AUTHOR]

• Hollow spherical and flake-shaped microparticles can improve vibration reduction. • Three-phase model can be used for estimating the loss factor of microparticles. • FE strain energy method can predict the loss factor of cementitious composites. Recently, some microparticles have been proven to be effective in improving the damping performance of cementitious composites, which is described by the damping loss factor. Related studies have analyzed damping loss factors of cementitious composites with microparticles to determine optimum mixing proportion, but no efficient numerical analysis method is available for cementitious composites with microparticles. In this study, the micromechanical three-phase model and finite element (FE) strain energy were applied to cementitious composites reinforced with hollow sphere and flake-shaped microparticles. These methods have been widely used with fiber composites but never used with microparticle-reinforced composites. The three-phase model was used here to estimate the damping loss of microparticles, and FE strain energy method was used to analyze the damping loss factor of microparticle-reinforced cementitious composites with the damping loss factor from the three-phase model. This research highlights that the FE strain energy method can be an effective method for estimating the damping loss factor of cementitious composites with different types of microparticles at various volume fractions of fillers with less than 0.1% the least square error between the experimental and simulation results. [ABSTRACT FROM AUTHOR]

In this paper, a new micromechanical model is developed for graphene-reinforced metal matrix nanocomposites (MMNCs) to effectively describe the mechanical properties of the new attractive engineering materials with high specific strength. The key influence of the misorientation of randomly-distributed graphene nanoplatelets (GNPs) is especially considered. The strain rate and temperature effects are also introduced through the dislocation-mechanics-based metal matrix model. Then the new model is applied to the nanocomposites of GNP/Al2024, GNP/Al and GNP/Cu, respectively. The comparison of model predictions and experimental data suggests that the model can represent the elastoplastic deformation behaviors of the graphene-reinforced MMNCs well. The strengthening effect by graphene in the nanocomposites is approximately linear to its volume fraction within a small range and also to the aspect ratio of graphene platelets when their average length is less than a critical value. Moreover, the dynamic thermomechanical behavior of the GNP/Al2024 nanocomposite is predicted for the first time. The temperature-softening effect becomes weaker under dynamic loading conditions while the rate sensitivity would be enhanced at elevated temperatures. [ABSTRACT FROM AUTHOR]

Syntactic foams are lightweight composite materials that find extensive application as core materials for sandwich panels in marine and aerospace structures. While several models have been proposed to analyze the elastic response and failure of these composites at small strain rates, the understanding of syntactic foam behavior at high strain rates remains elusive. In this work, we simulate the response of polymer-glass syntactic foams under high strain rate compressive loading conditions, by using a three-dimensional micromechanical model consisting of fifty hollow spheres randomly dispersed in the matrix material. The mechanical response of the matrix is described by generalizing a phenomenological viscoplastic constitutive model from the literature to the three-dimensional stress state. The filler behavior is assumed to be linear elastic until brittle failure, which is predicted on the basis of a structural criterion for glass microballoons. The collapse of the first glass microballoon is hypothesized to trigger the failure of the whole composite. Such a micromechanical model is implemented in the commercial finite element code ABAQUS. We focus on glass-vinyl ester syntactic foams and perform a parametric study to elucidate the roles of strain rate, microoballoon density, and microballoon volume fraction on the compressive modulus, strain energy, and effective strength. Comparisons between model findings and available experimental data are presented to assess the accuracy of the proposed numerical model. Our results enable the study of syntactic foam behavior at high strain rates, for a wide range of strain rates, microballoon densities, and microballoon volume fractions. This knowledge is expected to aid in the design of lightweight composite materials subjected to high strain rate compressive loading. [ABSTRACT FROM AUTHOR]

Austenite stainless steels with gradient nanostructure exhibit exceptional combination of high yield strength and high ductility. In order to describe their structure-property relation, a theoretical model is proposed in this work, in which the depth-dependent bimodal grain size distribution and nanotwin-nanograin composite structure are taken into account. The micromechanical model and the Voigt rule of mixture are adopted in deriving the constitutive relations. Furthermore, the evolution and influence of the nano/micro cracks/voids are considered for predicting the failure strain. The numerical results based on the theoretical model agree well with experimental results in terms of the yield strength, ductility, and the strain hardening rate, demonstrating that the proposed model can well describe the mechanical properties of gradient-nanostructured austenite stainless steels. We further study the variations of the yield strength and ductility of gradient-nanograined and gradient-nanotwinned 304 stainless steels with different distribution of grain size and twin spacing along the depth, which shows that the present model can be applied to optimize the combination of strength and ductility of the gradient-nanostructured metals by tuning depth-dependent distributions of microstructures. [ABSTRACT FROM AUTHOR]

By means of the experimental method, micromechanical model and Finite Element Method (FEM), this paper studied the compressive behaviors of the three-dimensional random fibrous (3D RF) material in the through-the-thickness (TTT) and in-plane (IP) directions at elevated temperatures. The compressive experiments showed that the fracture strength and Young's modulus of the 3D RF material in the TTT and IP directions decrease as increasing temperature. The specimens fracture through breaking the fibers under the bending deformation, while almost all the bonding zones keep intact. A simple micromechanical model and a FEM model are developed to simulate the mechanical properties of the 3D RF material. The micromechanical model ignores the randomness of the fibers, while in the FEM model special attention is drawn to the influence of the morphological characteristic. Numerical results from the micromechanical model and FEM model agree well with the observations from the compressive experiments. [ABSTRACT FROM AUTHOR]

Recycled concrete fines (RCF) are fine aggregates and particles from the demolition waste of old concrete. Unlike recycled coarse aggregates, RCF is seldom used to replace sands in concrete due to its high surface area and attached old mortar on the surface of RCF. This study investigated potential use of RCF as microsilica sand substitute in the production of engineered cementitious composites (ECC), a unique high performance fiber-reinforced cementitious composites featuring extreme tensile strain capacity of several percent. The results showed that it is viable to use RCF as microsilica sand substitute in the production of ECC and the resulting RCF-ECCs possess decent compressive strength and strain capacity. Microstructure investigation on the component level revealed that RCF size and content modify matrix toughness and fiber/matrix interface properties. The influence of RCF size and content on ECC properties was clearly revealed and explained by the resulting fiber bridging σ(δ) curves of RCF-ECCs calculated from the micromechanical model. Micromechanics-based design principle can therefore be used for ingredients selection and component tailoring of RCF-ECCs. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT)/cement composites have been proposed as a multifunctional material for self-sensing and traffic monitoring due to their unique electric conductivity which changes with the application of mechanical load. However, material constituent and environmental factors may significantly affect the potential application of these materials. Therefore, it is necessary to understand an influence of material constituent such as porosity and dispersion of CNT and environmental factor such as moisture on the electrical conductivity of CNT/cement composite. This paper investigates the effect of moisture on the effective electrical conductivity of CNT/cement composites. To prepare the specimens, multi-walled carbon nanotubes (MWCNTs) are well dispersed in cement paste, which is then molded and cured into cubic test specimens. By drying the specimens from the fully saturated state to the fully dry state, the effective electrical conductivity is measured at different moisture contents. As the water in the specimen is replaced by air voids, the electrical conductivity significantly decreases. Different ratios of MWCNTs to cement have been used in this study. Micromechanical models have been used to predict the effective electrical conductivities. A comprehensive model is proposed to take into account the effects of individual material phases on the effective electrical conductivity of CNT/cement composites with moisture effect. [ABSTRACT FROM AUTHOR]

This study presents a new micromechanical model that is simple, explicit, and directly applicable for broad engineering applications to predict the effective elastic moduli of very high-contrast component property composites containing high concentrations of particles. The approach is based on the Morphological Representative Pattern scheme, where the first pattern comprises a spherical fictitious inclusion embedded in an infinite effective homogeneous medium with physical properties of the matrix, while the others correspond to the classical three-phase generalized self-consistent problem. Instead of using the mean distance between particles, as addressed in existing literature, the volume fraction of patterns is calculated based on the maximum packing fraction estimated from the packing model. This approach shows perfect coherence with experimental data for benchmark examples of effective properties of suspensions of monodisperse particles in an elastic matrix and porous materials. Furthermore, a refined version of the model is proposed, which includes a free parameter representing the shape of the fictitious inclusion to evaluate the polydisperse effect on the overall properties of these materials. • New model for predicting properties of high-filler inclusion-matrix composites. • Morphological Representative Pattern approach with maximum packing fraction. • Good consistency with experimental data for benchmark examples. [ABSTRACT FROM AUTHOR]

• The effect of the size and shape of pores on the Balshin's model was studied. • The porosity of the foamed mixture and the size of the sand used are some of the factors influencing the change in the pore characteristics. • As the pores became smaller and more spherical, the power value of Balshin's model decreased. The Balshin's model is the most well-known of the models used to predict the compressive strength of aerated concrete. Among the pore characteristics such as the amount of porosity, the size of the pores, and their shape, Only the amount of porosity is placed as a specific parameter in the Balshin's model. The impact of the other two characteristics, on the other hand, is included in the power value of the Balshin's equation. Compressive strength tests and identifying the characteristics of air voids using microscopic imaging were performed on the mixtures produced in this study, which had weight ratios of sand to the cement of 1, 1.5, and 2, and the percentage of foam volumes of 0, 15, 25 and 35. In this study, a review of some of the factors influencing the change in the pore characteristics was performed, including the porosity of the foamed mixture and the size of sand used, in addition to the effect of the pore characteristics such as size and shape on the compressive strength of the foamed mixture. This study aims to conduct a comparative analysis of the models introduced in previous research to determine the effect of the pore characteristics of semi-structural and structural foamed mixtures (with sand) caused by mixture porosity and the sand size on the Balshin's model. Among the types of relationships presented for the Balshin's model, the relationship based on the paste fraction porosity was used. According to the findings of this study, foam porosity is the most important factor influencing pore size change, followed by sand size. The increase in the size of the pores and their non-sphericality decreased the relative compressive strength and, as a consequence, increased the power of the Balshin's model because the maximum level of stress concentration was created adjacent to the middle diameter of the pores at the period of concrete rupture. [ABSTRACT FROM AUTHOR]