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In this research, the effects of induced delamination on the variation of the mechanical properties of composite laminates subjected to bending loads are investigated using a micromechanical model. For this purpose, the variation of the mechanical properties of delaminated laminates is determined using stress analysis of damaged ply and classical laminate theory (CLT) relationships. Using the proposed model and CLT, the fracture toughness due to induced delamination formation is presented in cross-ply laminates. Subsequently, the variation of strain energy release rate (SERR) is calculated in terms of crack density using analytical and finite element models to detect dominant failure modes in different crack densities. The results are compared with those of matrix cracking propagation. The results obtained by the proposed analytical model are in good agreement with those obtained by existing numerical and experimental approaches. The proposed model can be utilized to predict induced delamination formation in composite laminates subjected to bending loads.

The fracture strain of carbon fiber-reinforced plastics (CFRPs) within CFRP/steel hybrid laminate composites is reportedly higher than that of CFRPs due to transverse compressive stress induced by the steel lamina. A micromechanical model was developed to explain this phenomenon and also to predict the mechanical behavior of CFRP/steel hybrid laminate composites. First, the shear lag theory was extended to calculate stress distributions on fibers and matrix material in a CFRP under multiaxial stress condition, considering three deformation states of matrix (elastic and plastic deformation and fracture) and the transverse compressive stress. Then, the deformation behavior of CFRP was predicted using average stress in the ineffective region and the Weibull distribution of carbon fibers. Finally, the mechanical properties of CFRP/steel hybrid laminate composites were predicted by considering the thermal residual stress generated during the manufacturing process. The micromechanical model revealed that increased transverse compressive stress decreases the ineffective lengths of partially broken fibers in the CFRP and results in increased fracture strain of the CFRP, demonstrating the validity of the current micromechanical model.

Innovative pothole patching materials reinforced with a high-toughness, low-viscosity nanomolecular resin, dicyclopentadiene (DCPD, C10H12), have been experimentally proven to be effective in repairing cracked asphalt pavements and can significantly enhance their durability and service life. In this paper, a three-dimensional micromechanical framework is proposed based on the micromechanics and continuum damage mechanics to predict the effective elastic-damage behaviors of this innovative pothole patching material under the splitting tension test (ASTM D6931). In this micromechanical model, irregular coarse aggregates are approximated and simulated by randomly allocated multi-layer-coated spherical particles in certain representative sizes. Fine aggregates, asphalt binder (PG64-10), cured DCPD (p-DCPD), and air voids are formulated into an isotropic elastic asphalt mastic matrix based on the multilevel homogenization approach. The theoretical micromechanical elastic-damage predictions are then systemically compared with properly designed laboratory experiments as well as three-dimensional finite elements numerical simulations for the innovative pothole patching materials.

This study presents an accurate and easy-to-use micromechanical model to predict the ultimate strength of unidirectional polymer composites under an arbitrary load condition only upon independently measured constituent properties. In this model, the micromechanical method based on generalized model of cells (GMC), which effectively predict the nonlinear deformation of unidirectional composites, is used to analyze the repeating unit cells of composites. At the same time, a unified plastic theory (i.e. modified Ramaswamy-Stouffer model) is incorporated into the GMC's analytical framework to describe viscoplastic behaviors of matrix phase. Additionally, because of the stress concentration effect which causes the difference between the matrix in-situ and original strength behaviors, a stress concentration factor is introduced in order to utilize the measured constituent properties directly. The prediction results with SCF match better with the experimental results than the prediction results without SCF. In addition, the prediction results show that the presence of thermal residual stress and material plastic effects generally has important influence on the strength prediction of a composite.

An analytical model was developed for rectangular overlapped platelet reinforced composites subjected to unidirectional axial load. Two sets of the matrix/platelet displacement solutions (far-field...

The mechanical properties of a cementitious composite are strongly affected by interfacial transition zone (ITZ) between the matrix and the aggregates, mainly by its strength and thickness. A micromechanical model based on Mori-Tanaka scheme coupled with an estimation of deviatoric stress in ITZ was developed for evaluation of the effect of selected secondary cementitious materials (SCMs – silica fume, fly ash and metakaolin) on the properties of ITZ in high-strength concrete (HSC). The model was validated by means of comparison of predicted ITZ thickness with direct ITZ thickness measurements performed by a combination of scanning electron microscopy and grid nanoindentation. Very good agreement between the theoretical and experimental results was reached, therefore the developed micromechanical model can be used for further research and optimization of HSC containing SCMs. Silica fume was determined to be the most efficient supplementary cementitious material from the point of view of ITZ thickness reduction.

The paper focuses on the nonlinear vibration of functionally graded graphene nanoplatelet reinforced composite doubly curved shallow shells resting on elastic foundations. The graphene nanoplatelet reinforced composites are assumed to be distributed uniformly and functionally graded through the thickness. The material properties are assumed to be temperature-dependent and are estimated through the Halpin–Tsai micromechanical model, while the Poisson’s ratio, density mass, and thermal expansion are implemented by the rule of mixtures. The mathematical formulation is developed based on the classical shell theory and Von Karman-Donnell geometrical nonlinearity assumption. The dynamical responses of a simply supported functionally graded-graphene nanoplatelet reinforced composite doubly curved shallow shells are obtained by employing the Airy’s stress function and the Galerkin’s method. The responses of nonlinear vibration as time history, frequency-amplitude curve, phase plane graphs, and Poincare maps are carried out in this paper. In addition, the effects of the environment, graphene nanoplatelets weight fraction, graphene nanoplatelets distribution patterns, and thickness-to-length ratio are scrutinized. The obtained results are also compared and validated with those of other studies.

In the present research, a novel rate-dependent micromechanical model was presented to predict the stiffness and strength of unidirectional glass/epoxy composites. To predict the strain-rate dependent stress–strain behavior of glass fibers, using the Maxwell model with the aid of semi-empirical relations, a new viscoelastic constitutive model was proposed. Moreover, to predict the strain-rate dependent ultimate strength of brittle glass fibers, the elasto-plastic strain-rate dependent Cowper-Symonds material model was simplified by deleting the plastic terms. The strain-rate dependent mechanical properties of the polymer were also investigated by using the modified Goldberg model. Then, by modifying the Mori-Tanaka micromechanical model, a rate dependent micromechanical model was developed to predict the effective elastic properties (stiffness and strength) of unidirectional fibrous composites at arbitrary strain rates. The present model was called the strain-rate dependent Mori-Tanaka micromechanical model. As inputs, the present model just needs the viscoelastic and viscoplastic properties of fibers and polymer. Therefore, the present model reduces the necessary experimental data to predict the rate-dependent mechanical properties of unidirectional composites. For verification of the present model, the results were compared with experimental data and very good consistency in predicting the rate-dependent behavior of unidirectional composites was observed.

In this work, we use polycrystal modeling to study the interactions between slip and twinning during load reversals of commercially pure titanium. The constitutive response incorporates anisotropic elasticity, crystal plasticity, a dislocation density based hardening law for prismatic slip, basal slip, and pyramidal type I 〈c + a〉 slip, and micromechanical model for twin reorientation on two types: { 101 2 ¯ } extension twinning and { 11 2 ¯ 2 } contraction twinning. The key feature of the model is the inclusion of slip-system level backstress development due to dislocation density accumulation. To demonstrate, the model is used to simulate the stress-strain response and texture evolution in a series of compression-tension and tension-compression tests carried out to different strain levels and applied in two different load directions to a strongly textured CP-Ti plate. Material parameters associated with the slip strengths for the three slip modes are reported. The model identifies the few systems within the pyramidal 〈c + a〉 slip mode as developing the most backstress among the three slip modes. It also indicates that the backstresses that develop in the forward loading path promote pyramidal slip in the reversal loading path. We also find that reverse loading changes negligibly the relative slip mode contributions from monotonic loading but it strongly affects the twinning-detwinning behavior. This work highlights the ability of polycrystal modeling to account for the co-dependent nature of multiple crystallographic slip and twinning modes, the hysteresis in plastic response during the forward-reversal cycle, and the two sources of hardening engendered by history-dependent dislocation density accumulation.

Unsuitable surface quality is frequently observed in the machining of composites due to their heterogeneity and anisotropic properties. Thus, minimizing the machining damages requires a thorough understanding of the machining process. In this study, two different finite element models were developed using Abaqus/Explicit to simulate the cutting process of unidirectional carbon fiber-reinforced polymer: (i) a macromechanical model based on the homogenization approach and (ii) a micromechanical model in which the composite constituents were treated separately. The effects of CFRP mechanical properties, the energy of breaking and hourglass control were analyzed using a macromechanical model. The results revealed that CFRP properties and the numerical parameters highly influenced the cutting process. A comparative study was also performed between the macromechanical and the micromechanical models to study the mechanisms of chip formation. It was demonstrated that the material removal mechanisms for both models are in good agreement with the experimental observations for different fiber orientation angles.

The current work models a weak (soft) interface between two elastic materials as containing a periodic array of micro-crazes. The boundary conditions on the interfacial micro-crazes are formulated in terms of a system of hypersingular integro-differential equations with unknown functions given by the displacement jumps across opposite faces of the micro-crazes. Once the displacement jumps are obtained by approximately solving the integro-differential equations, the effective stiffness of the micro-crazed interface can be readily computed. The effective stiffness is an important quantity needed for expressing the interfacial conditions in the spring-like macro-model of soft interfaces. Specific case studies are conducted to gain physical insights into how the effective stiffness of the interface may be influenced by the details of the interfacial micro-crazes.

In this study, we developed a micromechanical model for the growth and remodeling of a soft tissue based on the concurrent action of collagen deposition and degradation. We assumed in the model that collagen degradation causes a reduction in the fiber radius, while collagen deposition can increase both the radius and length of the collagen fibers growing under load. The latter arises from the assumption that collagen is deposited in an unstressed state, which increases the reference length of a fiber growing under mechanical load. The rate of collagen deposition and degradation can be stimulated and inhibited, respectively, by the fiber axial strain energy density. From these assumptions, we derived kinetic relationships for the fiber radial and axial growth stretch, and constitutive relations for the stress response and growth and remodeling of the tissues. We applied the model to study the growth of collagen fibers under a static and cyclic force. Cyclic force loading can drive the continual axial growth of collagen fiber, while the axial growth under a constant force eventually halts when an equilibrium state is reached. We then applied the model to investigate the development of stress and strain homeostasis of a spherical collagenous tissue membrane in response to a perturbation in the internal pressure. The model showed that an increase in the pressure produced growth in the tissue radius and thickness, such that the stress response was able to recover the equilibrium membrane stress before the pressure perturbation. Tissues composed of slender, or low-crimp collagen fibers also recovered the equilibrium mechanical stretch level before the perturbation. These results indicated that concurrent mechanics-stimulated collagen deposition and mechanics-inhibited degradation can produce stress homeostasis and for some fiber morphology strain homeostasis without prescribing a target stress or fiber strain.

Much attention has recently been paid to investigating the internal mechanisms between the void structures of foamed concrete and its mechanical behavior. This study adopted the X-ray compu...

AbistractAs one of the most promising smart materials, magnetorheological (MR) gels have been widely applied in the vibration mitigation of engineering structures. An accurate and effective model f...

A micromechanical model for short fiber-reinforced composites (SFRCs) with functionally graded interphases and a systematic prediction scheme to determine the effective properties are presented. The matrix and the fibers are regarded to be linear elastic, isotropic, and homogeneous. Fibers are assumed to be ellipsoids coated perfectly by functionally graded interphases, which is supposed to be formed chemically or physically by the constituents near the interface. First, to analyze the grading interphase effect, layer-wise concept is followed to divide the functionally graded interphases into multi-homogeneous sub-layers. Next, to take the effect of functionally graded interphases into account, a combination of multi-inclusion method and Mori–Tanaka method is applied to predict effective elastic properties of this unidirectional SFRCs with respect to the content and aspect ratio of the inclusions. By employing coordinate transformation, spatially elastic moduli are obtained. Finally, Voigt homogenization scheme is used to obtain the overall, averaged, symmetrical elastic properties of the SFRCs. Numerical examples and analyses demonstrate the applicability of the proposed method and indicate the influences of graded interphase, orientation, and aspect ratio of inclusions as well as properties and contents of the constituents on the overall properties of SFRCs.

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 Nf = 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 Nf = 2124, the computation gain became 43.4% (and 73.4% with respect to number of jumped cycles) with a relative error of 3%.

The main objective of this work is to apply the Principal Component Analysis (PCA) to the key parameters of a micromechanical model, namely the shape parameter of inclusion (grain) (ratio =a/b) and γ viscoplastic parameter in view of a better simulation. In this work, the sensitivity of the model to parameters and γ is evaluated on the stabilized global stress during cyclic Tension-Compression (TC) loadings and out-of-phase Tension–Torsion, with a sinusoidal waveform and a phase lag of 90 between the two sinusoidal signals TT90 loadings. Indeed several values ​​of and γ are pulled thanks to these loading, we use later the PCA in order to choose the couple (, γ) adequate to launch our simulation. The model used is expressed as part of the self-consistent approach and time-dependent plasticity. Based on the Eshelby tensor, this model considers that the elastic behavior is compressible. For a polycrystalline structure, the grains are deformed by crystallographic sliding located in the most favorably oriented systems and which support a strong constrained stress . Keywords: PCA, grain shape , viscoplastic parameter γ, Self-consistent model, Non-incremental interaction law, Elasto-inelastic. TC and TT90 loading

Freeze-thaw damage in asphalt pavements is a complex phenomenon dependent on many parameters such as moisture infiltration, temperature and mechanical properties of the asphalt constituents as well...

An analytical model of rain erosion of coatings from segregated polyurethanes is developed. The model proposes an interrelation between the structure and morphology of segregated polyurethanes, damping properties and the erosion lifetime. For linking viscoelastic properties and the morphology of segregated polyurethanes, the embedded box model is used. With view on the available observations about the high variability of blade erosion and role of manufacturing defects, the critical role of statistical, random effects for the erosion damage initiation is assumed, and the statistical theory of strength is applied for the damage and fatigue analysis of the coatings. It is observed that the larger is the mechanical loss coefficient tan δ, the less is the stored elastic energy in the material after the impact. Further, it is observed that the higher the mechanical loss coefficient (damping) of the coating material, the higher is the lifetime of the coating under the erosion conditions.

This paper introduces a new method of determining the mechanical properties of carbon nanotube-polymer composites using a multi-inclusion micromechanical model with functionally graded phases. The nanocomposite was divided into four regions of distinct mechanical properties; the carbon nanotube, the interface, the interphase and bulk polymer. The carbon nanotube and the interface were later combined into one effective fiber using a finite element model. The interphase was modelled in a functionally graded manner to reflect the true nature of the portion of the polymer surrounding the carbon nanotube. The three phases of effective fiber, interphase and bulk polymer were then used in the micromechanical model to arrive at the mechanical properties of the nanocomposite. An orientation averaging integration was then applied on the results to better reflect macroscopic response of nanocomposites with randomly oriented nanotubes. The results were compared to other numerical and experimental findings in the literature.

The foundations of a new micromechanical model of rate and state friction are established. Based on the assumption that the relative sliding of two material surfaces is accommodated by the viscoplastic deformation of junctions in their entire volume, the model parameters are characterized in terms of loading conditions, geometrical contact characteristics and rheological properties of the bulk material. A relationship is established between the state parameter of the friction law and the mean microscopic normal stress exerted on the real contact area. Original results are obtained for the transition from stable to unstable slip regimes and applications to geological faults are considered.

A multi-scale micromechanical model is proposed to predict the damage degree of hybrid fiber-reinforced concrete under or after high temperatures. The thermal degradation of hybrid fiber-reinforced concrete is generally composed of the damage of the cement paste caused by thermal decomposition and thermal incompatibility, the deterioration of aggregates and fibers, and the interfacial damage between aggregates and the matrix. In this multi-scale model, four levels of hybrid fiber-reinforced concrete structures are considered when the thermal damage degree is derived; namely, the equivalent calcium silicate hydrate (C–S–H) product level, the cement paste level, the concrete level, and the hybrid fiber-reinforced concrete level. At the cement paste level, thermal decompositions of C–S–H product and calcium hydroxide are taken into account. In addition, a dimensionless parameter of the crack density is introduced to represent the thermal cracking of the matrix. At the concrete level, the interfacial damage of aggregates is simulated by a spring–interface model, in which the interfacial parameters are assumed to be functions of temperature. Moreover, at the cement paste level and the hybrid fiber-reinforced concrete level, a sub-stepping homogenization method is proposed to determine the effective properties. Comparisons between previously published experimental data and predictions and discussions illustrate the feasibility of the proposed multi-scale model in predicting thermal damage of concrete and hybrid fiber-reinforced concrete.

This study is aimed at investigating short- and long-term aged properties of glass fibre (GF)-reinforced asphalt mixtures using indirect tensile strength (ITS) and associated fracture energy, moist...

This article presents an investigation on the postbuckling behavior of doubly curved graphene-reinforced composite (GRC) laminated panels supported by an elastic foundation and subjected to lateral pressure and in thermal environments. The piece-wise GRC layers are arranged in a functionally graded (FG) pattern along the thickness direction of the panels. The overall mechanical properties of the FG-GRCs are assumed to be temperature dependent and are estimated through the extended Halpin-Tsai micromechanical model. The governing differential equations for the doubly curved panels are based on a higher order shear deformation shell theory with von Karman strain-displacement relationships and the panel-foundation interaction. The initial deflections caused by lateral pressure and thermal bending stresses are both taken into account. The governing equations are first deduced to a boundary layer type that includes nonlinear prebuckling deformations and initial geometric imperfections of the panel. The...

Failure prediction of metallic parts fabricated by 3D printing process is still challenging so that it is of vital importance to develop accurate microstructural-based simulation tools. In this study, a micromechanical model is proposed to predict the relationship between microstructure features, such as grains and melt pools, and the damage properties of powder bed fusion additive manufacturing (AM) products. The model reproduces the role of multiple effective key parameters on the mechanical response of the AM parts, which are observed experimentally, and reveals the effects of the microscopic defects, melt pool sizes, and the crystal orientations of grains on the failure response of AM parts. The materials presented in this paper can be used as a practical reference for predicting the failure response of AM products. In addition, it provides an important step toward the development of a multidisciplinary computational package for the sake of understanding and controlling the AM build process.

The effect of fiber distribution, in glass/carbon hybrid fiber composites, on the compressive kinking strength is studied using a 3D finite element-based micromechanical model. Existing experimental data from literature have indicated negative effects of hybridizing glass to carbon on the compressive strength. In this study a micromechanical modeling approach has been adopted to study the role of relative locations of glass and carbon fibers and their distributions on the predicted peak compressive strength. In the micromechanical model, the hybridization ratio was varied by changing the number of glass fibers relative to the number of carbon fibers. The effect of fiber distribution was studied by changing the interfiber spacing and location. Results obtained from the analysis indicate the importance of symmetric fiber distribution. It was found that the distribution with glass fiber in the center with a distribution of carbon fibers on the exterior is able to enhance the compressive strength as compared to an unsymmetrical arrangement of fibers in the model.

This study examines the effects of temperature and fiber and matrix diffusivities on the diffusion of fluid in glass fiber-reinforced polymer composites. Glass fiber-reinforced polymer thin plates were immersed in deionized water at two temperatures: room temperature and 50℃. During the diffusion process, the overall mass changes and dimension changes were recorded, which relate to the volumetric change and the through-the-thickness strain. Different constitutive models are considered in order to understand the diffusion of fluid through the glass fiber-reinforced polymer plates. The macroscopic models of this work, Fickian and Gurtin coupled deformation–diffusion, are first considered in order to describe the macroscopic diffusion behaviors. Two microscopic models that include fiber volume contents and diffusivities of the constituents (fiber and matrix) are then considered in order to gain fundamental insight into the effects of microstructural morphologies and constituents' diffusivities on the diffusion process in the glass fiber-reinforced polymer specimens.

A multi-scale simulation framework based on finite element method is developed to model the impact failure behavior of triaxially braided composite. The model integrates micromechanical model, meso-mechanical model and macro subcell model for the purpose of determining effective properties of fiber tows, estimating effective properties of subcell components, and simulating impact failure behavior of a braided composite structure, respectively. The meso-mechanical model compares excellently with experiments for mechanical behavior of both single-layer and six-layer specimens under quasi-static loading conditions. A new meso-macro homogenization approach is proposed to estimate effective properties of subcell components with consideration of geometry continuity effect. The subcell model is validated against experiments and utilized to simulate the high-speed impact behavior of a composite panel. The results of the subcell impact model compare well with experimental failure phenomena. The presented multi-scale modeling approach demonstrates its feasibility for impact analysis and design of braided composite structures.

Electrophoresis can be an effective approach for depositing carbon nanotubes (CNTs) on the surface of carbon fiber (CF). Nevertheless, it has been rarely reported on polyphenylene sulfide (PPS) composites filled with CFs surface-modified by CNTs based on electrophoresis. In this study, we investigated the electrophoresis process conditions that can completely coat CF with multi-walled CNTs (MWCNTs) using self-manufactured electrophoresis equipment, and the enhancement of interfacial, electrical and flexural properties of PPS composites by introducing CFs coated with MWCNTs based on electrophoresis. In particular, interfacial shear strength (IFSS) of the PPS composites was measured by microbond tests and improved by about 41.7% due to the MWCNTs introduced on the surface of CFs. These enhancements were theoretically explained by an interface-modified CF-based micromechanical model. Introducing MWCNTs on the CF surface based on electrophoresis was demonstrated to be an effective method for improving the interfacial, electrical and flexural properties of PPS composites.

Most concrete structures repaired by the electrochemical deposition method are not fully saturated and the healing interfaces are not always perfect in reality. To demonstrate these issues, micromechanical models are presented for unsaturated concrete repaired by electrochemical deposition method with the healing interfacial transition zone based on our latest work. The repaired unsaturated concrete is represented as a multiphase composite made up of the water, unsaturated pores, intrinsic concrete, deposition products and the healing interfacial transition zone between the latter two components. The equivalent particle, matrix and composite for repaired unsaturated concrete are obtained by modifying the differential-scheme and the generalized self-consistent method. Modifications are utilized to rationalize the differential-scheme based estimations by taking into the water (including further hydration and viscosity effects), interfacial transition zone and the shapes of the pores into considerations. Furthermore, our predictions are compared with those of the existing models and available experimental results, thus illustrating the feasibility and capability of the proposed micromechanical framework.

A unit cell-based micromechanical model is presented to investigate the effect of PZT-7A piezoelectric interphase on the effective magneto-electro-elastic properties of CoFe2O4 piezomagneti...

Particulate composites are found in a wide range of applications. Their heterogeneous microstructure affects their bulk behavior and structural performance, however tools for predicting this important structure-property relationship are still lacking. In this study, a numerical method that can provide predictions of the mechanical response of a particulate polymeric matrix composite as a function of volume fraction and particle mean diameter is presented. The work is derived for an alumina trihydrate filled poly(methyl methacrylate) but the methodology is generic and can be used for any particulate composite. Representative Volume elements are determined through images obtained from scanning electron microscopy. The model takes into account the possibility of failure through interface debonding as well as cracks through the matrix. The model predictions for the modulus and fracture strength of the composites are validated through independent experiments on the composite. The numerical results are also used to qualitatively explain the trends measured regarding the fracture toughness of the composites. Compared to other literature on particulate composites, our study is the first to report accurate stress–strain distributions as well as fracture predictions whilst all the necessary model parameters defining the failure criteria are all derived through independent experiments. This paves the way for a relatively simple methodology for determining structure-property relationships in composites design, enabling smarter material utilization and optimal mechanical properties.

A distinct perspective of using the hybrid composite patches with varying stiffness for repair of a cracked Al 6061-T6 plate and its influence on repair performance is presented. The hybrid composi...

Al-XCu (X = 1.0, 1.5, and 2.5 wt%) alloys with and without 0.3 wt% Sc addition were prepared respectively. The effects of composition and heat treatment processes on the microstructural evolution were systematically investigated by using transmission electron microscope and atom probe tomography (APT). Both Al3Sc dispersoids and θ′-Al2Cu precipitates coexisted after artificial aging, and a strong Sc segregation at θ′-Al2Cu/matrix interfaces was detected and quantified through APT examinations. A Sc solute partitioning was demonstrated between in the Al3Sc dispersoids and at the θ′-Al2Cu/matrix interfaces, mediated by the Cu content. Increasing the Cu content, both the size and volume fraction of the Al3Sc decreased after solid solution treatment. As a result, the interfacial Sc segregation was accordingly intensified during subsequent aging treatment. A parameter of reduction in interfacial energy (Δγ), derived from APT analyses, was proposed to characterize the degree of interfacial Sc segregation. The coupling effect of Al3Sc dispersoids and θ′-Al2Cu precipitates on ductile fracture was discussed, where a micromechanical model was developed to describe a quantitative relationship between the fracture strain with Δγ as well as parameters of the Al3Sc dispersoids.

In quasi-brittle polycrystalline materials, damage by cracking or cleavage dominates plastic and viscous deformation. This paper proposes a micromechanical model for rock-like materials, incorporating the elastic-damage accommodation of the material matrix, and presents an original method to solve the system of implicit equations involved in the formulation. A self-consistent micromechanical approach is used to predict the anisotropic behavior of a polycrystal in which grain inclusions undergo intragranular damage. Crack propagation along planes of weakness with various orientation distributions at the mineral scale is modeled by a softening damage law and results in mechanical anisotropy at the macroscopic scale. One original aspect of the formulated inclusion–matrix model is the use of an explicit expression of Hill’s tensor to account for matrix ellipsoidal anisotropy. To illustrate the model capabilities, a uniaxial compression test was simulated for a variety of polycrystals made of two types of mineral inclusions with each containing only one plane of weakness. Damage always occurred in only one mineral type: the damaging mineral was that with a smaller shear modulus (respectively higher bulk modulus) when bulk modulus (respectively shear modulus) was the same. For two minerals with the same shear moduli but different bulk moduli, the maximum damage in the polycrystal under a given load was obtained at equal mineral fractions. However, for two minerals with different shear moduli, the macroscopic damage was not always maximum when the volume fraction of two minerals was the same. When the weakness planes’ orientations in the damaging mineral laid within a narrow interval close to the loading direction, the macroscopic damage behavior was more brittle than when the orientations were distributed over a wider interval. Parametric studies show that upon proper calibration, the proposed model can be extended to understand and predict the micro–macro behavior of different types of quasi-brittle materials.

Asphalt mixtures with high porosities (known as porous asphalt (PA) mixes) are becoming a popular choice among road authorities as it provides better skid resistance while also reducing tire-pavement noises. Towards the design and manufacture of PA mix pavement, the evaluation of the mechanical properties of PA mixes is of great importance. To predict the mechanical properties of PA mixes, micromechanical models have been considered as an effective tool. In most research studies, continuum-based micromechanical models, i.e. the Self-consistent model, the Mori-Tanaka model, etc. are widely used to predict the stiffness of asphalt mixtures. However, the limitation of these models is that they cannot describe the characteristics of individual particles and thus they cannot provide accurate predictions. On the other hand, the discrete-based micromechanical model (DBMM) which simulates a granular material as an assembly of bonded particles seems to be a promising alternative. Limited research studies have focused on studying the utilization and the applicability of this model for asphalt mixes. Therefore, this paper aims to propose a framework to use DBMM and to evaluate its performance in estimating a PA mix’s stiffness. Based on the obtained results, both the merits and limitations of this model were highlighted.

A particle-level simulation methodology is proposed to study the squeeze flow behavior of model magnetorheological fluids. The simulation algorithm takes into account Brownian motion and local field corrections to magnetic interactions of the particles. Simulation results obtained from using different initial configurations, including one single-particle-width chain per simulation box, random or lattice arrangements of preassembled single-particle-width chains as well as randomly dispersed particle suspensions, are compared with experimental data and predictions of a recently developed microscopic model. The assumption of single-particle-width chain structures in the systems has been shown to generate normal stresses larger than those found in experiments and the micromechanical model. However, much better agreement between the simulation and experimental results have been reached when using random initial configurations in the simulations.

The nanostructured Al-based composites possess the combination of high yield strength and good ductility. In this paper, a micromechanical model is presented to simulate the mechanical response of bimodal nanostructured Al and the particle-reinforced aluminum matrix composite (PAMC). The constitutive relations for different phases are addressed in the model, as well as the contribution of microcracks. Numerical results show that the model can successfully describe the enhanced strength and ductility of the bimodal nanostructured Al, and the predictions of the PAMC are in good agreement with the experimental data. It is worth noting that the strength and ductility are sensitive to the volume fraction of constituents and the distribution of microcracks in both bimodal nanostructured Al and PAMC. Therefore, the present theoretical results can be used to optimize the microstructure for improving the mechanical properties of nanostructured Al-based composites.

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.

This paper is devoted to the modelling of stress-sensitive Biot coefficient experimentally observed in low permeable sandstones. Sandstones are described as an assemblage of rigid inclusions surrounded by poroelastic interfaces representing joints between grains and pores. A micromechanical model of Biot coefficient under loading is developed, which highlights the role of interfaces closure on the poroelastic macroscopic behaviour. Experimental results available concerning low permeability sandstones are analyzed in view of this model.

In the present research, a micromechanical-analytical model was developed to predict the elastic properties and strength of balanced plain weave fabric composites. In this way, a new homogenization method has been developed by using a laminate analogy method for the balanced plain weave fabric composites. The proposed homogenization method is a multi-scale homogenization procedure. This model divides the representative volume element to several sub-elements, in a way that the combination of the sub-elements can be considered as a laminated composite. To determine the mechanical properties of laminates, instead of using an iso-strain assumption, the assumptions of constant in-plane strains and constant out-of-plane stress have been considered. The applied assumptions improve the accuracy of prediction of mechanical properties of balanced plain weave fabrics composites, especially the out-of-plane elastic properties. Also, the stress analysis for prediction of strain–stress behavior and strength has been implemented in a similar manner. In addition, the nonlinear mechanical behavior of balanced plain weave composite is studied by considering the inelastic mechanical behavior of its polymeric matrix. To assess the accuracy of the present model, the results were compared with available results in the literature. The results, including of engineering constants (elastic modulus and Poisson’s ratio) and stress–strain behavior show the accuracy of the present model.

Modeling and analysis of the postbuckling behavior of graphene-reinforced composite (GRC) laminated plates are presented in this paper. The GRC plates are in a thermal environment, subjected to uniaxial compression and resting on an elastic foundation. The temperature-dependent material properties of functionally graded graphene-reinforced composites (FG-GRCs) are assumed to be graded in the plate thickness direction with a piece-wise type, and are estimated through a micromechanical model. The postbuckling problem of FG-GRC laminated plates is modeled using a higher order shear deformation plate theory and the plate-foundation interaction and thermal effects are taken into consideration. A two-step perturbation technique is employed to determine the buckling loads and the postbuckling equilibrium paths. The compressive buckling and postbuckling behavior of perfect and imperfect, geometrically mid-plane symmetric FG-GRC laminated plates under different sets of thermal environmental conditions is obtained and is also compared with the behavior of uniformly distributed GRC laminated plates. The results show that the buckling loads as well as the postbuckling strength of the GRC laminated plates may be enhanced through piece-wise functionally graded distribution of graphene.

This article presents a new micromechanical model to predict biaxial tensile moduli of plain weave fabric composites by considering the interaction between the orthogonal interlacing strands. The two orthogonal yarns in micromechanical unit cell were idealized as curved beams with a path depicted using sinusoidal shape functions. The biaxial tensile moduli of plain weave fabric composites were derived by means of the minimum total complementary potential energy principle founded on micromechanics. Biaxial tensile tests were conducted on the resin transfer molding–made EW220/5284 plain weave fabric composites at five biaxial loading ratios of 0, 1, 2, 3 and ∞ to validate the new model. Predictions from the new model were compared with experimental data. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed model. Using the new model, the biaxial tensile moduli of plain weave fabric composites can be predicted based only on the properties of basic woven fabric.

A nondestructive technique for evaluating the strength of hull elements of submersibles is described. The technique is based on the micromechanical model of temporal dependences of the parameters of acoustic emission that is registered under an original novel technique of loading of a cylindrical hull section. The technique is also suitable for assessing the information value of resource-related acoustic-emission diagnostic indicators.

The electrical conductivity of carbon nanotube–epoxy composites is investigated analytically and experimentally. The theoretical predictions of the effective electrical conductivity of carbon nanotube–epoxy composites were performed by the analytical approach based on a micromechanical model of composites. The parametric analysis carried out revealed an influence of geometrical and electrical parameters of the micromechanical model on the effective electrical conductivity of carbon nanotube–epoxy nanocomposite. The nanocomposites made from the DGEBA-based and RTM6 epoxy resins filled with different weight content of Baytubes C150P and N7000 multi-walled carbon nanotubes were prepared. The experimental values of the electrical conductivity of the nanocomposites were compared with those calculated by means of the analytical model.

The safety assessment of short-fibre-reinforced (SFR) composites, commonly used in structural applications involving repeated loads, requires to evaluate the degrading phenomena taking place in the matrix and at the fibre–matrix interface. The mechanical behaviour under both static and cyclic loading can be simulated applying damage degradation to the matrix mechanical characteristics, and employing fracture mechanics concepts to examine the fibre–matrix detachment as a 3D growing crack with degrading interface properties. In the present paper, a micromechanical model for unidirectional or random SFR materials under fatigue is developed. Some applications related to SFR polymeric composites found in the literature are presented.

A new micromechanical model is developed for the prediction of the elastic properties of composite materials with embedded spherical multicoated inhomogeneities of various sizes and types. ...

International audience; Despite the great similarities in the physical and chemical properties of flax and primary hemp fibres, literature generally reports differences in their average tensile properties. This work proposes a numerical investigation of the relationships between the morphological, biochemical and cell wall features, along with their variability, and the mechanical properties of flax and hemp fibres. A previously developed 3D micromechanical model of plant fibre is used to carry out a sensitivity analysis. Results show that the difference observed in the average tensile properties of flax and hemp fibres is partly due to the differences in scattering of some their morphological and ultrastructural properties. Despite a similar mean value, the reduced variability in the flax fibre features, seems to lead to higher average tensile properties.

In order to investigate the ultra-low cycle fatigue (UCLF) fracture in welded connections of high-strength steel (HSS) under earthquakes, this paper studies micromechanical fracture models ...