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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.

A micromechanical analysis under large deformations for iron-based composites is introduced to predict the deformation behavior of iron (Fe)-copper (Cu) composites. In particular, pure Fe, pure Cu, Fe-17 wt. $$\%$$ Cu, and Fe-83 wt. $$\%$$ Cu are studied. In Fe-Cu composites, Cu is a soft-phase material. Hence, it undergoes a large deformation. Fe being the hard phase material shows elevated stresses. Because of the heterogeneity in the microstructure of Fe-Cu composites, the micromechanical model enables the capture of the flow behavior of Fe-Cu polycrystals. Both Fe and Cu constituents are rate-dependent elasto-viscoplastic materials. Hence, they are formulated in the framework of large deformations. The reliability of the prediction of flow behavior is investigated by comparing the numerical model (Taylor approach) and experiments.

The effect of NiTi alloy long wires on the viscoelastic behavior of epoxy resin was investigated by utilizing the dynamic mechanical analysis (DMA) and a novel micromechanical model. The present model is capable of predicting the viscoelastic properties of the shape-memory-alloy (SMA) reinforced polymer as a function of the SMA volume fraction, initial martensite volume fraction, pre-strain level in wires, and the temperature variations. The model was verified by conducting experiments. Good agreement between the theoretical and experimental results was achieved. A parametric study was also performed to investigate the effect of SMA parameters. According to the results, by the addition of a small volume fraction of SMA, the storage modulus of the composite increases significantly, especially at higher temperatures. Moreover, applying a 4% pre-strain caused a 10% increase in the maximum value of the loss factor of the SMA reinforced epoxy in comparison with the 0% pre-strained SMA reinforced epoxy.

Accepted: 2020-04-17, 資料番号: PA2120035000

A computational strategy based on the finite element method for simulating the mechanical response of arterial tissues is herein proposed. The adopted constitutive formulation accounts for rotations of the adventitial collagen fibers and introduces parameters which are directly measurable or well established. Moreover, the refined constitutive model is readily utilized in finite element analyses, enabling the simulation of mechanical tests to reveal the influence of microstructural and histological features on macroscopic material behavior. Employing constitutive parameters supported by histological examinations, the results herein validate the model’s ability to predict the micro- and macroscopic mechanical behavior, closely matching previously observed experimental findings. Finally, the capabilities of the adopted constitutive description are shown investigating the influence of some collagen disorders on the macroscopic mechanical response of the arterial tissues.

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 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.

A nested analytical method, a product of combining two micromechanical models is developed in this study. The proposed micromechanical method predicts the relaxation properties of polymer hybrid nanocomposites containing linearly visco-elastic matrix, transversely isotropic elastic carbon fibers, and graphene nanoplatelets. Calculations performed in this model are of two scales. The small scale, which is the domain of epoxy resin and graphene nanoplatelet interactions, and the large scale, which assumes the small scale as a homogenized isotropic matrix. In the large scale, the prescribed matrix is then reinforced by the unidirectional CFs. Each scale calculation gives the properties of the underlying material. Secant moduli and the field fluctuation techniques are adopted in this study. Resulting explicit formulae allows one to calculate the overall relaxation moduli of the graphene nanoplatelet/carbon fiber-reinforced polymer hybrid nanocomposites. By comparing the data obtained by experiments and the results extracted by the proposed micromechanical approach, the accuracy of the model becomes apparent. Addition of graphene nanoplatelets into the fibrous composites leads to an improvement in the relaxation properties of the hybrid nanocomposites. Also, the elastic properties of graphene nanoplatelet/carbon fiber-reinforced epoxy hybrid nanocomposites are reported. The role of graphene nanoplatelet agglomeration, frequently encountered in real engineering situations, in the mechanical response of unidirectional hybrid nanocomposites is examined. The effects of volume fraction of graphene nanoplatelets and CFs on the overall mechanical properties are investigated.

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.

Effective elastic modulus for the three different types of composites are calculated by using micromechanical approach. Three different types of unidirectional composites: AS4/3501-6, E-glass/MY750 and AS Carbon/epoxy are taken in the present analysis. Micromechanical model, an efficient tool for evaluation of the overall properties of the composite materials are used to determine the elastic modulus. Finally the present results obtained from micromechanical approach are compared and validated with experimental data available in the literature

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.

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...

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.

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

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 proposes a three-dimensional micromechanical model for evaluation of effective thermal conductivity of multiphase composite materials with periodic microstructure. The model consists in an extension of the parametric finite-volume theory which has demonstrated to be a promising tool for the analysis and homogenization of multiphase heterogeneous solids. The applicability and performance of the proposed formulation are examined through the solutions of different numerical examples of two- and three-phase composites. Such examples consist of composites reinforced with unidirectional solid and hollow long fibers and aligned short fibers. In order to verify the effectiveness of the model, its predictions are compared with analytical and finite-element results, as well as experimental data. The results indicate that the proposed model is efficient and accurate in predicting the effective thermal conductivity of periodic composites and can be seen as a competitive alternative to other existing procedures based on traditional numerical tools like the finite element method.

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.

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 Ti2Cu, 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.

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.

Some manufacturing processes of polymeric materials, such as injection molding or film blowing, cause the final product to be highly anisotropic. In this study, the mechanical behavior of drawn polyethylene (PE) tapes is investigated via micromechanical modeling. An elasto-viscoplastic micromechanical model, developed within the framework of the so-called composite inclusion model, is presented to capture the anisotropic behavior of oriented semicrystalline PE. Two different phases, namely amorphous and crystalline (both described by elasto-viscoplastic constitutive models), are considered at the microstructural level. The initial oriented crystallographic structure of the drawn tapes is taken into account. It was previously shown by Sedighiamiri et al. (Comp. Mater. Sci. 2014, 82, 415) that by only considering the oriented crystallographic structure, it is not possible to capture the macroscopic anisotropic behavior of drawn tapes. The main contribution of this study is the development of an anisotropic model for the amorphous phase within the micromechanical framework. An Eindhoven glassy polymer (EGP)-based model including different sources of anisotropy, namely anisotropic elasticity, internal stress in the elastic network and anisotropic viscoplasticity, is developed for the amorphous phase and incorporated into the micromechanical model. Comparisons against experimental results reveal remarkable improvements of the model predictions (compared to micromechanical model predictions including isotropic amorphous domains) and thus the significance of the amorphous phase anisotropy on the overall behavior of drawn PE tapes.

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.

In the present study the Hu-Cocks micromechanical model [1,2] for dislocation-obstacle interactions, implemented in a crystal plasticity self-consistent model, is employed to simulate thermo-mechanical histories typical for AGR nuclear plants in order to assess the implications of creep-fatigue interactions in 316H stainless steel. Their physical model is enhanced by including the effect of dynamic recovery, which introduces a new material parameter – the annihilated segment length ΔLr. The full model contains five independent material parameters; other parameters are prescribed by the fundamental physics of inelastic deformation processes. Having calibrated the model, we explore its ability to predict material response under complex loading histories to provide insight into the physical phenomena controlling cyclic-creep interactions. Introduction of strain dwells during cyclic loading results in an increase of the extent of relaxation with an increasing number of cycles, but histories with dwells at different strain levels indicate that relaxation is strongly dependent on initial stress and level of constant strain. Predictions of history-dependent relaxation demonstrate that the least stress relaxation results after creep into the secondary regime and the largest stress drop results during hold-dwells after monotonic elastic-plastic loading, with the cyclic-dwell history behaviour laying in between these two. Both prior cycling and the generated residual stress field are found to affect the primary creep regime under hold-stress dwells. These results are consistent with experimental observations; this demonstrates that deformation response is dependent on both the evolution of microstructural state and redistribution of stress between the grains of the polycrystalline aggregate.

In this research, we developed a four-phase model, which takes the aggregate gradation and porosity into account in the prediction of the elastic modulus of concrete, based on the micromechanical theories. The model has been verified with experimental results. First, using the Mori Tanaka and the differential self-consistent (DSC) methods, the pores in both the mortar and interfacial transition zone (ITZ) were homogenized. Then, the continuously graded aggregates were divided into finite aggregate size intervals. Further, using the generalized self-consistent model and multiphase composite model derived from the Mori Tanaka method, an aggregate gradation model for the prediction of the elastic modulus of concrete was developed. By simulating the pores in concrete with expanded polystyrene sphere (EPS) grains, the effect of overall porosity on the elastic modulus of concrete was investigated. The research results show that aggregate gradation and porosity have remarkable influence on the elastic modulus of concrete, and the proposed model is effective to estimate the elastic modulus of concrete, the deviation between the predicted elastic modulus and experimental elastic modulus is less than 8%. The elastic modulus decreases with increasing ITZ porosity. However, for ITZ porosity exceeding 40%, the decrease in the elastic modulus is large with increasing ITZ porosity. For a fixed overall porosity, the ITZ porosity owned more influences than the mortar porosity on the elastic modulus of concrete. Enhancing the ITZ elastic modulus and decreasing the ITZ thickness are efficient in increasing the elastic modulus of concrete.

Hydration induces significant structural rearrangements in biopolymer aerogels, resulting in a completely different mechanical behaviour compared to the one in the dry state. A network decomposition concept was earlier introduced to account for these changes, wherein the material network was decomposed into an open-porous aerogel one and a hydrogel-like one. Recent experimental evidences have supported this idea of the formation of a hydrogel-like network. Using these observations as a basis, in this paper, we present a micromechanical model describing the effect of hydration on the structural and mechanical properties of aerogels. The aerogel network is modelled based on the mechanics of their pore-walls, while the hydrogel-like network is modelled based on the statistical mechanics of their polymer chains by means of the Arruda-Boyce eight-chain model. The influence of diverse structural and material parameters on the mechanical behaviour is investigated. The effect of different degrees of wetting, from a pure aerogel to a pure hydrogel-like state, is captured by the model. The results are shown to be in good agreement with available experimental data.

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.

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.

Electroactive polymers with time-dependent behavior are considered in the present paper by way of a new physics-based micromechanical model; such viscoelastic response is described by the internal evolution of the polymer network, providing a new viewpoint on the stress relaxation occurring in elastomers. The main peculiarity of such internally rearranging materials is their capacity to locally reset their reference stress-free state, leading to a mechanical behavior that relaxes out (eases off) an induced stress state and that can thus be assimilated to a sort of internal self-healing process. Such high deformability and recoverability displayed by dynamically cross-linked polymers can be conveniently exploited when they are coupled in electromechanical problems; the deformation induced by an electric field can be easily tuned by the intensity of the electric field itself and the obtained shape can be maintained without any electric influence once the material microstructure has rearranged after a sufficient curing time. In the present paper, both features of the polymeric material, that is, internal remodeling and electromechanical coupled response, are considered and a theoretical framework is established to simulate representative boundary value problems.

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.

In this study a novel mesh algorithm is introduced to investigate the elastic properties of Polymer Nano-composite (PNC) materials based on the scaled boundary finite element method (SBFEM). The proposed procedure is applied efficiently with very simple mesh and few degrees of freedom compared to the classical finite element method. First, the nanoparticles are randomly distributed within the epoxy matrix to numerically shape the geometry of composite material. Second, a flexible sub-structuring technique in accordance with the random distribution is utilized to model the variation in material and geometry. Next, The interphase of nanoparticles is integrated properly by the new sub-domains generated from the algorithm. Finally, the elastic properties of the material are estimated. The result based on SBFEM showed full agreement with FEM predictions and the corresponding experimental measurements obtained from the literature.

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.

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...

In unidirectional laminated composites, fiber bridging as a toughening mechanism has a significant effect on the behavior of mixed mode I/II delamination. In the present paper, effects of fiber bridging and related micro-mechanisms were investigated quantitatively. To this end, a novel micromechanical model called “mixed mode I/II micromechanical bridging model” was proposed based on the calculation of the delamination crack bridging zone energy absorption. Firstly, different failure micro-mechanisms, occurring during the fiber bridging process, were identified. Then, different loading conditions on the bridged fibers were applied. In the next step, the absorbed energy of each failure micro-mechanisms was calculated. Finally, the energy absorbed by the fiber bridging zone was obtained by summation of the absorbed energy of each failure micro-mechanisms. The traction-separation behaviors in both the normal and tangential directions of the crack plane are the outcome of the proposed model. Moreover, the mixed mode I/II delamination failure response of the laminated composite was extracted by plotting GI versus GII and compared with the available experimental data. The results show that the proposed model is able to predict the mixed mode I/II delamination behavior of laminated composites considering fiber bridging effects.

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.

The safety level in advanced load bearing applications can be enhanced if the material would be able to detect the in-service deformation, allowing a real time evaluation of the reliability state of the components. Polymeric materials can be used to get such a functionality through the insertion of so-called mechanophore units, whose main property is to chemically respond to mechanical stimuli. In the present paper, a micromechanical approach is developed to model the response of polymers containing reporting units, whose activation is triggered by the deformation of the underneath network or by a chemical stimulus. The model, through an Arrhenius-like equilibrium reaction law, provides a quantitative evaluation of the fraction of stress-activated molecules. Moreover, if the mechanophore activation involves also a change in their geometrical conformation, it influences the network deformation and the corresponding mechanical effects must be also accounted for. The formulated micromechanical model is presented and implemented in a FE code in order to simulate structural elements made of a self-diagnostic material. In particular, we consider the fluorescence-based strain detection of pre-cracked elements made of polymers with supramolecular complexes cross-linked to the polymer’s chains; the fluorescence intensity is assumed to be proportional to the volume fraction of the activated units, thus enabling to quantify the associated material’s strain value.

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.

The effect of embedded shape memory alloy (SMA) wires on the fracture behavior of epoxy resin was studied. A micromechanical model was developed to predict the double cleavage drilled compression (DCDC) test results for SMA reinforced epoxy specimens. The DCDC tests were performed on SMA reinforced epoxy and the fracture behavior of specimens with different crack lengths was investigated. The experimental tests were conducted on the specimens with 1%, 2% and 4% pre-strain levels in order to investigate the enhancement of crack growth resistance ( K R ) in the epoxy polymer. The effects of SMA wire diameter, temperature change and applied pre-strain level on the fracture behavior of SMA reinforced epoxy were studied using the present model. The results showed a 67% increase in the changes in the crack growth resistance ( K R ) in 1% pre-strained SMA reinforced epoxy subjected to temperature change from 25 °C to 65 °C. This improvement was 38% and 16% for the 2% and 4% SMA pre-strained reinforced epoxy, respectively. The results also revealed that, at constant temperature (T = 65 °C), 2% and 4% pre-strains improved ( K R ) of epoxy by 2 and 4 times, respectively, in comparison with the case of 1% pre-strained wires. The effect of the interface region between SMA wires and epoxy was also discussed in the present study.

The interfacial failure behavior of sisal fiber-reinforced composites (SFRCs) was studied experimentally and theoretically. The residual pull-out strength of the SFRCs was observed to gradually decrease during the single sisal fiber pull-out test, after which the SFRCs presented multiple failure modes, including at the interface between technical fiber and matrix and at the interface between elementary fibers. To further investigate the failure mechanisms of SFRCs, using the traditional shear lag model, a double-interface model tailored to the unique multi-layer interface structure of plant fibers was developed to describe the fiber pull-out behavior and the interfacial adhesion status of single plant fiber-reinforced composites (PFRCs). By comparison with other existing models, using the experimental applied stress as reference, the proposed double-interface model was found to provide a more accurate quantitative theoretical prediction of the interfacial failure behavior of PFRCs during multi-stage fracture of the two interfaces.

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.

Cemented particulate composite is a kind of composite material with high strength, high energy absorption, and multifunctional characteristics, which is widely used in engineering practice. The calculation of the mechanical properties of granular composites based on theoretical methods has always been a topic of discussion. A micromechanical model with a three-dimensional rigid beam-spring network (3D-RBSN) is proposed here. The stiffness matrix of the model was calculated theoretically. The model was applied to the analysis of the mechanical properties of composites material with glass beads and epoxy resin. The results indicate that the 3D-RBSN model can effectively predict the mechanical properties of composite materials, such as Young’s modulus and Poisson’s ratio. Furthermore, the damage evolution process of cemented particulate composite with initial defects was analyzed based on the 3D-RBSN model.

The laminate load bearing capability is often compromised when delamination occurs even though the laminae remain intact. The out-of-plane components of the stress tensor, defined at the interfaces between plies, are typically responsible for the delamination of multi-layered materials. Commonly used failure criteria for delamination make use of both shear and normal interlaminar stresses. In this work the out-of-plane stresses inside a woven laminate were numerically evaluated using a micromechanical model. Under three point bending the existence of local normal interlaminar stress related to the fabric architecture was demonstrated. The influence of the due to texture normal interlaminar stress on the fracture occurrence was discussed. The reduction of the apparent interlaminar shear strength as effect of the span-to-depth ratio increase was successfully reproduced introducing a dependence of the delamination shear limit from the stress triaxiality gradient.

There is a demand for multi scale micromechanical models to disclose and analyze the effects of microstructure on macro mechanical properties of hybrid fiber reinforced concrete (HFRC). This study involved presenting a multi-level micromechanical model that involves cement paste level, concrete level, and hybrid fiber reinforced concrete level to quantitatively predict the effective isotropic and elastic properties of HFRC under ambient temperature. For the purposes of homogenization, the volume fractions of different phases at different levels are determined by means of a modified Power’s model. In the multi-level micromechanical model, hydration products of clinker, sand, coarse aggregate, and hybrid fiber are comprehensively considered. A homogenization stepping framework is presented to realize upscaling from microstructural properties to the effective elastic properties of a macrostructure for HFRC. Additionally, several substepping homogenizations are also presented to estimate the effective elastic properties of an equivalent medium with respect to the cement paste and hybrid fiber reinforced concrete. Comparisons with experimental data from extant studies are implemented level by level. Subsequently, the influences of aggregate, sand, fiber type, and hydration degree on the properties of HFRC are discussed based on a proposed multi-level micromechanical model. Finally, the mixture ratio of steel fiber and w/c are investigated with respect to the HFRC design to obtain anticipated elastic properties.

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.

Inter-particle effect and imperfect interface are the two major challenges during the micromechanical modeling of asphalt mixture due to its complex heterogeneity. This paper presents the development and validation of a micromechanical model regarding this concern. The linear spring model is adopted to simulate the imperfect interface between asphalt mortar and aggregates, and the replacement procedure is established to incorporate the imperfect interface effect into the Ju-Chen (J-C) model to coupling inter-particle effect and imperfect interface. The proposed model is used to predict the dynamic modulus of asphalt mixture and analyze the influence of inter-particle effect and imperfect interface. The results show that the predictions decrease with the interface parameter m r / m θ but increase with parameter Y ( g ) . The imperfect interfacial bonding weakens the overall property of asphalt mixture and the weaken effect for composites with stronger inter-particle effect is more significant.

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.