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To investigate the fracture initiation mechanisms and establish the relationship between the ductile fracture mechanism and macro stress–strain for high-strength structural steel, the mechanical response and fracture behavior of Q460C steel and its butt welds were studied via tests, numerical analysis and scanning electron microscopy (SEM) in this paper. The mechanical properties of high-strength steel (HSS) under different stress triaxialities were studied by uniaxial tensile tests on standard specimens and notched round rods. The finite element model is set up according to the characteristic length which is based on SEM observations. By combining experimental results and numerical simulations, the constitutive model and fracture prediction model were established. The relationship between the ductile fracture mechanism and the macro stress strain was obtained. The toughness parameters of the micromechanical model of Q460C steel and its welded joints were compared with those of Q345 steel and seven other types of structural steel from the United States and Japan. The results show that the characteristic length of the crack tip is the key factor affecting the accuracy of predicting fracture toughness under a large stress–strain gradient. The toughness predicted by the model is in good agreement with the traditional fracture toughness test results when taking the average value. The experimental results and finite element analysis verified the effectiveness of the VGM and SMCS micromechanical models in predicting the fracture toughness of Q460C steel and its welded joints, which can provide a theoretical basis and practical guidance for the anti-fracture design and application of HSS structures. [ABSTRACT FROM AUTHOR]

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Auxetic metamaterials have emerged as a class of advanced materials with exceptional physical and mechanical properties that are not typically found in conventional materials. This work mainly focuses on the buckling and free vibration of axially functionally graded (AFG) graphene origami (GOri)-enabled auxetic metallic metamaterial (GOEAM) beams. The beam is comprised of GOEAMs with GOri content varying through the beam length within different patterns to realize axially gradient-changing Young’s modulus, Poisson’s ratio and mass density. The material properties of AFG-GOEAMs are evaluated by using the micromechanical model including volume fraction and folding degree of GOri, geometric characteristics of graphene, material properties of matrix, and local temperature. The first-order shear deformation theory is employed to derive the governing equations via the state-space procedure, and then analytically solved with the discrete equilong segment model along beam length direction. The effects of GOri content, axial distribution pattern, folding degree and temperature on the buckling and free vibration of AFG-GOEAM beams are mainly focused on. The numerical results indicate that the development of auxetic metal metamaterials can be achieved by incorporating GOri into the metal matrix, leading to the tunable bucking and natural frequencies of AFG beams, which provide significant insights into the design of high-performance structures. [ABSTRACT FROM AUTHOR]

Nowadays, it is still a huge challenge to predict the interlaminar shear strength (ILSS) of three‐phase carbon fiber reinforced polymer (CFRP). Herein, the three‐phase micromechanical model is innovatively constructed to predict the ILSS of CFRP, and the conception of new matrix is proposed by establishing a connection between the third phase and the matrix, which effectively solves the problem of uneven distribution of the third phase. To verify the accuracy of the micromechanical model, the Ti3C2Tx MXene/CFf/epoxy composites were fabricated by the co‐blending, layer‐by‐layer assembly and hot‐pressing technology, and the finite element simulation analysis was also performed based on the micromechanical model. The results show that the micromechanical model possesses high accuracy. Specifically, the experimental value of ILSS of the composite with 1 wt% Ti3C2Tx MXene content is 52.12 MPa, and the errors of simulation value (56.64 MPa) and theoretical prediction value (58.69 MPa) are 8.67% and 12.61% MPa, respectively. Besides, the detailed fracture mechanism of the composite is presented based on the fracture morphology and simulation results. It is believed that this work will provide more possibilities for the prediction of the interlaminar shear performance of three‐phase composites. Highlights: A novel micromechanical model is used to predict the ILSS of three‐phase composite.The accuracy of the micromechanical model is verified by simulation and experiment.The main failure form of the Ti3C2Tx MXene/CFf/epoxy composite is matrix broken.The micromechanical model of the three‐phase composites has high accuracy. [ABSTRACT FROM AUTHOR]

AbstractIn this article, we organize a stretchable-thickness model to present a frequency analysis for a composite plate applicable in badminton court which is reinforced with origami graphene. A higher order kinematic model is extended in this work including three bending, shear, and stretching functions, where the stretching functions is responsible for satisfying the out of plane shear strains and stresses at top/bottom surfaces of the badminton equipment. The sport or composites plate is manufactured from a copper matrix reinforced with graphene origami where the effective material properties are calculated based on micromechanical models as a function of volume fraction and folding degree of graphene origami, material properties of matrix and reinforcement and temperature. The numerical results are presented with changes of volume fraction, folding degree of reinforcement, and thermal loading along the thickness direction. The main novelty of this work is accounting thickness stretching deformation for the analysis of a graphene origami reinforced plate and investigating the responses of graphene origami as a new reinforcement. A verification investigation is presented for approve of the methodology, and solution procedure. An investigation on the order of deformation is presented for various thickness ratio of the badminton sport plate. [ABSTRACT FROM AUTHOR]

AbstractThis paper studies the free vibration and harmonic response of Functionally Graded Graphene/Epoxy composite plates, considering the First Order Shear Deformation Plate Theory. The weight fraction of graphene variation along the thickness direction with graphene homogeneous dispersed in a polymer matrix. The effective Young Modulus of the plate is predicted by a new micro-mechanical model. The model includes the aspect ratio and weight fraction of nanoplatelets embedded into the matrix. The modal and harmonic of Graphene/Epoxy plates are obtained by the Boundary Element Method formulation for composite plates. The Young modulus calculated from the proposed micro-mechanical model highly agrees with those obtained from experimental results reported in the literature. Results demonstrate a high correlation of the micromechanical model with experimental results and other analytical models. Graphene weight fraction and ratio aspect increase the effective Young modulus of the composite. Boundary Element results show high agreement with Finite Element solutions. Numerical results for modal and harmonic analysis show concentrating graphene near the top and bottom surfaces of the plate is the most effective way to reinforce the plate for increased natural frequencies. The results demonstrate the BEM formulation and micromechanical model can be used as reliable engineering tools for the vibrational analysis of functionally grade graphene composite plates. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced cement-based material incorporating hollow glass beads (GFRC-HGB) is an innovative lightweight building material with exceptional energy-saving properties. Based on the framework of variational asymptotic homogenization theory, a micromechanical model is developed for predicting the effective elastic properties and recovering the local fields of unidirectional GFRC-HGB. This model starts with expressing the displacements of the heterogeneous GFRC-HGB in terms of those of the corresponding homogeneous material and fluctuation function. Then, the principle of minimum potential energy is used along with variation asymptotic method to formulate the governing variational statement for the micromechanics model, the micromechanical model is used to quantitatively investigate the influence of internal structural parameters of HGB on the elastic properties of unidirectional GFRC-HGB. The numerical results demonstrate the effectiveness and accuracy of the micromechanical model in predicting the effective elastic modulus and local fields. The numerical simulation and SEM images of the tensile fracture prove that the local stress distributions are closely related to the loading direction, and the transverse deformation is restrained by glass fibers. [ABSTRACT FROM AUTHOR]

The object of study is the vertical wave propagation in a sand deposit. This paper is aimed at analyzing the vertical wave propagation in a sand deposit through micromechanical modeling that inherently takes account of intergranular slips during deformation. Such a problem, which is part of the general framework of wave propagation in the soil, has long been analyzed using continuum models based on approximate behavior laws. For this purpose, a 2D Discrete Element Method (DEM) model is developed. The DEM model is based on molecular dynamics with the use of circular shaped elements. The intergranular normal forces at contacts are calculated through a linear viscoelastic law while the tangential forces are calculated through a perfectly plastic viscoelastic model. A model of rolling friction is incorporated in order to account for the damping of the grains rolling motion. Different boundary conditions of the profile have been implemented; a bedrock at the base, a free surface at the top and periodic boundaries in the horizontal direction. The sand deposit is subjected to a harmonic excitation at the base. Using this model, the fundamental and resonance frequencies of the deposit are first determined. The former is determined from the low-amplitude free vibration and the latter by performing a variable-frequency excitation test. It is noted that there is a significant gap between the two frequencies, this gap could be attributed to the degradation of the soil shear modulus in the vicinity of the resonance. Such degradation is well proven in classical soil dynamics. The effects of deposit height and confinement on resonance frequency and free-surface dynamic amplification factor are then investigated. The obtained results highlighted that the resonance frequency is inversely proportional to the deposit’s thickness whereas the dynamic amplification factor Rd increases with the deposit’s thickness. In the other hand, when the confinement increases the deposit becomes stiffer, which results in reducing the amplification. Such result is in accordance with theoretical knowledge which states that the most rigid profiles such as rocks do not amplify seismic movement. [ABSTRACT FROM AUTHOR]

The existing micromechanical damage plasticity models assume that penny-shaped microcracks are present in the rocks, but it is seldom a reality. These models result in the abstract values of the damage variable. It is fundamentally due to the assumption of penny-shaped microcracks. To overcome this limitation, we have modified the micromechanical damage plasticity model such that the damage variable obtained from the proposed constitutive model relates to the measured damage from the recorded Acoustic Emission (AE) signals. This research presents a micromechanical coupled damage plasticity model by utilising AE data to predict the nonlinear mechanical response of intact rocks under Conventional Triaxial Compression (CTC) loading. The novelty of the proposed model is that it overcomes the limitation of penny-shaped microcracks and accounts for arbitrarily shaped microcracks by using a phenomenological approach. The applicability of the proposed model is shown by different rocks originating from varying geology. We have modelled the nonlinear mechanical behaviour of rock salt and coal (sedimentary rocks), tuff (soft igneous rock), and marble (hard metamorphic rock). The model performance is verified by comparing the results with the test data using the coefficient of determination (R2) statistical parameter. The proposed model predicts well the experimental data of damage variables with strain. It also successfully presents both strain hardening and softening behaviour of the rocks. Highlights: The article contributes to the modification of the micromechanical coupled damage plasticity model such that the damage variable of the model relates to the experimentally obtained damage by Acoustic Emissions. The proposed model uses a phenomenological approach to account for arbitrarily shaped microcracks in the micromechanical coupled damage plasticity constitutive model. The proposed model is verified on different rocks with diverse geological genesis, such as rock salt, coal (sedimentary rocks), tuff (soft igneous rock), and marble (hard metamorphic rock) under uniaxial and triaxial compression loading conditions. [ABSTRACT FROM AUTHOR]

In this study, the simulation of a vacuum forming process employing a micromechanical inspired viscoelastic–viscoplastic model is investigated. In the vacuum forming process, a plastic sheet is heated above the glass transition temperature and subsequently forced into a mold by applying a vacuum. The model consists of a generalized Maxwell model combined with an dissipative element in series. Each Maxwell element incorporates a hyperelastic element in series with a viscous element based on a hyperbolical law. While the generalized Maxwell model considers the relaxation due to molecular alignment, the additional viscous element is a modification based on the approach of Bergström and thus considers molecular chain reptation. The model is designed with the aim to converge to the generalized linear Maxwell model in the limit of small deformation. Furthermore, the viscous modeling is temperature activated and follows the Williams–Landel–Ferry approach in the limit of linear viscoelasticity. To simulate rheological standard experiments, a physical‐network‐based implementation into Simscape is presented. To validate the performance of the model in thermoforming, it is implemented into Fortran programming language for finite element simulation with Abaqus/Explicit. It can be shown that the simulation is able to predict the thickness in high correlation with experimental results. [ABSTRACT FROM AUTHOR]

The present research focuses on proposing a novel theoretical micromechanical model (TMM) designed to derive the frequency-dependent storage and loss moduli of woven fabric (WF)-matrix composites, as well as WF-particulate matrix (Hybrid) composites, based on their constituent properties. The TMM serves as a higher-order modulus operator, accounting for the composite woven fabric unit cell geometry and the effective modulus of both the fabric and matrix using equivalent modulus theory. This model also incorporates viscoelastic parameters obtained from literature and experiments for each constituent, namely woven glass fabric and SiC particles embedded in an epoxy matrix. The proposed TMM is validated by comparing its predictions of the frequency-dependent storage modulus and loss factor with experimental data acquired through dynamic mechanical analyzer tests on samples with varying fiber and particulate volume fractions. To address the inherent complexities of the higher-order modulus operator, the model is streamlined into a lower-order form expressed as a function of two separate variables: volume fraction and a differential time operator. This advancement enhances the applicability and usability of the model for predicting the mechanical behaviour of these complex composite materials. This novel mathematical model eliminates the cost and time for conducting the explicit experiments as well as can be applied to different range of similar hybrid composites considering the fact that the constituent properties are known. [ABSTRACT FROM AUTHOR]

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

Carbon fiber reinforced polymer composites (CFRPC) are being used as primary structures in many applications. However, unlike metallic materials, they are susceptible to damage by lightning strikes. When lightning strikes, due to its poor electrical conductivity, the composite material generates localized resistive heating near the strike area. This resistive heat causes elevated temperatures near the strike area, which leads to material property changes and the structural material's stiffness and strength reduction. As part of this study, a finite element (FE)-based coupled electro-thermo-mechanical modeling approach was adopted to simulate the effect of lightning strikes on a unidirectional (UD) carbon fiber reinforced polymer composite model to predict the residual compressive strength of the material. In the current study, a two-dimensional (2D), micromechanical finite element model of CFRPC was used to quantify its residual compressive response when subjected to simulated lightning strikes with different peak currents using the software ABAQUS. The normalized residual compressive strengths for various peak currents obtained from the proposed electro-thermo-mechanical model were compared with the available experimental data from the literature. The effectiveness of an electrically conductive protective coating in minimizing the compressive strength reduction was also evaluated. Further, the optimum electrical conductivity of the coating in terms of the matrix conductivity, for maintaining the desired compressive strength was also estimated. Furthermore, the effect of change in thickness of the conductive coating in compressive strength change was evaluated by considering two different coating thicknesses. The results show that for a given peak current, the thinner coating will not compromise the compressive strength as long as the conductance of the thin and thick coating is the same. [ABSTRACT FROM AUTHOR]

This paper presents a constitutive model for the behavior of steel fiber reinforced concrete (SFRC) under mixed mode cracking taking into account the fiber orientation effect by using a micromechanical approach. Firstly, the resistant mechanisms of an inclined fiber are modeled by a closed-form analytical function. The bridging force is calculated by integrating on the cracked surface, the product of the fiber extraction force by its orientation probability. A modified model of the aggregate interlock mechanism is combined with the fiber bridging stresses to obtain the cohesive stresses. This mesoscale model is then extended using an elastic damage model and a fixed smeared cracking concept to assess the structural behavior. The model is finally implemented in a Finite Element Analysis (FEA) software, its performance is tested with some experimental results collected in the literature. The model successfully integrates the fiber orientation effect and shows a good prediction of stress transmission. [ABSTRACT FROM AUTHOR]

This work applies a higher order thickness-stretched model for the electro-elastic analysis of the composite graphene origami reinforced square plate sandwiched by the piezoelectric/piezomagnetic layers subjected to the thermal, electric, magnetic and mechanical loads. The plate is manufactured of a copper matrix reinforced with graphene origami where the effective material properties are calculated based on the micromechanical models as a function of volume fraction and folding degree of graphene origami, material properties of matrix, reinforcement, and local temperature. The governing equations are derived using the virtual work principle in terms of the bending, shear and stretching functions, in-plane displacements, electric, and magnetic potentials. The numerical results including various displacement components, maximum electric, and magnetic potentials are presented with changes of volume fraction, folding degree of reinforcement, electrical, magnetic, and thermal loading. A verification investigation is presented for approve of the methodology, and the solution procedure. The main novelty of this work is simultaneous effect of the thickness stretching and the multi-field loading on the electromagnetic bending results of the sandwich plate. Another novelty of this work is usage of graphene origami nano-reinforcement as a controllable material in a sandwich structure subjected to multi-field loadings. The results show an increase in bending, shear, and stretching deflections with an increase in electromagnetic loads, and folding degree as well as a decrease in volume fraction of reinforcement.

The use of organically modified clays as nano-reinforcement in polymer matrices is widely investigated owing to their remarkable reinforcement at low filler loading. In this body of work, the nanocomposites were prepared by melt blending nanoclay with polyamide 11 (PA 11) utilising a twin-screw extruder in order to maximise the dispersion of clay particles within the matrix during compounding. The main aim of the work was to study the reinforcing effect of nanoclay within PA 11 using two micromechanical model namely Halpin-Tsai and Mori-Tanaka composite theories. These theories were used to predict the effective tensile modulus of PA 11 nanocomposites and the results were compared to the experimental data. In addition, the Halpin-Tsai model was used to predict the storage modulus and heat distortion temperature (HDT) of PA 11 nanocomposites. It was found that the tensile modulus for nanocomposites with a high clay aspect ratio exhibits up to 10% higher when compared to the nanocomposites with lower clay aspect ratio. Thus, it is believed that the combination of clay aspect ratio and modulus contributes to the super reinforcing effect of nanoclay within the PA 11 matrix.

On the example of metal-diamond composites (MDC), a number of issues of thermomechanics of disperse-filled materials with high thermal conductivity used for thermal management are formulated and solved. Due to the importance of the thermal conductivity factor of the interfacial layer, a refined method is proposed for calculating the boundary thermal resistance. This method considers two counter heat flows: from the matrix to the filler and back, and also provides the condition of zero thermal resistance at the same values of the thermomechanical characteristics of these components. Based on the micromechanical model of the disperse-filled composite, an analytical method is developed for determining the effective thermal conductivity coefficient of the metal-diamond composites. The method makes it possible to take into account the boundary thermal resistance, the presence of a thin coating on the diamond particle, the anisometry of diamond particles and the porosity of the metal matrix. The results of the performed parametric analysis are compared with known experimental data and estimates obtained within the framework of existing models. The conclusion on the validity of the developed method is made. A simplified finite-element model is developed for a representative volume of the metal-diamond composites in the form of a cube formed by an aluminum matrix and containing 27 spherical diamond particles of the same radius with a modifying tungsten coating. At a given temperature difference on the opposite faces of the cube, the distribution of heat flux density and the effective heat transfer coefficient of the metal-diamond composites are calculated. Comparison of the results of using the finite element model and the analytical method mentioned above shows their good agreement. Modification of the finite element model is carried out in order to better match the real internal structure of the metal-diamond composites studied by high-resolution X-ray microtomography. Numerical analysis of the temperature field, thermal stress state and fracture kinetics of the aluminum-diamond composite during thermal cycling is performed.

Composite driveshafts have emerged as a potent substitute for traditional driveshafts because of their excellent strength-to-weight and stiffness-to-weight ratios. At the same time, usage of multi-walled carbon nanotubes (MWCNTs) as a reinforcement has gained a great momentum due to their superb mechanical, electrical, and thermal characteristics. In this work, a micromechanical model combining the rule of mixtures and the Halpin-Tsai (H-T) model was used to calculate elastic constants of MWCNTs-added carbon fiber reinforced epoxy resin. This micromechanical model considers the effect of agglomeration, aspect ratio, waviness, and random orientation of MWCNTs. Elastic constants of MWCNTs/epoxy resin calculated by using micromechanical model was compared by experimental results available in the literature. Moreover, finite element analysis (FEA) was carried out to predict the critical torsional buckling load of composite driveshafts for various MWCNTs concentrations and fiber orientation angles. The FEA results were compared with the results obtained theoretically. The results showed that Young's modulus of MWCNTs/epoxy resin calculated by using the micromechanical model follows the experimental findings. When compared to pure carbon fiber-reinforced epoxy resin, E1, E2, E12, and G23 (elastic constants of composite lamina) showed improvements of 0.66%, 27.80%, 49.02%, and 37.50%, respectively, in the case of 10vol.% MWCNTs addition. The ply orientation angle has a more dominant effect on Tcr than the Doi: 10.24012/dumf.1336638 MWCNTs concentration. [ABSTRACT FROM AUTHOR]

The use of organically modified clays as nano-reinforcement in polymer matrices is widely investigated owing to their remarkable reinforcement at low filler loading. In this body of work, the nanocomposites were prepared by melt blending nanoclay with polyamide 11 (PA 11) utilising a twin-screw extruder in order to maximise the dispersion of clay particles within the matrix during compounding. The main aim of the work was to study the reinforcing effect of nanoclay within PA 11 using two micromechanical model namely Halpin-Tsai and Mori-Tanaka composite theories. These theories were used to predict the effective tensile modulus of PA 11 nanocomposites and the results were compared to the experimental data. In addition, the Halpin-Tsai model was used to predict the storage modulus and heat distortion temperature (HDT) of PA 11 nanocomposites. It was found that the tensile modulus for nanocomposites with a high clay aspect ratio exhibits up to 10% higher when compared to the nanocomposites with lower clay aspect ratio. Thus, it is believed that the combination of clay aspect ratio and modulus contributes to the super reinforcing effect of nanoclay within the PA 11 matrix. [ABSTRACT FROM AUTHOR]

Large-scale 3D printed concrete structures with lattice infill will result in lightweight components with high mass-specific strength, and faster fabrication, compared to conventional casting methods. However, the effect of different infill patterns on mechanical performance is still not addressed clearly in many scientific publications. This study investigates the bending performance of 3D-printed concrete beams with four infill patterns such as lattice, triangular, lattice-triangular, and sinusoidal tested in vertical (layer deposition direction) and transverse (layer translation direction) loading directions. The load versus displacement curves and crack propagation patterns are investigated both via Finite Element (FE) simulations and experiments. The FE results corroborated by experiments indicated that the triangular patterns perform better than lattice-shaped infill counterparts particularly under the transverse loading direction exhibiting the highest flexural deformation resistance capacity. The findings of this study would be useful in latticing large-scale concrete structures for diverse applications.

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

The prediction of shear strength of unsaturated soils remains a significant challenge due to their complex multi-phase nature. In this paper, a review of prior experimental studies is first presented in order to outline important pieces of evidence, limitations and some design considerations. Then, an overview of existing shear strength equations is summarised, with a brief discussion. A micromechanical model with stress equilibrium conditions and multi-phase interaction considerations is presented to provide a new equation for predicting the shear strength of unsaturated soils. The validity of the proposed model is examined using published shear strength data for different soil types. The shear strength predicted by the analytical model was found to be in good agreement with the experimental data and to provide high performance in comparison with existing models. Evaluation of the results using two criteria – the average relative error and the normalised sum of squared error – proved the effectiveness and validity of the proposed equation. Using the proposed model, a non-linear relationship between shear strength, saturation degree, volumetric water content and matric suction was observed. [ABSTRACT FROM AUTHOR]

Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a piezoelectric semi-crystalline polymer whose electro-mechanical properties may be modulated via strain-induced α → β phase transition and the incorporation of polarized inorganic particles. The present work focuses on the constitutive representation of PVDF-based piezo-composites developed within the continuum-based micromechanical framework and considering the combined effects of particle reinforcement, α → β phase transition, and debonding along the interface between the PVDF matrix and the particles under increasing deformation. The micromechanics-based model is applied to available experimental data of PVDF filled with various concentrations of barium titanate (BaTiO3) particles. After its identification and predictability verification, the model is used to provide a better understanding of the separate and synergistic effects of BaTiO3 particle reinforcement and the micromechanical deformation processes on the electro-mechanical properties of PVDF-based piezo-composites. [ABSTRACT FROM AUTHOR]

Nano-reinforced composites have a wide range of useful applications thanks to their exceptional all-encompassing characteristics. Understanding the micromechanical model and the reinforcing process in nano-composites is crucial for a quantitative assessment of the reinforcement impact of nano-fillers and performance optimization. The original micromechanical model for common composite materials is no longer applicable since mechanical modeling of composite materials takes into consideration variables like multi-scale, multi-phase, and multi-morphology. The multi-scale parameter equivalent modeling theory of nano-reinforced composites is examined in this work. It is suggested to use a generalized modified Halpin-Tsai micromechanical model, which may accommodate any reinforcement form, size, or orientation, after theoretical and experimental comparison and verification. A tiny sample of the nano-reinforced composite material's mechanical tensile characteristics was examined, and its microscopic.

Photopolymerization, based on light-induced radical polymerization, is nowadays exploited in additive manufacturing (AM) technologies enabling to achieve high dimensional quality. The mechanical properties of the obtained material are heavily dependent on the chemistry of the photopolymer and on the way the AM process is performed. Here we study, through experiments and theoretical modeling, how the mechanical properties of liquid crystal shutter (LCD) printed photopolymers depend on the printing process setup, namely UV exposure time and layer thickness. To this end, a multi-physics simulation tool considering the light diffusion, chemical kinetics, and the micro-mechanics at the network level, has been developed. [ABSTRACT FROM AUTHOR]

Time-dependent nonlinear lateral vibrations of plates composed of a hyperelastic matrix and uniformly/nonuniformly distributed hyperelastic reinforcing inclusions are studied. Since the material constants of a hyperelastic must be extracted from the whole slope-varying stress-strain curve rather than a single slope, choosing power/exponential distributions for the material constants or using Voigt's rule of mixtures is quite wrong. The neo-Hookean and Mooney-Rivlin constitutive models are adopted, and their results are compared. Another hint is incorporating the incompressibility condition. The governing equations of motion are derived by using Hamilton's principle, a new energy-equivalence-based micromechanical model that can be employed for reinforcing phases with nonlinear constitutive laws, and von K'arm'an assumptions in the left Cauchy-Green deformation tensor, and solved by incorporation of an updating finite-element and Newmark's techniques. Not only the displacement but typical stress results are also reported here. Results show that the neo-Hookean model overestimates the rigidity in comparison to the Mooney-Rivlin model, and unlike the elastic plates, the effect of the stiffer phase is more remarkable in the uniform distribution in comparison to the nonuniform distribution of the stiffening materials because the magnitudes of the tensile stresses of the hyperelastic plate are much larger than that of the bending stresses. [ABSTRACT FROM AUTHOR]

This paper presents a novel and efficient micromechanical framework for finite element simulation of damage and failure in 3-D printed aligned discontinuous fiber-reinforced composites. The framework can predict the initiation and propagation of different types of damage in the composite under tensile loading along the fibers' axis. The micromechanical framework includes the microstructural representation of the composite with explicit fibers and matrix in addition to linear expansions at the ends. Accurate constitutive equations are utilized for fibers, matrix, and fiber/matrix interfaces in the microstructural representation. Fibers' locations and lengths are generated randomly; based on a target distribution for the fibers' aspect ratios measured experimentally; within the microstructural representation. Optimal microstructural representative dimensions for reliable investigation of the mechanical response are computed by conducting sensitivity analyses. The accuracy of the micromechanical framework is validated versus the experimental results of a 3-D printed aligned discontinuous fiber-reinforced composite as the composite of interest. It is shown that the proposed framework can simulate various aspects of the mechanical response, including the failure pattern and stress-strain behavior. Subsequently, the sensitivity of the mechanical response of the composite to a few constitutive equation-related parameters, including the strength and fracture toughness of the fiber/matrix interfaces and the matrix strength, is investigated. The correlation between the studied parameters and the composite's strength and failure pattern is also analyzed and discussed. This paper delivers valuable guidance on the mechanical response of printed aligned discontinuous fiber-reinforced composites, eventually resulting in the paradigm-shifting design, manufacturing, and analysis of such advanced composites. [ABSTRACT FROM AUTHOR]

The microencapsulated self-healing composite (SHC) has received much attention for their ability to automatically detect and repair cracks. However, the general micromechanical models relating to SHC did not adequately consider the complex interaction between components and the interfacial transition zone. To address these problems, the four-phase micromechanical model containing core-wall-interface-matrix is proposed based on the composite-sphere theory and the Mori–Tanaka method in this study, and the effective properties of SHC are investigated by regarding the parameter of microscopic component as variables. The results showed that the predictive effective properties of SHC lie between the upper and lower limits obtained from the investigations of Walpole, indicating that the proposed micromechanical model is feasible, and the effect of interfacial strength and interfacial thickness on the properties of SHC is significant, indicating that it is necessary to build the micromechanical model consisting of the interfacial phase in this study, the core-to-wall ratio, size, and the strength of capsule wall have high sensitivity to the effective properties of SHC. These results can help investigate the influence of individual components on the properties of SHC, which are useful to guide the selection of individual components for functional materials. [ABSTRACT FROM AUTHOR]

The paper analyzes the stress-strain state of antifriction and connective layers in a joint prosthesis which imitate their biological analogues: articular cartilage and connective tissue between joints and bones. A three-dimensional elasticity problem is solved assuming that these functional layers feature macroscopic homogeneity and transverse isotropy and that their thickness is small compared to the characteristic size of the zone exposed to surface loads. A general solution for arbitrary boundary conditions is derived as a power series in a small parameter which is equal to the ratio of layer thickness to contact zone radius. The solution provides more accurate estimates of the stress-strain state parameters than the Winkler and Pasternak elastic foundation models. A generalization of micromechanical models is presented for describing the deformation of gradient surface layers of a polymer joint prosthesis. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study is the development of geometrically non-linear vibration and Green–Naghdi-based coupled thermo-elasticity analysis with energy dissipation in a functionally graded multilayer cylinder reinforced by graphene platelets subjected to mechanical and thermal shock loadings. Methods: The mechanical and thermal properties of each graphene platelets-reinforced layer are estimated using the modified Halpin–Tsai model and rule of mixture. The meshless local Petrov–Galerkin method based on total Lagrangian approach is developed to derive the non-linear discrete system of governing equation with respect to the initial configuration. The obtained non-linear dynamic equations are solved analytically using the iterative Newmark/Newton–Raphson technique. Results: The obtained results by the proposed method for isotropic homogeneous cylinder are verified by results of finite element method with very fine meshing and good agreement is achieved. The effect of some parameters, such as number of layers, stacking sequences of layers and volume fraction exponent on dynamic characteristics of FG multilayer cylinder, is discussed in details. Conclusion: The results show that the volume fraction of graphene platelets in each layer and stacking sequences of layers have significant effect on non-linear dynamic behavior of cylinder. [ABSTRACT FROM AUTHOR]

The hard rock in the protective coal seam of the Pingdingshan Mine in China is a typical quasi-brittle material exhibiting complex mechanical characteristics. According to available research on the mechanical property, the inelastic deformation and development of damage are considered related with crack initiation and propagation, which are main causes of the material degradation. In the present study, an original experimental investigation on the rock sample of the Pingdingshan coal mine is firstly carried out to obtain the basic mechanical responses in a conventional triaxial compression test. Based on the homogenization method and thermodynamic theory, a damage–friction coupled model is proposed to simulate the non-linear mechanical behavior. In the framework of micromechanics, the hard rock in a protective coal seam is viewed as a heterogeneous material composed of a homogeneous solid matrix and a large number of randomly distributed microcracks, leading to a Representative Elementary Volume (REV), i.e., the matrix–cracks system. By the use of the Mori–Tanaka homogenization scheme, the effective elastic properties of cracked material are obtained within the framework of micromechanics. The expression of free energy on the characteristic unitary is derived by homogenization methods and the pairwise thermodynamic forces associated with the inelastic strain and damage variables. The local stress tensor is decomposed to hydrostatic and deviatoric parts, and the effective tangent stiffness tensor is derived by considering both the plastic yield law and a specific damage criterion. The associated generalized Coulomb friction criterion and damage criterion are introduced to describe the evolution of inelastic strain and damage, respectively. Prepeak and postpeak triaxial response analysis is carried out by coupled damage–friction analysis to obtain analytical expressions for rock strength and to clarify the basic characteristics of the damage resistance function. Finally, by the use of the returning mapping procedure, the proposed damage–friction constitutive model is applied to simulate the deformation of Pingdingshan hard rock in triaxial compression with respect to different confining pressures. It is observed that the numerical results are in good agreement with the experimental data, which can verify the accuracy and show the obvious advantages of the micromechanic-based model. [ABSTRACT FROM AUTHOR]

The present work addresses the question of the quantitative prediction of the biaxial response of polymer–clay nanocomposites experiencing strain-induced crystallization. Polyethylene terephthalate is taken as material model to represent the continuous amorphous phase of nanocomposites. A continuum-based micromechanical model is developed to predict the combined effect of strain-induced phase transformation and nanocomposite structural characteristics on the overall elastic-viscoplastic response. Comparisons with available experimental data are presented to illustrate the capabilities of the model in relation to various loading parameters in terms of loading path, loading rate and loading temperature. The model is used to provide a better understanding of the relationship between nanocomposite structural characteristics, phase transformation, intrinsic properties and loading parameters. [ABSTRACT FROM AUTHOR]

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

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

Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a piezoelectric semi-crystalline polymer whose electro-mechanical properties may be modulated via strain-induced α → β phase transition and the incorporation of polarized inorganic particles. The present work focuses on the constitutive representation of PVDF-based piezo-composites developed within the continuum-based micromechanical framework and considering the combined effects of particle reinforcement, α → β phase transition, and debonding along the interface between the PVDF matrix and the particles under increasing deformation. The micromechanics-based model is applied to available experimental data of PVDF filled with various concentrations of barium titanate (BaTiO3) particles. After its identification and predictability verification, the model is used to provide a better understanding of the separate and synergistic effects of BaTiO3 particle reinforcement and the micromechanical deformation processes on the electro-mechanical properties of PVDF-based piezo-composites.

Microcapsule based glass fiber‐reinforced polymer (GFRP) composites have attracted enormous attention due to enhancement of structures' longevity, reducing expenses, and simplicity of fabrication process. In this study, a micromechanical model of a woven E‐glass/epoxy composite containing microcapsules was developed based on finite element analysis (FEA). Modified sequential adsorption algorithm was chosen to generate and disperse microcapsules in three types of representative volume elements (RVEs). Also, mechanical properties of microcapsules and composite were assigned based on nanoindentation tests and standard experimental tests, respectively. Eventually, multi‐scaling method was implemented to homogenize maximum tensile stress, and subsequent evaluation of tensile after impact (TAI) healing efficiency. Therefore, a healing efficiency of 71% was obtained based on three types of simulations encompassing low‐velocity impact (LVI) and quasi‐static tensile tests on the RVEs. In order to validate the results; first, an electrospraying set‐up was exploited to fabricate multicore microcapsules. The fabricated microcapsules contained mercaptan hardener and epoxy resin as the healing agents, and they were covered by alginate shell. Second, incorporated composite specimens with microcapsules were fabricated via the hand‐layup method. The average TAI healing efficiency of 67% was achieved by experimental tests. Furthermore, scanning electron microscope images of the fractured surfaces confirmed rupture of microcapsules in the LVI test. [ABSTRACT FROM AUTHOR]

In this paper, a micromechanics-based constitutive representation of the deformation-induced phase transformation in polyethylene terephthalate is proposed and verified under biaxial loading paths. The model, formulated within the Eshelby inclusion theory and the micromechanics framework, considers the material system as a two-phase medium, in which the active interactions between the continuous amorphous phase and the discrete newly formed crystalline domains are explicitly considered. The Duvaut–Lions viscoplastic approach is employed in order to introduce the rate-dependency of the yielding behavior. The model parameters are identified from uniaxial data in terms of stress–strain curves and crystallization kinetics at two different strain rates and two different temperatures above glass transition temperature. Then, it is shown that the model predictions are in good agreement with available experimental results under equal biaxial and constant width conditions. The role of the crystallization on the intrinsic properties is emphasized thanks to the model considering the different loading parameters in terms of mechanical path, strain rate and temperature. [ABSTRACT FROM AUTHOR]

This study focused on an innovative practical method using computer vision for particle size measurement, which serves as a key precursor for predicting the elastic modulus of polymer nanocomposites. This approach involved the morphological segmentation of the nanodispersed phase. It aimed, for the first time, to address the impractical conditions resulting from the assumption of idealized single-particle sizes in a monodispersed system during modeling. Subsequently, a micromechanical finite element framework was employed to determine the interphase thickness and modulus in ultrahigh molecular weight polyethylene/nanozeolite composites, following the quantification of nanoparticle sizes. The size measurement approach relied on morphological images extracted from scanning electron microscopy micrographs of impact-fractured surfaces. To compute the interphase thickness, experimental data was fitted to an interphase-inclusive upper-bound Hashin-Shtrikman model, with the measured average particle size per composition serving as a crucial input. Subsequently, the interphase elastic modulus was computed based on its thickness, employing a hybrid modified-Hashin-Hansen and Maxwell model. These estimated interfacial variables were then utilized as inputs for the finite element model to determine the tensile modulus. A comparison between the model results and measured data revealed a maximum discrepancy of 3.29%, indicating the effectiveness of the methodology employed in quantifying interfacial properties.

Nanomaterials have shown more interests to the field of nanotechnologies. Polymeric nanocomposites combine the lightweight and low cost of manufacturing for polymers with nanoparticles of higher performance properties. The aim of this paper is to find the mechanical properties of nanocomposite of polymer reinforced by nanoparticles with considering matrix viscoelasticity. The viscoelasticity of the polymer was obtained from the experimental tests for the thermoplastic polymer of Poly ether ether Ketone (PEEK) at a range of temperatures and frequencies. The viscoelasticity of the polymer was confirmed by comparing the experimental results with a finite element model. The approved viscoelasticity was used for the matrix of the nanocomposite numerically. To obtain the mechanical properties of the nanocomposite, a micromechanical model was developed. It was used to find their homogeneous mechanical properties with range temperatures. 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It is a long-standing puzzle that whether the micromechanical theory is still valid to CNTs-reinforced polymer nanocomposites and why these nanocomposites always show inferior mechanical properties. Herein, we introduced the concept of the real volume fraction for CNT, based on the hypothesis that only the tube walls having direct contact with the polymer matrix carry the external loading. A new micromechanical model on the modulus of nanocomposites was then developed based on this concept. Through a joint study of molecular dynamics (MD) simulations and experimental tests, the correctness and applicability of the proposed micromechanical model were verified, which strongly demonstrate that the micromechanical theory is still applicable to nanocomposites when it sufficiently considers the unique nature of CNTs, such as the real volume fraction, orientations, and aspect ratio. Moreover, the low real volume fraction of multi-walled CNTs is the key reason for the inferior mechanical properties of nanocomposites with uniformly dispersed fillers. [Display omitted] • Micromechanical theory is still applied to CNTs/epoxy nanocomposites. • Low real volume fraction of MWCNTs is the key reason for the inferior nanocomposite stiffness. • CNTs in an agglomeration maintain their aspect ratio although the real volume fraction is dramatically reduced. [ABSTRACT FROM AUTHOR]

Despite the ubiquity of porous materials, their mechanical behaviors (e.g., fracture) remain only partially understood. Here, we propose a novel analytical stochastic micromechanical damage model to describe the fracture of porous materials subjected to uniaxial tension. This analytical model relies on parallel elastic and plastic elements to describe the nonlinear stress–strain curve of porous phases. We then develop a stochastic damage model to describe the propagation of randomly scattered voids or microflaws. This model allows us to identify the key influential features that govern the failure of porous materials. Finally, we demonstrate the accuracy of our model by validating its outcomes by a series of peridynamic simulations. [ABSTRACT FROM AUTHOR]

Earthquake-induced fractures in steel structures are characterised by high-strain low-cycle conditions. In order to investigate the ultra-low cyclic fatigue fracture of steel welded joints under earthquakes, two most commonly used structural steels (Q235B and Q345B) and the corresponding welds were studied by experiments and numerical analysis in this paper. Specimens were extracted from the base material, the weld metal and the heat affected zone to investigate the behaviour in different parts of the welded joint. Eighteen smooth round bars were tested under large strain amplitudes, the hysteretic properties, damage degradation characteristics and failure process were analyzed. Constitutive model named Chaboche model was calibrated to describe the cyclic hardening behaviour of these materials. Seventy-two notched round bars with three different notch sizes and two loading protocols were tested to study the fracture behaviour of different materials at different stress triaxialities and different strain amplitudes. Two micromechanical fracture models: cyclic void growth model and degraded significant plastic strain model were calibrated based on the test results. The micromechanical models and Chaboche model were incorporated into numerical simulations by software ABAQUS with subroutine VUMAT to predict the materials fracture. The results show that the failure process under cyclic loads is opposite to that of monotone loads. The dissipation capacity of Q345B is superior to that of Q235B. The fracture resistance deteriorate more in the weld zone under the same loading conditions. The validated models can be used to effectively and accurately evaluate the fracture in steel welded connections under ULCF conditions. [ABSTRACT FROM AUTHOR]

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

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