Three-dimensional Micromechanical Model Research Articles

Three-Dimensional Micromechanical Simulation and Evaluation of High-Toughness Ultra-Thin Friction Course with X-Ray Computed Tomography

As a novel pavement wear layer material, the micromechanical mechanisms of High-toughness Ultra-thin Friction Course (HUFC) have not been fully elucidated. This paper presents a new method for the three-dimensional micromechanical simulation of high-toughness asphalt mixtures based on a viscoelastic parameter calibration model. X-ray Computerized Tomography (CT) was employed to scan samples of high-toughness asphalt mixtures to obtain detailed information on the internal structure (aggregate, fine aggregate matrix FAM and voids), and a three-dimensional micromechanical model was constructed based on the real-scale distribution of these components. Aggregates in the high-toughness asphalt mixture were modeled as elastic bodies, while FAM was treated as a viscoelastic material characterized by the Burgers model. Using the Boltzmann linear superposition principle and Laplace transform theory, the viscoelastic properties of FAM were converted into Prony parameters recognizable by finite element software, and the viscoelastic parameters were calibrated. Micromechanical simulations were conducted for three different gradings of high-toughness asphalt mixtures, and the results show that the predicted deformation closely matched the measured deformation. This method accurately reflects the deformation characteristics of different gradings of high-toughness asphalt mixtures, overcoming the limitations of traditional numerical simulations based on homogeneous material models. It represents an advancement and refinement of micromechanical simulation methods for high-toughness asphalt mixtures.

Three-Dimensional Micromechanical Modeling of Martensite Particle Size Effects on the Deformation Behavior of Dual-Phase Steels.

The objective of this study was to examine the influence of martensite particle size on the formation of stress and strain in microstructures of dual-phase steels. In order to achieve this objective, the 3D representative volume element (RVE) method was utilized. Particle size distributions were obtained from the microstructures of DP600 and DP1000 dual-phase steels as they actually exist. Virtual dual-phase steel microstructures were generated according to the above distribution and subsequent validation analyses were performed. In the subsequent phase, microstructures of varying martensite particle sizes (1 µm, 1.98 µm, 3 µm for DP600 and 1.15 µm, 2 µm, 3 µm for DP1000) were formed, and the effects of particle size on deformation behavior under tensile loads were determined. The findings indicated that an increase in martensite particle size resulted in a reduction in tensile strength, accompanied by an increase in deformation amount.

Analyzing strain localization of Chang'E-5 lunar regolith through discrete element analysis

The current understanding of the geotechnical behavior of lunar in-situ resources, particularly lunar regolith (LR), is significantly limited due to its scarcity. To address this gap, this research utilized the morphological characteristics of LR particles obtained from the Chang'E-5 (CE-5) mission to construct numerical simulants using the discrete element method (DEM). This approach was then employed to investigate the mechanical properties of LR. Firstly, high-definition lunar particle images from the CE-5 mission were selected to capture the morphological characteristics and grain size distribution. These morphological characteristics were linked with the rolling resistance parameter and incorporated into the three-dimensional (3D) micromechanical contact model. Additionally, a flexible boundary condition was employed in the triaxial simulation to ensure the evolution of strain localization. The relative particle translation gradient (RPTG) concept was utilized to capture the onset and development of strain localization during the shear process. The results indicated that the numerical lunar simulants can effectively reproduce the mechanical response of LR. Furthermore, at the particle scale, particle shape characteristics play a crucial role in particle rotation and translation during the shear process. This study may establish a foundation for lunar resource exploration and utilization techniques.

Continuous damage of concrete structures due to reinforcement corrosion: A micromechanical and multi-physics based analysis

Deterioration of concrete and composite structures due to the corrosion of embedded steel components (rebar, structural steel components, and steel fiber, etc.) is a self-accelerating process involving multiple chemophysical processes that occur concurrently in the heterogeneous structure of concrete. The multiple-inclusion matrix of concrete and the multi-chemophysics nature of steel corrosion synergistically challenge an accurate analysis and evaluation of the deterioration process using homogeneity-based continuum mechanics. This study presents a three-dimensional micromechanical model developed for quantifying the continuous deterioration of concrete by steel corrosion. Continuous damage theory of solid-state materials was applied to a steel-concrete sample that consists of mortar, aggregate, and steel phases as were reconstructed from high-resolution X-ray CT images. With due consideration of the variations in environmental temperature and moisture, the complex chemophysical processes involved in corrosion-induced deterioration of concrete were solved concurrently using finite element analysis. Results of the study indicate that capillary suction in a variably saturated concrete plays an important role in steel corrosion and that removal of chloride by an externally applied electrical field can effectively mitigate steel corrosion and the incurred concrete deterioration.

A 3D micromechanical model to predict the complete stress-strain relation of microencapsulated self-healing concrete

The research on the concrete structure built with self-healing materials brings inspiration to increase the safety and sustainability of underground structures in the whole life cycle. The utilization of microencapsulated healing agents in self-healing concrete has demonstrated efficacy in the repair of microcracks within concrete structures. Nevertheless, there exists a dearth of effective methodologies for assessing the impact of microcapsule parameters on the mechanical properties of self-healing concrete. This study introduces an innovative three-dimensional micromechanical model that can be utilized to analyze the micromechanical response of microencapsulated self-healing concrete under tensile loading conditions. The 3D micromechanical model is accomplished through the utilization of the elastic secant compliance tensor. Subsequently, a comprehensive examination is undertaken to analyze the progression of damage-healing in self-healing concrete incorporating microcapsules. Finally, a parametric investigation is conducted to elucidate the impact of the micro-parameters on the mechanical behavior of self-healing concrete. The present discovery holds significant implications for the development of microencapsulated self-healing concrete for underground structures, particularly in terms of establishing appropriate parameters.

Three-dimensional elastic properties of open-cell porous structures: Analytic and finite element modelling

The current paper introduces a three-dimensional micromechanical model of open-cell cellular solid materials and presents the homogenization of the model to an orthotropic continuum. An orthotropic microstructural beam model was created and tested under pure stretch and pure angular distortion to identify the dominant deformation modes by mapping the contributions of normal-, bending- and torsional stiffness to the total strain energy. In the case of unidirectional tension, the deformation mode was dependent primarily on the proportion of normal- and bending stiffnesses, except for the cases with similarly small bending- and torsional stiffness values, where the contribution of torsion was significant. In the case of the pure angular distortion, the key deformation mode was defined by the ratio of bending- and torsional stiffness values, except for the case of large normal- and torsional stiffness values, which resulted in normal-deformation-driven behaviour.The homogenization of the micromodel was conducted by creating an equivalent spring model, by means of which the equivalent elastic modulus values for the main directions of orthotropy have been derived as functions of the geometric and elastic properties of the beams. With the aid of the equivalent spring models, the relative density dependence of Young’s modulus and shear modulus have been examined. The typical second-degree relationship was found to become inaccurate in the range of lower porosity. In the case of increasing relative density values, the exponent of the elastic modulus function decreased while the exponent of the shear modulus increased.

3D micromechanical modeling of orthogonal hole saw cutting on CFRP composites

In the interest of developing a comprehensive understanding of the drilling process using the hole saw tool, this article aims to build a three-dimensional (3D) micromechanical model representing the orthogonal cutting of CFRP using one tooth of the hole saw tool. For this purpose, a finite element model is developed using Abaqus Explicit code. The influence of various drilling parameters like rake angle, inclination angle and cutting-edge radius on the drilling quality is explored. Especially, chip formation mechanisms, cutting force and lateral damage are analyzed. Through finite element simulations and computational analyses, it is found that these outputs results are highly influenced by drilling parameters. When the fiber orientation angle is set to 0°, increasing the rake angle results in a change in the chip formation mechanism from buckling to bending. In contrast, with a fiber orientation angle of 90°, bending and shear governs the chip formation process, irrespective of the rake angle. In both cases, whether the fiber orientation angle is 0° or 90°, chips tend to fragment more favorably with increasing the inclination angle. Regarding the cutting-edge radius, when the fiber orientation angle is 0°, an increase in the cutting-edge radius leads to a transition in the chip-forming mechanism from buckling to bending. However, for a fiber orientation angle of 90°, the chip formation remains governed by bending even as the cutting-edge radius changes. Decreasing the rake angle, the inclination angle, and the cutting-edge radius contribute to a reduction of the cutting force. As the inclination angle and the cutting-edge radius increase, the lateral damage increases, while the rake angle has showed a negligible impact on the damage. These results provide a guidance on the appropriate hole saw tool parameters for a good drilling quality namely, a rake angle of 20°, an inclination angle of 5° and a cutting-edge radius of 0.03 mm.

Three-dimensional analytical model for composite laminate with transverse cracks by assuming parabolic crack opening

In this study, a model for the three-dimensional effective compliance of composite laminates with transverse cracks is developed based on continuum damage mechanics. Three-dimensional laminate theory is used to reproduce all the thermoelastic properties of the damaged laminate. The damage variable, which describes the degree of stiffness reduction caused by transverse cracking, is formulated based on a three-dimensional micromechanical model, with a loose boundary condition and assuming parabolic crack opening. These assumptions contribute to the analytical accuracy of the stiffness reduction model, while simplifying the damage variable expression. The effective thermomechanical properties of various composite laminates are predicted using the proposed model and compared with finite element analysis (FEA) and experimental results. We found that the proposed model with derived damage variable successfully reproduces the FEA and experimental results of stiffness degradation of damaged composite laminates.

A three-dimensional micromechanical model for simulating ply crack formation in laminates under in-plane tensile loading

Micromechanical models were established to simulate ply cracking in [0/90/0] laminates under tension. A new user-defined material model was developed within a finite element framework to capture inelastic deformation of the matrix and local cavitation-induced and ductile failure. A damage model was used to capture corresponding post-peak behaviour. Representative volume elements (RVEs) of laminates were generated, where the fiber and matrix constituents were explicitly represented in the 90° ply. The experimentally verified simulations revealed local matrix failure onset was governed by brittle cavitation, while subsequent microcracking was influenced by local ductile failure. The model accurately captured the delay in first full ply crack formation for laminates with thinner plies. The role of thermal residual stress, ply constraints, and fiber volume fraction on ply crack formation were investigated. The associated effective energy release rate was predicted and can be used for predicting ply crack multiplication in meso- or macro-scale models.

Modelling of micro-damage and intrinsic self-healing in unidirectional CFRP composite structures

This work presents a micromechanical constitutive model of an intrinsically self-healing unidirectional CFRP composite material. The model is implemented into Abaqus/Standard user material subroutine UMAT and validated using experimental results of three-point bending tests available in the literature. Tested specimens consist of thermally mendable bis-maleimide tetrafuran (2MEP4F), and GA045 unidirectional carbon fibres. The matrix material is modelled using the elastic-plastic micro-damage-healing constitutive model. On the other hand, the reinforcing fibres are modelled as linear elastic. A three-dimensional micromechanical model, based on principles of the Rule Of Mixtures, is employed to model the homogenised composite. Finally, a parametric analysis is conducted to evaluate the effect of various parameters on the damage evolution and the healing performance, and afterwards, the results are discussed. The validation results have shown that the developed constitutive model is able to accurately simulate the micro-damage and healing processes in the intrinsically self-healing unidirectional composite structures.

Prediction of the cohesive strength for simulating composite delamination by a micro-mechanical model based on random RVE

A three-dimensional micro-mechanical model based on the random RVE is developed to predict the cohesive strengths of all the three delamination modes in unidirectional laminates. The interface RVE with two layers of randomly distributed fibers is established to represent the cohesive layer. Two types of random microstructure corresponding to the square and hexagonal periodic packing are defined. Delamination is assumed to be induced by matrix yield and cracking. The extended linear Drucker–Prager yield criterion and a paraboloidal yield criterion are used to predict the crack initiation in the matrix and compared with the major principal stress criterion. The predicted results show that the cohesive strengths are largely dependent on the type of random microstructure and the random microstructure morphology described by the minimum inter-fiber distance and the fiber alignment angle. Global sensitivity analysis based on a polynomial chaos expansion surrogate model is done to quantify the influence of the geometrical parameters on the variance of the cohesive strengths. Moreover, the predicted cohesive strengths are found to be unequal.

A new three-dimensional finite-volume model for evaluation of thermal conductivity of periodic multiphase composites

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.

Three-dimensional micromechanical pavement model development for the study of block cracking

Block cracking in asphalt pavements is a primary form of surface cracking but has been the subject of very few scientific investigations. Although this deterioration mode is covered in many pavement evaluation guides and condition rating systems, the underlying mechanisms of block cracking have not been fully investigated. Therefore, understanding the mechanisms behind block cracking and tailoring preventive solutions merits rigorous investigation. In this paper, a 3D discrete element viscoelastic and inhomogeneous microstructure-based pavement model subjected to thermal straining was introduced. A typical PG 64-22, dense-graded Illinois asphalt surface mixture was adopted as the baseline material because it typically experiences block cracking later in its service life. The mechanisms of block cracking patterns were investigated as a function of the dimension of pavement segments, relaxation capacity and aging state of materials, including spatial gradients, cooling rate and pre-existing crack presence using the aforementioned discrete element models. Discrete element simulations showed that initial block cracking primarily occurred in the upper one-to-two centimeters of the surface, which agreed with field observations. In addition, it was found that block cracks formed at a warmer temperature than that associated with the onset of thermal cracking. This implied that current test criteria for thermal cracking mitigation may need to be updated or supplemented in order to control block cracking. Finally, the techniques presented herein can be extended to identify candidates for preventive maintenance, and in developing tailored maintenance techniques.

A micromechanical model for the analysis of multidirectional fiber reinforced polymer laminates

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

A three-dimensional micromechanical model of brain white matter with histology-informed probabilistic distribution of axonal fibers

This paper presents a three-dimensional micromechanical model of brain white matter tissue as a transversely isotropic soft composite described by the generalized Ogden hyperelastic model. The embedded element technique, with corrected stiffness redundancy in large deformations, was used for the embedment of a histology-informed probabilistic distribution of the axonal fibers in the extracellular matrix. The model was linked to a multi-objective, multi-parametric optimization algorithm, using the response surface methodology, for characterization of material properties of the axonal fibers and extracellular matrix in an inverse finite element analysis. The optimum hyperelastic characteristics of the tissue constituents, obtained based on the axonal and transverse direction test results of the corona radiata tissue samples, indicated that the axonal fibers were almost thirteen times stiffer than the extracellular matrix under large deformations. Simulation of the same tissue under a different loading condition, as well as that of another white matter tissue, i.e., the corpus callosum, in the axonal and transverse directions, using the optimized hyperelastic characteristics revealed tissue responses very close to those of the experiments. The results of the model at the sub-tissue level indicated that the stress concentrations were considerably large around the small axons, which might contribute into the brain injury.

Static Bending and Free Vibration Analysis of Hybrid Fuzzy-Fiber Reinforced Nanocomposite Beam-A Multiscale Modeling

Static and free vibration multiscale analysis of fuzzy-fiber-reinforced composite (FFRC) beam is investigated using a three-dimensional micromechanical model together with two-dimensional elasticity macromechanical theory. In the hybrid nanocomposite, aligned carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of carbon fibers. Influence of the carbon fiber orientation, volume fraction and arrangement; CNT volume fraction and interphase region characteristics on the FFRC beam deflection and natural frequencies are studied. Good agreements are reported for the presented results compared with available experiments and the other modeling strategies at both micro and macro levels. The results reveal that the FFRCs properties are strongly dependent on the carbon fiber off-axis angle. By increasing the off-axis angle from [Formula: see text] to [Formula: see text], the FFRC beam deflection sharply increases up to [Formula: see text] fiber angle and then its value decreases. It is shown that the growth of CNTs on the carbon fiber surface leads to the highest decrease in the beam deflection for 90[Formula: see text] coupon. Also, increasing the interphase thickness decreases the beam deflection and increases the natural frequencies, especially for [Formula: see text] coupon. Moreover, the increasing the interphase Young’s modulus gives maximum 1.74% increase in the natural frequencies.

Micromechanical characterizing the effective elastic properties of general randomly distributed CNT–reinforced polymer nanocomposites

This work deals with a comprehensive study on the general off-axis mechanical properties of polymer nanocomposites reinforced by carbon nanotubes (CNTs) using a three-dimensional micromechanical model. The representative volume element (RVE) of the model consists of three phases including CNT, polymer matrix and interphase formed due to the non-bonded interaction between a CNT and the polymer. The CNTs are assumed to be transverse isotropic. Both random under several statistical distribution and regular arrangements of the CNTs within the matrix are considered in the analysis. The results are shown to be consistent with the results of other theoretical methods and experiment. Effects of various parameters, including the CNT aspect ratio, orientation, distribution, cross sectional shape and volume fraction, the interphase characteristics and the matrix material properties are examined on the effective elastic properties of CNT–reinforced polymer nanocomposites. The results reveal that the mechanical properties of the nanocomposite are extremely dependent on the CNTs off-axis angle. The interphase effect is more significant for the elastic modulus of 70°off-axis coupon. It is found that CNT volume fraction has the maximum effect for the longitudinal elastic modulus. For 90°coupons, elastic modulus of the nanocomposite is significantly affected by the matrix properties. The results obviously indicate that the elastic modulus, especially in the longitudinal direction increases up to a threshold value and then saturates as the CNT aspect ratio increases. Also, it is found that the CNT arrangement does not affect the longitudinal elastic modulus of CNT–polymer nanocomposites, whereas the transverse elastic modulus is significantly affected by the CNT arrangement.

Three-dimensional micromechanical analysis models of fiber reinforced composite plates with damage

A three-dimensional micromechanical analysis model was established to investigate the force-bearing mechanisms and damage in fiber reinforce composite plates. In the proposed model, the matrix and fibers were described by the extended layerwise method (XLWM) and the three-dimensional bar elements, respectively. The final governing equation of composite with damage was developed from combing the governing equations of matrix and fibers by the displacement compatibility conditions at the coupling interfaces. The equivalent material property of matrix calculated by the volume faction of fibers was used to remove the contribution of the redundant matrix shaved the overlapping region with fibers. In the numerical examples, the unidirectional composite plates with damage were investigated to validate the proposed model, and the results calculated by the proposed model are compared with those of the 3D elastic models developed in the general commercial finite element code. In addition, the effects of the damage on the stress distribution in fibers were investigated.

Micromechanics-based Analysis of Effect of Internal Structure on Creep Anisotropy of Asphalt Concrete

In order to investigate the effect of internal structure on creep anisotropy of asphalt concrete (AC), a three-dimensional (3D) micromechanical model was developed using discrete element method. The digital AC specimen composed of coarse aggregates, asphalt mastic and air voids was generated. The corresponding micromechanical models among the interactions of microscale components of digital AC specimen were assigned. The microscale viscoelastic parameters were obtained from laboratory dynamic shear test. Simulation of uniaxial creep tests were conducted on a number of cubic digital AC specimens with different aggregate orientations and sphericity. It was observed that the longer projected length of aggregates in loading direction, the smaller the creep strain is. The creep strain of AC was much smaller in the major axis direction of aggregate orientation as compared with the minor one. The creep anisotropy of AC became obvious with decreasing aggregate sphericity, especially when projected length of aggregates varied greatly in different directions.

A micromechanical model to study failure of polymer-glass syntactic foams at high strain rates

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