3D Micromechanical Model Research Articles

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.

A periodic micromechanical model for the rate- and temperature-dependent behavior of unidirectional carbon fiber-reinforced PVDF

The rate- and temperature-dependent mechanical behavior of unidirectional carbon fiber-reinforced polyvinylidene fluoride (PVDF) is investigated through uniaxial tension and compression experiments under various off-axis loading conditions. To improve the understanding of the behavior of the composite, a 3D micromechanical model is developed. Microscopic analyses are used to characterize the geometrical properties of the UD composite at the fiber length-scale. These properties are used to construct a periodic 3D representative volume element (RVE). In combination with periodic boundary conditions, uniaxial macroscopic deformation (in any possible direction) is applied to the RVE to accurately and efficiently model off-axis loading. The rate- and temperature-dependent behavior of the PVDF matrix is accurately described using an elasto-viscoplastic constitutive model. The finite element simulations of uniaxial tension and compression tests are compared to the experimental data and the micromechanical response is analyzed. The micromechanical model accurately describes the rate-dependent macroscopic behavior of unidirectional carbon fiber-reinforced PVDF for various off-axis loading directions at different temperatures. Analysis of the local matrix response in the RVE reveals the influence of the matrix on the macroscopic behavior of the composite.

Understanding the effect of microstructure on the failure behavior of additively manufactured Al2O3 ceramics: 3D micromechanical modeling

Additively manufactured (AM) ceramics are gaining popularity due to improved flexibility in the design of customized structures. Microstructure-based finite element (FE) models were developed to study the strain-rate-dependent failure behavior of AM Al2O3 ceramics under uniaxial compression. Upon validation with experimental data, the model was leveraged to quantify the history of intergranular and transgranular failure mechanisms across microstructures. It was revealed that the intergranular mechanism plays a key role in the material strength across strain rates. Crystallographic orientations were found to remarkably decrease the material strength due to the earlier initiation and faster growth of the intergranular mechanism. The increase in porosity was found to amplify the transgranular mechanism resulting from a higher number of pores acting as crack nucleation sites, decreasing the material strength regardless of strain rate. The model reflected the existence of a threshold for grain boundary strength, beyond which further enhancements yield marginal improvements in material strength. Additionally, the effect of grain size on the initiation and evolution of failure mechanisms was studied and the corresponding limitations of the model were discussed. The current work correlates the microstructure of the material to its macroscale response through micromechanical models, informing the design of better-performing AM Al2O3 ceramics.

Micromechanical modeling of longitudinal tensile behavior and failure mechanism of unidirectional carbon fiber/aluminum composites involving fiber strength dispersion

This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations. A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite. The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests, respectively. Then, a 3D micromechanical numerical model, innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories, was established to simulate the progressive failure behavior of the composite under longitudinal tension. Due to the dispersion of fiber strength, the weakest link of the fiber first fractures, and stress concentration occurs in the surrounding fibers, interfaces, and matrix. The maximum stress concentration factor for neighboring fibers varies nonlinearly with the distance from the fractured fiber. Both isolated and clustered fractured fibers are present during the progressive failure process of the composite. The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters, and their mutual action leads to the final collapse of the composite.

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.

Analysis of crack-tip stress field in unidirectional fiber-reinforced composites based on 3D micromechanical model

Accurately clarifying the influence of cracks on the mechanical behaviors of unidirectional fiber-reinforced composites (UD FRCs) is of great significance for the structural integrity evaluation of UD FRCs with defects. Although several experiments and numerical analyses have explored the impact of cracks on stress field, satisfactory quantitative characterizations of crack size, a/W and location, Δ, fiber content, Vf have not yet been obtained. In this paper, the accurate and detailed microscopic models containing crack were first established and thoroughly validated. Then, a parametric study was conducted using three-dimensional micromechanical analysis to investigate how the crack size and location, fiber content affect the von Mises, stress triaxiality, Lode angle and J-integral of UD FRCs. Results showed that homogeneous models, whether isotropic or anisotropic, cannot accurately describe the mechanical behavior of cracked UD FRCs. The von Mises stress and J-integral are greatly influenced by the crack and fiber content, while stress triaxiality and Lode angle are not sensitive to changes in these factors. Further, the von Mises and J-integral increase with the decrease of Vf and the increase of a/W, but show a more complex trend in the variation of Δ. These findings will help clarify the failure mechanism of cracked UD FRCs and can be used for reliability evaluation.

An Ogden hyperelastic 3D micromechanical model to depict Poynting effect in brain white matter

Shear and torsional load on soft solids such as brain white matter purportedly exhibits the Poynting Effect. It is a typical nonlinear phenomenon associated with soft materials whereby they tend to elongate (positive Poynting effect) or contract (negative Poynting effect) in a direction perpendicular to the shearing or twisting plane. In this research, a novel 3D micromechanical Finite Element Model (FEM) has been formulated to describe the Poynting effect in bi-phasic modeled brain white matter (BWM) representative volume element (RVE) with axons tracts embedded in surrounding extracellular matrix (ECM) for simulating brain matter's response to pure and simple shear. In the presented BWM 3D FEM, nonlinear Ogden hyper-elastic material model is deployed to interpret axons and ECM material phases. The modeled bi-phasic RVEs have axons tied to the surrounding ECM. In this proof-of-concept (POC) FEM, three simple shear loading configurations and a pure shear case were analyzed. Root mean square deviation (RMSD) was calculated for stress and deformation response plots to understand the effect of axon-ECM orientations and loading conditions on the degree of Poynting behavior. Variations in normal stresses (S11, S22, or S33) perpendicular to the shear plane underscored the significance of axonal fiber-matrix interactions. From the simulated ensemble of cases, a transitional dominance trend was noticed, as simple sheared axons showed pronounced Poynting behavior, but shear deformation build-up in the purely sheared brain model exhibited the highest Poynting behavior at higher strain % limits. At lower strain limits, simple shear imparted across and perpendicular to axonal tract directions emerged as the dominant Poynting effect configurations. At high strains, the stress-strain% plots manifested mild strain stiffening effects and bending stresses in purely sheared axons, substantiated the strong non-linearity in brain tissues’ response.

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.

Discrete 3D modeling of porous-cracked ceramic at the microstructure scale

The porous-cracked microstructure of plasma sprayed ceramics coatings directly influences their macroscopic mechanical response.A 3D micromechanical model based on the discrete element method (DEM) is developed to reproduce their behavior. 3D observations are conducted with FIB-SEM nano-tomography and image analysis is used to extract and discretize the microstructure. A modeling strategy is developed to incorporate both pores and cracks into the model while preserving the computation performance. The lattice nature of DEM is used for the modeling of crack thickness that are smaller than the discrete element size. A method to compute the crack thickness from gray level images is proposed.Virtual quasi-static tests are performed on a sample of yttria-stabilized-zirconia. The results are in accordance with the literature data, such as the anisotropy and the non-linear behavior. The model is helpful to precisely investigate the role of the microscopic components, and micro-cracking on the macroscopic failure.

A resilience assessment framework for microencapsulated self-healing cementitious composites based on a micromechanical damage-healing model

In this paper, a resilience assessment framework for microencapsulated self-healing cementitious composites is proposed based on a micromechanical damage-healing model. A 3D micromechanical analytical model is constructed to analyze the performance evolution during the damage-healing process of self-healing concrete. The resilience assessment of microencapsulated self-healing concrete is defined by virtue of the residual stiffness, self-healing effect on stiffness and damage cumulative on stiffness, which corresponds to three main features of resilience; namely, the robustness, recoverability and adaptability. The assessment results indicate that the release of healing agents within microcapsules and healing process of extended microcracks allows the microencapsulated self-healing concrete to have higher resilience than conventional concrete. Moreover, a parameter sensitivity analysis is conducted to investigate the influence of the healing efficiency, the applied initial damage and the fracture toughness of the repaired microcrack on resilience of microencapsulated self-healing concrete. The results indicate that higher healing efficiency and applied initial damage leads to high resilience, and fracture toughness of the repaired microcrack makes less difference to the results. The findings of this paper lay a theoretical foundation for the resilience design of self-healing material layer of underground structures.

Investigation on the effects of asphalt mixes and their combinations on asphalt mix shear strength by 3D discrete element method

ABSTRACT This study investigated the effects of asphalt mixes and their combinations on the asphalt mix shear strength (SS) by a three-dimensional (3D) discrete element method (DEM). The uniaxial penetration test (UPT) for testing the asphalt mix SS was succinctly depicted. 3D micromechanical models used to predict the asphalt mix SS were built through X-ray computed tomography and discrete particle model implemented in particle flow code in three dimensions (PFC3D). The effects of asphalt mixes and their combinations on the SS were analysed on the basis of these models. Simulation results were proven against laboratory UPTs. As shown, the presented simulation results were in good agreement with the laboratory results, and the deviations between them were below approximately 6%, and most were less than 4%. The SS of high modulus asphalt mixes was greater than that of SBS-modified asphalt mixes and rubber-modified asphalt mixes. The asphalt mix SS increased with the increase in aggregate size, and it decreased with the rise in void content. The double-layer asphalt mix SS was more remarkably influenced by the bottom asphalt layer. The crumb rubber content also affected the rubber-modified the asphalt mix SS. The rubber-modified asphalt mix SS increased with the rise in crumb rubber content.

A novel experimental method and computational micromechanical model for in-situ damage detection and prediction of stiffness degradation in cross-ply FML

A novel experimental method for in-situ damage detection in symmetrical and balanced glass/epoxy laminates composed of unidirectional layers is introduced in this paper. A 3D finite-element micromechanical model accompanies this method to predict stiffness degradation in a cross-ply fiber-metal laminate caused by transverse cracks and metal damage. The model is developed in Abaqus. Two user-defined subroutines, UMAT and UHARD, are coded in FORTRAN and linked to the model. Using a Python script, periodic boundary conditions are applied to the model. The predictions are validated against conventional loading-unloading experimental tests. Validation shows excellent agreement between the proposed model and the experiment.

Interplay of strain and phase evolution of laser powder bed fusion Ti–6Al–4V

While additive manufacturing (AM) provides a method of producing geometrically complex and highly detailed structures, the generation of residual strain in AM processes like laser powder bed fusion (L-PBF) can negatively impact performance-enabling properties. In applications such as orthopedic implants, specific performance windows require optimized microstructures in order to obtain desirable properties from multi-phase alloys like Ti–6Al–4V. This research aims to quantify the microscale origins of strain in L-PBF manufactured Ti–6Al–4V by understanding how strain is distributed at the grain and sub-grain scale, the interplay between phase evolution and strain, and examining post-processing strain relief strategies to control these features. Model spinal cage implants were manufactured from Ti–6Al–4V powder via L-PBF and then subjected to strain relieving heat treatment cycles above and below the Ti–6Al–4V β transus as a function of time and cooling rate. Residual strain was then studied via high resolution electron backscatter diffraction (HR-EBSD), and 2D strain maps with sub-micron resolution were generated for each post-processing state. It was found that macroscale thermal strains decreased with heat treatment time, but additional contributions from phase stabilizing residual strains retained primarily in the α′ grains as lattice distortive strain remained. Additionally, the retention of β phase significantly changed the strain and dislocation distribution while reducing overall residual strain. These results were validated and reinforced with 3D mesoscopic micromechanical modeling of strain behavior across simulated microstructures, confirming that the local lattice dilation of α’ martensite is a primary contributor of microscale strain generation and retention in L-PBF Ti–6Al–4V.

Analysis of work hardening mechanisms in Quenching and Partitioning steels combining experiments with a 3D micro-mechanical model

Quenching & Partitioning (Q&P) steels owe their good strength-ductility combinations to the martensite/austenite (α’/γ) mechanical interactions and to the formation of mechanically-induced martensite (α′mech) through the transformation-induced plasticity (TRIP) effect. An essential role is played by carbon, whose distribution among the phases can be modified through the Q&P route. This study presents a methodology to systematically and quantitatively examine the influence of the α’/γ mechanical interactions on the overall work hardening of the steel with respect to the role of carbon in the martensite. The methodology rests on the generation of a 3D micro-mechanical model that allows to derive, by crystal plasticity simulations, the overall response of a mechanically-stable α’/γ virtual microstructure. In combination with theoretical knowledge on hardening, the comparison between the experimental and simulated mechanical responses enables the quantification of the influence of the martensite carbon content and distribution on the overall TRIP strengthening contribution of the steel. The approach is applied to two low carbon Q&P-processed α’/γ microstructures of similar initial volume fractions of austenite and α′mech formation kinetics with strain, but one containing a Nb-microaddition and displaying improved strength-ductility values. It is shown that the martensite strength and work hardening ability might additionally enhance or partially counteract the strengthening contribution from the austenite-to-α′mech transformation during uniaxial loading. The results of this study highlight that the processing-dependent properties of the carbon-depleted martensite should be considered in the optimization of Q&P processed steels.

Mechanical Properties of Cemented Particulate Composite: A 3D Micromechanical Model.

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.

Effect of Off-Axis Ply on Tensile Properties of [0/θ]ns Thin Ply Laminates by Experiments and Numerical Method.

The effect of off-axis ply on the tensile properties of unbalanced symmetric [0/θ]ns laminates was explored through experimental and numerical analysis. Six CFRP [0/θ]2s plies with different off-axis angles θ were fabricated for tensile tests. In situ observations of the damage to the laminates were conducted to investigate the initiation and progressive growth of the laminates during the tension tests. The fiber fractures, crack initiation, and progressive propagation were analyzed by observing the free edge of the laminates, and the difference in damage behavior caused by different off-axis angles was investigated. All the six [0/θ]2s plies with off-axis angles θ ranging from 15° to 90° showed approximate linear stress–strain responses in the tensile tests. Matrix cracks were not observed prior to the final catastrophic failure in the off-axis layers of the [0/θ]2s laminates with a θ in the range of 15–60°. Finite element analysis (FEA) of the [0/θ]s plies was conducted using a 3D micromechanical model, in which matrix cracking and fiber-matrix debonding in the off-axis layer were simulated using a cohesive interface element. Three micromechanical crack-free, cohesive interface, and initial crack models were analyzed to predict the influence of the matrix cracks inside the off-axis layer on the damage behavior of the [0/θ]s laminates. The numerical results from the initial crack micromechanical model show a lower bound of the tensile strength of the [0/θ]s plies. A high stress concentration is observed adjacent to the cracked off-axis layer, inducing a tensile strength loss of about 20%.

Mechanical response analysis of self-healing cementitious composites with microcapsules subjected to tensile loading based on a micromechanical damage-healing model

For the past several years, research in the field of self-healing construction materials becomes a hotspot with broad application prospects. This paper mainly focuses on the self-healing cementitious composites with microcapsules. To quantitatively interpret the self-healing effect of micro-encapsulated healing agents on microcrack-induced damage, a three-dimensional evolutionary micromechanical model is established to predict the mechanical response of the cementitious composites with the microcapsules subjected to tensile loading during the damage-healing process. The evolutionary domains of microcrack growth (DMG) and the corresponding compliances at the initial, activated and repaired stages are obtained. On the basis of the proposed 3D micromechanical model of the self-healing cementitious composites with microcapsules, elaborate studies of constitutive relations and compliance are conducted to investigate the effects of various system parameters involving the healing efficiency, fracture toughness and preloading-induced damage degrees on the compliances and stress-strain relations. The results indicate that relatively significant healing efficiency, preloading-induced damage degree and the fracture toughness of polymerized healing agent with the matrix will lead to higher tensile strength and stiffness. However, based on the two different failure modes of self-healing concrete, the excessive values of healing efficiency, preloading-induced damage degree and the fracture toughness of polymerized healing agent with the matrix will not affect the tensile strength of the cementitious composites. For the sake of the desired optimal healing effect, the specific parameters of both the matrix and the microcapsules should be selected carefully.

Investigation of the possible origins of the differences in mechanical properties of hemp and flax fibres: A numerical study based on sensitivity analysis

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

Three dimensional modelling of closed-cell aluminium foams with predictive macroscopic behaviour

This study presents an efficient approach to generate a realistic micromechanical model for closed-cell foams using irregular Voronoi models. Starting with a reference microstructure consisting of regular Kelvin cells, the nucleating points underlying each reference unit cell is subjected to a random displacement, the magnitude of which depends on the pore size and a misalignment parameter. For convenience, the misalignment parameter is calibrated from available statistical data on unit cell geometries for the commercially available closed-cell aluminium foam, and a common value is utilised for all cases considered. Numerical analyses with the irregular 3D micromechanical models are done using ABAQUS/Explicit. Considering both uniaxial and hydrostatic compressive loading cases, the numerical responses compare well with the experimental data in literature, over a wide range of relative densities. The deformation mechanism is next elaborated. In uniaxial compression, the deformation initiates at the weaker regions induced by the geometrical irregularities, before evolving into a localized deformation band through the coalescence between neighbouring regions of local weakness. This localized deformation band forms an irregular 3D relief in space, a phenomenon which cannot be captured by regular periodic microstructures. In hydrostatic compression, the irregular geometry also induces deformation through cell wall bending. In tension, a stretching mode induces a shift in the yield surface towards the positive mean stress quadrant, which is consistent with experimental observations. The proposed approach thus generates the irregular 3D microstructures efficiently through a single calibrated misalignment parameter, leading to realistic deformation mechanisms, with good predictions on the macroscopic behaviour, over a wide range of relative densities and different loading conditions.

A micro–macro scale approach for thermal effects in ferroelectrics

The influence of thermal fields on the electromechanical behavior of ferroelectric ceramics under cyclic electric loading is presented. To predict the temperature effect, a 3D micromechanical model for tetragonal domain switching is extended by including thermal effects. Numerical simulations were done through the finite element program Abaqus with the help of a user-defined element. Besides external heat sources, a change in temperature is considered by internal heat generated due to domain switching. Material properties are assumed to be linearly dependent on the temperature. The temperature influence on the behavior of ferroelectrics is shown by means of the strain and polarization hysteresis loops. The model shows a good qualitative agreement with the experimental results available in the literature.