Three-dimensional Microstructural Model Research Articles

A physically-based computational approach for processing-microstructure-property linkage of materials additively manufactured by laser powder bed fusion

A physically-based approach is proposed for evaluating the microstructure-to-property linkage of AlSi10Mg produced by Laser Powder Bed Fusion (L-PBF). The approach includes the simulation of the microstructure evolution during processing and subsequent micromechanical analysis of its deformation behavior. Three-dimensional microstructural model is simulated by coupling the Cellular Automata (CA) model of solidification and the Finite-Difference model of heat transfer. The CA model is based on the nucleation and growth characteristics of the alloy such that the generated microstructure is well aligned with the experiments in terms of the grain structure and texture. Micromechanical analysis for a representative microstructure is performed using Crystal Plasticity (CP) Finite-Element calculations. The sequentially coupled CA and CP models provide a physically-based approach for grain-scale understanding of process-structure-property relationship of L-PBF products. Uniaxial tension along three perpendicular directions is simulated to investigate the deformation behavior of the grain structure. The stress and strain field analyses show an essential anisotropy of the mechanical properties at the grain scale. It is demonstrated that the stress-strain state of the material under uniaxial tension is complex and all stress tensor components make a comparable contribution to the deformation behavior.

Three-Dimensional Numerical Simulations and Antifouling Mechanism of Microorganisms on Microstructured Surfaces

As marine biofouling seriously affects the development and utilization of oceans, the antifouling technology of microstructured surface has become a research hotspot due to its green and environmentally friendly advantages. In the present research, the motion models of microorganisms on the surfaces of five rectangular micropits, in co-current and counter-current flow direction, were established. Dynamic mesh technology was used to simulate the movements of microorganisms with different radii in the near-wall area, and the fluid kinematics and shear stress distributions in different-sized micropits were compared. Furthermore, moving microorganisms were included in the three-dimensional microstructure model to achieve the real situation of biofouling. Simulation results revealed that the vortex flow velocity in the micropits increased with the increase of the inlet flow velocity and the existence of the vortex flow effectively reduced the formation of conditioning layers in the micropits. In the downstream and countercurrent directions, the average shear stresses on the wall decreased with the increase of the micropit depth and width, and the shear stress on the inner wall of the Mp1 micropit (a patterned surface arranged with cubes of 2 µm × 2 µm × 2 µm) was found to be the largest. A low shear stress region with a low flow velocity was formed around microorganisms in the process of approaching the microstructured surface. The shear stress gradient of micro-ridge steps increased with the approach of microorganisms, indicating that microridge edges had a better effect on reducing microbial attachment.

Multi-scale crystal plasticity finite element simulations of the microstructural evolution and formation mechanism of adiabatic shear bands in dual-phase Ti20C alloy under complex dynamic loading

A dynamic compression test was performed on α + β dual-phase titanium alloy Ti20C using a split Hopkinson pressure bar. The formation of adiabatic shear bands generated during the compression process was studied by combining the proposed multi-scale crystal plasticity finite element method with experimental measurements. The complex local micro region load was progressively extracted from the simulation results of a macro model and applied to an established three-dimensional multi-grain microstructure model. Subsequently, the evolution histories of the grain shape, size, and orientation inside the adiabatic shear band were quantitatively simulated. The results corresponded closely to the experimental results obtained via transmission electron microscopy and precession electron diffraction. Furthermore, by calculating the grain rotation and temperature rise inside the adiabatic shear band, the microstructural softening and thermal softening effects of typical heavily-deformed α grains were successfully decoupled. The results revealed that the microstructural softening stress was triggered and then stabilized (in general) at a relatively high value. This indicated that the mechanical strength was lowered mainly by the grain orientation evolution or dynamic recrystallization occurring during early plastic deformation. Subsequently, thermal softening increased linearly and became the main softening mechanism. Noticeably, in the final stage, the thermal softening stress accounted for 78.4 % of the total softening stress due to the sharp temperature increase, which inevitably leads to the stress collapse and potential failure of the alloy.

Modeling Effective Ionic Conductivity and Binder Influence in Composite Cathodes for All-Solid-State Batteries.

In the pursuit for future mobility, solid-state batteries open a wide field of promising battery concepts with a variety of advantages, ranging from energy density to power capability. However, trade-offs need to be addressed, especially for large-scale, cost-effective processing, which implies the use of a polymeric binder in the composite electrodes. Here, we investigate three-dimensional microstructure models of the active material, solid electrolyte, and binder to link cathode design and binder content with electrode performance. Focusing on lithium-ion transport, we evaluate the effective ionic conductivity and tortuosity in a flux-based simulation. Therein, we address the influence of electrode composition and active material particle size as well as the process-controlled design parameters of the void space and binder content. Even though added in small amounts, the latter has a strong negative influence on the ion transport paths and the active surface area. The simulation of ion transport within four-phase composites is supplemented by an estimation of the limiting current densities, illustrating that application-driven cell design starts at the microstructure level.

Three-Dimensional Microstructure Model for Discontinuously Fiber Reinforced Concrete

Three-Dimensional Microstructure Model for Discontinuously Fiber Reinforced Concrete

Microstructural Modeling of Rheological Mechanical Response for Asphalt Mixture Using an Image-Based Finite Element Approach.

In this paper, an image-based micromechanical model for an asphalt mixture’s rheological mechanical response is introduced. Detailed information on finite element (FE) modeling based on X-ray computed tomography (X-ray CT) is presented. An improved morphological multiscale algorithm was developed to segment the adhesive coarse aggregate images. A classification method to recognize the different classifications of the elemental area for a confining pressure purpose is proposed in this study. Then, the numerical viscoelastic constitutive formulation of asphalt mortar in an FE code was implemented using the simulation software ABAQUS user material subroutine (UMAT). To avoid complex experiments in determining the time-dependent Poisson’s ratio directly, numerous attempts were made to indirectly obtain all material properties in the viscoelastic constitutive model. Finally, the image-based FE model incorporated with the viscoelastic asphalt mortar phase and elastic aggregates was used for triaxial compressive test simulations, and a triaxial creep experiment under different working conditions was conducted to identify and validate the proposed finite element approach. The numerical simulation and experimental results indicate that the three-dimensional microstructural numerical model established can effectively analyze the material’s rheological mechanical response under the effect of triaxial load within the linear viscoelastic range.

Micromechanical Modelling of the Cyclic Deformation Behavior of Martensitic SAE 4150—A Comparison of Different Kinematic Hardening Models

A fundamental prerequisite for the micromechanical simulation of fatigue is the appropriate modelling of the effective cyclic properties of the considered material. Therefore, kinematic hardening formulations on the slip system level are of crucial importance due to their fundamental relevance in cyclic material modelling. The focus of this study is the comparison of three different kinematic hardening models (Armstrong Frederick, Chaboche, and Ohno–Wang). In this work, investigations are performed on the modelling and prediction of the cyclic stress-strain behavior of the martensitic high-strength steel SAE 4150 for two different total strain ratios (R ε = −1 and R ε = 0). In the first step, a three-dimensional martensitic microstructure model is developed by using multiscale Voronoi tessellations. Based on this martensitic representative volume element, micromechanical simulations are performed by a crystal plasticity finite element model. For the constitutive model calibration, a new multi-objective calibration procedure incorporating a sensitivity analysis as well as an evolutionary algorithm is presented. The numerical results of different kinematic hardening models are compared to experimental data with respect to the appropriate modelling of the Bauschinger effect and the mean stress relaxation behavior at R ε = 0. It is concluded that the Ohno–Wang model is superior to the Armstrong Frederick and Chaboche kinematic hardening model at R ε = −1 as well as at R ε = 0.

Size Effects of Finite Element Model for Three-Dimensional Microstructural Modeling of Asphalt Mixture

Asphalt mixture is a particulate composite material consisting of aggregate, mastic, and air voids. The computed tomography (CT) image-based finite element approach is used as an effective method to simulate micromechanical response of asphalt mixture. For finite element analysis, the accuracy of the finite results is determined by the size of the finite element. In this paper, a voxel-based three-dimensional (3D) digital reconstruction model of asphalt mixture with the CT images after being processed was proposed. In this 3D model, the aggregate phase was considered as elastic materials while the asphalt mastic phase was considered as linear viscoelastic material. Four micromechanical digital models were generated, whose voxel sizes were 0.5 mm, 0.67 mm, 1.0 mm, and 2.0 mm, respectively. The four digital models were used to conduct uniaxial creep test for predicting creep stiffness modulus to investigate the effect of voxel size. Simulation results showed that the voxel sizes had a significant effect on creep stiffness modulus. For the creep simulation test, the most appropriate voxel size whose creep stiffness modulus changes within 2.5% is 1.0 mm with regard to time steps, computational time, aggregate, and mastic shape representations.

Microstructure-based constitutive model of coronary artery with active smooth muscle contraction

Currently, there is no full three-dimensional (3D) microstructural mechanical model of coronary artery based on measured microstructure including elastin, collagen and smooth muscle cells. Many structural models employ mean values of vessel microstructure, rather than continuous distributions of microstructure, to predict the mechanical properties of blood vessels. Although some models show good agreements on macroscopic vessel responses, they result in a lower elastin stiffness and earlier collagen recruitment. Hence, a full microstructural constitutive model is required for better understanding vascular biomechanics in health and disease. Here, a 3D microstructural model that accounts for all constituent microstructure is proposed to predict macroscopic and microscopic responses of coronary arteries. Coronary artery microstructural parameters were determined based on previous statistical measurements while mechanical testing of arteries (n = 5) were performed in this study to validate the computational predictions. The proposed model not only provides predictions of active and passive stress distributions of vessel wall, but also enables reliable estimations of material parameters of individual fibers and cells and thus predicts microstructural stresses. The validated microstructural model of coronary artery sheds light on vascular biomechanics and can be extend to diseased vessels for better understanding of initiation, progression and clinical treatment of vascular disease.

Limestone and silica powder replacements for cement: Early-age performance

Developing functional concrete mixtures with less ordinary portland cement (OPC) has been one of the key objectives of the 21st century sustainability movement. While the supplies of many alternatives to OPC (such as fly ash or slag) may be limited, those of limestone and silica powders produced by crushing rocks seem virtually endless. The present study examines the chemical and physical influences of these powders on the rheology, hydration, and setting of cement-based materials via experiments and three-dimensional microstructural modeling. It is shown that both limestone and silica particle surfaces are active templates (sites) for the nucleation and growth of cement hydration products, while the limestone itself is also somewhat soluble, leading to the formation of carboaluminate hydration products. Because the filler particles are incorporated as active members of the percolated backbone that constitutes initial setting of a cement-based system, replacements of up to 50% of the OPC by either of these powders on a volumetric basis have minimal impact on the initial setting time, and even a paste with only 5% OPC and 95% limestone powder by volume achieves initial set within 24 h. While their influence on setting is similar, the limestone and silica powders produce pastes with quite different rheological properties, when substituted at the same volume level. When proceeding from setting to later age strength development, one must also consider the dilution of the system due to cement removal, along with the solubility/reactivity of the filler. However, for applications where controlled (prompt) setting is more critical than developing high strengths, such as mortar tile adhesives, grouts, and renderings, significant levels of these powder replacements for cement can serve as sustainable, functional alternatives to the oft-employed 100% OPC products.

A validated 3D microstructure-based constitutive model of coronary artery adventitia.

A structure-based model that accurately predicts micro- or macromechanical behavior of blood vessels is necessary to understand vascular physiology. Based on recently measured microstructural data, we propose a three-dimensional microstructural model of coronary adventitia that incorporates the elastin and collagen distributions throughout the wall. The role of ground substance was found to be negligible under physiological axial stretch λz = 1.3, based on enzyme degradation of glycosaminoglycans in swine coronary adventitia (n = 5). The thick collagen bundles of outer adventitia (n = 4) were found to be undulated and unengaged at physiological loads, whereas the inner adventitia consisted of multiple sublayers of entangled fibers that bear the majority of load at higher pressures. The microstructural model was validated against biaxial (inflation and extension) experiments of coronary adventitia (n = 5). The model accurately predicted the nonlinear responses of the adventitia, even at high axial force (axial stretch ratio λz = 1.5). The model also enabled a reliable estimation of material parameters of individual fibers that were physically reasonable. A sensitivity analysis was performed to assess the effect of using mean values of the distributions for fiber orientation and waviness as opposed to the full distributions. The simplified mean analysis affects the fiber stress-strain relation, resulting in incorrect estimation of mechanical parameters, which underscores the need for measurements of fiber distribution for a rigorous analysis of fiber mechanics. The validated structure-based model of coronary adventitia provides a deeper understanding of vascular mechanics in health and can be extended to disease conditions.

Generation of Three-Dimensional Microstructure Model for Discontinuously Reinforced Composite by Modified Random Sequential Absorption Method

Computer simulation of mechanical behavior of discontinuously reinforced composites containing randomly oriented short-fibers/whiskers presents an attractive opportunity for reduction of the number of experiments and resources required for microstructure design of such advanced materials. It is desirable to perform such simulations using microstructure model that accounts for randomness in angular orientations and locations of the short fibers/whiskers. In this contribution, a methodology is presented for efficient simulation of the required microstructural model through modification of well-known random sequential adsorption (RSA) algorithm for microstructure simulation through its application to the microstructure of Mg–alloy matrix composite containing randomly oriented short carbon fibers. The modified RSA algorithm enhances accuracy and efficiency of the complex geometric details of the randomly oriented short-fiber reinforced composite microstructure. Simulated microstructural model of composite is implemented in abaqus to simulate the mechanical response of the Mg–matrix composite containing randomly oriented short carbon fibers. The generated complex microstructure model in abaqus code is sliced into thin slices for reducing computing resources. The simulated results from multiple sliced models were averaged to approximate the result for the full volume element. The simulated mechanical response by use of multiple sliced models is validated via comparison with the experimental data.

A three-dimensional realistic microstructure model of particle-reinforced metal matrix composites

A new and robust methodology is presented for the complete computer simulation of large three-dimensional (3D) microstructures of particle-reinforced metal matrix composites (PRMMCs), by integrating the boundary representation scheme, the random cutting algorithm and the random sequential adsorption algorithm. The methodology allows large realistic 3D microstructure models to be generated that can be used for multi-scale investigation of PRMMC structure and design. The effect of the simulation parameters on the simulated microstructure is investigated by applying a quantitative metallographic analysis of the distribution functions of aspect ratio, diameter and the area of reinforcements. Simulated large realistic homogenous 3D microstructures of PRMMC are in close agreement with the experimental microstructures.

Three-Dimensional Microstructural Modeling Framework for Dense-Graded Asphalt Concrete Using a Coupled Viscoelastic, Viscoplastic, and Viscodamage Model

This paper presents a three-dimensional (3D) image-based microstructural computational modeling framework to predict the thermoviscoelastic, thermoviscoplastic, and thermoviscodamage response of asphalt concrete. X-ray computed tomography is used to scan dense-graded asphalt concrete (DGA) to obtain slices and planar images, from which the 3D microstructure is reconstructed. Image process- ing techniques are used to enhance the quality of images in terms of phase identification and separation of particles. This microstructure is divided into two phases: aggregate and matrix. The aggregate phase is modeled as an elastic material and the matrix phase is modeled as a thermoviscoelastic, thermoviscoplastic, and thermodamage material. Stress-strain response, damage propagation, and the distributions of the viscoelastic and viscoplastic strains are predicted by performing virtual uniaxial and repeated creep-recovery tests of the developed 3D model of asphalt concrete. The effects of loading rate, temperature, and loading type on the thermomechanical response of asphalt concrete are investigated. In addition, the microscopic and macroscopic responses of DGA are compared with those of stone matrix asphalt (SMA). The results demonstrate that SMA can sustain higher strain levels at the microscopic level and higher macroscopic ultimate strength. The damage in SMA is more localized than in DGA. The microstructure-based framework presented in this paper can be used to offer insight on the influence of the distribution and properties of microscopic constituents on the macroscopic behavior of asphalt concrete. DOI: 10.1061/ (ASCE)MT.1943-5533.0000860. © 2014 American Society of Civil Engineers. Author keywords: X-ray computed tomography; Three-dimensional microstructure; Finite element method; Dense-graded asphalt concrete; Damage mechanics.

Three-Dimensional Microstructural Modeling of Asphalt Concrete by Use of X-Ray Computed Tomography

This paper presents a framework that combines experimental techniques and computational methods for modeling the microscopic response of asphalt mixtures subjected to various loading conditions. The basis of this framework is capturing the three-dimensional microstructure of asphalt mixtures with X-ray computed tomography and a sequence of image-processing methods to identify the microstructure components or mixture phases. This microstructure is then converted to a finite element model in which the various phases are represented with constitutive models that describe their mechanical behavior. In this study, the coarse aggregate phase was modeled as a linear elastic material, and the matrix phase (asphalt, fine particles, and air voids) was represented as a thermoviscoelastic, viscoplastic, and damage model. The analysis results showed that the model captured the effects of temperature, rate of loading, repeated loads, and mixture design on the microstructure response. These results demonstrate that the developed framework will help engineers and researchers to understand the effects of mixture design and material properties on performance and to establish the link between microscopic response and macroscopic behavior.

Multiscale finite element simulations of piezoelectric materials based on two- and three-dimensional electron backscatter diffraction–measured microstructures

This article presents a computational procedure for evaluating effective homogenized material properties of polycrystalline piezoelectric materials and constructing two- and three-dimensional realistic microstructure models based on electron backscatter diffraction crystal orientation measurement. Microstructural features of a polycrystalline piezoelectric material, barium titanate, were investigated through electron backscatter diffraction measurements using an amorphous osmium coating to prevent charging. Realistic crystal orientations obtained from the electron backscatter diffraction measurements were introduced into multiscale finite element simulations based on homogenization theory to reveal the relationship between the macrostructure and the microstructure. First, a two-dimensional microstructural model was constructed, and the effect of the sampling area of the electron backscatter diffraction–measured crystal orientations was analyzed. We discuss the representative volume element determined from two points of view: the macroscopic homogenized material properties and the microscopic localized material behavior in response to external loads. Second, the surface of specimen was ground and polished at regular intervals and was measured by electron backscatter diffraction iteratively. Then a three-dimensional microstructural model was constructed by stacking in-plane crystal orientations in series along the out-of-plane direction, and the influence of the microstructural thickness, which indicates the stacking dimension in the out-of-plane direction, was investigated. We compare the macrostructural homogenized material properties between the two- and three-dimensional microstructures.

Kozeny–Carman and empirical formula for the permeability of computer rock models

Increasing interest in physical properties of rocks for purposes such as reservoir engineering and environmental geophysics has stimulated increased use of computer modeling of rock microstructure. Three-dimensional rock microstructure models based on spherical and non-spherical grain models are presented in this paper. The models are used to calculate the permeability. Important parameters such as tortuosity, which is difficult to measure in the laboratory, can be calculated easily by means of Lattice Boltzmann Method applied to the constructed models. The Kozeny–Carman formula gives lower prediction than the measured permeability. Modified power laws of porosity give better estimates if divided into two separate formulas, one for porosities lower than 20% and another for porosities higher than 25%. This new empirical formula gives better prediction for all models, except pigeon-hole.

Three-dimensional microstructural modeling of asphalt concrete using a unified viscoelastic–viscoplastic–viscodamage model

This paper presents a three-dimensional (3D) microstructure-based computational model to predict the thermo-mechanical response of the asphalt concrete using a coupled thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamage constitutive model. The 3D microstructure of the asphalt concrete is reconstructed from slices of two-dimensional X-ray computed tomography images that consist of the matrix and the aggregate phases and ignoring voids. The matrix is considered as a thermo-viscoelastic, thermo-viscoplastic, and thermo-viscodamage material; while, the aggregates are considered to be linear elastic. The 3D model is subjected to uniaxial compression, tension, and repeated creep recovery tests at different temperatures to investigate the stress–strain behavior, damage propagation, and the patterns of the recoverable and irrecoverable strains. The presented results show that the generated 3D microstructure model along with the presented constitutive model can be used effectively to predict the overall thermo-mechanical response of asphalt concrete. Therefore, the presented framework can be used to provide insight on the influence of the asphalt concrete microstructure on its macroscopic response. In addition, it is a tool to select the mixture components and its proportions to achieve the desired macroscopic properties and performance.

Effects of non-ideal structures and high temperatures on the insulation properties of aerogel-based composite materials

The multi-scale, temperature related structural characteristics of aerogel-based composite insulation materials that contain nano-scale aerogels, as well as micron-scale fibers, opacifiers and cracks were evaluated using various instruments for 300 to 1423 K. The structural tests were used to develop a three-dimensional multi-scale microstructure model to investigate the effects of non-ideal structures and high temperatures on the insulation performance of aeogel-based composite materials. The predictions agree well with experimental with literature. The model, thus provides theoretic guidelines for manufacturing with optimal parameters, such as the type, loading, and distribution of fibers and opacifiers. The structural analysis shows that the insulation performance of the composite materials degrades significantly with the deformation of the pore structure at high temperatures conditions.

Study on Multi-Void Microstructure of Asymptotic Homogenization for Topology Optimization

One kind of multi-void three-dimensional microstructure models based on homogenization method is constructed. Based on multi-void microstructure, the mathematical models for the topological structural optimization which takes maximizing the total potential energy as the objective function is constructed, then the Kuhn-Tucker optimality condition of the update method about the designs variable based on the porous microstructure can be gotten when optimization iterates. Finally, in explaining the employed algorithm an example is provided.