Behavior Of Grains Research Articles

Heterogeneous components removal mechanism and grinding force model from energy aspect in ultrasonic grinding continuous fiber reinforced metal matrix composites

Continuous fiber reinforced metal matrix composites (CFMMCs) offer higher specific strength, specific modulus, and operating temperature than matrix metals due to the unique enforcement mechanism of the one-to-one scale arrangement of matrix and reinforced phases. Due to the heterogeneous characteristics between the plastic matrix and brittle fibers, the removal mechanism of CFMMCs during processing is exceptionally complex. Ultrasonic vibration-assisted grinding (UVAG) shows great advantages in machining difficult-to-cut materials (i.e., ceramics and composites) by changing the motion trajectory between grains and workpieces, effectively reducing grinding force and improving machining quality. However, little is known about the removal mechanism of UVAG for CFMMCs composed of the ductile (i.e., metal matrix) and brittle (i.e., SiC fiber) phases with highly anisotropic structure characteristics. This raises the question of how CFMMCs with heterogeneous components perform under abrasive processing and how to predict their processing forces. Hence, UVAG and conventional grinding (CG) experiments with single CBN grain were carried out on SiC fiber reinforced TC17 matrix composites (SiCf/TC17) in this work. A grinding force model considering both phases and materials structure from energy aspect was proposed. A theoretical model for suppressing SiC fiber damage has been proposed, which is expected to guide low-damage processing of brittle materials. According to the results, the removal models of CFMMCs are revealed including: i) macro fracture of SiC fiber, ii) neat fracture of SiC fiber, and iii) TC17 matrix massive adhesion on the SiC fiber. Besides, no cracks crossing fibers are observed on the subsurface of SiC fiber under both UVAG and CG due to the good support of the TC17 matrix on SiC fibers. The grinding force predicted model error decreases as ap increases. When ap is 50 μm, the errors between predicted and experimental values are 7.8 % and 9.1 % for normal forces (Fn) and tangential forces (Ft), respectively. Ultrasound suppresses the severe wear behavior of grains, thereby improving the tool life. This paper aims to comprehensively reveal the characteristics of abrasive processing of CFMMCs from various aspects (surface morphology, subsurface features, grinding force prediction, and tool wear), which will promote the industrial application of CFMMCs.

A Review on Social Interaction Effects of Farmers’ Water-saving Production Behavior in Grain

This paper systematically combs through the relevant literature on the social interaction effects of water-saving production behavior of grain farmers, and puts forward the shortcomings. The existing related literature mainly includes research on social interaction and its evaluation system, research on the driving factors of water-saving production, research on the effects of water-saving production, and research on the enhancement path of water-saving production. The shortcomings of the existing studies mainly include the insufficient research on the influence of social interaction of water-saving production behavior of grain, the social interaction path of the spillover effects of water-saving production of grain has to be tested, and the research on the incentive mechanism of water-saving production of grain has to be improved.

Review of Multiscale Modeling and Simulation Techniques in Metal Forming, Bending, Welding, and Casting Processes for Enhanced Predictive Design and Analysis

Multiscale modeling and simulation offer crucial insights for designing and analyzing metal forming, bending, welding, and casting processes, all of which are vital across automotive, aerospace, and construction industries. This paper overviews multiscale techniques used in these areas. Macroscopically, continuum-based methods like finite element analysis (FEA) model the overall process and its impact on metal materials. FEA reveals deformation, stress distribution, and temperature changes during manufacturing processes. Mesoscale techniques, including crystal plasticity, phase field methods, and cellular automata, focus on microstructural evolution and mechanical properties. They model the behavior of grains and phases within the metal. These models combine macro and mesoscale data for accuracy. This allows for the prediction of grain growth, recrystallization, and phase transformations – critical for optimizing processes, refining component design, and ensuring quality. For example, multiscale modeling successfully captured microstructural evolution during casting (demonstrating ±2% average grain growth deviation) and predicted defect formation in welded joints with high accuracy (demonstrating a 0.95 correlation coefficient with non-destructive testing).

Investigating the Degradation Behavior of Grain Refined WE43 Magnesium Alloy Produced by Friction Stir Processing for Medical Implant Applications

Developing Magnesium (Mg) based degradable implants for orthopedic applications is an attractive research area for the past two decades in the biomedical engineering. Mg is well accepted by human system and does not cause any health abnormalities during its degradation in the physiological environment. However, in order to improve its life span by controlling the aggressive degradation, novel Mg alloys are developed and subjected to different treatments to enhance their performance to tailor as promising candidates for implant manufacturing. In this context, recently, a special attention is paid towards using rare earth containing Mg alloys due to their excellent mechanical and corrosion resistance properties. Hence, in the present work, WE43 Mg alloy has been selected and the microstructual modification was carried out by friction stir processing. The role of grain refinement on the degradation behavior of FSPed WE43 Mg alloy was assessed by immersing the samples in simulated body fluids. From the microstructural studies, grain size reduction from 46 ± 4.2 µm to 16.1 ± 5.4 µm was achieved after FSP. The larger intermetallic particles were also observed as dissolved into the solid solution grains and fewer intermetallic particles were remained in the stir zone of FSPed alloy. After immersion studies, the surface of the samples was deposited with mineral phases and were analyzed by X-ray diffraction analysis and scanning electron microscope and found that the grain refinement achieved by FSP has a significant effect on increasing the mineral depositions which helps to control the degradation rate of the samples.

Effect of irradiation-induced strength anisotropy on the reorientation trajectories and fragmentation behavior of grains in BCC polycrystals under tensile loading

We present a combined experimental and computational study exploring the effects of strength anisotropy on the grain reorientation trajectories in neutron-irradiated BCC polycrystals subjected to uniaxial tensile loading. We observe through in situ high-energy X-ray diffraction microscopy measurements of a model BCC alloy, Fe-9wt.%Cr, that the grains in irradiated samples exhibit reorientation trajectories that deviate more substantially from classical expectations than those in the unirradiated counterpart. We hypothesize that irradiation-induced strength anisotropy is a major influence on this behavior. Utilizing crystal plasticity finite element modeling, we isolate the effects of strength anisotropy by performing a suite of simulations in which we systematically strengthen select slip systems. Reorientation trajectories are compared against a datum of Taylor model predictions, and the deviation from classical expectations is analyzed through the lens of slip activity and availability. We further describe observations regarding the propensity of samples with high degrees of strength anisotropy to exhibit grain fragmentation. Overall, computational results provide insight on and quantification of the effects of strength anisotropy on reorientation trajectories and grain fragmentation, and align well with experimental observations, suggesting strength anisotropy as a plausible contributing mechanism to the observed phenomena.

A photoelastic method for stress analysis of granular terrain beneath a wheel

This paper presents a photoelastic method for the stress analyses of granular terrains beneath a traveling wheel. Recently, wheel terramechanics have been studied using various advanced techniques such as particle velocimetry and machine learning. However, the dynamic profiles of the stress distributions in soil have not been directly observed. In this paper, we propose a photoelastic method to experimentally demonstrate the two-dimensional stress analysis of a granular terrain. This method uses photoelastic disks as terrain particles; thus, the internal stress and propagation of the granular terrain can be visualized using the interference fringe of light. This study aimed to observe the dynamic behavior of grains, typically simulating circular or spherical objects of the granular terrain. To demonstrate the photoelastic method for simulated ground, we developed a single-wheel testbed using photoelastic materials. Moreover, the effects of mixing with non-photoelastic materials were investigated to simulate steady states with small and large wheel-slip conditions. This paper presents a force chain analysis of the photoelastic particles beneath a single traveling wheel. The force chain structure was geometrically compared with the propagation angle and length. In addition, the orientational orders of the force chains were quantitatively evaluated under both small and large wheel slip conditions. The experimental results confirmed that the photoelastic method can reveal dynamic changes in the internal stress structures of granular terrain beneath the wheel under various slip conditions.

Origin of improved Na+ ionic conductivity in the NASICON-type solid state electrolyte with Sm modification

The NASICON-type (Na1+xZr2SixP3-xO12, 0≤x ≤ 3) sodium-ion solid state electrolyte (SSE) has emerged as an alternative for liquid electrolyte due to its good chemical/electrochemical stability, high thermal stability and high safety. However, the insufficient ionic conductivity and poor understanding of Na+ transport mechanism hinder the further development of sodium-ion SSE. Herein, we report Sm modified Na3+xZr2-xSmxSi2PO12 (0≤x ≤ 0.4) electrolytes with a highest ionic conductivity of 2.25 × 10−3 S cm−1 at 25 °C when x = 0.2. The introduction of Sm element adjusts the Si/P ratio in NASICON phase and densifies the electrolyte pellets by formation of Na3Sm(PO4)2. To get a deep insight into the enhanced mechanism of Na + transport in grains, low-temperature electrochemical impedance spectra (LT-EIS) and Jonscher's power law relationship are employed to analyze the electrical behavior of grains. The results demonstrate that the regulation of Si/P ratio can evoke lower migration energy, more charge carrier concentration and higher hopping frequency, which synergistically improve the ionic conductivity in grains.

In situ observation of the specific nucleation behavior of grains during the solidification of Al alloy inoculated by Sc

The specific behavior of grains nucleation on primary Al3Sc particles and its effects on subsequent nucleation events have not been uncovered by previous ex situ analysis. Here, the real-time grains nucleation during the solidification of Al-10Cu alloy inoculated by Sc is first observed via synchrotron radiography. The results show that grains can nucleate on one face and grow along other faces of relatively large cuboid Al3Sc particles, leading to the incomplete engulfment of particles. Hence, two or more grains can nucleate on the same Al3Sc particle and grains can easily detach from particles, both of which promote grains nucleation during solidification. The discoveries modify the previous common view on the role of particles between grain boundaries and enlighten the better application of flow-induced technologies to the refinement of Al alloys inoculated by Sc.

Evaluation of particle models of corn kernels for discrete element method simulation of shelled corn mass flow

Bulk handling behavior of grains can be studied experimentally, but large-scale investigations of grain flow especially at the commercial scale are expensive, time consuming, and are therefore limited in the treatment factors that can be evaluated in any one study. Recent research has demonstrated the potential of discrete element method (DEM) in simulating grain flow in handling operations. However, application of DEM for simulating grain flow, requires development of appropriate particle models for each grain type. In this study, particle models comprised of one to four overlapping spheres were developed for shelled corn and tested. With these models, measurement of bulk properties, namely bulk density and angle of repose, both involving bulk flow were simulated using EDEM™ software with published data of material and interaction properties of shelled corn as inputs associated with each particle shape. Predicted time for the complete outflow from the bulk density test hopper (hopper emptying time), designated as simulation time in the study, was also recorded as another discriminant for model selection. Variable inputs into the simulation modeling were material properties particle shape, particle size distribution, Poisson's ratio, shear modulus, and density and interaction properties particle coefficients of restitution, static friction, and rolling friction. Computation time is critical in DEM modeling so single sphere particle models were emphasized over multi-sphere particles in the research even though multi-sphere particles represent the corn kernel shape more precisely because their simplicity can provide markedly reduced computation times to complete simulations. Predicted results for hopper emptying time, bulk density, and angle of repose were compared to experimental results or published data to select the most appropriate particle models for simulating bulk behavior of corn kernels in free-flowing grain applications using DEM. From the study, the most appropriate particle model (particle shape/physical properties combination) for corn kernels involved a single-sphere shape particle shape with a particle coefficient of restitution of 0.30, particle coefficients of static friction of 0.30 for corn-corn contact and 0.20 for corn-steel contact, particle coefficient of rolling friction of 0.05, normal particle size distribution with a standard deviation factor of 0.4, and particle shear modulus of 20 MPa.

Investigation of maize grains penetrating holes on a novel screen based on CFD-DEM simulation

Maize cleaning is one of the important processes in maize cleaning operations. To enhance the screening performance of the bionic screen further, the screening process of maize mixture was simulated by CFD-DEM, and the simulation results were validated experimentally. The behaviour of grains penetrating the bionic screen under different gestures was investigated. The grains that penetrate the screen holes by falling, rolling, and sliding account for 22.2%, 35.8%, and 42.0% of the total grains penetrating the screen holes. The results show that the grains exhibiting sliding and rolling behaviour are more easily able to penetrate the screen holes. The quantity of grains penetrating the screen holes in the plates 1–8 is gradually increased from 0 to 79, and the grains penetrate the screen holes better during the screen plates flattening upward. This study can provide a basis for designing a new screen and improving cleaning performance.

Grain and Grain Boundary Conduction Channels in Copper Iodide Thin Films

Due to the textured nature of random in‐plane orientation of sputtered γ‐CuI (111) thin films, the crystalline grains and grain boundaries (GBs) influence charge carrier transport. Herein, current probe atomic force microscopy (cp‐AFM) measurements for differentiation and correlation of these morphological features and their contribution to electrical conductivity are presented, thus showing a clear difference between the conductive behavior of grains and GBs. A localized high and linearly voltage‐dependent current at the boundaries as well as a rectifying behavior between the platinum‐coated AFM tip and the grain surfaces is observed. Also, a different temporal evolution of voltage‐dependent conductivity is observed for grains and GBs. Further, the charge carrier transport through the surface vanishes with time. It is suspected that atmospheric oxygen causes these time‐dependent surface changes because accelerated degradation of the conductivity after oxygen plasma treatment is also measured.

Natural fractures and their contribution to tight gas conglomerate reservoirs: A case study in the northwestern Sichuan Basin, China

Well-developed natural fractures in the tight gas conglomerate reservoirs of the northwestern Sichuan Basin, China, are proved to greatly contribute to the porosity and permeability of such reservoirs. Natural fractures can be storage space for hydrocarbons in the reservoir and also serve as fluid flow conduits. Outcrops, cores, and image logs were assessed in order to understand the natural gas production from the tight conglomerate reservoirs. Based on the type of interaction between fractures and clast grains, here we present three types of fractures in the conglomerate tight gas reservoirs: intergranular fractures, intragranular fractures, and grain-edge fractures. These fractures may be tectonic, diagenetic, or combined tectonic-diagenetic. Factors affecting natural fracture development in conglomerates include composition of grain and interstitial material, grain size, contact behavior of grains, and structural position. Well-developed open fractures make up over 70% of the porosity within the tight conglomerate reservoir, while the local permeability can be 3-5 orders higher than that of the matrix reservoir. Natural fractures can also significantly impact the natural gas productivity from individual wells. Production data suggests that higher natural fracture intensity correlate with higher natural gas productivity from wells. Compared with the intensity of intragranular fractures and grain-edge fractures, the high intensity of intergranular fractures shows a notably stronger correlation with high gas productivity. The impact of fractures on natural gas productivity varies greatly with fracture orientation. East-West fractures are predominant flow channels under the existing East-West stress field, contributing significantly to gas production. Northeast-Southwest-oriented fractures are of secondary importance.

Multiphase-field simulation of grain coalescence behavior and its effects on solidification cracking susceptibility during welding of Al-Cu alloys

Solidification cracking (SC) is highly related to the grain coalescence behavior during welding of aluminum alloys. In this study, the grain coalescence behavior and its effects on solidification cracking susceptibility (SCS) were investigated using the multiphase-field approach. Why SCS is high at a certain value of Cu concentration and why SC often occurs at high misorientation angles are revealed. Firstly, nominal compositions of Cu affect the morphology of microstructure during solidification. The crystals morphology is cellular at the low concentration, while the crystals are dendritic at the high concentration in the columnar grain region. The SCS of cellular grains is higher than dendrites due to the high volume fraction of solid when the grains/subgrains bridge. Under the action of tensile stress, the scarce residual liquid phase cannot backfill in time. Secondly, high misorientation angles make grain boundary energy in the solid–solid interface (σSS) is high. It is found that σSS suppresses the grain coalescence and increases the SCS of alloys. This leads the emergence of SC at high misorientation angles during welding. In this study, the coalescence behavior of grains during solidification is visually presented by simulation and the coherency point at the last-stage solidification is achieved accurately.

Microstructures and Electrical Conduction Behaviors of Gd/Cr Codoped Bi3TiNbO9 Aurivillius Phase Ceramic.

In this work, a kind of Gd/Cr codoped Bi3TiNbO9 Aurivillius phase ceramic with the formula of Bi2.8Gd0.2TiNbO9 + 0.2 wt% Cr2O3 (abbreviated as BGTN−0.2Cr) was prepared by a conventional solid-state reaction route. Microstructures and electrical conduction behaviors of the ceramic were investigated. XRD and SEM detection found that the BGTN−0.2Cr ceramic was crystallized in a pure Bi3TiNbO9 phase and composed of plate-like grains. A uniform element distribution involving Bi, Gd, Ti, Nb, Cr, and O was identified in the ceramic by EDS. Because of the frequency dependence of the conductivity between 300 and 650 °C, the electrical conduction mechanisms of the BGTN−0.2Cr ceramic were attributed to the jump of the charge carriers. Based on the correlated barrier hopping (CBH) model, the maximum barrier height WM, dc conduction activation energy Ec, and hopping conduction activation energy Ep were calculated with values of 0.63 eV, 1.09 eV, and 0.73 eV, respectively. Impedance spectrum analysis revealed that the contribution of grains to the conductance increased with rise in temperature; at high temperatures, the conductance behavior of grains deviated from the Debye relaxation model more than that of grain boundaries. Calculation of electrical modulus further suggested that the degree of interaction between charge carriers β tended to grow larger with rising temperature. In view of the approximate relaxation activation energy (~1 eV) calculated from Z″ and M″ peaks, the dielectric relaxation process of the BGTN−0.2Cr ceramic was suggested to be dominated by the thermally activated motion of oxygen vacancies as defect charge carriers. Finally, a high piezoelectricity of d33 = 18 pC/N as well as a high resistivity of ρdc = 1.52 × 105 Ω cm at 600 °C provided the BGTN−0.2Cr ceramic with promising applications in the piezoelectric sensors with operating temperature above 600 °C.

Correlation between Taylor Model Prediction and Transmission Electron Microscopy-Based Microstructural Investigations of Quasi-In Situ Tensile Deformation of Additively Manufactured FeCo Alloy

Within this research, the multiscale microstructural evolution before and after the tensile test of a FeCo alloy is addressed. X-ray µ-computer tomography (CT), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) are employed to determine the microstructure on different length scales. Microstructural evolution is studied by performing EBSD of the same area before and after the tensile test. As a result, langle001rangle||TD, langle011rangle||TD are hard orientations and langle111rangle||TD is soft orientations for deformation accommodation. It is not possible to predict the deformation of a single grain with the Taylor model. However, the Taylor model accurately predicts the orientation of all grains after deformation. {123}langle111rangle is the most active slip system, and {112}langle111rangle is the least active slip system. Both EBSD micrographs show grain subdivision after tensile testing. TEM images show the formation of dislocation cells. Correlative HRTEM images show unresolved lattice fringes at dislocation cell boundaries, whereas resolved lattice fringes are observed at dislocation cell interior. Since Schmid’s law is unable to predict the deformation behavior of grains, the boundary slip transmission accurately predicts the grain deformation behavior.

INVESTIGATION ON THE ROCK CUTTING MECHANISM OF HETEROGENEOUS GRANITE USING A GRAIN-BASED MODELING APPROACH

A good understanding of rock cutting mechanism is of great importance for improving the cutting efficiency and reducing the costs in hard heterogeneous formation drilling. This paper implements the grain-based modeling approach to mimic the granite considering the highly heterogeneous mechanical behaviors of grains in granite. The rock cutting mechanism of granite, accounting for the influence of hydrostatic pressure, mineral size, random distribution, rake angle, cutting depth and velocity of cutter, are investigated. The research results demonstrate that the inter-grain shear crack and intra-grain tensile crack are the two main crack types generated during rock cutting process. The cutting force responses show strong vibration with respect to the cutting distance. The magnitude of cutting force sharply drops and abruptly rises during the cutting process, which becomes more obviously with the increasing hydrostatic pressure, cutting depth and rake angle of cutter. The hydrostatic pressure, grain size and random distribution of grains have great influence on chip morphology. In contrast, comparing with the above three factors, the cutting depth, rake angle of cutter and cutting velocity have little influence on the chip morphology. These results lead to an enhanced understanding of rock breaking mechanisms in granite, and provide a basis for improving the design of rock-breaking bits.

An innovation in finite element simulation via crystal plasticity assessment of grain morphology effect on sheet metal formability

Experimental and numerical study regarding the uniaxial tensile test and the forming limit diagram are addressed in this paper for AL2024 with the face-centered cube structure. First, representation of a grain structure can be obtained directly by mapping metallographic observations via scanning electron microscopy approach. Artificial grain microstructures produced by Voronoi Tessellation method are employed in the model using VGRAIN software. By resorting to the finite element software (ABAQUS) capabilities, the constitutive equations of the crystal plasticity were utilized and implemented as a user subroutine material UMAT code. The hardening parameters were calibrated by a trial and error approach in order to fit experimental tensile results with the simulation. Then the effect of the changing grain size, the heterogeneity factor, and the grain aspect ratio were studied for a uniaxial tensile test to emphasize the importance of the microstudy behavior of grains in material behavior. Furthermore, the polycrystal plasticity grain distribution was employed in the Nakazima test in order to obtain the forming limit diagram. The crystal plasticity-driven forming limit diagram reveals more accurate strains, taking into account the involving the micromechanical features of the grains. An innovative approach is pursued in this study to discover the necking angle, both in tensile test or Nakazima samples, showing a good agreement with the experiment results.

Grain for Green Project in farmers’ minds: perceptions, aspirations and behaviours in eco-fragile region, Xinjiang, China

PurposeThis study aims to focus on the analysis of the internal mechanism of farmers’ ecological cognition and the behaviour of Grain for Green Project (GGP), and the further relationship between ecological cognition and ecological aspiration, proposing climate change strategies and management from the perspective of farmers.Design/methodology/approachTheory of planned behaviour and social exchange theory were used to construct a theoretical framework and an ecological cognition under the influence of external factors, the aspiration and the behaviour of GGP, using ecological fragile areas in Bazhou and Changji, Xinjiang of 618 peasant households’ survey data. The structural equation model and Heckman two-step model were applied to analyse the relationship between ecological cognition and ecological aspiration of farmers, the impact of peasant households’ ecological cognition and aspiration to the behaviour of GGP and the influence factors of GGP behaviour.FindingsThis research’s results show that the three characterizations of ecological cognitive variables, attitude towards the behaviour (AB), subjective norms (SN) and perceived behaviour control (PBC), have significant positive impact on farmers’ GGP ecological aspiration. The comprehensive impact path coefficients of ecological cognition are PBC (0.498) > SN (0.223) > AB (0.177). Also, income change is a moderating variable, which has a significant moderating effect on the influence of AB and SN on ecological aspiration. Further, farmers’ ecological cognition has an influence on the behaviour of GGP, and the change of farmers’ income has a significant positive effect on farmers’ choice of returning farmland to forests.Practical implicationsThe ecological protection policy suggestions and countermeasures can be drawn from the research conclusions, adapted to China’s ecologically fragile regions and even similar regions in the world to response the climate change.Originality/valueCombining the theory of planning behaviour and social exchange, this paper empirically analyses the path of farmers’ ecological cognition and ecological aspiration, as well as the influencing factors.

Intermittent nucleation and periodic growth of grains under thermo-solutal convection during directional solidification of Al-Cu alloy

The presence of natural convection during solidification of alloys significantly influences the heat and mass transfer processes in the liquid phase, and thus affecting the nucleation and growth behaviors of grains. It is crucial to understand the impacts of thermo-solutal convection on the solidification process to control the final properties of casting ingots. In this study, the directional solidification of Al-15 wt.% Cu alloy under different temperature gradients has been in-situ observed using synchrotron radiation X-ray radiography. The solute distribution in the field of view (FOV) and three dimensional solid microstructure are obtained by our proposed image processing technique, which aims to determine the permeability and solutal Rayleigh number in the mushy zone over time. Then the interplay between the thermo-solutal flow and microstructure is quantitatively studied. Results indicate the solute elements are periodically discharged out of and confined to the mushy zone owing to the solutal instability in the mushy zone, which results in the periodic oscillation of solute concentration. Therefore, the oscillatory constitutional undercooling gives rise to the intermittent nucleation and periodic growth of grains, which in turn cause the periodic oscillation of permeability and the associated solutal Rayleigh number, thereby in turn resulting in the oscillation of solute concentration. Moreover, owing to the superposed solute flow and convective flow, the oscillation amplitudes of solute concentration and nucleation number vary in a sinusoidal manner in general.

Study on the effect of micro-geometric heterogeneity on mechanical properties of brittle rock using a grain-based discrete element method coupling with the cohesive zone model

The micro-geometric heterogeneity has a significant effect on the mechanical behavior and failure mode of brittle rocks. To study the influence of the size distribution and preferred orientation of mineral grains, a statistical grain-based discrete element method coupling with the cohesive zone model is proposed on the basis of the universal distinct element code (UDEC) in this study. First, a mixed-mode cohesive model was developed and implemented in UDEC to simulate the nonlinear behavior of grain interfaces. Then, a micro-parameter calibration procedure based on the Plackett-Burman design, central composite design, and particle swarm optimization was established to reproduce the macro-properties of the Lac du Bonnet granite. Finally, the strength characteristics, deformation response, and failure mode of rocks were numerically examined using the proposed model by varying the size distribution and preferred orientation of mineral grains. The relationship between the micro-geometric heterogeneity and the uniaxial compressive strength, the crack initiation stress, the crack damage stress, the elastic modulus, the Poisson's ratio, and the failure mode of rocks are obtained respectively.