At high rotational speeds, ultra-thin grinding wheels undergo elastoplastic deformation due to the combined effects of centrifugal and grinding forces. This deformation causes the actual cutting depth to deviate from the theoretical depth, thereby compromising machining accuracy. To address this issue, this study establishes a mathematical model incorporating the concept of dynamic diameter (Dd). By comparing finite element simulations with experimental measurements, the study identifies the key factors influencing Dd. It is found that the dynamic diameter evolves through two distinct stages: elastic and plastic deformation. Based on these results, this paper optimises the theoretical formula for calculating the dynamic diameter and innovatively introduces a plasticity compensation coefficient derived from a bilinear isotropic hardening model, thereby enabling, for the first time, a quantitative analysis of irreversible radial expansion under high-speed conditions. Furthermore, the work provides a mechanistic link between the macroscopic Dd and the microstructural plastic flow of the metallic binder. These findings not only provide guidance for investigating the elastoplastic behavior of wheels in high-speed precision cutting but also offer critical insights for designing ultra-thin grinding wheels with minimal deformation and enhanced wear resistance.

Powder paving is an intermediate process of selective laser sintering (SLS). The dimensional accuracy and mechanical properties of sintered components are directly affected by the quality of the powder paving process, which is closely related to the flow characteristics of the powder and the process parameters of powder paving. This study investigated the simulation and optimization of the nylon powder paving in SLS by combining a discrete-element-method numerical simulation with a process test. A dynamic model was established to describe the flow and paving process of nylon powder at a preheating temperature considering mesoscopic van der Waals and electrostatic forces. The effects of the physical parameters and ambient temperature on the flow characteristics of nylon powder were analyzed, and the intrinsic relationship between the physical parameters of nylon powder, the process parameters of powder paving, and the quality of the powder paving were explored. A multi-objective regression model of the quality of powder paving was established using the response surface methodology, and a genetic algorithm was adopted to optimize the quality of the powder paving. A scientific and intelligent database of the nylon powder paving process in SLS was constructed by matching the process parameters of powder paving and physical parameters of the nylon powder, and the level of the SLS process was improved.

In this paper, a magnetic and elastic core-shell Fe3O4/PS/CeO2 abrasive was first synthesized via a simple and reproducible method. First, magnetic polystyrene (PS) microsphere cores were synthesized by adding modified magnetic particles in a soap-free emulsion polymerization process, followed by coating the microspheres with a CeO2 shell via an in-situ chemical precipitation method. Comprehensive and detailed characterizations of the prepared abrasives were carried out by means of TEM, XRD, FT-IR, TGA and VSM. In addition, the effects of partial preparation process parameters on the morphology, particle size distribution and solid content of the abrasives were investigated, providing quantitative analysis results for the precise preparation of the abrasives. Meanwhile, the abrasives can be rapidly separated from the dispersion system under an external magnetic field, exhibiting great recycling potential and economy.

This study aims to develop and validate a DEM-CFD coupled simulation model for the wet abrasive jet blunting process of cemented carbide inserts, to better understand the underlying mechanism of this process and to provide a theoretical basis for process parameter optimization. To this end, the DEM contact parameters were calibrated and validated through a combined experimental and simulation approach. The bonded particle model (BPM) parameters for the cemented carbide inserts were calibrated using response surface methodology (RSM), and the CFD model was established with appropriate mesh generation and grid independence verification. The outlet velocities under different blasting pressures were simulated and compared with theoretical calculations, yielding a maximum relative error of 5.32%, which confirms the validity of the model. Based on this model, the motion characteristics of the abrasive flow were further analyzed. The results demonstrate that after being accelerated by the jet, the particle velocity gradually decays and spreads laterally with increasing blasting distance in the main flow region. The blasting pressure and abrasive concentration exhibit opposite effects on the particle velocity.

Due to the shear-induced particle migration and the wall effect, the inhomogeneous distribution of coarse aggregate (CA) would change the rheological behavior of fresh concrete in pumping pipe. In this paper, a CFD-DEM coupling method was proposed to investigate pumping behavior, considering the effect of uneven distribution of CA. The pump pipe was divided into three zones and the CA particle concentration at each zone was calculated. Then, the rheological behavior of fresh concrete was calculated according to the relationship between the CA particle concentration and Bingham constants. It is found that the CA size has no obvious effect on the particle migration and wall effect is dominant. Due to the gravity of concrete, the thickness of lubrication layer becomes inhomogeneous in the horizontal straight pipe. Under pumping pressure, CA particles move towards convex side of bent pipe, resulting in a relatively thinner lubrication layer.

The significant application potential of silicon carbide (SiC) ceramics stems directly from their excellent physical and chemical properties, however, the limitations of traditional processing technology in processing of the hard and brittle materials have restricted the further application of SiC ceramics. As an effective polishing technique, ultrasonic vibration assisted chemical mechanical polishing (UV-CMP) has garnered increasing interest in the field of SiC ceramic processing. However, the cavitation effect induced by high-frequency vibrations in the slurry accelerates the removal of surface materials while simultaneously increasing the damage of material surface. In this study, polystyrene/ceria (PS/CeO2) abrasive particles were prepared and characterized. Subsequently, their polishing performance was investigated based on the self-built UV-CMP platform. Additionally, the structural stability of abrasive particles under varying polishing durations was examined and analyzed. The experimental results show that the material removal rate (MRR) of PS/CeO2 reaches 8.44 mu m/h, and the surface roughness (Ra) of the material is reduced from 0.118 mu m to 0.106 mu m. Meanwhile, it also has lower surface damage. Nevertheless, it was observed that the structural stability of abrasives declines with increasing polishing time.

Ultra High Performance Concrete (UHPC) is a highly innovative fiber-reinforced cementitious material. The uniformity of steel fibers in fresh UHPC will have a significant impact on its mechanical properties. In this paper, an ultrasonic non-destructive testing (NDT) method is proposed to evaluate the spatial distribution of steel fibers in fresh UHPC. Cubic specimens with 0%, 30%, 60% and 90% steel fiber agglomeration rates were designed and their acoustic time domain signals were acquired. As the agglomeration rate increased from 0% to 90%, the time domain integral area decreased by 57.3% and the maximum amplitude decreased by 54.1%. The frequency domain signals at different agglomeration rates were extracted and the signal density (SD) at different agglomeration rates was analyzed. The SD decreased by 41% when the agglomeration rate was increased from 0% to 90%, and a linear equation between the SD and the agglomeration rate of steel fibers was proposed. In addition, in order to analyze the ultrasonic propagation process in UHPC, simulations were performed using the Comsol Multiphysics finite element method. It was found that the refraction, scattering and reflection of ultrasonic waves in the agglomerate region were enhanced with the increase of agglomeration rate, resulting in energy dissipation of ultrasonic waves through the UHPC. Higher frequency ultrasonic waves are more likely to dissipate energy.

The freezing damage in ballasted railway tracks constitutes a widespread challenge in cold areas. There exists a critical need to develop suitable numerical simulation approaches to investigate the mechanical properties of track structure under low temperatures, particularly icing conditions. The discrete element method (DEM) has proven effective for characterizing the macro-meso mechanical behavior of granular ballast bed, while the bonded particle model (BPM) in DEM enables explicit modeling of the ice-bonded behavior between ballast particles. However, the relationship between the microscopic contact parameters in BPM and the macroscopic material properties has been confusing. To address this, an efficient parameter calibration strategy is imperative. Traditional trial-and-error calibration not only suffers from computational inefficiency but also introduces subjective bias. This study proposes a DEM calibration framework for frozen ballast aggregate based on the response surface methodology (RSM) with central composite design (CCD). Through uniaxial compression simulations implemented with a dilated polyhedron BPM, explicit second-order response surface functions were established between the bond micro-parameters and macro-mechanical properties (the compressive strength and elasticity modulus). Model validation against experimental data confirmed the predictive accuracy of the calibrated parameters. Finally, a DEM-FEM coupled model of the ballasted railway track was developed to evaluate structural responses in unfreezing and freezing conditions. The results show that the freezing behavior of granular ballast bed enhances the overall stiffness and load-bearing performance of the structure and helps to reduce the dynamic stress effect of the subgrade below.

The multiphase reactive flow behavior of pyrites in fluidized roasters is closely related to particle size distribution (PSD) and gas temperature. The coupled computational fluid dynamics-discrete element method (CFD-DEM) is used to stress the effect of PSD and gas temperature on the minimum fluidization velocity (Umf). Firstly, the accuracy of the model is verified via the previously well-established correlations. Then, the influence of four types of PSD (Gaussian-type, Mono-type, Flat-type and Binary-type) and three temperatures on Umf is explored. Numerical results show that the Umf for the Flat-type PSD is the smallest among the four while the one for the Mono-type PSD is the largest. The minimum fluidization velocities for the Mono-type and Gaussian-type PSD share quite similar values. With the same PSD, increasing the gas temperature results in a decrease in the minimum fluidization velocity. Finally, predictive correlations for the minimum fluidization velocity of the gas-solid fluidized bed reactors are established based on the numerical results.

Grinding results affect the quality of the final product. A single abrasive grain cutting test is an important method to study the complex grinding process. In this study, the discrete element method (DEM) is used to simulate diamond single abrasive grain cutting alumina ceramics to study the damage mechanism of the grinding process, analyze the effects of process parameters and single abrasive grain parameters on the machining damage, cutting force and residual stress, and make a comparative analysis with the single abrasive grain cutting test. Results indicate that the cutting depth and abrasive angle have obvious effects on machining damage, cutting force, and residual stress, while the cutting speed and abrasive grain size have smaller effects. The cutting effect of regular quadrilateral pyramid abrasive grains and regular octahedral abrasive grains is better, the effect on the cutting process is smaller, and the machining damage, cutting force, and residual stress are smaller. The simulation matches the test results, which verifies the reasonableness of the discrete element simulation of single abrasive grain cutting.

Coral sand concrete is a sustainable building material in island engineering with unique fluidity and hardened strength. In this study, a numerical method based on Engineering Discrete Element Method (EDEM) was developed to investigate the fluidity and mechanical properties of steel fibre reinforced coral mortar (SFRCM) and steel fibre reinforced ordinary mortar (SFROM) with/without an external magnetic field. The simulated result is in agreement with experimental results, and the fluidity of SFRCM is lower than that of SFROM, but with a 30 % increased bending strength. Moreover, as the magnetic flux density increases, the bending strengths of SFRCM and SFROM increase by a maximum of 10.6% and 15.4 %, respectively. The effect of the magnetic field direction on the fluidity of steel fibre mortar depends on the interval between steel bars. When the interval is small, a magnetic field aligned with the flow direction can improve the fluidity of steel fibre mortar, with the Lflow distance increasing by 8.1 %. When the interval is larger, a magnetic field perpendicular to the flow direction can improve the fluidity of steel fibre mortar, with the L-flow distance increasing by up to 13.4 %. Regardless of the interval, a magnetic field aligned with the flow direction can increase the gap passing ability of steel fibre mortar, with the maximum increase in the gap passing coefficient G of 8.0 %.

The flexural performance of standard composites has been extensively studied; however, the response of stitched composites with different stitch patterns and densities has received little attention and is not well understood. This study systematically explored the flexural performance of stitched composites with different stitch patterns and densities. The stitches weakened the flexural strength while improving the residual strength of the composites, particularly under a high stitch density. In addition, the stitch threads in the longitudinal stitch pattern preferably resisted the deformation of the bottom side of the specimen, showing superior flexural strength compared with the diagonal and transversal stitch patterns. However, the stitch threads in the diagonal and transverse stitch patterns impeded crack propagation and enhanced the residual strength of the composites. In addition, acoustic emission was used to confirm that the acoustic emission signals and the first moment of rapid increase in cumulative acoustic emission energy were detected earlier under a high stitch density, suggesting that the increase in stitch defects promotes damage initiation and severe damage. The durations with high values and a continuous increase in the cumulative acoustic emission energy after brittle failure indicated that the stitched composites experienced non-catastrophic failure.

Core-shell composite abrasive particles are a topic of great interest in surface finishing. It is important to explore the preparation technology and performance parameters associated with them. In this paper, a core-shell composite abrasive particle made of polystyrene and cerium oxide (PS&CeO2, CSPC), which is rigid on the outside and flexible on the inside, is proposed. The microstructure, physical phase characteristics, and mechanical properties of the inner core and composite abrasive particles are investigated. PS microspheres and CSPC composite abrasive particles with different structural features were prepared through a series of experiments, morphological observations, and physical and chemical characterization experiments. Their microstructures and physical phase properties were investigated. The indentation load curves of the PS microspheres and CSPC composite abrasive samples were measured by using an atomic force microscope. The analysis focused on the effects of various dimensional and structural parameters on the modulus of elasticity of both PS microspheres and CSPC composite abrasive particles. The analysis shows that the experimentally prepared PS microspheres have good dispersion, a smooth surface, and a uniform particle size distribution. The prepared CSPC composite abrasive particles are regular spheres with rough, rice-like surfaces, low modulus of elasticity, and overall nonrigid and soft elastic properties. The results of this paper can provide a guide for the preparation technology, performance regulation, and application of polymer microspheres and core-shell composite abrasive particles in CMP.

Discrete element simulations were carried out to investigate the elastic impact damage mechanism of PS@CeO2 core-shell abrasive (CSCAP). Aiming at understanding the deformation behavior and damage mechanism of CSCAP during the polishing process, effects of the impact velocity, impact angle on the rates of deformation and recovery deformation, stress distribution, the number of microcracks were systematically investigated. Tensile cracks formed owing to the CSCAP deformation was gradually increasing when impacting the workpiece downwards. After the CSCAP reached the maximum deformation, macroscopic cracks at the interface were extended gradually. Owing to the redistribution of the compressive force, the interface was observed to predominantly occur in shear cracks, while the shell layer was found to be distributed with tensile cracks. The number of microcracks increase with the increase in impact speed, the impact angle was within the range of 15° to 45°. This investigation enhances the comprehension of nanoscale deformation damage mechanism in CSCAP during ultra-precision machining processes.

Vibration can increase the flow ability of fresh concrete and may cause segregation. The rheology behavior of fresh concrete after vibration is different from that in the unvibrated state. In this paper, a CFD-DEM coupling method was developed to investigate the rheological behavior of fresh concrete before and after vibration. The Bingham model and Hershcel-Bulkley were respectively used as the constitutive relationship of fresh concrete in unvibrated and vibrated state. The Hertz-Mindlin with bonding bond is employed to describe the interaction between coarse aggregate. To analyze the effect of vibration on the rheological behavior of fresh concrete, the rheometer test was conducted. The relationship of shear stress and shear strain rate is linear before vibration and is nonlinear after vibration. Vibration reduces the yield stress and plastic viscosity of concrete. The shear zone decreases when fresh concrete is vibrated.

The fluidity of fresh concrete undergoes changes during transportation, exerting a direct influence on the pumping process and the ultimate quality of the hardened concrete. This study utilized the discrete element method to explore the impact of the time-dependence of fresh concrete on the transportation process. Specifically, a JKR contact model incorporating surface energy was employed to characterize the constitutive behavior of fresh concrete. The research established a relationship between surface energy and transportation time. The investigation delved into the mixing process after varying transportation durations through numerical simulations. The relative velocity between coarse aggregate and mortar increase with transportation time. The findings reveal a diminishing trend in both mixing and discharging homogeneity as transportation time increases. Enhancing the mixing speed of the drum to a critical value before discharge can ameliorate discharging homogeneity. However, excessive mixing speed may lead to detrimental effects on homogeneity.

A coupled computational fluid dynamics - discrete element method (CFD-DEM) model for simulating supercritical water fluidized bed reactors (SCWFBR) is established and verified using the previous correlations based on experimental data. The CFD-DEM model is then adopted to investigate the pulsation effects on the mixing behaviour of binary particles with different densities in the SCWFBR. Numerical results show that external energy pulses can be effective in promoting the mixing of binary particle systems with different densities in SCWFBR which cannot be achieved by simply increasing the flow rate constantly. Within the current parameter range: low-frequency pulses are favored to promote particle mixing rather than high-frequency pulses, and an optimal frequency exists. The role of low amplitudes in influencing mixing degree is slight, but the particle mixing degree can be greatly enhanced by increasing the pulse amplitude beyond a certain value. The mechanism that pulsed inlet fluid promotes particle mixing is to raise the heavy particles which are inclined to stay at low positions during the fluidization. The Fast Fourier Transform (FFT) method to predict the optimal frequency established for size-induced segregation can be applicable to solve the problem of the density-induced segregation.

Considering the spatial arrangement characteristics of bonded irregular particle systems, this paper first constructs irregular dilated polyhedron elements based on the Voronoi cutting algorithm and Minkowski Sum theory. Subsequently, by extending the traditional sphere-based BPM (Bonded Particle Model) to irregular particle elements, a novel dilated polyhedron bonding-breaking model considering different fracture modes is developed under arbitrary contact modes. A collision example between two bonded square particles and a rigid plate is adopted to verify the stability of the model. Later, the difference between the tensile-shear fracture mode and the mixed fracture mode with damage process for contact bond is compared by the discrete element simulations of the tension-fracture behavior between two bonded square particles and the uniaxial compression simulation of frozen ballast aggregate. Finally, the influence of section size on the lateral resistance of the ballast bed structure at low temperatures is discussed using the dilated polyhedron BPM. The results showed that the developed dilated polyhedron BPM considering different fracture modes can realize mechanical behaviours between bonded irregular particles. Compared with the tensile-shear fracture mode, the mixed fracture mode not only considers the combined effect of normal and tangential stress on the bond but also realizes the damage deformation and stiffness attenuation of the bond, which can achieve the “delayed” fracture effect. Meanwhile, the model also shows good reliability in analyzing large-scale engineering problems, such as the mechanical performance of low-temperature ballast beds. The research effectively develops the bonding and breaking model of irregular elements and provides a new perspective for the contact-bond-fracture behavior simulation of irregular granular materials.

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PS@CeO2 is a novel abrasive used in the polishing process, consisting of an organic polymer core (polystyrene, PS) that is prone to elastic deformation and an outer shell made of inorganic abrasives (CeO2). Core-shell composite abrasives are susceptible to deformation or damage caused by impact during the polishing process, which presents challenges for damage analysis and assessment. This paper proposes a method for calibrating the micro-parameters of discrete element model with PS@CeO2 core-shell composite abrasives (CSCAP). The geometry parameters and the elasticity modulus of the core-shell composite abrasives were measured. The average elasticity modulus of the PS core, interface and total CSCAP in the specimens were 3.85 +/- 0.2 MPa, 78.8 +/- 0.9 MPa and 12.03 +/- 0.9 MPa, respectively. Based on the principle of structural similarity, the core-shell composite abrasives with the core-to-shell ratio of 21.34 was established using the discrete element method (DEM). A serial of indentation experiments were conducted on the core, interface, and total core-shell composite abrasives, respectively. The elasticity modulus was used as an evaluation index to calibrate the micro-parameters of discrete element model of core-shell composite abrasives. The simulation results of elasticity modulus were 3.82 MPa and 12.26 MPa on the core PS, the interface, and the core-shell composite abrasives, respectively. Comparing the numerical simulation results with the experimental results, the elasticity modulus of the coreshell composite abrasives differs within 5 %. Finally, the discrete element simulation of core-shell composite abrasives impacted with workpieces was performed. The research results indicate that the established calibration method can accurately describe the damage and deformation of core-shell composite abrasives that occur in indentation experiments.