Search Results (101)

The xylem of cotton stalks is a high-quality biomass feedstock with strong high-value utilization potential. However, existing studies lack accurate calibration of discrete-element parameters for separated stalk components, which limits the optimization of the design of separation equipment. This study uses phloem, xylem, and pith of cotton stalks as research objects and measures the intrinsic physical and mechanical parameters and paired contact parameters of the three components. Given the strong agglomeration tendency of crushed phloem long fibers, the Hertz–Mindlin with JKR model is used to calibrate the adhesion parameter. The applicability of this model to low-moisture, high-aspect-ratio fibrous materials is verified, and the measured equivalent surface energy of phloem reaches 2.887 J/m². CFD-DEM-coupled air separation verification is performed. The relative errors of xylem impurity content and loss rate between simulation and experiment are both below 10%, confirming the good reliability of the calibrated parameters. This study provides data to support the development of cleaning equipment for crushed cotton stalks. It provides a methodological reference for calibrating discrete-element parameters for similar long-fiber biomass materials. Full article

Affected by moisture cohesion, wet rice seeds exhibit poor flowability and frequent arching blockage during silo discharging, which seriously restricts stable grain storage and conveying. To address this issue and reveal its intrinsic flow mechanism, this study establishes a discrete element method (DEM) model for wet rice seed-silo systems adopting the Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) contact model, which incorporates surface energy to reflect moisture-induced cohesive effects. The model is verified via physical silo discharge tests, with consistent flow patterns, wall pressure error below 3.7% and discharge time error of 2.14%. EDEM parametric simulations are conducted to analyze velocity fluctuation at different silo heights. Coordination number and normalized contact force distribution are adopted to assess micro-contact force distribution in discharge areas, and a force chain extraction algorithm is used to explore variations in force chain length and orientation. Results demonstrate that during discharge, average particle velocity drops from silo bottom to top with growing fluctuation amplitude, presenting obvious stratified flow and intense upper-layer velocity pulsation. Weak contacts dominate wet rice seed groups and conform to exponential decay distribution. The force chain network undergoes three evolution phases: formation, force arch generation and collapse. Quantitative analysis reveals long force chain proportion falls steadily from 81.40% to 3.68% throughout discharge. Short force chains rise to 60.54% in the arch-forming stage and reach 96.32% after arch collapse. Horizontal force chains account for a maximum of 71.09% during arch formation, while vertical ones decline from 99.52% initially to 61.57% post collapse. This research offers mechanical references and quantitative parameters for the design and operation of silos for wet granular farm grains like rice seeds, and is particularly relevant to post-harvest engineering, grain storage safety, and agricultural machinery design. Full article

Accurate discrete element simulation parameters for the mechanically harvested cotton stalks and cotton residues mixture are currently unavailable. This lack hinders the effective design and optimization of equipment for separating and recovering cotton residues from the mixture. This study focused on the cotton stalks and cotton residues mixture. The intrinsic parameters of cotton residues were measured through physical experiments. Using the inclined plane and collision methods, the coefficients of restitution for cotton residues–cotton stalks and cotton residues–steel were determined to be 0.228 and 0.364, respectively. The corresponding static friction coefficients were 0.632 and 0.266, and the rolling friction coefficients were 0.199 and 0.156. The Hertz–Mindlin with JKR contact model was employed. Combined with repose angle tests, the coefficient of restitution, rolling friction coefficient, static friction coefficient, and surface energy for cotton residues–cotton residues were calibrated as 0.393, 0.140, 0.742, and 1.471 J/m², respectively. A vibrating spreading test was conducted to validate the calibrated parameters. The proportion of cotton residues on the material surface was used as the test index. The mean relative error between simulation and physical test results under four working conditions was 4.91%. The results indicate that acceptable consistency is achieved between simulation and experimental results under the tested conditions, and the calibrated discrete element parameters are applicable for the simulation of cotton stalk–cotton residue mixture systems. This study provides a theoretical basis and data support for the development of equipment to separate and recover cotton residues from cotton stalk and cotton residue mixtures. Full article

ZERODUR glass-ceramic is widely used in ultra-precision optical components because of its extremely low thermal expansion and excellent dimensional stability. However, its two-phase microstructure, composed of crystalline and amorphous phases with different mechanical properties, may cause non-uniform material removal during magnetorheological polishing, thereby limiting further improvement of nanoscale surface quality. To address this issue, this study investigates the effect of oxide abrasives on the surface homogenization of ZERODUR. A single-particle abrasive–workpiece contact model based on modified Hertz contact theory and elastoplastic contact analysis was established to compare the indentation responses of CeO₂, SiO₂, and ZrO₂ abrasives in the two constituent phases. Magnetorheological polishing experiments were conducted under identical process parameters, and the polished surfaces were characterized by AFM over scan areas of 2 μm × 2 μm, 5 μm × 5 μm, and 10 μm × 10 μm. The results show that all three abrasives improved the surface quality of the ring-polished substrate, with ZrO₂ achieving the best surface homogenization performance. The lowest roughness, Ra = 0.104 nm, was obtained at a 2 μm field of view, and the ZrO₂-polished surface showed more stable roughness evolution across different scan sizes than the CeO₂- and SiO₂-polished surfaces. These results indicate that the elastic modulus, hardness, and mechanical compatibility of abrasives with ZERODUR play key roles in governing contact stress, indentation behavior, and final surface quality. This work addresses the lack of mechanistic understanding of abrasive-dependent surface homogenization in the magnetorheological polishing of two-phase ZERODUR glass-ceramic. The main innovation is the integration of contact-mechanics-based abrasive–workpiece modeling with multi-scale AFM characterization to clarify how abrasive mechanical compatibility affects nanoscale surface uniformity and to guide abrasive selection for ultra-smooth optical manufacturing. Full article

In this work, we extended our previous studies on the limitations of classical contact models from polymers to a biological system. We used yeast as a model system to investigate how contact evolution during indentation affects the accuracy of AFM-based determination of Young’s modulus. We proposed a practical correction framework for the classical Hertz and Sneddon flat-punch models to improve the extraction of mechanical properties from experimental data. Force-indentation curves were measured using a spherical (SPHERE) probe with a 2 μm radius and a flat (FLAT) probe with a 4 μm radius of plateau. The experimental results were analyzed using both corrected and uncorrected contact models, while a finite element analysis (FEA) model was used to determine the contact radius-indentation dependence. It showed that Young’s modulus estimated from AFM indentation using classical formulations is probe-dependent because the contact radius is inadequately described. By incorporating the FEA-derived effective contact radius into Hertz and Sneddon contact models, the same Young’s modulus was obtained for yeast with both probes and compared to reference values with other techniques. These findings establish contact evolution as a governing factor in AFM-based cell mechanics and provide a practical route toward robust, probe-independent, and more accurate determination of mechanical properties for living cells. Full article

Accurate discrete element method (DEM) modelling of mature peanut plants is essential for simulating peanut harvesting, pod detachment, and harvest-loss formation. However, existing peanut DEM models are usually simplified as isolated pods, rigid cylindrical particles, or partial stem–pod structures, which limits their ability to represent the flexible deformation of vines and pod stalks and the fracture behaviors at the pod–pod stalk junction. In this study, a DEM-based flexible plant model was developed for mature peanut plants. The geometric dimensions, contact parameters, and mechanical properties of peanut pods, pod stalks, and stems were measured through physical experiments. The Hertz–Mindlin model was used for non-bonded contacts, whereas the Hertz–Mindlin with Bonding model was adopted to represent the flexible connections among plant organs and the fracture behaviors of the pod–pod stalk junction. The main DEM parameters were calibrated using Plackett–Burman screening, steepest ascent experiments, and central composite design. The results showed that the tangential stiffness per unit area and tangential critical stress at the pod–pod stalk junction were the dominant factors affecting pod detachment force. The optimized parameter combination was a tangential stiffness per unit area of 4.738 × 10⁵ N/m³ and a tangential critical stress of 9.350 × 10⁵ Pa, corresponding to a simulated tensile force of 6.73 N. Model validation was performed by comparing peanut harvesting simulations with field trials. The relative error of pod loss rate between simulation and field measurement was less than 7.55%, and the t-test result indicated no significant difference between the two datasets (p > 0.05). These results demonstrate that the proposed flexible peanut plant model can effectively characterize pod–pod stalk separation and can provide a reliable DEM modelling basis for peanut harvesting process analysis and equipment optimization. Full article

To clarify the spreading law of river crab pellet feed in a centrifugal spreading mechanism and provide a physical basis for the path planning of automatic feeding boats, this study took 4.0 mm sinking extruded river crab feed as the research object. A systematic research method combining physical experiments and Discrete Element Method (DEM) simulation was established. Physical experiments were conducted to calibrate the intrinsic parameters (density, Poisson’s ratio, elastic modulus) and contact parameters (friction coefficients and restitution coefficients between feed and 304 stainless steel/ABS plastic, as well as between feed particles) of the pellet feed. On this basis, a DEM simulation model of a vibration blanking-dual disc centrifugal spreading mechanism was constructed using the multi-sphere aggregation method and the Hertz-Mindlin (no-slip) contact model. A Central Composite Design (CCD) response surface experiment was employed to investigate the spreading law, with boat speed (0.5–1.5 m/s) and spreading disc rotation speed (800–1000 rpm) as independent variables, and unilateral spreading width (W), track superposition uniformity (ω), and transverse coefficient of variation ($Cv$) as response indicators to characterize spreading range and particle distribution. The results showed that the spreading disc rotation speed had an extremely significant effect (p < 0.0001) on all three response indicators, while boat speed had no significant effect. The feed exhibited a characteristic double fan-shaped superposition distribution pattern. Through multi-objective optimization, the optimal operational parameters were determined as a boat speed of 1.0 m/s and a spreading disc rotation speed of 879 rpm, yielding a unilateral spreading width of 2.9 m, a track superposition uniformity of 88.31%, and a transverse coefficient of variation of 8.33%. This study establishes a quantitative method for analyzing feed spreading characteristics and clarifies the spreading range and particle distribution law, providing a reliable physical basis for full-coverage path planning of crab pond feeding boats. Full article

To address the significant differences in the structure and mechanical properties of various components of the Shanghai bok choy plug seedling, and the lack of an accurate and reliable discrete element model of the whole plant and key bonding parameters in the simulation of the automatic transplanting process, a 128-cell Shanghai bok choy plug seedling was selected as the research object. Morphological, physical, mechanical, and contact property tests were systematically conducted to obtain the basic parameters of the seedling pot, leaf, petiole, and stem. A whole-plant discrete element model of Shanghai bok choy plug seedling, consisting of the seedling pot, leaf, petiole, and stem, was established using a combined method of component-wise modeling and overall reconstruction. The Hertz–Mindlin (no slip) and Bonding V2 contact models were jointly adopted to characterize interparticle contact, continuous structural behavior, and failure characteristics. Taking the ultimate compressive failure load of the seedling pot, leaf compression density, ultimate bending failure load of the petiole, and ultimate bending failure load of the stem as response indices, significant parameters were screened using the Plackett–Burman test, the optimization ranges were determined through the steepest ascent test, and the key bonding parameters were optimized and calibrated using the Box–Behnken response surface test. The results showed that the relative errors between the simulated and experimental values of the ultimate compressive failure load of the seedling pot, leaf compression density, ultimate bending failure load of the petiole, and ultimate bending failure load of the stem after optimization were 1.19%, 1.13%, 0.99%, and 0.72%, respectively, indicating that the established model can accurately characterize the mechanical response of the constituent parts of Shanghai bok choy plug seedling. The results provide a basis for discrete element simulation of the interaction between Shanghai bok choy plug seedling and key components of automatic transplanting equipment, as well as for the design optimization of automatic transplanting equipment. Full article

Residual film recovery is a crucial approach to mitigating agricultural “white pollution” and ensuring sustainable land use. Currently, the development of residual film recovery machines relies primarily on theoretical analysis and field performance tests. The lack of support from computational simulation models often leads to suboptimal mechanical performance, severely restricting the design and optimization of recovery equipment. To address this, this study proposes a method for constructing and experimentally validating a discrete element model of plow-layer residual film using EDEM software. First, field tests were conducted to measure soil compaction and residual film distribution at various depths. The ultimate tensile force of the residual film was also evaluated to provide fundamental data for model development. Using the Hertz–Mindlin with bonding contact model in EDEM, the intrinsic parameters of the residual film were selected and optimized. Combined with a Box–Behnken experimental design, a quadratic regression model relating normal stiffness per unit area, critical normal stress, and bond radius to the ultimate tensile force of the film was constructed. The optimal parameter combination was determined as follows: normal stiffness = 1.11 × 10⁶ N·m⁻³, critical normal stress = 2.45 × 10⁶ Pa, and bond radius = 0.03 mm. Under these parameters, the theoretically predicted ultimate tensile force was 1.18 N, and the simulated value yielded a relative error of only 1.69%, validating the effectiveness of the single-film model. Furthermore, using the field-measured data, a coupled film–soil model was established via the “rainfall” method to conduct simulated penetration tests. Parameter calibration was executed using the multivariate Newton–Raphson iteration method. The optimal bonding parameters for soil particles were identified as follows: normal stiffness per unit area = 9.6 × 10⁵ N/m², shear stiffness per unit area = 9.6 × 10⁵ N/m², critical normal stress = 5.38 × 10⁵ Pa, critical shear stress = 5.38 × 10⁵ Pa, and bond radius = 4.3 mm. The average simulated penetration resistance was 59.61 N, showing a relative error of 5.91% compared to the field-measured value of 56.28 N. These results demonstrate that the developed coupled film–soil DEM can be effectively applied to simulate the lifting and throwing processes of plow-layer residual film recovery machines, thereby providing vital modeling support for the design and optimization of residual film recovery mechanisms. Full article

In biomass pellet combustion, the formation of ash layers on particle surfaces severely hinders combustion reactions and heat transfer, while the key parameters governing particle motion behavior and ash pre-separation in rotating cone burners remain insufficiently understood. To address these challenges and to optimize particle mixing and ash separation performance, this study adopts a combined numerical approach. The discrete element method (DEM) coupled with the Hertz–Mindlin (no-slip) contact model is employed to simulate particle motion and mixing dynamics, while a separate cold-state computational fluid dynamics (CFD) model based on the Realizable k-ε turbulence model and the discrete phase model (DPM) with Rosin–Rammler particle size distribution is established to investigate ash separation mechanisms. The Lacey mixing index is used to quantify mixing uniformity, and grid independence verification is performed to ensure numerical reliability. Key findings reveal that the rolling regime (rotational speed: 1.7–11 r/min), a uniform particle size of 25 mm, and a cone inclination angle of 45° collectively optimize particle mixing. Rotational speed is identified as the dominant factor affecting mixing effectiveness. Furthermore, an optimal secondary-to-primary air ratio of approximately 7:3 (within the tested range) balances enhanced centrifugal separation with flow field stability by mitigating backflow and excessive turbulence. This work not only fills the knowledge gap regarding the coupled effects of operational and structural parameters on particle behavior in rotating cone burners but also provides novel, quantitative guidance for the rational design and parameter tuning of such burners to improve combustion efficiency and operational stability. Full article

Severe coronary artery calcification (CAC) remains a major challenge in percutaneous coronary intervention (PCI), driving stent under-expansion and higher rates of restenosis and adverse events. Balloon-based calcium modification remains central to lesion preparation, with the available tools ranging from high-pressure non-compliant balloons and ultra-high-pressure balloons to cutting, scoring, and intravascular lithotripsy (IVL) balloons. While traditional IVL has advanced the field by permitting circumferential fracture of deep calcium through acoustic shockwaves, important drawbacks persist, including problems in deliverability, energy distribution, and questionable efficacy in nodular or eccentric calcium. This review examines all contemporary balloon-based modification strategies and introduces the novel Hertz-contact IVL (HC-IVL), a new technology designed to transmit mechanical energy through direct contact rather than shockwave propagation. Based on Hertzian mechanics, this device may facilitate more focused energy delivery, improved lesion crossing, and enhanced calcium fracture in complex morphologies. A detailed comparison between HC-IVL and standard IVL is provided, along with a proposed algorithm for device selection. Taking into consideration the limitations of current tools, HC-IVL represents a promising mechanistic innovation in balloon-based calcium modification, warranting further validation in randomized, imaging-guided clinical studies. Full article

This paper investigates deflection deformation and premature bearing failure in deep-hole machining spindles with high length-to-diameter ratios under eccentric loading. A contact stiffness model for angular contact ball bearings was developed based on Hertz contact theory. Combined with the finite element method (FEM), a comprehensive mechanical analysis model of the spindle was established. The results show that spindles with high length-to-diameter ratios exhibit significant cantilever behavior, leading to considerable front-end deflection under eccentric loading. This deflection causes the inner and outer rings to incline, resulting in localized stress concentrations, which are the primary contributors to spindle fatigue failure. To improve the spindle’s stress distribution and dynamic performance, an optimized design replacing the metal housing with carbon fiber composite material is proposed. Static and modal analyses were performed using Abaqus and Romax. The analysis results demonstrate that the carbon fiber shell reduces self-weight deformation by 35.8%, decreases coupled deformation under self-weight and grinding loads by 28.6%, and increases modal fundamental frequencies by 20.88% to 47.41%. These improvements significantly enhance structural stiffness and dynamic stability. Experimental vibration monitoring during machine testing validated the accuracy of the modeling and simulation. Full article

Contact mechanics models are often inaccurate, due to (i) unknown contact radius, (ii) mechanical models not parameterizing it, (iii) in some models it is neither assumed meaningfully nor determined, and (iv) uncertain probe radius arising from manufacturer-specified nominal values and manufacturing tolerances. In this paper, an FEA model was used to quantify the evolution of the contact radius during indentation for two probe geometries: a pyramidal indenter (TRIANG2 nominal apex radius 2 nm) and a flat-ended punch (FLAT4000; nominal punch radius 4000 nm) on poly (vinyl chloride) (PVC), for which Young’s modulus (E_ref) was obtained by a standard mechanical tensile method. The effective contact radius, $R_{eff}$, determined from FEA, was subsequently used in a Hertz-based force–indentation parametrization. Uncertainty in the probe apex radius due to manufacturer tolerances was addressed by SEM measurement of the conical tip, enabling assessment of its impact on the modulus estimated from AFM indentation. Based on these results, we propose a practical, geometry-aware analysis methodology that is transferable across probe geometries. The effective contact radius, $R_{eff}$, is first established using a well-characterized reference material and subsequently applied to a mechanical model to extract Young’s modulus. In this approach, the Hertz-based parametrization is used as a consistent mathematical framework, while the effective contact radius accounts for probe-dependent contact evolution. Full article

The peanut, a globally important oil and economic crop, has thin, brittle pods that are prone to breakage under external forces during mechanical harvesting, transportation, and processing. To minimize this loss and reduce production costs, we conducted an in-depth study of the pod-breaking process by integrating manual and automatic filling approaches within the discrete element method (DEM) with the Hertz–Mindlin with bonding model. A breakable layered bonding model for peanut pods was developed, which is capable of precisely characterizing the disparities in the mechanical properties of peanut pod shells and kernels. Physical tests were performed to obtain the relevant contact parameters of peanut pods. Compression tests combined with calibration approaches were employed to identify the bonding parameters of peanut pods, which are not easily accessible via direct experimental measurements. The optimal combination of simulation parameters for the model was determined via a Plackett–Burman test, steepest ascent test, and Box–Behnken test. The results indicated that the critical normal stress between pod shells is the most significant influencing factor. The optimal parameter combination for the proposed model is as follows: the normal stiffness per unit area between pod shells is 7.81 × 10¹⁰ N/m³, the shear stiffness per unit area between pod shells is 9.00 × 10⁸ N/m³, the critical normal stress between pod shells is 2.17 × 10⁵ N/m³, and the critical shear stress between pod shells is 2.25 × 10⁵ N/m³. The established layered bonding model for breakable peanut pods was validated using both cylinder-lifting simulation tests and physical shelling experiments. The relative error in the angle of repose between the cylinder-lifting simulation and physical tests was 1.6%, while the deviation in the shelling experiment was only 0.7%. This model provides a theoretical foundation for the design and optimization of machinery used in peanut pod harvesting, transportation, and processing. Full article

In most AFM nanoindentation experiments on soft biological samples, classical contact mechanics models, such as Hertz or Sneddon’s equations, are commonly employed to determine the Young’s modulus. However, biological materials are inherently heterogeneous, and their mechanical properties often depend on the indentation depth. In this work, we present a novel and simple approach to quantify how the apparent modulus varies with increasing indentation depth. The method is based on the general indentation equation for axisymmetric indenters combined with a straightforward polynomial fitting of the force–indentation data. The proposed approach offers significant advantages, as it greatly simplifies the fitting process without requiring any advanced algorithms, while maintaining high accuracy. In addition, it is shown that the depth-dependent mechanical properties of cells can be described by a simple law, $E\left(h\right)=C_d/h+E_l$ , where $E_l$ is the limiting value of the apparent modulus at large indentations, and $C_d/h$ represents the depth-dependent contribution dominant at the initial stages of the indentation process. Here, $C_d$ is a positive stiffness coefficient, and $h$ is the indentation depth. This is a very important result, indicating that by using the pair of coefficients $C_d$ and $E_l$, we can fully describe the mechanical properties of cells, capturing their depth-dependent mechanical behavior. Experiments on fibroblasts and H4 human glioma cells confirm the accuracy of this equation. The proposed methods provide an accessible and reliable framework for nanoscale mechanical characterization, offering insights into the depth-dependent elasticity of heterogeneous soft materials and revealing mechanical patterns in biological samples. Full article