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2024 Vol. 45, No. 5
Published: 2024-10-28
565
Simulation of Uniform Corrosion Process of U71Mn Hot-Rolled Rail Based on Cellular Automata
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.027
The damage caused by environmental corrosion in the rail service process will directly threaten operation safety. Therefore, the quantitative characterization of rail corrosion damage is of great significance to the reliability evaluation of rails. The uniform corrosion experiments of U71Mn hot-rolled rail samples in 3.5wt.% NaCl solution at room temperature were first carried out, and the change of diameters of two samples with corrosion time was measured. According to the experimental results, the corrosion mechanism of rail samples in 3.5wt.% Nacl salt solution was analyzed. Then, the corrosion model of rail samples was established using the cellular automata method, and the uniform corrosion behavior of rail samples in 3.5wt.% NaCl solution was simulated. The corrosion rate was quantified according to the changes in sample diameters after different corrosion time simulated by the cellular automata method. A unified prediction formula for different sample diameters with corrosion time was established. The results show that the average relative error between the predicted results and the actual measured results is 8.7%, which implies that the uniform corrosion process of U71Mn hot rolled rail samples can be reasonably simulated using the cellular automata method.
2024 Vol. 45 (5): 565-575 [
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576
Research on the Mechanism of Transition from Static to Dynamic Microscale Friction Behavior
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.018
Micro scale contact and friction behavior are widely present in various important industrial devices and systems. With the development of high integration and miniaturization of various electromechanical systems, the impact of friction on devices cannot be ignored. At the microscale, friction behavior exhibits a strong dependence on interface adhesion and size. Understanding the transition from static to dynamic friction at the microscale is of great significance for controlling friction and reducing energy consumption. This study conducted a series of studies on the friction transition process of microscale friction behavior using molecular dynamics methods. By developing a series of modifiable potential functions to quantitatively regulate the friction interface properties, the influence of interface adhesion and contact stiffness on the static friction coefficient was elucidated, and the competition mechanism between them was revealed. In addition, this study also investigated the influence of model size on the static friction coefficient, observed the saturation phenomenon of the peak value of static friction force, and explained it through the contact layer cloud maps.
2024 Vol. 45 (5): 576-586 [
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35
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587
Phase-Field Simulation of Lithium Dendrite Growth in Polymer-Based Composite Solid-State Electrolytes
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.029
Solid-state lithium-metal batteries are the most promising next-generation high-energy-density energy storage technology, but one of the most pressing problems they face is the inhomogeneous growth of lithium dendrites. At present, the mechanism of inhibiting the growth of lithium dendrites by low-modulus composite solid-state electrolytes, especially low-modulus multiphase composite solid-state electrolytes, has not been fully clarified. Therefore, in this paper, a force-chemistry model is constructed by the phase field method to investigate the effect of different elastic moduli of three-phase composite solid-state electrolytes on the growth of lithium dendrites, and the results show that the higher the modulus of the electrolyte, the higher the stress on the Li metal, which s the plastic deformation of lithium dendrites, and therefore inhibits the growth of lithium dendrites. The study in this paper deepens the understanding of the mechanism of inhibition of lithium dendrites by low-modulus multiphase composite solid-state electrolytes, and provides guidance for the design of composite solid-state electrolytes.
2024 Vol. 45 (5): 587-594 [
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33
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595
A Study on the Characterization of Crack Tip Constraint Effect from Double Cracks
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.026
To gain a deeper understanding of the constraint effect exerted by the double crack tip and to accurately characterize this effect, this study focuses on non-collinear parallel double cracks in a homogeneous plate. It examines the stress and strain fields associated with these double cracks, paying particular attention to their behavior at various horizontal distances (s) and vertical distances (h). Additionally, by leveraging the unified constraint parameter Ap, the authors compare the constraint of the double crack tip with that of an equivalent single crack tip. The findings reveal significant differences in the distribution and magnitude of stress and strain at the crack tips of double cracks compared to their equivalent single crack counterparts. Attempting to calculate the constraint of double cracks using the stress or strain field at a crack tip, as per the conventional method for single crack tips, would yield inaccurate results. Therefore, it is imperative to initially calculate the total strain field both inside and outside the crack tips of double cracks (Atotal). Based on the calculations, the magnitude of the double crack constraint ranges from 0.10 to 0.30 of the total strain field (Atotal). This study offers valuable insights into the constraint effect of double crack tips and presents a novel approach for characterizing the constraint associated with double cracks.
2024 Vol. 45 (5): 595-609 [
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24
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610
Fracture Mechanics of Periodic Type-III Cracks Emanating from a Nano-Hole in One-Dimensional Hexagonal Quasicrystals
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.030
The material properties of the quasicrystals are greatly affected by the defects attribute to the high brittleness. It is necessary to understand fracture behavior of quasicrystals in order to develop the application of the materials. In this paper, the fracture mechanical of one-dimensional hexagonal quasicrystals with periodic Type III multiple cracks emanating from a nanoscale hole is investigated theoretically. Based on the complex elasticity theory and the Gurtin-Murdoch surface elasticity theory, the stress fields of a nano-hole with periodic multiple cracks considering surface effect are obtained by using the theory of boundary value problems of analytic function and the conformal transformation technique. The analytical expressions of stress intensity factors and energy release rate of the phonon field and the phase field at crack tip under the same conditions are further derived. The effects of the aperture size, the number of periodic cracks, the crack-length/aperture ratio, the phonon field-phase field coupling coefficient and the applied loads on the dimensionless stress intensity factors and dimensionless energy release rate are discussed. The results show that the coupling coefficient, the applied loads and the aperture size have no influence on the dimensionless stress intensity factors without considering the surface effect. The larger the aperture size, the more significant the size dependence on the dimensionless stress intensity factors and the dimensionless energy release rate becomes when considering the surface effect. There is an obvious coupling effect between the phonon field and the phase field. The influences of the number of periodic cracks on the dimensionless stress intensity factors and energy release rate are restricted by the size of defects. The effects of the phonon field loads and the phase field loads on the dimensionless stress intensity factors and energy release rate are different. This work reveals the specific influence of surface effect on the fracture behavior of multi-cracks at the hole edge, and has important academic significance in the development of quasicrystal fracture mechanics.
2024 Vol. 45 (5): 610-621 [
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622
Acquisition of Metal Plastic Parameters Based on Neural Network Learning and Residual Indentation Morphology
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.028
Compared with the other traditional mechanical testing methods, indentation method has the advantages of simple manufacturing of samples and in-situ testing. Different from the existing acquisition methods of material mechanical parameters dependent on indentation load-depth curve, this study provides an effective method for inversion of metal plastic mechanical parameters based on residual indentation morphology and neural network learning. Spherical indentation tests?of Cu, Mg and Fe have been carried out by the Instron universal material testing machine, the?residual indentation?morphology of Cu, Mg and Fe was scanned?by?the contour morphology system and the obtained?morphology?feature will?be?used?as?the data?basis?for subsequent?studies. The characteristics of extracted data were analyzed and the corresponding data processing of amplification, rounding, binarization, and high-order digit supplementation were performed. Based on the secondary development of Abaqus software, the residual indentation depth data from numerical simulations with different material parameters were automatically extracted to be used for neural network learning. The activation function, method of initializing neural network parameters, neural network parameters update mode, loss function, optimal parameter finding strategy and neural network structure were compared and selected, ensuring that the neural network learning can achieve a good effect. Based on the residual indentation morphology feature data from indentation test and the neural networks after learning, the plastic mechanical parameters of Cu, Mg and Fe were obtained. Also,?the?related?plastic?mechanical?parameters of Cu, Mg and Fe were?acquired?through?the conventional uniaxial tensile test?and?characterization based on the Instron?universal?material?testing?machine. By comparing?the neural network learning results and?the?tensile?test?characterization?results,?the?relative?errors?of related?plastic?mechanical parameters?of?Cu, Mg and Fe?obtained?from?neural network learning?were?identified, and the effectiveness of the proposed method for obtaining metal plastic mechanical parameters based on neural network learning and residual indentation morphology was verified. The provided method in this study can be extended to the mechanical properties characterization and plastic parameters acquisition of other metal/alloy materials.
2024 Vol. 45 (5): 622-637 [
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26
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638
Investigation on the Influence of Surface Topography Reconstruction and Yield Strength of High-Strength Aluminum Alloys in Additive Manufacturing
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.020
To investigate the impact of surface topography on the mechanical properties of additive manufacturing materials, in this paper, high-strength aluminum alloy specimens were fabricated by the selective laser melting method. The influences of scanning speed, heat treatment, deposition direction, and surface roughness on tensile mechanical properties were examined. The surface topography measured by an optical microscope was reconstructed based on the Fourier series and MATLAB software, and the analytical solution of the stress concentration coefficient of the surface topography was derived using the Airy stress function. Finite element analysis was conducted using ABAQUS software to validate the analytical results. The probability density function of the stress concentration coefficient was obtained through normal fitting, and a method for evaluating the reliability of the material based on yield strength was proposed. The proposed methodology in this paper is of reference significance for the quantification of surface roughness and its effect on yield strength of other additive manufacturing materials and specimens.
2024 Vol. 45 (5): 638-651 [
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23
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652
Sensitivity of Structures to Random Defects in Film-Substrate Systems
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.021
Random defects due to differences in raw materials and the complexity of the manufacturing process are inevitable in engineering structures. Based on the inherent characteristics of sensitivity to defects in the film-substrate system, Monte Carlo method is applied in the study of stability for structures with random defects, coupled with numerical simulation to investigate the morphological evolution and post-buckling equilibrium path of film-substrate systems with random defects under instability. The numerical results show that the critical load of the structure with random defects is unstable, in which the defects significantly reduce the critical load of the structure, and the random defects destroy the symmetry of the structure, transforming the ordered checkerboard pattern into a disordered fold nuclear pattern and affecting the subsequent morphological trend. It assesses the potential risks and effects of random defects in thin film structures and aims to improve the reliability and performance of thin film devices, coatings and surface treatments, while narrowing the gap between theoretical stability research findings and practical design applications.
2024 Vol. 45 (5): 652-664 [
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23
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665
Biomimetic Construction of CPC Foam Microstructure and Its Compressive Mechanical Properties
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.023
CPCs (Conductive Polymer Composites) foam exhibits excellent characteristics such as high plasticity, energy absorption, thermal and acoustic insulation, and holds enormous potential for applications in various fields including construction, transportation, electronics, etc. However, due to the complexity of CPC processing, it is challenging to achieve controlled design of micro-porous structures, resulting in simplistic and random porous structures, which limits its further applications. Inspired by the idea that biomaterials can enhance their mechanical properties by virtue of their well-aligned anisotropic microstructures, highly aligned anisotropic porous biomimetic microstructures are constructed by a bidirectional freeze-casting process to enhance the compressive mechanical properties of CPCs foams. Compared to traditional unidirectional freezing, the compressive elastic modulus and peak stress of aligned anisotropic porous microstructured CPCs foam increase by 18.7% and 25.4%, respectively. The chances of buckling and collapsing during cyclic compression are significantly reduced, and a peak stress of 91.1% and a strain recovery of 89.6% are still maintained after 2,000 cycles of cyclic compression at 50% strain. Combined with the finite element compression simulation, the main enhancement mechanisms of compressive mechanical properties include: optimizing stress distribution, effectively avoiding plastic deformation caused by the local stress concentration; the high elastic behavior of micrometer pore wall and its 3D structure gave the bionic structure strong resilience; the highly aligned anisotropic channels provided enough deformation space, improved the deformation coordination ability, and enhanced the reversibility of the structure during loading and unloading.
2024 Vol. 45 (5): 665-678 [
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31
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679
Dynamic Response Characteristics of Laminated Composite Sandwich Structures under Airborne Explosive Loads
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.025
To improve blast and impact resistance of sandwich structures, this study introduces a composite sandwich structure comprising a re-entrant (RE) negative Poisson’s ratio core, polyethylene (PE) fibers, and silicon carbide (SiC) ceramics. Utilizing the coupled Eulerian-Lagrangian (CEL) algorithm within ABAQUS, the dynamic response of this structure under explosive loading was simulated, assessing the impact of various core layer configurations on protective performance through structural deformation mechanisms, velocity response features, and energy absorption capacities. At equivalent areal densities, the incorporation of ceramic and polyethylene layers led to reductions in upper and lower panel deformations by up to 53% and 5.7%, respectively, relative to an RE-only sandwich layer. Notably, a core configuration of SiC-PE-RE optimized interlaminar load distribution, minimizing lower panel deformation; an increase in panel support strength correspondingly reduced panel velocities. Positioning the SiC and PE layers at the upper and middle core layers, respectively, achieved peak reductions in upper and lower panel deformations by 18.84% and 16%, compared to the RE sandwich layer, exhibiting the most rapid rate of decay. Conversely, positioning the RE layer at the upper core resulted in augmented local deformations, leading to localized crushing failures in the PE and SiC layers, thereby maximizing the energy-absorption incrementby up to 14%.
2024 Vol. 45 (5): 679-693 [
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27
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694
Study on the Dynamic Behaviors in Contact Resonance Atomic Force Microscopy in Liquid Environments
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2024.019
Contact resonance atomic force microscopy (CR-AFM) is a powerful technique that enables the measurement of topography and the mechanical properties of various materials at the micro/nanoscale. It can be used in both air and liquid environments. However, when CR-AFM is operated in a liquid environment, the dynamic behaviors of the microcantilever can be significantly different from those in air or vacuum due to the complex fluid-solid coupling of the microcantilever-liquid-sample system and the tip-sample interaction. In this study, we explore the effects of liquid density and viscosity, as well as tip-sample normalized contact stiffness and contact damping, on the dynamics of the AFM microcantilever in liquid environments. We treat the influence of the liquid on the dynamics of the AFM microcantilever as added mass and added damping. Our results show that in free vibration, the natural frequencies of the AFM microcantilever are primarily dominated by the liquid density, while the liquid viscosity plays a dominant role in the quality factor compared to the liquid density. Higher modes exhibit higher sensitivity to changes in liquid viscosity and liquid density. As the normalized tip-sample contact stiffness increases, a higher mode shows increased sensitivity to changes in normalized contact stiffness in a liquid environment. On the other hand, a lower mode is more sensitive to changes in normalized contact damping in a liquid environment. In addition, the dynamic responses of the AFM microcantilever under three different excitation approaches are compared and discussed. Variations in boundary conditions and hydrodynamic loads applied to the microcantilever under these approaches lead to diverse dynamic responses. The findings in this study are essential for the development of micro/nanoscale mechanical property imaging techniques using CR-AFM in liquid environments, as well as the improvement of measurement accuracy and sensitivity.
2024 Vol. 45 (5): 694-708 [
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26
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