The impact of environmental corrosion on rail service operations poses a direct safety threat. Therefore, the quantitative characterization of rail corrosion damage is of great significance for evaluating rail reliability. Uniform corrosion experiments on U71Mn hot-rolled rail samples in a 3.5 wt. % NaCl solution at room temperature were first carried out. Changes in the diameters of two samples with corrosion time were measured. According to the experimental results, the corrosion mechanism of rail samples in the 3.5 wt. % Nacl solution was analyzed. A corrosion model employing cellular automata was developed to simulate the uniform corrosion behavior of rail samples in the NaCl solution. The corrosion rate was quantified by tracking sample diameter changes through the cellular automaton simulation over varying corrosion time. A unified prediction formula for different sample diameters with corrosion time was established. Results revealed an average relative error of 8.7% between predicted and measured data, indicating the efficacy of cellular automata in accurately simulating the uniform corrosion process of U71Mn hot-rolled rail samples.

Microscale contact and friction behavior are widely present in various important industrial devices and systems. As electromechanical systems become more integrated and miniaturized, the impact of friction on devices becomes increasingly important. At the microscale, friction behavior exhibits a strong dependence on interfacial viscosity and contact size. By developing a series of modifiable potential functions to quantitatively regulate interfacial properties, friction on atomically smooth interfaces with different properties is fully simulated using molecular dynamics methods. The study first examined the influence of various interfacial potential energies on the static friction coefficient, revealing a nonlinear relationship between the static friction coefficient and interfacial potential energy intensity. Furthermore, it was found that this nonlinearity is attributed to the competition between interfacial viscosity and contact stiffness. Additionally, the study investigated the influence of contact size on static friction coefficient. The simulation results showed that as the tangential contact length of the interface increases, the peak static friction force first increases and then stabilizes. By analyzing the contact layer cloud maps obtained through post-processing, interfacial friction is observed as a “nucleation-propagation” process, influenced by different contact sizes which affect the dynamic process and lead to changes in the peak static friction force. This study provides new insights into the effects of interfacial potential energy and contact size on microscale friction through molecular dynamics simulations, it is feasible to regulate friction by changing interfacial potential energy, but attention should be paid to the nonlinear changes in the friction coefficient. Besides, solely increasing the contact size cannot infinitely increase the peak static friction force.

Lithium metal is a highly promising anode material due to its high theoretical capacity and low reduction/oxidation potential, and has received extensive attention. However, the formation and growth of lithium dendrites poses the biggest challenge to its commercialization. The use of solid-state electrolyte, instead of liquid electrolyte, has become a potential path to inhibit the growth of lithium dendrites. However, issues such as poor metal-lithium interface contact and low ionic conductivity in solid-state electrolytes persist. Composite solid-state electrolytes, prepared by combining polymers with inorganic ceramic electrolytes, have shown effectiveness in inhibiting the growth of lithium dendrites. Although these composite solid electrolytes typically have high ionic conductivity, their elastic moduli are low. Currently, the mechanism of dendrite suppression by low-modulus composite solid-state electrolytes, especially low-modulus multiphase composite solid-state electrolytes, remains incompletely clarified. Therefore, this paper considers the mechanical effects of solid electrolytes and builds a mechanical-chemical model using the phase field method. By taking poly (ethylene oxide) (PEO)-based composite-state electrolyte as an example, the study investigates the influence of composite solid electrolyte modulus on dendrite growth. The results show that the higher the electrolyte modulus, the greater the stress on the lithium metal, leading to a more uniform distribution of lithium ions on the interface between the electrolyte and the lithium anode electrode. The higher stress also tends to cause the plastic deformation of lithium dendrites, thus inhibiting their growth. This research deepens the understanding of the mechanism of inhibition of lithium dendrites by low-modulus multiphase composite solid electrolytes, and provides guidance for the design of composite solid electrolytes.

To gain a deeper understanding of the constraint effect from double crack tips and accurately characterize it, 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, employing the ABAQUS finite element analysis software. Particular attention is paid to their behaviors at various horizontal distances (s) and vertical distances (h). Additionally, by leveraging the unified constraint parameter A_p, the constraints of double crack tips are compared with those of coalesced single crack tips. The findings reveal significant differences in the distributions and magnitudes of stress and strain at double crack tips compared to coalesced single crack counterparts. The conventional method of calculating the constraints from double cracks based on the stress or strain field at a crack tip, as done for single cracks, would lead to inaccurate results. Comparison of A_total, A_inside, and A_outside with A_single shows that considering both inside and outside crack tip strain fields aligns the variation trend of A_total more closely with A_single, with a remarkably narrow fluctuation. The constraint magnitude for coalesced single cracks ranges from 0.10 to 0.30 of the total strain field (A_total). This approach demonstrates a degree of universality, unaffected by whether the double cracks coalesce or not. It can be directly applied to quantify the constraints imposed by double cracks, regardless of their coalescing status. This study offers valuable insights into the constraint effect of double crack tips and presents a novel method for characterizing the constraints associated with double cracks. In summary, this novel approach offers a more comprehensive and accurate understanding of the complex constraints from double cracks, providing scientific support for evaluating structural integrity with double and multiple cracks.

The material properties of quasicrystals are significantly affected by defects due to high brittleness. Understanding the fracture behavior of quasicrystals is crucial for material applications. In this paper, the fracture mechanics of one-dimensional hexagonal quasicrystals with periodic Type-III multiple cracks emanating from a nanoscale hole is investigated theoretically. Based on complex elasticity theory and the Gurtin-Murdoch surface elasticity theory, stress fields of a nano-hole with periodic multiple cracks, considering surface effects, are obtained using boundary value problems of analytic function theory and the conformal transformation technique. Analytical expressions for stress intensity factors and energy release rates of the phonon field and phase field at the crack tip under the same conditions are further derived. The effects of aperture size, number of periodic cracks, crack-length/aperture ratio, coupling coefficient between phonon field and phase field, and applied loads on dimensionless stress intensity factors and dimensionless energy release rate are discussed. Results indicate that the coupling coefficient, applied loads, and aperture size do not affect dimensionless stress intensity factors without surface effects. Larger aperture sizes show stronger size dependence on dimensionless stress intensity factors and dimensionless energy release rate when considering surface effects. An obvious coupling effect between the phonon field and the phase field is observed. The influence of the number of periodic cracks on dimensionless stress intensity factors and energy release rate is restricted by defect size. The effects of phonon field loads and phase field loads on dimensionless stress intensity factors and energy release rate differ. This work reveals the specific influence of surface effects on the fracture behavior of multi-cracks at the hole edge, offering significant academic insights into quasicrystal fracture mechanics.

Compared to conventional mechanical testing methods, the indentation method offers the advantages of simple manufacturing of samples and in-situ testing. This study proposes an alternative to deriving material mechanical parameters solely from indentation load-depth curves. It introduces an effective method for deducing metal plastic mechanical parameters based on residual indentation morphology and neural network learning. An Instron universal material testing machine was used to conduct spherical indentation tests on Cu, Mg, and Fe, followed by scanning their residual indentation morphology through the contour morphology system. The extracted morphology features served as the basis for further analysis. Data processing techniques such as amplification, rounding, binarization, and high-order digit supplementation were applied to the acquired data. Through Abaqus software and numerical simulations, residual indentation depth data associated with various material parameters were automatically extracted for neural network learning. Selections of activation function, neural network parameter initialization and updating mode, loss function, parameter optimization strategy, and neural network structure were carefully conducted to ensure effective learning. The plastic mechanical parameters of Cu, Mg, and Fe were obtained based on the residual indentation morphology feature data from indentation tests and the neural networks after learning. Additionally, the related plastic mechanical parameters of Cu, Mg, and Fe were also acquired through conventional uniaxial tensile tests and characterization using the Instron machine. By comparing the neural network learning results with tensile test data, relative errors in plastic mechanical parameters were identified. The effectiveness of the proposed method in obtaining metal plastic mechanical parameters based on neural network learning and residual indentation morphology was validated. This method can be expanded for characterizing mechanical properties and acquiring plastic parameters of other metal/alloy materials.

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.

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, the Monte Carlo method is applied in the study of the stability of structures with random defects, coupled with numerical simulations to investigate the morphological evolution and post-buckling equilibrium path of film-substrate systems with random defects during instability. The numerical results show that the critical load of the structure with random defects is unstable. The defects significantly reduce the critical load of the structure, and the random defects destroy the symmetry of the structure, leading to a transformation from an ordered checkerboard pattern to a disordered fold nuclear pattern, hence affecting the subsequent morphological trend. This analysis assesses the potential risks and effects of random defects in thin-film structures, aiming to improve the reliability and performance of thin-film devices, coatings and surface treatments, and to bridge the gap between theoretical stability research findings and practical design applications.

Conductive polymer composite (CPC) foam exhibits excellent characteristics such as high plasticity, energy absorption, as well as thermal and acoustic insulation, and holds enormous potential for applications in various fields including construction, transportation, electronics, etc. However, the porous structure of CPC foam is usually simple and random, which limits its further application. The complexity of CPC processing makes it challenging to achieve a controlled design of micro-porous structures. 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 CPC foam. Compared to traditional unidirectional freezing, the compressive elastic modulus and peak stress of aligned anisotropic porous microstructured CPC foam increase by 18.7% and 25.4%, respectively. Buckling and collapsing risks 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 at 50% strain. A finite element model of the porous structure in CPC foam is built with parameters including elastic modulus, hole wall thickness, and Poisson's ratio, obtained from measured data or literature. The quasi-static compressive behaviors of biomimetic and disordered structures are investigated using the finite element method, and the deformation and stress distribution are compared with the corresponding experimental results. Through finite element simulations and experimental tests, it is found that the main mechanisms enhancing the compressive mechanical properties of the materials are as follows: stress distribution optimization effectively prevents plastic deformation caused by local stress concentration; the highly elastic behavior of micrometer pore wall and its 3D structure enhance the bionic structure's resilience; and the highly aligned anisotropic channels provide ample deformation space, improve deformation coordination, and enhance the structure's reversibility during loading and unloading.

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%.

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.