Ultra-high cycle fatigue experiments can be conducted using traditional testing methods such as electromagnetic vibration (30-3000 Hz) and ultrasonic vibration (20 kHz). Differences in fatigue life for the same material may arise when tested under varying loading frequencies. To fully utilize the ultra-high cycle fatigue life data obtained from different testing systems, the impact of loading frequency on the ultra-high cycle fatigue life of materials needs to be studied imperatively. This paper presents novel prediction models for ultra-high cycle fatigue life, taking into account loading frequency. The models incorporate the crack initiation life prediction model based on Tanaka's dislocation theory and the Paris crack growth life prediction model. The influence of loading frequency is integrated into effective stress and fatigue strength. The proposed models are verified using available very high cycle fatigue test data for titanium alloy TC17 and nickel-based superalloy GH4169 under different loading frequencies. The results show that the models proposed in this work can reasonably characterize the ultra-high cycle fatigue test data of materials under varying loading frequencies, establishing the correlation of fatigue life data under different loading frequencies.

For some polymers below or near their glass transition temperature, a particular type of non-Fickian solvent diffusion, known as Case Ⅱ diffusion, is typically observed. To describe the coupling effect of Case Ⅱ diffusion and swelling deformation in polymers, theoretical models are established based on continuum mechanics. Here, governing equations for solvent penetration into polymer are derived and specialized in the reference configuration, including the mechanical-chemical equilibrium state equation, the concentration-dependent diffusion equation, and the molecular number conservation equation. Additionally, a visco-hyperelastic constitutive equation taking into account the time-dependent deformation characteristics of the material is integrated to reflect the competition mechanism between relaxation rate of the polymeric network and migration of solvent in Case Ⅱ diffusion. This modeling approach is used to analyze the transient free swelling process for two material systems, so as to investigate the behavior of unidirectional Case Ⅱ diffusion in columnar and tabular polymer specimens without constraint. By applying appropriate boundary and initial conditions, the concentration, stress, and deformation field variables during the unidirectional diffusion are directly obtained. The distribution and evolution of these calculation results are compared with experimental observations, moderately validating the effectiveness and adaptability of the proposed coupling analysis method regarding polymer swelling. This developed theory may provide important guidance for practical applications such as membrane designing or drug delivery systems, where Case Ⅱ diffusion commonly occurs. It also aids in enhancing understanding of the combination of different polymer-solvent diffusion scenarios, from Fickian to non-Fickian circumstances.

Using fused deposition modeling (FDM) 3D printing technology, a lattice structure was created. After adhering composite conductive materials to the surface of its structural elements, the 3D lattice structure with sensing capability (LSS) was fabricated. Based on three-unit configurations, a study was conducted to investigate the mechanical properties and piezoresistive characteristics of different lattice structures in LSS. Utilizing the conductive percolation phenomenon in conductive composites, this study explored the patterns of piezoresistive behavior in LSS with varying structures and composites under both small and large strain conditions. Key factors such as stress caused by structural deformation and self-contact between lattice surfaces were identified, leading to the observed three-stage trend in the change of electrical resistance response. By analyzing the experimental data from compression tests, the optimal lattice structure and composite mass fraction for LSS were determined, providing a reliable basis for deformation monitoring in perceptual structures. The approach of creating a 3D structure and then incorporating conductive composites offers benefits such as structural controllability and good mechanical performance. The sensing structure can detect compressive stress in objects and serve as a high-quality buffering or damping material that effectively absorbs vibration and energy. This research demonstrates promising applications in various fields.

Research on vibration characteristics of functionally graded materials (FGMs) in the aerospace field is a hot topic of current research. In this paper, the vibration characteristics of metal-ceramic functionally graded (FG) stepped cylindrical shells under arbitrary boundary conditions are studied. To conduct this research, a mechanical model of a metal-ceramic FG stepped cylindrical shell based on the axial segmentation concept is developed. First, the properties of metal-ceramic FGMs are obtained using the Voigt model and power function volume fraction. Second, the artificial spring technique is introduced to simulate continuous coupling conditions of shell segments and arbitrary boundary conditions at the ends of the shell. The energy expression for the cylindrical shell is then derived based on the first-order shear deformation theory. Finally, the admissible function is constructed via the Chebyshev polynomial, and the dynamic differential equations of the metal-ceramic FG stepped cylindrical shell under arbitrary boundary conditions are calculated using the Rayleigh-Ritz method. The validity and convergence of the method are verified through comparison with existing literature, and the effects of boundary conditions, volume fraction, geometric parameters, and spring stiffness on modal frequencies are analyzed. It is found that the natural frequency of the FG stepped cylindrical shell initially decreases and then increases with increased number of circumferential waves under classical boundary conditions, and it increases with the number of circumferential waves under both elastic boundary conditions. The natural frequency of the shell increases exponentially with volume fraction. The effects of length-to-radius ratio and thickness-to-radius ratio on the vibration characteristics of the shell differ, with the natural frequency of the shell decreasing with increased length-to-radius ratio and increasing with thickness-to-radius ratio. Additionally, the stiffness of translational springs significantly influences the vibration characteristics of the shell compared to rotational springs.

At a microscopic level, composite materials exhibit intricate structural designs, necessitating detailed finite element mesh discretization for their analysis and design, leading to extensive computational demands. While the in-plane periodic structure, a typical composite structure, can sustain various directional forces at a macroscopic level, defining its performance remains challenging and its design and analysis are complex. This paper introduces a method for optimizing the topology of in-plane periodic structures based on thick plate theory and a multi-resolution meshing strategy. Initially, a coarse mesh is used to distinguish between macro and micro configurations, address the micro boundary value problem, and perform a similar analysis of the mechanical characteristics of the irregular single cell; subsequently, the macroscopic boundary value problems are solved using uniform equivalent properties, and a fine mesh is employed to revise the design variables and chart the density variables. It is found that assuming a thick plate that accounts for out-of-plane shear deformation makes the two-scale topology optimization design closer to real load-bearing scenarios. Employing a multi-resolution meshing strategy circumvents the issue of limited solvable problem size caused by excessive finite element computation, while maintaining the resolution of the optimized configuration.

The study examined the two-anchor system of Extension-Type Bamboo/Rebar Tension-Pressure (EBTP) anchor rods in earthen sites. Indoor two-anchor digital image correlation (DIC) pullout tests with anchor spacing of 0.3 m and 0.6 m were conducted to clarify the load-displacement relationship and typical failure modes. Based on the characteristics of anchor slip failure modes, a 2D finite element method (FEM) was proposed for the two-anchor system. The slurry/soil interface under compression and rod/pulp interface in tension were simulated using the contact pairs and nonlinear springs, respectively. Experimental results indicated that, at 0.3 m spacing, horizontal cracking along the rammed earth layer was the primary failure mode, while at 0.6 m spacing, a conical cracking pattern emerged with a transition between tension and compression at an angle of 30°～45°, yielding a maximum crack radius of approximately 24 cm at the soil top surface. The bearing capacity decreased by approximately 7% at 0.3 m spacing compared to 0.6 m spacing. The simulation analysis illustrates that anchor spacing has a significant influence on the group anchor effect. For one thing, when the spacing exceeds 0.6 m, the group anchor effect is more limited, which is consistent with experimental results. For another, the depth of the expansion body demonstrates an approximately linear correlation with the ultimate bearing capacity of the anchor. Therefore, as anchor length increases, the bearing capacity initially increases sharply, followed by a more moderate increase. Although the group anchor effect gradually strengthens, the increment in bearing capacity due to increased anchor length outweighs the loss caused by the group anchor effect. These findings provide valuable insights for the design of EBTP anchor groups in earthen sites. The simulation methodology in this study can be used to predict and optimize anchorage design parameters for anchoring works at earthen sites.

Zirconium and its alloys are used as nuclear fuel cladding materials due to their excellent mechanical properties, corrosion resistance, and small thermal neutron absorption cross-sections. When exposed to radiation, a large number of irradiation-induced defects emerge in the zirconium alloy, seriously diminishing its mechanical properties and service life. This study employs molecular dynamics simulations to investigate the interaction between the stacking fault pyramid and point defects (i.e., interstitial atoms and vacancies) in zirconium. It is found that, at 0 K and 300 K, the stacking fault pyramid exclusively absorbs interstitial atoms; while at 600 K, it absorbs both interstitial atoms and vacancies. To explain this phenomenon, the binding energy of interstitial atoms/vacancies and the stacking fault pyramid is calculated. The results indicate that the binding energy is related to the type/position of point defects: the binding energy of interstitial atoms is much greater than that of vacancies, making interstitial atoms more likely to be absorbed. At the same time, the proximity to the stacking fault pyramid amplifies the binding energy, rendering both point defects more susceptible to absorption. These simulation results provide a new insight into understanding the growth mechanism of irradiation-induced defects in zirconium.

Metals and alloys are widely used in industry due to their excellent mechanical properties. Researchers have been continuously searching new materials with better properties or mechanisms to enhance existing ones. In the metal and alloy forming process, hot deformation can effectively refine the grain and improve mechanical properties such as yield strength and tensile strength. Therefore, it is necessary to study the deformation behavior of metal and alloy materials at high temperatures. The hyperbolic-sinusoidal Arrhenius-type model has been widely used by researchers because of its good simulation effect at high temperatures. In this paper, the building process of the model is studied, and the modeling process is optimized with the help of a neural network model. A neural network model is constructed to efficiently determine the hyperbolic-sinusoidal Arrhenius-type equations, based on which the flow stress of high-entropy alloys (HEAs) for different high temperatures and strain rates can be well predicted. The reported hot deformation behaviors of Al_0.3CoCrFeNi HEAs are examined by current model. The results show that the coefficients obtained by the neural network method can better describe the experimental hot flow stress, especially at high strain rate or low temperature conditions. The root-mean-square error (RMSE) and the correlation coefficient R are used to assess the degree of difference between the results. The RMSE and R of the neural network method at total data are 27.7 and 0.985, respectively, which are better than 33.1 and 0.979 of the traditional method. To show the general applicability of the model, the hot deformation behaviors of (CoCrNi)₉₄Ti₃Al₃, FeCrCuNi₂Mn₂, and AlCrCuFeNi are analyzed by the model. The research work presented in this paper can improve the efficiency and accuracy of the hyperbolic-sinusoidal Arrhenius-type model and reduce the difficulty of establishing the model, and is of positive significance for the wide use of the model.

Elastic wave metamaterials are artificial periodic structures that can control elastic waves. They can be used in aeronautics and astronautics, vehicle engineering, and other fields. This paper proposes a tunable metamaterial with two magnetic resonators. In this structure, a stainless steel plate connects the magnetic resonator to the external frame. Adjusting the distance between the magnets can affect the in-plane stress of the stainless steel plate and thus the internal stiffness. By adjusting the cell structure, a double-cell system with different internal stiffnesses can be formed to achieve a wider coupling band gap. First, the variations of the stiffness of the thin plate and the negative stiffness of the magnetic force with the distance between two magnetic resonators are determined. The dispersion relationship and the transmissibility of the single-cell metamaterial with double magnetic resonators and the double-cell metamaterial formed by adjusting the distance between magnets are obtained using a theoretical model. Then, the effect of the distance between two magnetic resonators on the metamaterial bandgap and double-cell coupled bandgap in a specific case is further studied. Finally, an experimental model is designed and manufactured using 3D printing technology. The transmissibility curves at different distances between two magnetic resonators are measured, and the bandgap coupling results of double-cell metamaterial structures are verified. The theoretical prediction of the bandgap of the metamaterial agrees well with the experimental results. This adjustment method can provide a new idea for the active control of restraining elastic wave transmission.

Fatigue failure is the most common form of failure in engineering. Under the interaction betweenthe corrosive environment and fatigue load, the fatigue life of a structure is significantly reduced. It often consumes a lot of time and economic costs to evaluate the fatigue properties of materials or structures through corrosion fatigue experiments. Therefore, it is crucial to establish a reliable numerical prediction model for scientific research and engineering design. In this study, we develop a peridynamic corrosion fatigue model, which combines the peridynamic fatigue crack model and the peridynamic stress-corrosion model, according to the superposition model of corrosion fatigue. In this model, corrosion fatigue damage is a linear superposition of corrosion damage and fatigue damage, and the coupling between stress and corrosion is considered. Consequently, the effect of structural deformation on the corrosion rate, the heterogeneity of the products, and the geometry of the corrosion front can be considered simultaneously in the model. The new model is then applied to simulate the corrosion fatigue failure process (including crack initiation and crack growth phases) of stainless steel compact tensile specimens. The simulation results show that the model can accurately describe the complete corrosion fatigue failure process of the compact tensile specimen, with the corrosion fatigue crack initiating randomly but consistently around the expected high-stress region. The decrease in fatigue life due to the interaction between the corrosion environment and fatigue load is captured, and prolonged corrosion time exacerbates the reduction in fatigue life when a lower load is applied. The influence of loading frequency on corrosion fatigue behavior is investigated by calculating the crack initiation life and comparing crack length curves. The model can also capture the significant influence of loading frequency on the fatigue life in corrosion fatigue processes. Reducing the loading frequency extends the corrosion time between each cyclic load, intensifying corrosion damage and ultimately reducing the crack initiation life while accelerating crack growth. The numerical results demonstrate that the introduced mechano-chemical damage model can capture the loading frequency sensitivity.