The interaction between a penetrating-type circular-arc crack and a screw dislocation in magnetoelectric composites is studied. Firstly, according to the basic equations of magnetoelastic composites and the theory of complex function, the relationship between the anti-plane shear stress, the normal component of the electric displacement, and the normal component of the magnetic induction along the boundary arc c is derived. Then, based on the conformal mapping technique, the complex form of the generalized stress field is obtained by analyzing the stress conditions of the dislocation. In order to discuss the dislocation, dislocation shielding effect, and crack shielding effect at the crack tip, the force-electric-magnetic field intensity factors and the image forces acting on the dislocation are further deduced. By analyzing the analytical solutions and numerical examples, the results show that the shielding effect of the field strength factor decreases with increasing the distance between the circular-arc crack tip and the dislocation point, and the angle formed by their connecting line and the positive half of the x-axis, indicating that the dislocation has a shielding effect on the crack. Additionally, the effect of dislocation on a circular-arc crack is more prominent than on a straight crack. Besides, the image force on the dislocation is affected by the surface properties of the circular-arc crack. Finally, the screw dislocation can reduce the stress intensity factor of the circular-arc crack tip, and the shielding effect rapidly weakens as the angle increases. The shielding effect of the screw dislocation on the crack tip is strengthened as the ratio between the distance from the dislocation point to the crack tip and the half-chord length of the circular-arc crack increases. These conclusions carry meaningful significance for fracture mechanics research and provide a theoretical basis for improving and evaluating the performance of electromagnetic devices.

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.

The mechanical properties of materials are affected by inevitable defects such as inclusions and cracks. Accurate knowledge of their elastic fields is required to prevent stress concentration, which can lead to fracture and plastic damage. To study mutual interactions in an isotropic plane with cracks and inclusions, heterogeneous inclusions are approximated as homogeneous inclusions with the same elastic modulus as the matrix plus unknown eigenstrain based on the equivalent inclusion method, while mixed-mode Ⅰ/Ⅱ cracks are approximated as climb/glide dislocations with unknown densities according to the distributed dislocation technology. Interactions in the plane are fully considered in the governing equation system, and a solvable matrix is established with all unknowns in a unified framework. The conjugate gradient method is used to iteratively solve the unknowns, and the fast Fourier transform is introduced to improve computational efficiency. The stress field of cracks in any direction is settled by the stress transformation law, and the stress intensity factors at crack tips are determined by the converged dislocation densities with the assumption of crack-induced displacements in parabolic shapes. The influence of the heterogeneous properties of inclusions on stress intensity factors at crack tips is then properly captured. The situations of cracks/inclusions are discussed in detail, providing a description of the elastic fields and stress intensity factors. The complexity does not necessarily increase with the number of inclusions and cracks, and the calculation cost depends only on the mesh density. The effectiveness of the model developed in this study is verified using the finite element method. This model has potential application prospects in the fracture failure of heterogeneous materials and the plastic zone problems near crack tips. The conclusions may offer insight into the modeling scheme of various defective structures and the fracture behavior of materials.

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.

In this paper, an asymmetric bristle model based on the combination of bristle model and LuGre model is proposed to explain the direction-dependent friction (i.e., asymmetric friction) phenomenon exhibited by steel brushes. In this model, friction is generated through the horizontal frictionless contact between asymmetric bristles and the contacted substrate. Numerical simulation and expreimental results demonstrate that the asymmetric bristle model can effectively illustrate the direction-dependent friction phenomenon. Furthermore, in a simulation study of a planar biped robot, results show that applying this model can improve the maximum motion speed of the planar biped robot compared to using a symmetric friction model. Additionally, exmprimental resutls indicate that compared to rubber materials, steel brushes possess the advantages of high friction and abrasion resistance. Therefore, due to these propterties, steel brush structures may have great application prospects and potential benefits in the field of legged robotics.

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.

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.

Ultrasonic resonance technology is the most effective method for studying the ultra-high-cycle fatigue properties of metallic materials. Ultrasonic fatigue specimens typically need a distinctive geometric design to fulfill the resonance requirements. Conventional specimens, such as round rods and dog bones, do not have planar characteristics, making quantitative microscopic characterization difficult. This paper presents an ultra-high-cycle tensile fatigue specimen with a featured plane based on a traditional dog-bone tension-compression specimen design. Different from the traditional specimen design, the dog-bone specimen herein has a flat observation area, readily enabling quantitative microscopic characterization. Using GH4169 nickel-based alloy as an example, the proposed plane-featured dog-bone fatigue specimen design is validated. As expected, the ultrasonic fatigue test results show that the proposed dog-bone plane specimen can resonate at 20 kHz. The measured fatigue life data are basically consistent with available S-N results in the literature. The proposed method provides new ideas for the design of ultrasonic cycle fatigue specimens and helps in the study of micro-deformation mechanisms of ultra-high-cycle fatigue.

To investigate the vibration characteristics of graphene-platelet-reinforced porous composite (GPLRPC) cylindrical shells under arbitrary boundary conditions, a semi-analytical method using Gegenbauer polynomials as admissible functions is proposed in this paper. First, the effective material properties of the GPLRPC cylindrical shell are derived based on the Halpin-Tsai micromechanical model and open-cell body theory. The artificial spring technique is utilized to simulate the boundary conditions at both ends of the shell and continuous coupling conditions between shell segments. Then, based on the first-order shear deformation shell theory, the motion equations of the structure are derived and its dimensionless frequencies are obtained with the Rayleigh-Ritz method. Numerical calculations are performed to analyze the effects of boundary conditions, porosity coefficients, porosity types, graphene distribution patterns, graphene mass fractions, boundary spring stiffness, and geometric parameters on the vibration characteristics of the shell structure. The results show that Gegenbauer polynomials have excellent convergence and accuracy as admissible functions. It is also found that boundary conditions have different effects on the frequency of cylindrical shells, and the GPL-A distribution pattern and Type-II pore distribution exhibit the best stiffness enhancement effect. Additionally, it is observed that the influence of translational springs on frequency is greater than rotational springs, and the effect of cylindrical shell length-to-diameter ratio is greater, but the effect of diameter-to-thickness ratio is less. Overall, applying graphene to cylindrical shells has a wide range of applications, and the research results can provide data support and theoretical reference for the engineering design.

Coal-rock mass exhibits extremely complex and discontinuous deformation, as well as heterogeneous characteristics. Traditional numerical methods, such as the finite element method (FEM), are difficult to accurately describe the entire process of damage accumulation and progressive failure. Based on the non-local peridynamics (PD) method, the corresponding micro-modulus function and critical elongation are derived by reconstructing the kernel function of the constitutive force function. This approach introduces heterogeneity by incorporating random pre-breaking bonds into the homogeneous discrete model. As a result, peridynamics can be applied to the simulation and analysis of deformation and failure of natural heterogeneous materials and structures. Taking the Fucun coal mine as an example, a heterogeneous peridynamics simulation model is established. The deformation and failure laws of the roadway's surrounding rock and failure characteristics of coal pillars with different widths are analyzed. It is found that when the width of the coal pillar is 5 m, the roadway is at the edge of the extrusion deformation zone. The significant change in abutment pressure results in severe deformation and damage to the roadway's surrounding rock. When the width of the coal pillar increases to 6 m and 7 m, the roadway's surrounding rock gradually moves away from the extrusion deformation area. Consequently, the influence of the basic roof rotation movement in the goaf on the coal pillar weakens, resulting in reduced deformation and damage to the roadway. However, when the width of the coal pillar continues to increase, the roadway's surrounding rock enters an area where the stress increases. The high bearing pressure from the external stress field leads to an increase in deformation and damage to the roadway. Considering the deformation and damage characteristics of the roadway's surrounding rock and coal pillar, a reserved width of 7 m for the coal pillar is finally determined. The proposed peridynamics simulation model provides a new and effective simulation tool for optimizing the size of coal pillars in gob-side entry driving.