Additive manufacturing (AM) techniques have attracted widespread attention in aerospace and biomedical fields due to advantages like high material utilization and extensive design flexibility. However, process-induced defects in AM-built components pose significant challenges for evaluating fatigue performance. The AM-built components are subjected to complex alternating loads in service, making it imperative to develop accurate fatigue life prediction models. Currently, two main approaches are widely employed: theoretical analysis and data-driven methods. Traditional life prediction models like continuum damage mechanics (CDM) suffer from limitations such as low accuracy and restricted applicability. Conversely, data-driven models, such as artificial neural networks (ANN), encounter constraints when dealing with limited sample sizes. To address these issues, knowledge-data hybrid models have emerged as a promising approach that combines physical principles with data insights. In view of this, this study has developed a calibrated CDM model and seamlessly integrated it with an ANN-based data-driven model. Employing methods of feature, parameter, and output fusion, three types of hybrid models based on CDM and ANN have been developed. To quantitatively analyze the prediction accuracy and data requirements of these models, calculations using fatigue data obtained from laser powder bed fusion (LPBF)-processed AlSi10Mg alloy have been performed. The results highlight the crucial role played by the corrective function of training data in the parameter fusion-based model, while indicating a relatively minor influence from the CDM model in terms of prediction accuracy. Moreover, this model retains a commendable level of accuracy even with suboptimal fitting outcomes from the CDM model. The hybrid model, which leverages feature fusion, maximizes the utilization of physical information from the CDM model, thus achieving the highest prediction accuracy and stability when ample data are available. The model based on output fusion, primarily guided by results of the CDM model and enhanced by ANN adjustments, demonstrates relatively superior predictive capabilities in domains outside of the training set compared to other models. These findings provide significant reference value for the further development of high-accuracy, knowledge-data hybrid fatigue life prediction models in AM.

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 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.

Stress intensity factor is a crucial parameter for modeling and predicting structural fracture failure. This study evaluates the dynamic stress intensity factor for solving three-dimensional dynamic fracture problems using the adaptive phantom node method. This technique combines the phantom node method with adaptive mesh refinement, automating the generation of a dense mesh around the crack. In this approach, strong discontinuities at cracks are modeled using phantom nodes without crack tip enrichment functions or extra degrees of freedom. The theoretical framework of this technique is straightforward and easy to implement based on the finite element method, but it requires a relatively dense mesh to ensure computational accuracy. Adaptive mesh refinement technology and criteria suitable for crack problems are introduced into the phantom node method, thus obviating the need for a globally dense mesh with high computational consumption while improving computational accuracy and efficiency. A concise approach, known as constrained approximation, is adopted to deal with hanging nodes presented in the locally refined mesh. It is convenient to implement numerically, does not involve special elements or complex shape functions, and retains the interpolation and numerical integration of the standard finite element method. The stress intensity factors for several three-dimensional crack problems are evaluated using the adaptive phantom node method and compared with the theoretical solutions and numerical results obtained by the standard phantom node method. It is found that the numerical results of this method are in good agreement with the theoretical solutions, and the computational accuracy is effectively improved compared to the standard phantom node method. Additionally, compared to the locally pre-refined mesh with equivalent accuracy, the adaptive refined mesh exhibits higher computational efficiency and reduced computational consumption. This holds considerable potential value for the efficient simulation and prediction of dynamic fracture failure in large-scale complex engineering structures.

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.

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.