In the topology optimization of compliant mechanisms, positional and shape factors significantly affect structural mechanical properties. The formation of concentrated hinge regions not only weakens structural strength but also hinders manufacturability. To this end, we propose a topology optimization method for hinge-free compliant mechanisms, incorporating geometric nonlinearity and utilizing the bi-directional evolutionary structural optimization (BESO) method. Initially, the design domain is discretized, where the 0-1 distribution of the BESO method prevents element distortion during nonlinear finite element analysis, thus enhancing numerical stability and convergence. The deformations of the compliant mechanism at the input and output are constrained under unit excitation, effectively suppressing the emergence of concentrated hinges. This leads to improved structural strength and manufacturability. Finally, hinge-free mechanisms are fabricated via additive manufacturing. Experimental results from samples show excellent agreement with finite element simulations, validating the effectiveness of the proposed hinge-suppression strategy in compliant mechanism design.

Magnesium (Mg), a lightweight metal material, is constrained in its applications due to poor plasticity and low strength at high temperatures. Graphene (Gr) possesses a large specific surface area and high strength, making it an ideal reinforcement for improving the mechanical properties of materials. A molecular dynamics (MD) simulation was employed to investigate the mechanical behaviors of single-crystal Mg and Gr/Mg composites under compressive loading. Through the analysis of stress-strain curves, atomic structure diagrams, and dislocation distributions, the microscopic deformation mechanisms of single-crystal Mg and Gr/Mg composites under compressive loading were explored. Additionally, the influence of factors such as the number of Gr layers, loading strain rate, and temperature on the mechanical properties of materials was studied. Results reveal that single-crystal Mg exhibits anisotropic characteristics under compressive loading. Addition of Gr enables the activation of difficult-to-initiate slip systems in the Mg matrix due to grain refinement. This leads to stress release and difficulty in initiating twinning deformation. Near the Gr interface, defects such as dislocations and twins nucleate and proliferate, effectively transferring the load to Gr, thereby elevating the average flow stress during the plastic deformation stage of the composites. Furthermore, the Mg matrix restricts the folding and bending of Gr, leading to an enhancement in material toughness. As a result, when the Gr/Mg composite is compressed along the [0 0 0 1] crystal direction to a strain of 0.35, the Gr remains intact without fracture. Dislocations in Gr/Mg composite materials cannot penetrate the Gr layer, thus suppressing Mg matrix damage. Increased dislocation lines can resist compressive plastic deformation. In composites featuring multiple layers of Gr, the yield stress, yield strain, and average flow stress during the plastic deformation stage increase with the number of Gr layers. Additionally, the yield strain is higher when Gr layers are separated compared to being stacked. Within the temperature range of 10 K-600 K, the elastic modulus and yield stress of Gr/Mg composites decrease with increasing temperature. However, the strain rate has a minor effect on the elastic modulus and average flow stress during the plastic deformation of Gr/Mg composites. Nonetheless, increasing the strain rate can enhance the yield stress and yield strain of the composites.

This study examines the tensile properties of skin suturing interfaces created through a silica gel reverse molding process, focusing on the reliability of clinical adhesive properties post-suturing. Four types of skin suturing interfaces, inspired by natural bionic structures, are designed, with primary attention on their tensile stiffness. An equivalent mechanical model is constructed using mechanical theories of suturing interfaces, and a theoretical model is developed to predict the tensile stiffness of each structure. Numerical simulations and physical experiments are conducted to analyze the brittle failure behavior and tensile failure modes of the suturing structures. The influences of shape factor, tooth tip angle, and tip region on the tensile properties of the interface are thoroughly investigated. A parameter mapping model using tensile strength as the evaluation index is constructed for each sensitive factor. It is found that the skin suturing interface exhibits brittle failure behavior, with the zigzag structure showing significantly higher tensile stiffness compared to other suturing structures. As the tooth tip angle increases, the stiffness of the suturing structure decreases, while the tip area enhances the tensile properties of the interface. These results are anticipated to help improve skin wound healing rate after clinical suturing.

The pseudo-Stroh formulism can transform the governing equations of multi-field coupling materials such as quasicrystals into a linear eigensystem, enabling the exact solution of multilayered structures with simply-supported boundary conditions. This provides an important reference for various numerical and experimental methods of quasicrystal beams in engineering practice. In this paper, the free vibration and bending problems of one-dimensional (1D) hexagonal quasicrystal (QC) laminated beams with functional gradients are investigated using the pseudo-Stroh formula. A simply-supported QC laminated beam is modeled, and the transfer matrix method is used to derive the exact solutions for natural frequency of free vibration and bending deformation displacements of the beam under simply-supported boundary conditions. The obtained results are compared with the existing ones to verify the accuracy and precision of the presented model. Numerical examples are provided to show the effects of high span ratio, layer thickness ratio, and functional gradient coefficient on the natural frequency, bending deformation, and mode shape of simply-supported 1D QC laminated beams under two different stacking sequences. The results show that natural frequency increases with the increase of functional gradient coefficient. Phonon displacement decreases while phason displacement increases with the increase of functional gradient coefficient under the two stacking sequences. Functional gradient coefficient and stacking sequence minimally affect phonon displacement modes but significantly impact phason displacement modes. Moreover, they notably affect phason stresses compared to phonon stresses in QC laminated beams. Thus, the optimal natural frequency and deformation displacement of a QC beam can be achieved by adjusting geometric size, stacking sequence, and functional gradient coefficient of the layered beam. These findings can provide theoretical references for various numerical methods and experimental studies on QC beams.

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.

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.

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.

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.

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.