Microstructural topology optimization for acoustic-structure interaction systems typically involves iterative response analysis, sensitivity calculation, and design variable updates, leading to high computational costs and low efficiency. To address these issues, a microstructural topology optimization method based on long-short term memory (LSTM) neural network is proposed. This method treats microstructural configurations in topology optimization process as a time series. The LSTM network, known for its powerful ability to process sequential information, is used to learn the patterns of configuration evolution. A data set is generated through microstructural topology optimization based on the finite element-boundary element coupling analysis. Numerical examples show that the trained LSTM network accurately predicts the optimization process and significantly reduces computational cost compared to conventional optimization methods. In addition, the influence of LSTM network structure is discussed.

Electrical connectors are critical components in electronic systems, enabling the conduction of electrical current and the transmission of signals. They are extensively used in various fields such as aerospace, telecommunications, computing, and the automotive industry. The reliability and stability of an entire system often depend on the performance of these connectors. Any failure may not only disrupt normal device operation but also result in severe equipment damage. Among known failure mechanisms, contact failure caused by inadequate insertion and extraction force accounts for a significant proportion. To address this issue, a general analytical formula for calculating insertion and extraction force was derived based on a cantilever beam model. This model was used to analyze the mechanical behavior and force variation during the insertion and extraction of the pin and socket components. A comprehensive understanding of the force distribution during these processes was established through this approach. Subsequently, a finite element model was developed for a specific type of electrical connector's contact components. Simulation analyses were conducted to examine how the insertion and extraction force changes with displacement. These simulation results were then validated through controlled experimental tests. The findings indicate that the relative error between the theoretical predictions, simulation outputs, and experimental measurements remains below 8%. The strong agreement among these methods confirms the accuracy and applicability of the developed models. To fulfill practical engineering requirements and avoid excessive mechanical stress, the validated theoretical model was further applied to optimize the design parameters of the connector's contact springs, with a particular focus on their length and thickness. A qualified design range was identified, effectively distinguishing safe and failure regions. This provides clear engineering boundaries for failure-resistant design and enhanced service life. Additionally, the outcomes offer valuable guidance for the structural optimization of contact components in electrical connectors, supporting enhanced performance, stability, and durability in demanding applications.

Fatigue failure, recognized as one of the most prevalent failure modes in engineering structures, remains inadequately understood in terms of its fundamental mechanical mechanisms. Existing fatigue crack growth models are highly dependent on experimental fatigue data while lacking a universal theoretical framework. To overcome these limitations, we develop a Fatigue-Free Calibration Cohesive Zone Model (F-free model), which can efficiently predict fatigue crack growth rates without the need for fatigue data. Through the definition of cohesive endurance limit and its associated separation displacement, a cyclic damage increment triggering criterion is established. The concept of conditional yield stress in elastoplastic materials is extended to the framework of the cohesive zone model. The cohesive endurance limit is determined as the intersection point between the actual traction-separation curve and a straight line parallel to its initial linear segment. The proposed F-free model is validated by comparing its simulated fatigue crack growth rates with experimental data from two key test scenarios: interlaminar delamination in composite laminates and face-core debonding in sandwich structures. The prediction range of this model can effectively encompass the experimental observation results, accurately capturing both the crack growth rates and the Paris' exponent values for mode I interfacial fatigue cracking. The applicability of the F-free model is further evaluated. The fatigue crack growth rates of interlaminar delamination in double cantilever beam (DCB) specimens under different cohesive endurance limits are simulated. The results indicate that the F-free model can provide a prediction region for interfacial fatigue crack growth rates and a prediction range for the Paris' exponent between 0.99 and 6.3. The proposed F-free model is applicable for predicting the fatigue crack growth of elastoplastic materials or at ductile fracture interfaces. This advancement provides a novel theoretical framework for fatigue damage analysis, effectively bridging the gap between empirical observations and mechanical modeling. The proposed F-free model is able to significantly improve the computational efficiency of fatigue damage tolerance analysis.

Concrete structures in marine environments will be attacked by corrosive ions in seawater, including chloride ions, sulfate ions, etc. Those ions can significantly cause the degradation of the mechanical properties and durability of concrete. They can also cause problems like reinforcement corrosion, cracking, and spalling, and lead to the decrease of the service life of concrete structures and pose serious threats to structural safety. Investigating the evolution of mechanical properties of concrete under the combined action of sulfate and chloride ions is crucial for designing more durable concrete structures in marine environment. However, there is currently no consensus on the evolution of concrete modulus under such combined corrosion conditions. To address this gap, this paper presents an experimental study on the modulus evolution of concrete under the combined corrosion of sulfate and chloride ions. Concrete samples were prepared and subjected to accelerated corrosion experiments in artificial seawater. Ultrasonic non-destructive testing (NDT) was used to measure the changes in ultrasonic wave velocity in concrete. This allowed us to track the evolution of concrete modulus under corrosion conditions. Based on the experimental results, a mechanical-chemical model was developed. The model integrates the continuous hydration of concrete, the chemical reactions of sulfate ions with concrete, the complexation reactions of chloride ions, and other chemical processes. The model helps explain the competitive mechanism between sulfate and chloride ions during the corrosion process. The results show that the elastic modulus of concrete initially increases due to the filling effect of hydration products and the formation of ettringite and Friedel's salt. However, as the corrosion continues, the excessive filling of pores by expansive products caused by sulfate ions leads to a gradual decrease in modulus. The model successfully captures these changes and fits well with the experimental data. Additionally, it was found that chloride ions react with tricalcium aluminate to form Friedel's salt. This reduces the amount of ettringite formed by sulfate ions, thereby reducing the expansion force and delaying the decline in dynamic elastic modulus. This also reduces the damage caused by the expansion force. The findings provide a theoretical basis for designing concrete structures in marine environments with stronger resistance to sulfate and chloride corrosion. This can help engineers develop more effective strategies to enhance the durability of concrete in marine environments. This, in turn, can extend the service life of marine infrastructure and reduce maintenance costs.

The frictional interface at the moment of transition from static to dynamic state may undergo two types of disturbances: rupture-fronts and stress waves. Rupture-fronts are driven by the fracture of micro-contacts of the frictional interface, change the shape of the frictional interface, and propagate within the frictional interface under different speeds. By contrast, stress waves are driven by radiation from kinds of resources on the frictional interface, and have no effect on the shape of the frictional interface. Both rupture-fronts and stress waves imply important information of the dynamic behavior of frictional interfaces in nature. Here, stress wave structures associated with a frictional interface are studied for a finite-sized slider subjected to impact loading. First, SHPB experiments for frictional sliding of two glass sliders under shock wave loading are performed, and the fine wave structures near the frictional interface are directly measured with high-sensitivity piezoelectric sensors. The characteristics of stress waves related to the frictional interface are then simulated by finite element method for different frictional boundaries and constitutive model parameters to analyze the factors affecting stress wave propagation and profiles. Finally, the generation mechanism of the wave structures within the frictional interface is discussed based on the theory of the 1D stress wave. A new stress wave structure is first found experimentally and numerically. Unlike the traditional “rupture-fronts” phenomenon, this new wave, though generated from the overall dynamic response of the frictional interface, does not travel along the interface. Instead, it propagates perpendicularly to the interface as a plane longitudinal wave into the substrate. More interestingly, this new plane stress wave exhibits discretization enhancement in time but weaker in space. Within wave theory and simulations, it is found that the new wave does not stem from the fracture of micro-contacts on the frictional interface, but rather from the envelope of the spherical wave fronts radiated by the entire interface. This discovery reveals a new stress wave structure coming from frictional interfaces and its discretization characteristics, which is expected to provide a new stress wave structure criterion for earthquake prediction and non-destructive testing of engineering components.

FeNiCrCoCu high-entropy alloys (HEAs) have excellent mechanical properties due to high mixing entropy, lattice distortion, sluggish diffusion, and the cocktail effect, so they are widely used in aerospace, energy, machinery manufacturing, and other fields. Experimental studies have revealed that FeNiCrCoCu HEAs exhibit Cu elemental segregation at grain boundaries (GBs); however, the mechanism of Cu segregation on shear deformation at GBs remains unclear. To address this phenomenon, this study adopted a combination of molecular dynamics (MD) simulation and Monte Carlo (MC) simulation to investigate the effect of Cu segregation on GB deformation under shear loading, using Σ11(113) GB as a model system. Initially, the hybrid MC/MD simulation technique was used to generate the models with Cu segregation, and then the cases of random Cu distribution were considered for comparison. The stress-strain curves, dislocation density, and GB behavior under shear loading were analyzed in detail. The results showed that under shear stress, the GB without Cu segregation exhibited GB migration dominated by disconnection nucleation and extension. In contrast, as the degree of Cu segregation at the GB increased, the GB deformation gradually transformed into dislocation emission from the GB, while the required shear strength also increased. Further analysis revealed two reasons for the change in GB behavior. First, the Cu element segregation at the GB changed the chemical environment near the GB, reduced stress concentration at the GB, decreased GB energy and GB free volume, thereby hindering GB migration. Second, the high concentration of Cu elements at the GB region had a pinning effect on the GB, which further impeded GB migration. The inhibitory effect of Cu segregation on GB migration was also observed in Σ5 (210), Σ17 (410), and Σ27 (115) GBs. Overall, this study demonstrates the effect of GB segregation of Cu on the mechanical properties and GB deformation response of FeNiCrCoCu HEAs and highlights the importance of GB composition for tailoring high-strength materials. These findings provide a new perspective for understanding GB behavior of high-entropy alloys and contribute to the design and development of future high-performance alloys.

Water diffusion in hydrogels significantly affects their mechanical behavior. The existing experimental studies on the fracture behavior of hydrogels affected by water diffusion mainly focused on macroscopic crack observations. The experimental characterization of crack tip deformation fields in aqueous environments remained unexplored. Furthermore, theoretical analysis of water diffusion effects on crack tip deformation lacks validation across different loading conditions. In this study, utilizing a custom-built mechano-chemical coupled tensile platform and digital image correlation (DIC) method, we investigated the effects of water diffusion on crack tip deformation in polyacrylamide (PAAm) hydrogels under constant force and constant displacement. Experimental results revealed a non-equilibrium diffusion competition mechanism at the crack tip under different loading conditions. Finite element simulation based on the equilibrium theory coupling large deformation with water diffusion was performed to analyze the swelling ratio near crack tips under constant force. The simulation results confirmed that stress-induced chemical potential gradients drive water accumulation at crack tips. Further, comparative experiments in oil and aqueous environments were performed to compare the time scale of water diffusion within the hydrogel and the time scale of water diffusion between the hydrogel and the surroundings. It is found that the load applied to the crack tip leads to a decline of chemical potential around the crack tip. The difference of chemical potential drives the water diffusion from the surroundings to the crack tip. This experimental result validates the existing theoretical analysis. The experimental result also demonstrates that water exchange between hydrogels and their surroundings instead of the water migration within the hydrogel itself dominates the crack tip deformation evolution. The elucidated mechanism of crack-tip diffusion and environmental interaction hold significant potential for guiding the design of hydrogels with enhanced fracture resistance and tailored mechanical performance in demanding applications such as biomedical implants and soft robotics operating in aqueous settings.

The stress exerted on skin during suturing plays a critical role in the healing process of postoperative incisions. Understanding the underlying mechanisms and patterns of skin stress in different suturing methods is therefore essential for optimizing surgical outcomes. In this study, four common surgical incision geometries were designed for investigation, including the traditional straight incision, as well as Z-shaped, S-shaped, and sawtooth-shaped incisions. All incisions were standardized by their horizontal length and incision width to ensure comparability. To address the issue of excessive specimen deformation compromising experimental data accuracy, failure load tests were performed on each suturing structure. These tests established appropriate load limits to be used in subsequent tension-reducing performance assessments. Material constitutive models derived from tensile tests on skin specimens provided the theoretical basis for analyzing the distributions of stress and strain along different incision patterns. Additionally, digital image correlation techniques were employed to capture detailed strain distributions occurring within the suture zones during the suturing process. By combining experimental data with numerical simulations, the study further elucidated tension distribution in skin at the suture line. The results demonstrate that incision geometry is fundamental to reducing skin tension during suturing. Compared with traditional straight incisions, Z-shaped, S-shaped, and sawtooth-shaped incisions exhibit longer effective incision lengths and intrinsic curvature, both of which contribute to lowering suturing tension. The tension-reducing effects are most pronounced under low to moderate external loads. Although these effects gradually diminish as external loads increase, they remain significantly superior to those observed with straight incisions. Notably, the sawtooth-shaped incision displayed the lowest principal strain at the suture line under equivalent loading conditions, indicating the most effective tension reduction among the four incision types. These findings provide valuable biomechanical insights that could inform the design of suturing techniques to enhance postoperative skin wound healing rates and improve clinical outcomes.

The load-bearing capacity of slender structural systems, particularly those comprising assemblages of beam elements, is critically governed by their geometric stiffness properties. Conventional methodologies for deriving the geometric stiffness matrix of beam elements are typically rooted in stability functions or variational energy principles and entail mathematically intricate formulations that frequently obscure physical interpretations, especially concerning the treatment of higher-order displacement terms. In marked contrast to these established approaches, the present study introduces a physically insightful framework by first investigating the induced moment matrix. This fundamental mechanical attribute rigorously preserves nodal moment equilibrium during finite three-dimensional rotations. Its formulation is established through the incremental virtual work principle, derived from consistent linearization of three-dimensional solid beam kinematics integrated with exact spatial rotational transformations. A pivotal theoretical finding demonstrates that while the induced moment matrix inherently exhibits asymmetry when examined at the individual element level, this asymmetry vanishes upon assembly into the global structural system, resulting in a symmetric structural-level geometric stiffness matrix. Building upon this foundation, a three-dimensional geometric stiffness matrix incorporating undetermined coefficients is systematically constructed by rigorously enforcing displacement compatibility conditions across the element. Subsequently, by exploiting the proven symmetry of the assembled global geometric stiffness matrix and strictly imposing the rigid body rule, which necessitates zero straining energy for arbitrary rigid displacements, a concise and fully explicit analytical expression for the three-dimensional beam element geometric stiffness matrix is derived. This expression is further simplified to yield its corresponding two-dimensional counterpart for planar analyses. Comprehensive numerical validations encompass eigenvalue buckling analyses of axially compressed prismatic members and geometrically nonlinear analyses of diverse structural configurations: cantilever beams, arches, spatial frames, and curved beams. These extensive simulations consistently confirm that the proposed geometric stiffness matrix achieves exceptional computational accuracy and numerical efficiency in predicting both critical buckling loads and complex post-buckling equilibrium paths. This work establishes a novel, mechanically transparent, and mathematically streamlined paradigm for deriving geometric stiffness matrices, offering a unifying perspective readily extensible beyond beam elements to potentially encompass plate and shell finite elements in future developments.

In response to the defects in the right-angled domain, this paper conducts a theoretical study on the variation of the concentrated stress at the edge of an elliptical hole in this domain. Firstly, the iterative mirror image method is employed to transform the right-angled domain space into the full space. By using the polar coordinate transformation method, the expressions of the mirrored elliptical hole in the original complex-plane coordinate system are derived. Secondly, the stress expressions are deduced by using the Hankel wave function combined with the complex variable function. Then, with the help of the elliptical hole equation, the relationship between the argument of a point on the elliptical edge and the angle between the perpendicular line of this point and the coordinate axis is established, thus avoiding the use of the traditional conformal transformation method. Based on the free-stress boundary conditions of the elliptical hole edge, an infinite system of linear algebraic equations is established. Finally, a finite number of terms are intercepted to solve the unknown coefficients. Through the analysis of the distance between the center of the elliptical hole and the upper and right boundaries, the incident angle, the deflection angle of the elliptical hole, and the incident wave number, the following conclusions are obtained: the larger the incident wave number, the higher the fluctuation frequency of the dynamic stress concentration factor; when the incident wave is at a low frequency, as the distance from the right boundary increases, the dynamic stress concentration factor first decreases and then tends to be stable, and the stable value of the distance is 5. This research provides numerical conclusions for the dynamic stress factor at the edge of elliptical defects in the right-angled domain and offers detailed theoretical results for the defect detection of right-angled plates in practical engineering.