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2025 Vol. 46, No. 4
Published: 2025-08-27
437
Research on Microstructural Topology Optimization of Acoustic-structure Interaction System Based on LSTM network
The typical microstructural topology optimization for acoustic-structure interaction system is achieved through a cyclic iteration of response analysis, sensitivity calculation, and design variable updates, suffering from expensive computation cost and low computational efficiency. To address these issues, a microstructural topology optimization method based on Long-Short Term Memory (LSTM) neural network is proposed. The core idea of this method is to treat the 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. The data set is generated through microstructural topology optimization process based on the finite element-boundary element coupling analysis. Numerical examples show that the trained LSTM network can accurately predict the optimization process and reduce much computational cost compared to the conventional optimization method. In addition, the influence aspects of LSTM network structure is discussed.
2025 Vol. 46 (4): 437-448 [
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449
Numerical Analysis and Precise Control of Insertion and Extraction Forces in Contact Component of Electrical Connectors
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.
2025 Vol. 46 (4): 449-461 [
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462
Fatigue-free calibration cohesive zone model: a novel approach for predicting interface crack growth rates under fatigue loading
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 was 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.
2025 Vol. 46 (4): 462-472 [
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473
Concrete Modulus Evolution in Multiple Chemical Corrosion Processes
The corrosion of concrete by seawater has many chemical characteristics, including sulfate ion, chloride ion and their coupling action. At present, there is no consensus on the evolution of concrete modulus under the corrosion of sulfate ion and chloride ion. First, the accelerated corrosion experiment of artificial seawater was carried out with concrete samples prepared in this paper. Then, non-destructive detection technology was used to explore the change of ultrasonic propagation speed in concrete under the joint corrosion of sulfate ions and chloride ions, and the evolution law of concrete modulus under corrosion conditions was obtained. On this basis, combined with the reaction equations of the chemical processes such as the continuous hydration of the material, the chemical reactions of sulfate ions with concrete in solid and liquid phase, the complexation reaction of chloride ions, and the corresponding chemical reaction rate equations, a mechanical-chemical model of the modulus evolution of concrete under the coupled sulfate-chloride erosion was established, and the competition mechanism of the two ions was elucidated. It provides theoretical support for the design of Marine concrete with better durability.
2025 Vol. 46 (4): 473-487 [
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488
Study on the discretization characteristics of a new stress wave structure from frictional interfaces
The friction 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 on 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 an 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 by 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 for different constitutive model parameters to analyze the factors affecting the 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 1-D stress wave. A new stress wave structure is first found experimentally and numerically. Unlike the traditional “rupture-fronts” phenomenon, this new wave, though generates 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 discretized characteristics, which is expected to provide a new stress wave structure criterion for earthquake prediction and non-destructive testing of engineering components.
2025 Vol. 46 (4): 488-501 [
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502
Effect of Cu segregation on grain boundary shear deformation of FeNiCrCoCu high-entropy alloys
FeNiCrCoCu high-entropy alloys (HEAs) have excellent mechanical properties due to high mixing entropy, lattice distortion, sluggish diffusion and cocktail effect, so they are widely used in aerospace, energy, machinery manufacturing and other fields. Experimental studies have revealed that FeNiCrCoCu HEAs have Cu elemental segregation at grain boundaries (GBs); however, the mechanism of Cu segregation on shear deformation at GB 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 the deformation of GB under shear loading, using Σ11(113) GB as the model system. Initially, the hybrid MC/MD simulation technique was used to generate the models with Cu segregation, and further the cases of random Cu distribution were considered for comparison. The stress-strain curves, dislocation density and GB behavior during 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 GB increased, 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, 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 impeding 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 reveals 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.
2025 Vol. 46 (4): 502-519 [
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Mechanism of Water Diffusion-Driven Crack Tip Deformation in Hydrogels
Water diffusion in hydrogels significantly affects their mechanical behavior. Previous experimental studies on hydrogel fracture under water diffusion mainly focused on macroscopic crack observations, while experimental characterization of crack tip deformation fields in aqueous environments remained unexplored. Furthermore, theoretical analyses of water diffusion effects on crack tip deformation lack validation across different loading conditions. In this study, based on the digital image correlation (DIC) method, a self-designed mechano-chemical coupled tensile platform was employed to investigate the effects of water diffusion on crack tip deformation in polyacrylamide (PAAm) hydrogels under constant force and displacement loading. Experimental results reveal non-equilibrium diffusion competition mechanism at crack tip under different loading conditions. Finite element simulation based on a coupled large-deformation-diffusion theory was conducted to analyze the swelling ratio near crack tips under constant force loading. The simulation results confirm that stress-induced chemical potential gradients drive water accumulation at crack tips. Further, comparative experiments in oil and aqueous environments demonstrate that water exchange between hydrogels and their surroundings dominated crack tip deformation evolution.
2025 Vol. 46 (4): 520-532 [
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Research on the Tension Reduction Performance of Skin Sutures Driven by Geometric Configuration
The stress on skin suturing has a significant impact on the postoperative healing of the incision. It is necessary to clarify the corresponding mechanism and pattern of skin stress during different incision suturing processes. Based on common surgical incisions for skin suturing, with the standard of horizontal length and incision width, four types of incisions were designed: traditional straight shape, Z shape, S shape, and sawtooth shape. Considering that excessive deformation of the sample would reduce the extraction of experimental data and be unfavorable for the study of the reduction tension rule during the sample stretching process, the failure load tests of corresponding suturing structures were carried out and an appropriate test range was determined for the reduction tension research; based on the material constitutive model obtained from the sample stretching test, the stress distribution and strain distribution along different suturing incisions were theoretically analyzed; using the digital image correlation method, the strain distribution generated during the suturing process in different incision suture areas was obtained; finally, through the comparison of experiments and simulations, the tension distribution effect of the skin at the suture line was further explored. The results show that the shape of the incision is the basis for tension reduction. Compared with the traditional straight incision, the Z shape, S shape, and sawtooth shape incisions can reduce the suture tension due to the actual incision being longer and having a certain curvature. The tension reduction effect is better under low to medium loads, and it will decrease as the external load increases, but it is still significantly better than the straight incision. Under the same load, the sawtooth shape incision has the minimum main strain during suture, that is, the tension reduction effect is the best.
2025 Vol. 46 (4): 533-545 [
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Derivation and application of the geometric stiffness matrix for beam elements based on the rigid body rule
Geometric stiffness is a critical factor influencing the buckling load and nonlinear characteristics of structures. By leveraging the linearized incremental virtual work equation and the spatial torque-rotation characteristics of three-dimensional solid beams, this study analyzes the induced moment matrix, which represents the key attribute enabling equilibrium at beam element nodes. Subsequently, the geometric stiffness matrix for three-dimensional beam elements is constructed. Using the symmetry and rigid-body compliance of the geometric stiffness matrix, a concise explicit expression for the geometric stiffness matrix of three-dimensional beam elements is derived. Additionally, the geometric stiffness matrix for two-dimensional beam elements is obtained by simplifying that of the three-dimensional beam elements. Through linear buckling analysis and nonlinear analysis of typical numerical cases, the results demonstrate that the derived geometric stiffness matrix can be effectively applied to the buckling and post-buckling analysis of beam-type structures. This method for deriving the geometric stiffness matrix of beam elements possesses clear physical significance and a straightforward derivation process, offering a novel approach to deriving the geometric stiffness in finite element analysis.
2025 Vol. 46 (4): 546-559 [
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Dynamic analysis of an elliptical hole in the right-angle domain of SH wave incidence
Abstract: 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. Key words: Right - angled domain; Iterative mirror image method; Elliptical hole equation; Dynamic stress concentration factor
2025 Vol. 46 (4): 560-570 [
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