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2025 Vol. 46, No. 6
Published: 2025-12-27
707
Application of Infrared Thermography in Very High Cycle Fatigue Research
Very high cycle fatigue (VHCF) has emerged as a critical scientific challenge in the domains of structural integrity and operational safety, characterized by fracture and failure behaviors fundamentally distinct from conventional fatigue mechanisms. This paper systematically reviews the mechanisms of crack initiation and propagation in metallic materials under VHCF loading, and, grounded in thermodynamic principles of condensed matter physics, elucidates the intrinsic coupling among fatigue fracture, energy dissipation, and thermal response. Building on this theoretical framework, recent advances in the application of infrared thermography to fatigue research are comprehensively assessed, encompassing fatigue limit prediction, crack detection and monitoring, quantitative evaluation of internal cracks, and life assessment. The review underscores the unique advantages of thermally informed approaches at both theoretical and experimental levels, providing new perspectives for efficient fatigue life prediction. Finally, drawing on the latest research progress, prospective directions for advancing infrared thermography in fatigue studies are outlined. Overall, this work establishes a systematic research paradigm for thermal approaches in VHCF, offering both deeper insights into its thermodynamic essence and a foundation for broader engineering applications.
2025 Vol. 46 (6): 707-730 [
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731
Analysis of the Large-Deflection Mechanical Behavior of a Cantilever Beam Loaded via a Transmission Mechanism
To investigate the large-deflection mechanical response mechanism of elastic components under the load exerted by a transmission mechanism, this paper selects the elastic cantilever beam as the research object and conducts both theoretical analysis and verification research on large-deflection beams subjected to such loads. First, based on the equilibrium equation of curved beams and incorporating geometric nonlinearities, the governing differential equation that describes the large-deflection deformation of the elastic beam under the action of the transmission mechanism is derived and established. Subsequently, considering the strong nonlinearity of the governing differential equation and the coupling relationship between load and deformation, a numerical solution scheme integrating the shooting method with the Newton–Raphson iteration method is developed. Through iterative convergence calculations, the deflection distribution and stress state of the elastic beam are obtained. Finally, the theoretical results are compared and analyzed against finite element simulation results under various working conditions. The results demonstrate that the deflection values and stress states obtained from theoretical calculations are in excellent agreement with those from finite element simulations, thereby effectively validating the accuracy of the established mechanical model and the reliability of the numerical solution method. This model can accurately characterize the large-deflection deformation behavior of elastic beams under the influence of transmission mechanisms and provides theoretical support for structural analysis and performance prediction in engineering applications such as the design of flexible nozzles in wind tunnel test sections and railway track turnouts. It holds significant academic value and broad application prospects.
2025 Vol. 46 (6): 731-741 [
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742
Research on Topology Optimization Design Method of Rocket sled Structure under Severe Load Conditions
Lightweight design of rocket sled structure is very important to improve the level of rocket sled test. However, the dynamic characteristics and uncertainties of the rocket sled are complex. How to reduce the weight of the structure and ensure the reliability of the structure is the key. This paper proposes a novel reliability-based topology optimization method for rocket sled structure considering the dynamic characteristics and multi-source uncertainty based on the level set method. Firstly, this paper analyzes the characteristics of rocket sled structures and provides specific ways of rigid flexible coupling. Based on the joint simulation of ANSYS and ADAMS, the dynamic simulation of rocket sled structure under rigid flexible coupling condition is realized. The severe load cases between the slider and the track are extracted and used as the load input for the topology optimization of the rocket sled structure. Furthermore, the influence of uncertainties such as material properties and load amplitude is quantified based on the interval model. The reliability index is constructed to evaluate the structural performance. Then, a topology optimization model for the rocket sled structure is constructed based on the level set method, where the constraint condition is the reliability constraint of structural displacement. The example achieved a weight reduction of over 30% for the rocket sled structure under the condition of reliability not less than 90%. And all calculations can be completed in about 2 minutes. The numerical results show that considering the influence of uncertainty is important for topology optimization of rocket sled structures. Improving structural reliability can be achieved by using more materials or designing new force transmission paths. Although this article simplifies the rocket sled structure into a two-dimensional region for topology optimization, the simulation under rigid flexible coupling conditions, equivalent boundary conditions of the rocket sled structure, and methods for handling uncertainties involved are universal and also applicable to the design of three-dimensional rocket sled structures.
2025 Vol. 46 (6): 742-752 [
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753
Viscoplastic behavior of Sn-3.0Ag-0.5Cu-xBi low-melting-point lead-free solder alloys and the thermal fatigue reliability of their packaging interconnections
As electronic products become more pervasive, issues of thermal reliability during their service period have attracted extensive attention. Rate/temperature-dependent mechanical behavior of low-melting-point lead-free solder alloy and thermal reliability study of its packaging interconnection are an important foundation for the lead-free, high equipment quality and reducing energy consumption requirements in the field of electronics industry. Firstly, uniaxial tensile tests of three low-melting-point lead-free solder alloys, namely Sn-3.0Ag-0.5Cu-xBi (x = 0 wt.%, 1.5 wt.%, 2.5 wt.%), are conducted at different temperatures and strain rates using an Instron universal material testing machine. The influence of temperature, strain rate, and Bi element content on the tensile deformation behavior (elastic modulus, saturation stress) of the three solder alloys are analyzed. Additionally, the thermal expansion coefficients of the three solder alloys are obtained through thermal expansion tests and the melting points of three solder alloys are measured by Differential Scanning Calorimetry. Based on nonlinear fitting, the unified viscoplastic Anand constitutive parameters for three solder alloys are obtained and compared with the experimental data to verify the validity of the obtained parameters. Furthermore, combined with the obtained viscoplastic parameters and numerical simulation, the thermal fatigue reliability of SAC305-xBi low-melting-point lead-free solder alloys in packaging interconnections is analyzed. The positions of key solder joints during the temperature cycling process are determined, and the effects of Bi element content on the maximum equivalent stress and maximum equivalent plastic strain of key solder joints were analyzed. Finally, the thermal fatigue life of critical solder joints is evaluated based on the modified Coffin-Manson fatigue model considering plastic deformation. Results show that the addition of Bi element can lower the melting point and improve the thermal fatigue reliability of SAC305 solder alloy in packaging interconnection. The related research is of great significance for the system design of low-melting-point lead-free solder alloys and the improvement of their thermal reliability in packaging interconnections.
2025 Vol. 46 (6): 753-768 [
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769
Study on the Frictional Behavior of Soft Materials Based on Strain Increment of Contact Zone
In recent years, with the widespread application of soft materials in fields such as tactile sensing, robotic grippers, and wearable devices, the study of their friction and contact behavior has become crucial not only for optimizing material performance but also for guiding the development of high-precision industrial technologies. This study employs a self-developed visual in-situ loading device to observe the evolution of contact area morphology during friction. Digital Image Correlation (DIC) technology combined with a second-order polynomial displacement function was applied to determine strain increments. Results indicate that the presence of tangential force induces contact anisotropy during the slip friction of soft materials, primarily originating from their large-deformation mechanical properties and the heterogeneity of surface strain response. This work preliminarily explores the interface mechanical behavior regulated by strain, providing an experimental basis for the characterization and prediction of tribological properties in soft materials.
2025 Vol. 46 (6): 769-779 [
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780
Nonlinear vibration of flexible actuator with cone-shaped PVC gel structure under electromechanical coupling condition
Polyvinyl chloride (PVC) gel is an electroactive polymer material with low cost, large deformation, light weight and fatigue resistance. It has two-way electromechanical coupling performance and has important application prospects in intelligent sensing and flexible driving. The material is often prepared into a conical structure for driving soft robots, flexible pumps, etc. However, limited research exists on the theoretical modeling of PVC gel's conical structures and their nonlinear deformation behavior under dynamic loads, hindering broader application. This study addressed this gap by developing an electromechanical coupling model for the spatial conical structure actuator and establishing its nonlinear vibration control equation using the Euler-Lagrange framework. The Helmholtz free energy was used to describe the system energy change of the PVC gel cone actuator. The Gent constitutive model of the hyperelastic material was used to characterize the elastic strain of the PVC gel material, and the nonlinear dynamic behavior of the PVC gel cone structure was analyzed. The damping effect, tensile limit factor, and external factors, such as pre-stretching mechanical external force, external periodic sinusoidal voltage, and spring stiffness coefficient, were considered. The critical threshold of the transition from steady-state to chaotic vibration of PVC gel cone-shaped structure actuator under different parameters was explored. The threshold was qualitatively and quantitatively defined and analyzed by bifurcation diagram and Lyapunov exponent. This study provides a theoretical basis for the further application of PVC gel cone structure actuator.
2025 Vol. 46 (6): 780-793 [
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794
Refined Discrete Element Simulation and Machine Learning Prediction of Mechanical Behavior in Compression Molding of Energetic Crystalline Materials
This study proposes an artificial intelligence-based constitutive modeling framework that integrates discrete element modeling (DEM) with machine learning algorithms to efficiently predict the mechanical response of energetic crystals during the compaction process. The primary objective is to overcome the limitations of traditional experimental methods and pure numerical simulations in capturing complex mesoscopic mechanisms and achieving rapid performance forecasting. The research methodology commenced with the development and meticulous calibration of a high-fidelity DEM model capable of accurately replicating the realistic morphology and mechanical response of crystalline particles. This validated model was subsequently employed to systematically generate a comprehensive numerical experimental dataset, comprising 75 distinct samples covering a wide range of median particle sizes (D??), uniformity coefficients (C?), and porosity levels. This process yielded an extensive and reliable database containing 4,500 stress-strain data points, providing a robust foundation for subsequent data-driven analysis. Leveraging this dataset, a comparative investigation was conducted to evaluate the predictive performance of two machine learning algorithms under small-sample conditions: a conventional Artificial Neural Network (ANN) and a Physics-Informed Neural Network (PINN). The study demonstrates that the PINN, which effectively incorporates physical prior knowledge by embedding constitutive constraints—specifically strain-hardening monotonicity and a stress-zero constraint at zero strain—as residual terms into the loss function, significantly outperforms the data-driven ANN. The PINN achieved a remarkable coefficient of determination (R2) of 0.99 on the test set, substantially surpassing the ANN's performance (R2 = 0.92). This result underscores the superior predictive accuracy, enhanced generalization capability, and improved physical consistency of the physics-informed approach. Furthermore, parameter sensitivity analysis confirmed that the established model reliably captures the underlying physical relationships: an increase in median particle size or uniformity coefficient, or a decrease in porosity, leads to a corresponding increase in compressive stress. Crucially, even for parameter combinations not present in the training dataset, the model's predictions remain strictly consistent with established physical trends, demonstrating its powerful extrapolation capabilities. This research provides a reliable data-driven modeling framework for predicting mechanical properties and optimizing processing parameters for energetic crystal materials.
2025 Vol. 46 (6): 794-806 [
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807
Theoretical Explanation on the Ultrasonic Velocity Evolution in the Concrete subjected to Uniaxial Compression
Ultrasonic velocities in the concrete highly rely on its stress state. The nonlinear variation process of the velocities with the increase of the stress cannot be explained by current theories. Aiming at the prediction of ultrasonic velocities in the stressed concrete, this study extended the elastoplastic-damage concept from the infinitesimal strain field to the finite strain field, and proposed the new formulations for the calculation of the velocities with the initial elastic strain starting from the unloaded configuration. Based on the classic constitutive equations for concrete under uniaxial compression, the plastic strain and damage state was derived as the initial conditions for the velocity computation. This methodology has been verified by simulating experimental results. Theoretical results proved that this model could well describe the nonlinear variation process of the velocities as the stress raises. Sensitive analyses imply that the plastic anisotropy of the unloaded configuration and the damage effect of the 3rd order modulus can be ignored. Also, most of the test results from past research have underestimated the actual third order moduli of concrete.
2025 Vol. 46 (6): 807-820 [
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821
A Static Reanalysis Method for Large-Scale Structures Based on FDP-PCG
This work combines flexibility disassembly perturbation (FDP) and preconditioned conjugate gradient (PCG) methods to propose a new FDP-PCG static reanalysis method, which is then integrated with the Monte Carlo (MC) method for random finite element analysis of large-scale structures. The proposed method enables rapid computation of static responses for each random sampling of the structure, facilitating statistical analysis of response parameters and calculation of failure probabilities. Compared with traditional MC algorithms, the proposed method maintains similar computational accuracy while significantly improving computational efficiency. Results from two numerical cases demonstrate that the FDP-PCG method outperforms both traditional MC methods and the original PCG method. Taking a large-span cable-stayed bridge structure as an example, the computational time of the FDP-PCG method is only about 20% of that of the traditional MC method, and even in cases with high randomness in material properties, the calculation errors for various indicators are all less than 0.5%. The proposed method provides a new, fast, and reliable approach for random finite element analysis of large-scale structures.
2025 Vol. 46 (6): 821-835 [
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836
The Effect of Initial Defects on Aggregate Interfacial Cracking of Concrete under Microwave Irradiation Based on Phase Field Theory
High-quality recycling of aggregates is one of the important tasks in the recycling of waste concrete, and cracking at the aggregate-mortar interface under microwave action is key to improving the quality of recycled aggregates.To further investigate the cracking behavior at the concrete aggregate interface under microwave action and analyze the influence of initial defects on the law of crack propagation at the concrete interface, an electromagnetic-thermal-mechanical multi-field coupled phase field model was established. This model simulates the dynamic distribution of the electromagnetic field, temperature field, and stress field in concrete under microwave action, and reveals the influence of key factors such as microwave power, heating time, and the position and angle of initial defects on crack propagation at the concrete interface. The reliability of the phase field model was verified by comparing with the results of microwave heating tests.The results show that the presence of initial defects can change the propagation path of interface cracks and has a dual-path influence on the material crushing effect: on the one hand, it significantly alters the distribution characteristics of the electromagnetic field inside the test block, inducing changes in the local temperature field; on the other hand, it forms a stress concentration effect at the crack tip, which changes the overall stress distribution. This not only affects the area of interface cracking but also increases the overall crack propagation rate and the damage area.The research results provide important theoretical support for the optimization of engineering applications of microwave-assisted concrete crushing technology.
2025 Vol. 46 (6): 836-850 [
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