The influence of different multi-delamination forms on the tensile strength of blade spar cap laminates was studied. Static tensile tests were conducted on laminates with single and multiple delaminations. The continuous damage model(CDM) and cohesive zone model (CZM) were used to analyze the damage process and failure mode. The numerical results showed good agreement with test values, with an overall error rate below 7%. A numerical model of 1.5 MW-40.3 m blade spar cap equivalent laminates was established to predict the effect of different types of multi-delamination on the tensile strength. The results show that the arrangement, maximum area, and step difference of delaminations all have an impact on tensile strength. The tensile strength of triangular multi-delamination is higher than that of inverted triangular multi-delamination laminates, and the maximum delamination near the surface greatly affects the tensile failure load.

The aircraft’s inlet structure is connected to the engine sleeve using countersunk rivets. During maintenance,fatigue fractures were discovered in some rivets. It suggests that the inadequate perpendicularity of rivet holes during manufacturing causes the rivet misalignment, reducing the load-bearing capacity, and leading to fatigue fractures under aircraft vibrations. The finite element simulation was used to study the effect of inclined rivet holes on the load-bearing capacity,simulation results show that inclined holes cause uneven stress distribution across the rivet section. The higher the tilt angle,the higher the maximum stress and the more uneven stress distribution on the rivet head section. Fatigue tests under axial loads at different tilt angles demonstrated a reduction in the rivet’s fatigue life due to the hole inclination. The study concludes that non-compliance with perpendicularity standards during hole fabrication results in uneven stress distribution, decreasing load-bearing capacity. Therefore, the strict control over rivet hole perpendicularity during the aircraft manufacturing is crucial to ensure structural reliability.

In view of the problem that the formulary design load based on the design standard can't truly reflect the actual service conditions of the welded frames of subway vehicles, and a large number of online measured data information has not been fully explored in the structural design of the frame, an anti-fatigue design spectrum compilation method based on the stress-time history sample information measured at the weak position of the subway vehicle frame was proposed.The small stress threshold value was determined by clustering ordered samples using the rain-flow counting method to compile measured stress spectrum reflecting structural damage, determining the stress-frequency-damage relation based on the fatigue damage theory, and using the methods of Bayesian parameter estimation and kernel density estimation to obtain stress extrapolation results. Considering the stress concentration caused by structural geometry changes in the cross-section of the welding site, the hot spot stress method and stress linearization method were used to obtain the stress concentration coefficient, and the measured stress spectrum was corrected to achieve the compilation of the design load spectrum. The research results show that the small stress threshold value is 3.18 MPa determined by extrapolation of stress extremes and the relation analysis between normalized stress-frequency-damage, which is 8.19% higher than the stress threshold value determined by traditional methods, the effect of discarding the number of small stress cycles is significant. Considering the load dispersion and stress concentration factor at the weld seam, while ensuring that the structure meets the current service conditions, the relation between the design mileage and equivalent stress is determined, the necessity of compiling the design spectrum is emphasized further. The above research builds the construction method of load spectrum compilation and the equal strength design of structures.

To enhance the energy absorption efficiency of conventional sandwich panels, a biomimetic tree-like fractal core (BTLFC) inspired by the dendritic fractal structure of the royal lotus leaf vein was designed. Firstly, quasi-static compression tests revealed that the 2-order BTLFC exhibited a specific energy absorption 5.69% higher and an average load 4.46% greater than traditional honeycomb cores. Secondly, a finite element numerical model of the BTLFC was established;combined with quasi-static compression test data, the finite element model error was within 2.2%, demonstrating high accuracy of the model. Finally, Latin hypercube test design, Kriging surrogate model, and the non-dominated sorting genetic algorithm-II (NSGA-II) were employed to perform multi-objective optimization on the structural parameter combinations of the BTLFC (size ratio r, bifurcation angle θ, fractal order D). The optimized BTLFC structure exhibited superior comprehensive performance, with specific energy absorption increased by 10.19%, peak crushing force reduced by 12.27%,and mass decreased by 11.79% compared to traditional honeycomb cores. The findings provide novel biomimetic design insights for developing high-performance energy absorption structures.

To evaluate the performance of various equivalent stress intensity factor models in predicting mixed-mode fatigue crack growth and to address the challenge of parameter estimation under limited sample conditions. A crack growth parameter estimation method based on the Bootstrap method resampling technique was proposed firstly. Mode Ⅰ fatigue crack growth tests were conducted on CT specimens to obtain the material parameters, and the proposed method was employed to expand the sample set and mitigate the issue of data scarcity. Then, using the statistically augmented material parameters,mixed-mode Ⅰ+Ⅱ fatigue crack growth experiments were performed on 6005A-T6 aluminum alloy CTS specimens under loading angles of 0°, 30°, 45° and 60°, employing a Richard-type loading fixture, to validate the accuracy of various equivalent stress intensity factor models. The results indicate that the Irwin model achieved the highest goodness-of-fit, with a value of 0.942 1, demonstrating the best crack growth prediction performance. Increasing the loading angle was found to reduce the initial crack growth rate, highlighting the need for angle-specific experiments to obtain appropriate Paris law parameters. This study confirms the applicability of multiple ΔK_eq models and provides theoretical support for fatigue life prediction in mixed-mode crack growth scenarios.

To enhance the computational efficiency of structural lightweight design for complex structures, a structural lightweight design method based on the Kriging surrogate model is proposed. The proposed method incorporates a hybrid addition strategy and a sample deletion strategy considering a distance threshold，aiming to rapidly improve the fitting accuracy of the Kriging surrogate model. This model was then applied to a multi-objective lightweight design model of the truck frame, with the optimization objectives of minimizing frame mass and maximum stress. Subsequently, the multi-objective lightweight model was solved using the non-dominated sorting genetic algorithm-II (NSGA-II). The results demonstrate that the proposed hybrid addition strategy and sample deletion strategy considering the distance threshold effectively enhance the update process of the Kriging surrogate model. The structural lightweight design method based on the Kriging surrogate model exhibits significant advantages in both computational efficiency and lightweight performance.

To address the issue of damage caused by low-speed impacts on composite material laminates coated with polyurethane coating, a numerical analysis method based on three-dimensional progressive cumulative damage in composite laminates and a yield damage criterion for polyurethane coatings was proposed. Firstly, a damage numerical model of polyurethane coating-carbon fiber reinforced composite laminates under erosion was established, and a Vumat subroutine was written. Subsequently, referring to the ASTM D7136 test standard, impact tests with various energy levels were conducted on samples coated with 1 mm and 2 mm polyurethane coatings and uncoated samples. Simultaneously, the proposed damage model was employed to study the formation reasons and propagation patterns of primary damages such as fiber damage, matrix damage, and delamination, thereby revealing the mechanism of polyurethane coating in absorbing impact energy. The results indicated that the mechanical response results calculated by the proposed damage model showed a high degree of agreement with the test results, validating the correctness of the proposed model. Additionally, comparative tests demonstrated the enhancement effect of polyurethane coating on the impact damage resistance of carbon fiber composite laminates. The findings of this study can provide a reference for the design of protective coatings for aircraft.

High-temperature mechanical strength is a key performance determinant for the long term, stable operation of advanced energy systems and components in high-temperature service and has been a disciplinary branch in the mechanical strength theory. Its research and development have accompanied major industrial technological advances. The research paradigm has shifted from early empirical formulas and single damage model to a structural integrity assessment framework characterized by mechanistic interpretability, prediction orientation, and evidential reproducibility. Building on the historical trajectory of the field together with bibliometric analysis and keyword clustering, the phase specific migration of research hotspots and the evolving knowledge structure were delineated. Recent progress was synthesized along three complementary themes, namely multiscale modeling, multiple damage coupling, and multidisciplinary integration. The synthesis covered material deformation and damage mechanism, damage evaluation and life assessment, and in-service monitoring and reliability assessment, thereby establishing a traceable mapping from microstructural mechanisms to engineering applications. Looking ahead, advances are expected to deepen in multiphysics coupling, intelligent decision-making algorithms, and standards system development. Critical challenges include bridging high-fidelity models and real-time prediction, establishing robust mappings from microstructure to service life, and translating theoretical modeling into engineering codes.

In order to study the evolution laws of microstructure and properties during the hot ring rolling, carburizing heat treatment, and deep cryogenic treatment of high-speed railway bearings, the quantitative relationships among the forming manufacturing conditions, microstructure states, and mechanical properties of high-speed railway bearings were established.The optimal process conditions for high-performance forming manufacturing of high-speed railway bearings were determined.The electron back-scatter diffraction (EBSD), scanning electron microscope (SEM), X-ray diffraction (XRD) microstructural testing technologies and tensile, friction and wear, rolling contact fatigue performance testing technologies were used to reveal the evolution laws of the microstructure and mechanical properties of high-speed railway bearing rings during the forming and manufacturing process, and a forming and manufacturing process method for high-performance high-speed railway bearing rings was proposed. The research shows that ring rolling can refine grains, promote the refinement of carbides and increase the dislocation density after carburizing once quenching and tempering, reduce the grain size and carbides, and improve the volume fraction of carbides after secondary quenching and tempering. The deep cryogenic treatment process promotes the decomposition of retained austenite and the precipitation of carbides, reduces the content of retained austenite, enhances the stability of retained austenite, decreases the average size of carbides, and increases the volume fraction of carbides. The wear resistance of high-speed railway bearings is improved by 82.7%, and the contact fatigue performance is improved by 322.1%by applying the optimal hot ring rolling and carburizing heat treatment processes. The research can provide a scientific basis and technical method for the high-performance forming manufacturing of high-speed railway bearings.

Exponential distribution is widely applied to describe product life in reliability engineering. Correspondingly,product failure rate is a constant (not changing with the service time of the product). Nevertheless, only the products with special property or under particular load condition have exponentially distributed life and constant failure rate. Unrealistic hypothesis of exponentially distributed life will lead to serious error in reliability and failure rate analysis results. In the situations that component life follows exponential distribution, to assume component failures being independent of each other will mislead system reliability evaluation. The the property of product failure rate was analyzed and inferred from the aspects of product strength performance and load environment.The conditions for product failure rate to follow exponential distribution were revealed, and product failure dependency issues in condition of life following exponential distribution were explained.