This study utilized in-situ X-ray micro-computed tomography (mu CT) combined with digital volume correlation (DVC) to investigate the tensile damage and failure mechanisms of third-generation SiCf/SiC composites under room temperature and 1800 degrees C conditions. High temperature significantly alters the mechanical properties and failure behavior of SiCf/SiC composites. The strength decreases to half of its room-temperature value. At room temperature, damage is characterized by distributed mechanisms including multiple cracking, delamination, and fiber pull-out. In contrast, at elevated temperatures, failure becomes localized and dominated by primary cracks, accompanied by pronounced creep deformation. Pore analysis indicates that interlayer pore expansion is the primary driver of room-temperature damage, whereas at high temperature, accelerated evolution of micro-pores and intra-bundle pores promotes strain localization. Within the creep regime, DVC-derived epsilon(zz) peaks align precisely with the fracture paths, and SEM confirms this transition arises from enhanced fiber-matrix bonding and matrix softening under high temperature.

To address the high energy absorption requirement and limited space constraint of energy-absorbing components for high-speed rail transit vehicle, this study proposes a bamboo-inspired heterogeneous hybrid energy-absorbing structure based on the cross-sectional features of bamboo. Performance optimization is achieved through the synergistic design of an outer carbon fiber reinforced plastic (CFRP) layer and an inner AlSi10Mg alloy lattice structure fabricated by selective laser melting (SLM). Thirteen sets of experimental samples (including pure CFRP tubes, single lattice structures, and hybrid structures) were prepared based on two types of cells (Circular fit Body-Centered Cubic, CBCC and Circular fit Face-Centered Cubic,CFCC cells) adapted to circular cross-sections. Combined with quasi-static compression tests and multi-scale characterization techniques such as 3D scanning, digital image correlation, and scanning electron microscopy (SEM), the structural forming quality, mechanical response, and synergistic mechanism were analyzed. The results show that the hybrid structure achieves "1 + 1 > 2" synergistic enhancement: HS_FC_3 (CFCC cell, rod diameter 3 mm) achieves a 39.43% increase in total energy absorption (EA) relative to the theoretical superposition value, with its specific energy absorption (SEA) reaching 39.55 J/g, which represents a 7.15% improvement over pure CFRP tubes and demonstrates the successful reconciliation of high energy absorption efficiency with lightweight requirements.

To address the fatigue aging of 6005A-T6 aluminum alloy-widely used in rail transit structures-under longterm service, this study investigates its crack growth behavior and remaining useful life (RUL) prediction under different fatigue aging conditions. The simulation covered 4 fatigue aging states, achieved by applying different numbers of pre-fatigue cycles. Compact-tension-shear specimens were tested under mixed-mode I + II fatigue crack growth at 4 loading angles (0 degrees, 30 degrees, 45 degrees, and 60 degrees). Digital image correlation was employed to capture crack tip strain fields for analyzing crack growth behavior. Experimental results show that fatigue aging significantly reduces the material's resistance to crack growth. While increasing the loading angle suppresses crack growth rate, this suppressive effect is weakened under severe fatigue aging conditions. The antagonistic interplay between fatigue aging and increased loading angle in determining RUL is investigated for the first time. Fractographic analysis reveals that the reduction in fatigue striations and the increase in microcrack formation are the key microstructural mechanisms responsible for the fatigue aging-induced decline in crack resistance. Furthermore, an extended finite element model based on an energy release rate attenuation mechanism was developed. The simulation results show high agreement with experimental data, with a maximum standard deviation of 1.3887 and a maximum life prediction error within 7.5 %. These findings provide theoretical support and technical guidance for service life prediction and failure assessment of aluminum alloy structures.

Fused deposition modelling provides unique advantages for the rapid manufacture of complex, lightweight structures using continuous fibre-reinforced thermoplastic composites. However, the compressive failure mechanisms of carbon/glass fibre hybrid composites under additive manufacturing constraints remain insufficiently understood. In this study, seven layup configurations with varying fibre hybrid ratios and stacking sequences were fabricated using a multi-material extrusion process, and their mechanical responses and damage evolution were systematically evaluated. The results show that increasing glass fibre content led to reductions in compressive strength and modulus of 74.1% and 57.1%, respectively, from C16 to G16, accompanied by the activation of progressive damage modes and pronounced pseudo-ductile hardening behaviour. Under identical fibre ratios, a carbon fibre surface design (C4G8C4) effectively enhanced buckling resistance, achieving strengths and moduli of 101.85 MPa and 10.91 GPa. In contrast, a glass fibre surface design (G4C8C4) led to early structural instability, resulting in a 38.3% and 46.6% reduction in strength and modulus, respectively. The alternating stacking design (G2C2) suppressed the through-thickness crack propagation and promoted multi-path energy dissipation, demonstrating a maximum peak strain of 1.45% and excellent non-linear deformation capacity. The unit volume energy absorption for this configuration reached 0.82 MJ/m3, the highest in the group, consistent with its stress-strain response showing a closer approach to the plateau phase. These results reveal the regulation of the mechanical behaviour of additive-manufactured composites by fibre spatial layout, providing scientific guidance for the customised design of components with high stiffness/strength or high damage tolerance requirements, such as those used in rail transportation.

To achieve reliability equivalent verification of high-speed train transmission system bearings under rig test conditions, an equivalent test method based on the principle of damage consistency is proposed. Using the maximum contact stress within the contact zone as the equivalent bridge, an explicit mapping relationship among axial load, radial load, and theoretical life is established through finite element analysis combined with symbolic regression algorithms, enabling the equivalent transformation of multiaxial complex loads into a single equivalent radial load. To validate the effectiveness of the proposed equivalent method, comparative experiments are designed and conducted, in which standard defects are prefabricated on the bearing rollers and outer rings, and the damage evolution under conventional combined loads is compared with that under the equivalent radial load. A high degree of consistency in defect propagation trends, surface damage morphologies, and sequences of microscopic damage between the two loading conditions is revealed by macroscopic and microscopic observations. The validity of the equivalent method is further confirmed by quantitative statistical analysis. Based on the experimental results, a complete technical framework is established, encompassing service condition data acquisition, equivalent load back-calculation, and rig-based verification. The proposed equivalent test method significantly reduces equipment complexity and implementation costs for bearing rig tests, providing a theoretical foundation and engineering solution for reliability verification of high-speed train bearings.

ObjectiveTopology optimization is a widely used optimization method that optimizes material construction, finds the optimal shape of structural design under given design space and constraints, achieves lightweighting, and satisfies constraints. Based on the idea of variable density topology optimization method, taking the fixture structure of a certain test bench as the analysis object, and the establishment of a mathematical model and solution method for topology optimization were elaborated in detail, in order to provide reference for structural design based on advanced design methods.MethodsFirstly, a finite element model of the tooling was established in the HyperMesh simulation software using the OptiStruct module. With the minimum mass and maximum first-order frequency as the optimization objectives, topology optimization and size optimization were conducted on the tooling structure under a single working condition. The material distribution was reasonably arranged and the thickness of the plates was optimized to improve the quality of tooling design.Secondly, based on the optimization results and the practicality of manufacturing and processing, a new tooling structure was designed. Finally, in the Nastran module, the strength check of the tooling model was carried out in accordance with the GB/T 21563—2018 standard. After the actual processing of the tooling structure was completed, the tooling was placed on a vibration table, and longitudinal, transverse and vertical sweep frequency tests were conducted respectively. Subsequently, the test results were compared with the simulation results.ResultsThe results show that the first-order modal frequency has increased from 766 Hz to 1 009 Hz, representing a rise of 31.72%. Meanwhile, the fixture mass has decreased from 51 kg to 44.26 kg, a reduction of approximately 13.24%, its strength meets the design standards and the overall objective is successfully achiered.

It is essential to describe a material's yield strength, anisotropic hardening, and plastic flow behavior under various stress states and loading angles to analyze large plastic deformations such as material forming and structural collision. However, few existing yield functions can simultaneously accurately predict these mechanical responses. This paper constructs a new analytical yield function and corresponding plastic potential function in the framework of non-associated plastic flow. The function can analytically describe the yield stress or r-value at different angles for several important stress states and further improve the prediction accuracy and control the curvature of the yield surface or plastic potential surface by introducing additional parameters. Parametric sensitivity analysis and convexity analysis were carried out for the new functions. These were used to predict the mechanical properties of three crystal structures, including high-strength steel, aluminum alloy, commercially pure titanium, and titanium alloy. For comparison, several similar analytical yield functions were selected to predict these materials simultaneously. The results show that the proposed yield and plastic potential functions can more accurately describe the four materials' yield strength, strain hardening, and r-value. The different test data types further verify the new functions' flexibility and robustness. Finally, the stress invariant and stress state parameters are used to expand the yield function, and the simplification and convexity analysis of the function are further discussed.

To provide a unified assessment method for remaining useful life that is conducive to engineering applications and accurately considers the effects of material conditions and loading angles, addressing the current lack of models that consistently and physically incorporate these variables, this study proposes an improved fatigue crack growth normalization model. Through uniaxial and multiaxial fatigue crack growth tests, the crack growth behavior of base metal, as-welded, and post-weld heat treatment specimens under different loading angles was investigated. Using digital image correlation to obtain the local displacement field at the crack tip and combining it with the relative displacement method, an improved crack growth driving parameter, KCJP-eq, was introduced to normalize the description of crack growth behavior. The study shows that the proposed normalization model significantly improves data fitting, with the coefficient of determination increasing from 0.6164 to 0.8516, and exhibits strong adaptability to loading angles and material conditions. Furthermore, the variations in the plastic zone during crack propagation were analyzed, and for the first time, the interaction between the material’s microstructure, welding residual stress, and the crack deflection angle was revealed. Finally, fatigue fracture surface analysis indicates that the crack growth mechanism in the Paris region follows a similar mode I behavior.

The surface fatigue crack growth mechanism of welded structures under random loads in service is complex, and the assessment method based on failure life lacks an effective description of the crack growth process. This study investigates the surface crack evolution mechanism in welded joints under random fatigue loading. First, a series of experiments were conducted to determine the through-thickness crack growth rate parameters of aluminum alloy butt joints. These experiments revealed the influence of thickness and stress ratio on the fatigue crack growth rate. The normalization of the growth rate of surface cracks under variable fatigue loading was achieved through the introduction of the constraint factor of surface cracks and the crack closure function(Delta K-eff-da/dN). Moreover, the effect of mean stress on the crack growth threshold was considered to describe the crack growth behavior of welded joints more accurately under near-threshold conditions and at high stress ratios. Furthermore, a two-stage model for surface fatigue crack growth in welded joints under variable-amplitude loading is proposed. The random load was converted into an equivalent variable-amplitude load spectrum, enabling a dynamic calculation of the surface fatigue crack growth life. Finally, this model significantly narrows the prediction error for test fatigue life from -25% similar to 45% under the BS7910 standard analytical method to within -15% similar to 25%, verifying the effectiveness of the proposed life assessment method for variable-amplitude fatigue crack growth in welded joints.

Understanding the impact compression behavior of fiber reinforced polymer composites is critical to the lightweight and safety design of high-speed trains. Specimens of carbon fiber reinforced polymers (CFRP), glass fiber reinforced polymers (GFRP), and their hybridized composites were hygrothermal aged. Compression properties and deformation behavior were investigated at loading rates of 1.6 x 10-3 s-1, 750 s-1, and 1250 s-1 experimentally and numerically. Experimental results revealed that the compressive strength of all composites declined after hygrothermal aging. At quasi-static loads, the CFRP composite presented the minimum strength retention rate of 82.1 %, while the retention rate of GFRP and hybridized composites exceeded 87.2 %. At dynamic loads, the CFRP and GFRP composites showed the maximum and minimum retention rates, 96.6-98.3 % and 72.4-75.0 %, due to the complex interaction between strain rate enhancement and degradation caused by hygrothermal aging. Shear fracture failure dominated the failure modes of the CFRP composite, while buckling and delamination were observed in the GFRP composite. This difference results in the distinct strain rate-dependence between CFRP and GFRP composites. Placing glass fiber composites as outermost plies resulted in severe material damage while achieving a higher compressive strength. Simulation results revealed that hygrothermal aging degraded the mechanical properties of CFRP and GFRP plies, therefore, alleviating the inhomogeneous stress distribution among hybridized composites.

Abstract To investigate the evolution of fatigue crack growth (FCG) resistance in bogie frame materials after long-term service in high-speed trains, this study systematically evaluates the fatigue fracture behavior of key structural regions before and after aging, using full-scale frame fatigue tests, multiaxial FCG experiments, and numerical simulations. A finite element model was established based on strain measurements from full-scale fatigue tests to determine the equivalent crack loading. FCG experiments were then conducted on the as-welded (AW) and base metal (BM) regions before and after service, and digital image correlation was applied to obtain surface displacement fields for calculating the stress intensity factors. The results indicate that service significantly reduces the crack growth resistance of the frame materials, with a maximum remaining useful life reduction of 70.54% in the AW region and 22.31% in the BM region. Correspondingly, the strain response at the crack tip increases significantly after service, reaching more than twice the original value in the AW region and 1.44 times in the BM region, indicating a reduction in crack growth resistance. Microscopic fracture surface analysis reveals that post-service materials exhibit more secondary cracks, unstable crack paths, and blurred fatigue striations, confirming the detrimental effect of service-induced damage on fatigue performance.

[Objective]CFRP(carbon fiber reinforced poly-mer)and GFRP(glass fiber reinforced polymer)have been ap-plied to the structure of rail transit vehicle equipment cabin.Under impact loading,composite materials exhibit mechanical behaviors distinct from those under quasi-static loading.In view of the reduction in structural protection capability of the equipment cabin floor caused by ballast impact during service,it is necessary to conduct an in-depth study on the influence of strain rate effects of CFRP and GFRP on impact response.[Method]A constitutive model of continuous fiber-rein-forced composites considering strain rate effects is established,and a VUMAT(user-defined material subroutine)is developed based on the secondary development function of ABAQUS software.Dynamic tensile tests of CERP and GFRP are carried out,and dynamic enhancement factors are obtained by fitting the test results.Subsequently,dynamic tensile simulations of the two composite materials are conducted to verify the accura-cy of the model and material parameters.On this basis,CFRP and GFRP are considered respectively as panel materials for the equipment cabin floor structure.According to the GB/T 32060-2015 standard,a simulation model of the aluminum projectile impacting the equipment cabin floor at an initial ve-locity of 200.00 km/h is established for calculation.[Result&Conclusion]When CFRP is used as the panel material and the strain rate effect is considered,the residual velocity of the alu-minum projectile increased from-52.16 km/h to-66.33 km/h,and the maximum panel displacement decreased by 9.69%.When GFRP is used as the panel material and strain-rate effect-is considered,the residual velocity of the aluminum projectile increased from-40.25 km/h to-48.87 km/h,and the maxi-mum panel displacement decreased by 14.53%.

Collision safety is a core requirement in the design of rail vehicles. Collision simulation based on explicit finite elements has become a key means for safety assessment and structural optimization. The reliability of its results is highly dependent on the precise characterization of mechanical behavior under complex working conditions by material constitutive and fracture models. This paper systematically reviews the theoretical system, application status, and challenges of metal material constitutive and fracture models suitable for rail vehicle collision simulation, analyzes the theoretical expression, application scope, and parameter calibration methods of rate-independent models, dynamic coupling models, and machine learning-assisted models, and expounds the modeling basis and predictive ability of coupled and uncoupled fracture models. It is pointed out that there are trade-offs among different models in terms of computational efficiency, parameter rationality, and prediction accuracy, and a reasonable selection should be made based on the characteristics of the research object and scenario. In application practice, typical cases of fracture simulation of vehicle body structure, energy-absorbing components, and connection structures are listed, revealing that the selection of models needs to balance accuracy and efficiency. Facing challenges such as material response prediction, computational efficiency, and mesh sensitivity under complex loads, it is necessary to develop multi-mechanism coupling models and intelligent modeling paradigms in the future, promote the application of standardization and digital twin technology, and provide theoretical support and engineering guidance for high-confidence collision simulation.

In order to study the flexible dynamic vibration characteristics of railway freight cars, a rigid-flexible coupling dynamic model of railway freight cars C80 was established by joint simulation of NASTRAN and SIMPACK. The model was verified by modal test and dynamic calculation, in which the maximum error of mode is 9.70

The derailment behaviour of trains following a collision is a critical factor in driving safety. This paper builds upon the existing train collision dynamics model by integrating a finite-length Euler beam track model with elastic point support and a wheel-rail interaction solver. It employs a modified explicit double-step method for computation. The enhanced model and algorithm are utilized to examine train derailment post-collision. A specialized program for collision calculations is developed, with its accuracy and stability confirmed through comparison with finite element analyses. In determining train derailment, the dynamic model adopts a criterion from finite element simulations. It sets a threshold where the lifting height of at least two wheelsets on the same vehicle must not exceed 50% of the nominal flange height, and these wheelsets must not be on the same bogie. The model further investigates the impact of four factors on derailment behaviour in a collision: initial vertical height difference, lateral displacement, initial pitch angle, and initial yaw angle, across various speeds. This research offers significant insights into enhancing the safety measures against train collision derailments.

The 6005 aluminum alloy, widely used in transportation structures, is prone to dynamic load impacts during service. Therefore, it is necessary to understand its rate-related mechanics and fracture behavior precisely. This paper investigates the dynamic mechanics and fracture behavior of 6005 aluminum alloy by combining experimental data with modeling. Comprehensive tests covering seven stress states and strain rates ranging from 0.001 to 800 s-1 reveal that the material's fracture strain exhibits complex strain rate sensitivity, which is dependent on the stress state. Based on these findings, a new rate-dependent constitutive model was developed by introducing the high-order terms of the stress triaxial degree and Lode parameters into the yield function, which significantly improved the prediction accuracy of yield behavior under complex stress states. In addition, a non-coupled ductile fracture criterion was proposed, which uniquely describes the different influences of strain rate on the three stages of micro-void evolution. The model parameters were finely calibrated and verified through finite element analysis. The results show that the model demonstrates excellent accuracy in predicting fracture strain. The average relative errors at strain rates of 1 s-1 and 800 s-1 are only 4.52% and 2.74% respectively, which are significantly better than the traditional J-C type and parameter strain rate-related type correction models. This study provides a reliable modeling tool for the crashworthiness simulation and safety design of aluminum alloy structures under dynamic load conditions.

X-ray computed tomography has become an indispensable technique in the multi-scale study of damage mechanisms in fiber-reinforced composites. Industrial CT and synchrotron radiation CT (SR-CT) offer complementary high-resolution imaging solutions. This review summarized the latest advancements in CT-based post-processing methods. It assesses the key factors in selecting appropriate CT equipment, weighing the nanoscale resolution of SR-CT against the practical cost-effectiveness of industrial CT. Advanced deep learning models have been proven to address the shortcomings of traditional segmentation methods when applied to low-contrast, heterogeneous composites, enabling accurate defect identification and quantification. A novel hybrid digital volume correlation technique is introduced, which combines subset-based local analysis with global-based algorithms, considering different deformation increments. Additionally, an enhanced finite element simulation framework based on CT image geometry is proposed, leveraging peridynamics simulation to overcome the limitations of crack propagation modeling. The integration of these methods makes it possible to visualize internal defect evolution in three dimensions during in-situ tensile, compressive, and fatigue tests. The review concludes the future directions, including the development of highly integrated and automated CT data processing platform, aimed at addressing the challenges in damage prediction for composites in aerospace and rail transportation.

Objective The underground interval tunnel project between Xiata Rd. Station and Fumin Rd. Station (hereinafter referred to as the 'Xia-Fu Interval') of Qingdao metro line under construction passes beneath elevated highway bridge piles and rivers. The construction area has complex geological conditions, and some intervals need to pass through long strata featuring upper-soft and lower-hard layers. To ensure the smooth implementation of the interval project and the safety of residential buildings in adjacent areas, it is necessary to study the design scheme and interval construction scheme for this line. MethodThe planning status conditions and horizontal alignment of the Xia-Fu Interval are introduced. The horizontal and vertical alignment schemes of the line are refined in design to maximize the distance from risk sources as much as possible. Measures such as MJS (multi-directional high-pressure jet grouting) enclosure and grouting reinforcement are adopted to isolate the interval from residential buildings. Key construction schemes, including tunnel alignment design for under-passing elevated highway bridges, the arrangement of interval drainage pump stations and cross passages, and construction in short-spacing intervals with upper-soft and lower-hard strata, are discussed in detail. Considering the complex interval engineering conditions, multiple construction control measures are proposed. Result & Conclusion The tunnel design scheme for the Xia-Fu Interval is reasonable and effective. When the line passes beneath elevated bridge piles, the transfer piles are avoided, ensuring that the vertical clearance between the elevated bridge pile structure bottom and the metro interval tunnel is not less than one tunnel diameter. After optimization of the design scheme for the interval drainage pump stations and cross passages, structurally fractured zones are effectively avoided, and the interval length passing through upper-soft and lower-hard strata is reduced. After reinforcement by MJS pile enclosure, the risk of over-excavation in the interval is reduced, thus minimizing the impact on adjacent residential communities.

To investigate the effect of adhesive thickness on the mechanical properties of carbon fiber reinforced polymer (CFRP) and aluminum alloy single-lap adhesive-rivet hybrid joints, single-rivet and double-rivet joint specimens with adhesive thicknesses of 0.2 mm, 0.3 mm, and 0.4 mm were fabricated. Through quasi-static tensile tests combined with digital image correlation (DIC) technology, the load-bearing characteristics, failure displacement, and failure modes of the joints were systematically analyzed. The results indicate that the ultimate load of the double-rivet joints (10 kN) is twice that of the single-rivet joints (5 kN). The increase in adhesive thickness has a nonlinear effect on the failure load of the adhesive layer. When the thickness increases from 0.2 mm to 0.3 mm, the adhesive failure loads of the single- and double-rivet joints are improved by 12% and 14.6%, respectively, but when the thickness increases to 0.4 mm, the load tends to be saturated due to the increased eccentric bending moment or deteriorated stress distribution. In terms of failure modes, the single-rivet joints exhibit progressive failure dominated by CFRP delamination, showing a slow process and large displacement. In contrast, the double-rivet joints show sudden failure due to the instantaneous brittle fracture of CFRP induced by stress concentration. The increase in adhesive thickness significantly improves the failure displacement of the adhesive layer (both single- and double-rivet joints are improved by more than 40%). The effect of adhesive thickness on the mechanical properties and failure modes of different types of adhesive-rivet hybrid joints is revealed, providing guidance for the design of lightweight hybrid connections in fields such as rail transportation.