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.

Physics-informed neural networks have been widely applied to solid mechanics problems. However, balancing the governing partial differential equations and boundary conditions remains challenging, particularly in fracture mechanics, where accurate predictions strongly depend on refined sampling near crack tips. To overcome these limitations, a Kolosov-Muskhelishvili informed neural network with Williams enrichment is developed in this study. Benefiting from the holomorphic representation, the governing equations are satisfied by construction, and only boundary points are required for training. Across a series of benchmark problems, the Kolosov-Muskhelishvili informed neural network shows excellent agreement with analytical and finite element method references, achieving average relative errors below 1% and R^2 above 0.99 for both mode I and mode II loadings. Furthermore, three crack propagation criteria (maximum tangential stress, maximum energy release rate, and principle of local symmetry) are integrated into the framework using a transfer learning strategy to predict crack propagation directions. The predicted paths are nearly identical across all criteria, and the transfer learning strategy reduces the required training time by more than 70%. Overall, the developed framework provides a unified, mesh-free, and physically consistent approach for accurate and efficient crack propagation analysis.

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.

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.

Significant interactions exist among multiple surface cracks in railheads. This study investigates the competitive propagation behavior of rail surface cracks using the compact tension (CT) tests and a peridynamic (PD) model. Four sets of CT tests for multi-crack propagation were designed with U75V railhead material, and corresponding PD fatigue models were established. Significant shielding effects were observed among cracks during propagation, with the PD model accurately replicating crack propagation paths and fatigue lives from CT tests. A PD model was constructed to simulate the dynamic crack propagation on rail surfaces under rolling wheel loading, revealing significant promotion and suppression effects among cracks dominantly influenced by crack number and spacing. PD-predicted crack branching and coalescence align with field rail damage patterns.

To address the intrinsic conflict between macroscopic crystallographic continuity and microscopic performance degradation during the additive manufacturing (AM) repair of single-crystal (SX) Ni-based superalloys, this work investigates crystal integrity and failure mechanisms in a laser-cladded DD6 alloy. Tailoring cladding parameters generated a microstructural spectrum spanning high-quality SX, a pseudo-single-crystal (PSX) state, and polycrystalline (PX) structures. A distinct PSX regime within the epitaxial growth window retains excellent macroscopic orientation inheritance but exhibits pronounced substructural distortion. Characterization reveals the PSX state is dominated by high-density geometrically necessary dislocations (GNDs, exceeding 1.5 & times;10(14)m(-2)), dislocation cells, and overwhelming fractions of low-angle grain boundaries (LAGBs, >99%). These pre-existing defects serve as short-circuit diffusion pathways, accelerating Al solute migration and promoting anomalous gamma ' coarsening into irregular blocks. Mechanical testing uncovers a counterintuitive failure behavior: despite maintaining favorable easy-slip crystallographic characteristics (Schmid factor approximate to 0.46), PSX samples exhibit severely reduced ductility (similar to 1.4%), which is paradoxically lower than that of their PX counterparts. In-situ analyses demonstrate that this extreme embrittlement originates from intense strain localization. Synergistic coupling between anomalously coarsened zones and pre-existing dislocation networks rapidly exhausts the local strain-hardening capacity, acting as potent stress concentrators triggering premature fracture. This study establishes dislocation-mediated microstructural instability as a critical fracture mode determinant, highlighting that controlling internal defect density is as essential as preserving macroscopic crystallographic orientation to avoid the "strong but extremely brittle" PSX trap. These insights provide fundamental mechanistic guidance for optimizing the AM processing window and enhancing the damage tolerance of repaired turbine components.

Fatigue fracture often occurs in plug welded joints under shear loads, but an accurate fatigue life evaluation method for this special type of joint has not yet been proposed. Therefore, the fatigue failure behavior of plug welded joints through extensive shear fatigue tests was investigated in this study. To this end, the fatigue failure process and failure modes of plug welded joints under shear loading were obtained, and Fa-N curves were established. The investigation revealed that the overall Fa-N curve exhibited poor correlation and did not satisfy the engineering requirements. Consequently, an equivalent structural stress model that accurately captures the stress state of plug welded joints using the coupled node loads as input conditions was derived. A beam-shell finite element (FE) model that can accurately simulate the stress distribution of the plug welded joint was subsequently established to obtain the load inputs for the model. The forces and moments of the coupled nodes extracted from the FE model were input into the equivalent structural stress model to obtain the equivalent structural stress sigma s of the plug welded joint. Finally, Ss-N and P-Ss-N curves normalized for different Fa-N curves were developed, and a shear fatigue life prediction method for plug welded joints based on the equivalent structural stress method was established. The accuracy of this method was verified through random vibration fatigue test. The findings of this study provide a reference for the structural design and life prediction of plug welded joints.

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.

This study investigated the interfacial degradation behavior of continuous glass fiber-reinforced composites fabricated using the fused deposition manufacturing technique under accelerated hydrothermal aging. The accelerated aging was conducted at 60 degrees C and 100 % relative humidity for up to 30 days. The bonding strength of three interlayer structures, including the polyamide 6 (PA6) matrix layer/PA6 matrix layer (M/M), PA6 matrix layer/continuous glass fiber layer (M/G), and continuous glass fiber layer/continuous glass fiber layer (G/G), was evaluated through roller peeling tests. The results indicated that the M/M interlayer specimen (Inter-M/M) exhibited the highest peeling strength, while the G/G interlayer specimen (Inter-G/G) showed the lowest peeling strength for the as-prepared specimens. The primary failure mode in Inter-M/M was characterized by plastic deformation and ductile fracture of the matrix, while the main failure mode in Inter-G/G involved the debonding of continuous glass fibers from the matrix. After aging, the bonding strength of all three interlayer structures declined to varying degrees, with the M/G interlayer specimen (Inter-M/G) showing the greatest reduction. The effects of hydrothermal aging on interfacial degradation were primarily characterized by a change in the matrix failure mode, reduced crack initiation in adjacent layers, and weakened bonding between fibers and matrix.

The fatigue performance of railway axle steel is highly sensitive to microstructural heterogeneities and internal defects, which are inadequately captured by conventional life prediction methods. Motivated by this, a two-stage fatigue life prediction framework for LZ50 steel is employed that integrates the crystal plasticity finite element method with fatigue indicator parameters to account for microstructure-sensitive fatigue processes, including crack initiation and microstructurally short crack growth. To establish a typical experimental foundation, microstructural characterization via electron backscatter diffraction and scanning electron microscopy, displacement-controlled uniaxial tensile tests, and strain-controlled fatigue experiments were conducted. Representative volume elements were constructed based on the characterized microstructures, and crystal plasticity parameters were calibrated against both tensile and fatigue test results obtained at a strain amplitude of 0.9%, and further validated at amplitudes of 0.45%, 0.6%, and 0.75%. Compared to the approaches based on conventional fatigue indicator parameters, the two-stage framework that decouples crack initiation and microstructurally short-crack growth significantly improves prediction accuracy, with all results falling within the +/- 1.5x scatter band. The microstructurally short crack growth stage is found to contribute more than 50% of the total fatigue life. Furthermore, the effects of inclusions and pores with varying size, shape, and stiffness are systematically investigated. This study provides an effective and physically grounded framework for fatigue life prediction of defect-containing microstructures in structural steels.

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.

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.

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 this study, the fatigue behavior of cantilever bolted connections was investigated through numerous bending fatigue tests, and load amplitude-life (Fa-N) curves were established. Cantilever bolted connections are highly sensitive to geometric parameters, resulting in a low correlation of the overall Fa-N curve, which cannot directly predict the fatigue life of complex cantilever bolted connections. Therefore, an equivalent structural stress signal acquisition model that comprehensively considers the influence of geometric and loading parameters and accurately characterize the stress state of these connections was derived. This equivalent structural stress signal overcomes the shortcomings of excessive simplification of nominal stress and the inadequacy of hot-spot stress in characterising stress gradients by converting the three-dimensional local concentrated stress of the complex structure into an equivalent one-dimensional structural stress signal. To obtain the load inputs for the model, a beam-shell equivalent finite element model of the cantilever bolted connection was established. The load parameters of the bolted connection were obtained via simulation and coupled into concentrated forces and moments through the beam element nodes. The equivalent structural stress signal (sigma s) of the connection was obtained by inputting the nodal loads into the equivalent structural stress signal acquisition model. Subsequently, the fatigue characteristic curves (Ss-N and P-Ss-N curves) normalized to Fa-N curves with different geometric and loading parameters were established. Finally, using the proposed fatigue life prediction method, the fatigue life of a cantilever bolted connection for an antenna bracket was predicted. The prediction results were highly consistent with the test data, which fully verified the effectiveness and accuracy of the equivalent structural stress signal method.

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.

This paper systematically investigates the coupled effects of process parameters and sample build orientation on the tensile properties and microstructure of AlSi10Mg alloy fabricated by selective laser melting (SLM). Through 9 parameter combinations of laser power (135–225W) and scanning speed (975–1625mm/s), the anisotropy between XoY (perpendicular to build direction), YoZ (parallel to build direction, place horizontally), and XoZ (parallel to build direction, place vertically)orientations was quantified. The results show that increasing the volumetric energy density (VED) from 27.69J/mm³ to 76.92J/mm³ enhances the ultimate tensile strength (UTS) differentially across orientations: the UTS of XoY-oriented specimens rises by 48.1% (from 327.8MPa to 485.46MPa), whereas the YoZ orientation exhibits a larger increase of 67.9% (from 282.43MPa to 474.21MPa). Similarly, the XoZ orientation UTS increases by 50.7% (from 311.15MPa to 468.81MPa). Process parameters regulate melt pool dynamics via VED, while orientation determines the relationship between load and grain orientation, Si grid. This synergy induces orientation-dependent microstructural variations (e.g., equiaxed vs. columnar grains, porosity distribution), ultimately mediating mechanical anisotropy through melt pool boundary effects and dislocation evolution. The parameter combination by (Laser power: 225W and scanning speed: 1300mm/s) achieves the optimal strength-anisotropy balance and is recommended for manufacturing complex geometries or multi-directional components requiring uniform performance. This study elucidates the parameter-orientation coupling mechanism, providing a theoretical basis for anisotropy regulation in SLM aluminum alloys.

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.