In order to address the problems of high modeling difficulty, poor accuracy and low computational efficiency in the process of reliability analysis of complex aerospace agencies, a method combining data augmentation Latin hypercube sampling (DALHS), adaptive partitioned threshold rejection sampling (APTRS) and active learning Kriging is proposed for agency reliability analysis. First, the data enhancement technique is used to improve Latin hypercube sampling to obtain initial sample points and improve the diversity and representativeness of the initial sample points; second, an adaptive partitioning strategy is used to divide the design space and perform rejection weight sampling within the subspace to improve the local and global search capability of the samples; third, the active learning NU (Normalize U) function is proposed to screen high-quality samples, combined with the quasi-random fractal algorithm (QRFA) to dynamically optimize the Kriging model, and construct the DALHS – APTRS – Kriging model; finally, we use the convergence criterion of the coefficient of variation to realize the efficient calculation of the reliability of the aviation mechanism. The results show that the mechanism reliability of the general aviation piston engine is 0.987, with only 72 model calls, and a calculation error of only 5.7% compared to traditional methods. This indicates that the proposed method can not only obtain high-quality Kriging models with a small number of samples but also improve the efficiency and accuracy of reliability calculation by combining local and global search.
Laser Powder Bed Fusion (LPBF) offers significant advantages in the fabrication of complex metallic structures and the improvement of material usage. However, conventional Gaussian laser sources offer several limitations, including uneven energy distribution and small spot size, resulting in narrow processing window and low forming efficiency. This study employs a donut laser beam with a more uniform energy distribution using a beam shaping technology to fabricate IN939 nickel-based superalloy by investigating the microstructure regulation. The results indicate that, compared to the Gaussian laser, the donut laser beam effectively mitigates keyhole defects through a broader processing window. The melt pool aspect ratio was reduced to 0.14, and the heat transfer mode transitioned from keyhole mode to conduction mode. Simulation results show a significant reduction in the melt pool temperature gradient, with peak velocity decreasing by 37%, leading to more stable melt pool dynamics. Additionally, IN939 samples fabricated using the donut laser beam exhibited columnar grains preferentially oriented along the <001> direction, with a distinct cubic texture (texture strength reaching 12.59). The proportion of low-angle grain boundaries was 57.1%, which benefits from mitigating crack defects. The surface roughness of the samples was improved, with Ra decreasing from 5.8 μm to 4.0 μm, thereby significantly improving the overall forming quality by employing the donut laser beams.
This study focuses on the residual stress caused by local melting and solidification of metal powder in the laser powder bed melting forming process. The residual stress and deformation of the macroscale structure of TiB2/AlSi10Mg composite were predicted by multi-scale numerical simulation method. The influence of laser power, scanningspeed, and scanning direction on the residual stress and deformation of the structure was investigated. The multi-scale numerical results are in good agreement with those of the experimental measurements. An increase in laser power results in a proportional increase in the dimensions and temperature of the melt pool, as well as the equivalent inherent strain of the material and residual deformation of the structure. An increase in the laser scanning speed results in a reduction in the duration of the molten pool, a decrease in the equivalent inherent strain of the material and residual deformation of the structure. The laser scanning strategy exerts a significant influence on the deformation mode of the structure, primarily through its influence on the stress distribution. When the rotation angles between successive layers is 0°, the inherent strain of the material along the scanning direction is higher than that perpendicular to the scanning direction. Therefore, the rotation deformation of the bridge structure is maximum when all the laser scanning vectors are in the longitudinal direction and minimum when they are in the transverse direction. When the rotation angles between successive layers are 45°, 67°, and 90°, the anisotropy of the inherent strain of the material is comparatively reduced. Their residual deformations differences of the bridge structure are not significant, and the rotation deformation values are intermediate.
Micro selective laser melting (μSLM) has huge potential in high-quality and high-precision manufacturing of near-net-shape parts made of Inconel 718 superalloy. However, few studies investigate the optimization of μSLM parameters and mechanical properties of μSLMed materials. In this study, Inconel 718 fabricated via different parameter sets were analyzed, and a comparison on microstructure, mechanical property, and machinability between the optimal μSLMed material and the material fabricated by conventional SLM (cSLM) was implemented. It is found that the smallersized grains due to the higher cooling rate of μSLM (2.1×106 K/s) contribute to higher strength (1009 MPa, increased by 2.4%) and poor machinability. The low quality of cSLM material are ascribed to the application of larger laser spot and coarse powder. Vibration during the milling process is obvious due to the defects. Results of this study develops an optimal processing window for the μSLM of Inconel 718, reveals the relationship among processing parameter, microstructure, mechanical property, and machinability, which provides fundamental knowledge for the optimization of μSLM.
Aluminum alloy WAAM is a complex physical system with multi-parameter coupling, and the accurate prediction and control of its forming dimensions are affected by various process parameters. Aiming at the problems of insufficient modeling of parameter coupling effect, limited prediction accuracy and lack of model interpretability in existing prediction methods, this study proposes an interpretable data-driven model based on data augmentation strategy and ensemble learning method to achieve high-precision prediction of width and layer height in aluminum alloy forming process. First, the training dataset is augmented by data augmentation techniques to enhance the generalization ability of the model. Secondly, multiple models are trained based on the five-fold cross-validation method, and three base learners with the best performance are evaluated. Then, the SCSO algorithm is used to optimize the weight allocation of the basis learner, and a highly robust ensemble learning model is constructed. Finally, the SHAP method is used to quantify and explain the effects of process parameters on the forming process. The experimental results show that the ensemble learning model based on SCSO optimization significantly outperforms the single model and the traditional ensemble learning method in the prediction accuracy and interpretability of aluminum alloy forming dimensions (RMSE is 0.3518 and 0.0743, and MAPE is 0.0229 and 0.0364 when predicting width and layer height). This study provides a heoretical basis for process parameter optimization and forming quality control of aluminum alloy WAAM, with good practicality and engineering application value.
To address the issues of lack-of-fusion defects and performance degradation caused by the high laser reflectivity and thermal conductivity of pure copper during laser powder bed fusion (L-PBF) additive manufacturing, this study proposes constructing copper matrix composites by incorporating submicron tungsten carbide (WC) particles. The influence mechanisms of WC content (mass fraction of 1% and 3%) on microstructure and mechanical properties were systematically investigated. The results show that WC particles significantly enhanced the laser absorptivity of composite powders. The mass fraction of 3% WC-doped copper specimen achieved densification with elimination of lack-of-fusion defects, while the average grain size increased from 11.4 μm (pure copper) to 22.8 μm, accompanied by the formation of a preferred <110> orientation texture. Transmission electron microscopy (TEM) analysis revealed a 34 nm elemental transition zone at the interface between WC particle and Cu matrix, and the formation of a new phase (CuWO4). Tensile tests indicated that the mass fraction of 3% WC-doped copper specimen exhibited an ultimate tensile strength of (229±2) MPa and elongation of (41.6±1.6)%, representing 77.5% and 161.6% enhancements compared to pure copper (129±2) MPa, (15.9±0.6)%, respectively. Fracture surfaces displayed typical dimple characteristics. This study provides a theoretical basis for laser additive manufacturing of high-density, high-performance copper matrix composites.
The temporary fasteners are used in pre-joining during aircraft assembly. To improve the fit effect of assembly parts in pre-joining process, a layout optimization method for temporary fasteners in composite structure assembly pre-joining was proposed. An equivalent model for calculating the deformation and gaps of the panel in pre-joining process was established, and the calculation of key variables was improved. Layout optimization of temporary fasteners was performed based on the equivalent model. Assembly experiments of composite panel and metal frame wing box was conducted for verification. The results show that the improved calculation method can calculate key matrix variables in a shorter time. The single computation time for panel deformation during the optimization process is significantly reduced. The calculated deformation and gaps results are in good consistency with the experimental data. The established method can calculate the layout of temporary fasteners with high surface fit ratio, providing valuable reference for the development of pre-joining processes for large composite structure assemblies.
In response to the challenges about the low efficiency of welding in the aerospace field, particularly the complex intersection line welding, this paper proposes a teaching-free autonomous welding method for robots based on an optimized RANSAC and ICP point cloud algorithm for intersecting lines. First, based on the intersecting line theoretical model, the point cloud data of the collected workpiece is preprocessed. The optimized RANSAC algorithm is then used to select a set number of points as sample points to fit a surface, calculating the distance from all data points to the cylinder. Points that fall on the fitted surface are selected according to a preset threshold, and a new cylindrical surface equation is fitted using the selected points. Next, the ICP algorithm iteratively searches for the closest point pairs between two point clouds, calculating the optimal rigid transformation to align the source point cloud with the target point cloud in the target coordinate system. Finally, experimental results validate the proposed teaching-free autonomous welding method for complex spatial curves, using the optimized RANSAC and ICP point cloud optimization algorithms.
The ultraviolet nanosecond laser surface treatment of carbon fiber-reinforced polymer was studied to optimize surface morphology and enhance bonding strength. The samples were treated with various laser powers and pulse frequencies, and the effects were evaluated using contact angle measurements, surface energy analysis, and mechanical testing. The synergistic mechanisms of photochemical and photothermal effects were revealed, and the influence of energy density on surface morphology was analyzed. The results show that an appropriate energy density (160–203 mJ/cm2) effectively removes epoxy resin, exposes intact carbon fiber surfaces, and significantly improves surface energy and wettability. The water contact angle decreases from 82.7° to 69.7°, and the single lap shear strength increases from 23.6 MPa to 26.7 MPa, with an improvement of 13.1%. However, energy density exceeding 235 mJ/cm2 leads to carbon fiber breakage, reducing mechanical performance. This study demonstrates the effectiveness of ultraviolet nanosecond laser treatment in enhancing sample bonding performance, offering an efficient surface treatment solution for applications in aerospace and other demanding fields.
The ultrasonic-assisted laser shock peening (ULSP) technique improves the balance between tensile strength and elongation of aluminum alloys through the combined effects of laser shock peening (LSP) and ultrasonic rolling (UR). The 7075–T6 aluminum alloy was selected as the subject of study, and ULSP treatment was conducted. The metallographic structure, phase composition, surface morphology, microhardness, and residual stress were systematically examined. By analyzing the stress-strain curves, fracture morphology, and the improvement mechanism of tensile properties after ULSP treatment was elucidated. The results show that the ULSP treatment induces a significant grain refinement effect, resulting in a gradient structure comprising a severely refined grain layer, a refined grain layer, and the original coarse grain layer. Furthermore, the ULSP treatment effectively mitigated the issue of increased surface roughness associated with LSP treatment. The surface roughness Sa and profile roughness Ra of the ULSP samples are reduced by 74.0% and 82.3%, respectively, compared to the LSP samples. Benefiting from the grain refinement effect, high compressive residual stress, and low surface roughness, the ULSP samples achieved a substantial increase in tensile strength with only a minor sacrifice in elongation. Specifically, the tensile strength is enhanced by 13.3%, while the elongation is only decreased by 11.7%.
Based on the dual five axis linkage automatic drilling and riveting equipment, combined with the structural characteristics and sealing requirements of the aircraft seam sealing components, research on burr free automatic hole making and interference fit riveting technology was carried out. Through the development of drilling countersinking integrated tool, the test of automatic drilling technology parameters and the design of pre-connection technology, we have achieved breakthroughs in the processing of sealed metal laminated materials with burr-free drilling (burr height less than 0.13 mm) within the seam, achieving hole diameter accuracy better than H9. The deviation angle between the normal line of the curved surface where the hole is located before processing and the axis of the hole after processing is less than 0.3°, hole surface roughness reached Ra1.6 μm, ensuring high-precision hole making quality. In response to the requirements for long life and fatigue of the aircraft, experimental research was conducted on the influencing factors of riveting interference, and the influence trend of interference magnitude on fatigue life was analyzed. The optimal control range of interference and influencing factors under fatigue life was obtained, which meets the strict requirements for the overall sealing and fatigue life of the aircraft in the unique combat service environment of high salinity, high humidity and high temperature.
To solve the severe thermal fatigue problem faced by air turbo rocket turbine guide vane under fuelrich gas environment, a quasi-static thermoelastic coupling model of a homogeneous plate was established according to actual working condition of turbine guide vane. The effect of gas properties on the temperature rise characteristics, stress and life changes of the plate subjected to thermal shock was obtained through Laplace transform and residue theorem. The results agree well with the three-dimensional thermal-flow coupling calculation results of turbine guide vane. The results show that the main components of fuel-rich gas is hydrogen, which has high specific heat at constant pressure and thermal conductivity. As a result, the convective heat transfer coefficient is more than twice that of lean-burn gas under the same conditions. And the heat flux, temperature rise rate, and equilibrium temperature of the plate are higher than those of leanburn gas plate under the same conditions. These cause the temperature gradient inside the plate to increase under fuel-rich gas environment. Due to the high temperature and large temperature gradient under fuel-rich gas environment, the peak thermal stress to increase by 80% and its life is shortened by 32% compared to the plate under lean-burn gas conditions. During the thermal shock, the stress increases rapidly to the peak and then decreases gradually. The main determinant of the peak thermal stress is the gas properties, and the post-peak is mainly affected by coolant temperature. Additionally, The influence of gas properties on peak thermal stress and life decreases with the increase of plate thickness.
During the coordinate measurement and surface quality inspection processes conducted by touch-trigger probe on CNC machine tools, conventional measurement methodologies demonstrate suboptimal efficiency when acquiring workpiece coordinates for components with predefined surface coordinate ranges. To address this problem, an axial measurement coordinate optimization method based on kinematic modeling of the probe-workpiece interaction is proposed. First, based on the kinetics model of the CNC control system and the probe measuring mechanism, a probing kinetics model and a measuring error model are built. A high feedrate measuring error compensation method is proposed. Then a group of tests are carried out with a Renishaw OMP probe on a Bridgeport vertical milling machine to verify this proposed approach. The tests results demonstrate that this approach can precisely measure parts coordinates in high feedrate. Compared to the existing methods, this method reduced the measurement time for workpieces from 9.36 s to 0.36 s with the same measuring precision.
The creep deformation behavior of 2219T87 aluminum alloy under different stress states is studied through creep experiments. The results show that the total creep strain of 2219T87 aluminum alloy increases with the increase of stress, and the total creep strain in tensile state is higher than that in compressive state. Under the tensile stress of 300 MPa, the total creep strain after 300 h reaches 0.634%, which is 72.3% higher than that under the stress of 200 MPa and 13.6% higher than that under compression. The observation of microstructure shows that the precipitated phases in the original state are dot-like and reticulate, and evenly distributed on the aluminum alloy matrix. After creep, the number of precipitated phases decreased obviously. TEM observation and XRD calculation verified the occurrence of redissolution of precipitated phases. The calculated creep stress index is 3.17, which proves that the creep mechanism is controlled by grain boundary sliding.
