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The landing gear is one of the key components of an aircraft, enduring significant forces during takeoff and landing, and is influenced by various uncertain factors related to its structure. Therefore, conducting strength tests on the landing gear structure to study its ultimate load capacity is of great significance for structural design and analysis. This paper proposes a visual measurement method for dynamic pose of landing gear that combines stereo vision and CAD digital model. The method first establishes a measurement reference in CAD digital model and then uses close-range photogrammetry and binocular stereo vision technology to unify the coordinate system of the physical landing gear model with the measurement coordinate system of CAD model. Finally, during the motion of the landing gear, CAD model and the physical model can be synchronized by tracking a small number of key points, thus obtaining the complete motion state of the landing gear during the test. The experimental results demonstrate that the RMSE of the angle error is less than 0.1°, and the RMSE of the trajectory error is under 0.3 mm. This level of accuracy meets the requirements for pose measurement during the landing gear retraction and extension test. Compared to existing methods, this approach offers greater environmental adaptability, effectively reducing the impact of unfavorable factors such as occlusion during testing. It allows for the retrieval of pose information for any point on the landing gear, including its centroid.

Circular dots are widely used in various measurement applications due to their inherent symmetry, ease of detection, and scalability. However, when degraded by factors such as specular highlights, low contrast, strong noise, or friction damage, accurately extracting them from the background becomes a significant challenge. To address this issue, an enumeration-based thresholding method (EBTM) is proposed for degraded circular dot segmentation. Firstly, a series of candidate outputs are generated using an enumeration-based thresholding scheme. Next, an assessment criterion is developed to evaluate these candidate outputs. Finally, the optimal segments are selected from each candidate output and combined to produce a reasonable thresholding result. Unlike traditional methods, the novel approach does not focus on selecting the optimal threshold values, but instead aims to choose the best segments to produce the desired output. Owing to the enumeration-based thresholding mechanism, the novel approach demonstrates greater robustness in handling the challenges in degraded circular dot images. Extensive comparative studies demonstrate the superiority of the novel approach.

Taking the titanium alloy wing–body connection joint at the rear beam of a certain type of aircraft as the research object, this study analyzed the failure mechanism and verified the structural safety of the wing–body connection joint under actual flight loads. Firstly, this study verified the validity of the loading system and the measuring system in the test system through the pre-test, and the repeatability of the test was analyzed for error to ensure the accuracy of the experimental data. Then, the test piece was subjected to 400,000 random load tests of flight takeoffs and landings, 100,000 Class A load tests, and ground–air–ground load tests, and the test piece fractured under the ground–air–ground load tests. Lastly, the mechanism analysis and structural safety verification of the fatigue fracture of the joints were carried out by using a stereo microscope and scanning electron microscope. The results show that fretting fatigue is the main driving force for crack initiation, and the crack shows significant fatigue damage characteristics in the stable growth stage and follows Paris’ law. Entering the final fracture region, the joint mainly experienced ductile fracture, with typical plastic deformation features such as dimples and tear ridges before fracture. The fatigue crack growth behavior of the joint was quantitatively analyzed using Paris’ law, and the calculated crack growth period life was 207,374 loadings. This result proves that the crack initiation life accounts for 95.19% of the full life cycle, which is much higher than the design requirement of 400,000 landings and takeoffs, indicating that the structural design of this test piece is on the conservative side and meets the requirements of aircraft operational safety. This research is of great significance in improving the safety and reliability of aircraft structures.

Light spectrum plays a crucial role in regulating the growth of hemp ( Cannabis sativa L.) plants and the biosynthesis of secondary metabolites. Several studies have demonstrated that additional red-light exposure increases biomass accumulation, while supplementary UV-A light stimulates cannabinoid synthesis. Nevertheless, the potential of stage-specific supplementation of red and UV-A light remains underexplored in its capacity to optimize cannabinoid yield in indoor hemp cultivation. In the present study, the effect of red light in combination with UV-A light on hemp biomass and cannabinoid accumulation was investigated using a high-CBD strain. There were four treatments: (1) white light throughout the growth period (control; V W R W ); (2) red light supplementation during the vegetative stage (V WR R W ); (3) UV-A supplementation (V W R WUV ) during the flowering stage; and (4) combined red and UV-A supplementation (V WR R WUV ) during the vegetative and flowering stages. Results showed that V WR R W promoted the number of effective branches (increased by 18.0%) compared to the control (V W R W ), resulting in an increase in inflorescence yield by 17.9%. V W R WUV increased CBG and CBD content by 52.7% and 12.1%, respectively, relative to the control. The effect of V WR R WUV on biomass and cannabinoid accumulation was the strongest among the treatments, with CBG and CBD yields reaching 0.53 g and 4.62 g per plant, representing significant increase of 91.8% ( p  < 0.01) and 44.1% ( p  < 0.01), respectively, compared to the control. However, there were no significant differences in CBD yield among the V WR R W , V W R WUV and V WR R WUV treatments, indicating that the combined supplementation of red and UV-A light did not have an additive effect on CBD accumulation. These findings highlight the potential of stage-specific spectral strategy to optimize both plant growth and phytochemical quantity.

Morphing wing technology is crucial for enhancing the flight performance of aircraft. To address the monitoring challenges of full-scale variable-camber leading edges under flight conditions, this study introduces a ground-based strength testing technique aimed at precisely evaluating the deformation patterns and structural strength during actual operation. Firstly, the motion characteristics of the variable-camber leading edge were analyzed using numerical simulation based on kinematic theory. Secondly, a tracking loading test rig was designed and constructed to simulate the actuated deformation and aerodynamic loads of the leading edge. Next, mechanical boundary numerical simulation was then utilized to predict the motion trajectories of loading points on the upper and lower wing surfaces, and a multi-point coordinated control system was developed to achieve accurate experimental control. Finally, a multi-sensor iterative method was employed to ensure loading precision throughout the testing process. A case study was conducted using a leading edge test piece from a specific commercial aircraft. The results indicated that in the motion test of the variable-camber leading edge, the average error of the deflection angle was 4.59%; in the strength test, the average errors in the magnitude and direction of the applied load were 0.54% and 0.24%, respectively. These findings validate the effectiveness of the proposed technique in simulating the flight conditions of deforming wings and accurately obtaining the leading edge shape change curve, deformation accuracy curve, and strain curves of the upper and lower wing surfaces under deflection angles. Furthermore, this paper compares the deformation accuracy of different testing methods under test conditions, providing scientific evidence and technical support for the testing and evaluation of variable-camber leading edges.

Deterministic safety factor design is difficult to adapt to the characteristics of composite structures with many uncertainty factors and concurrent multiple failure modes, and the design results cannot quantitatively describe the level of risk. In this paper, based on the synergistic reliability analysis of multiple failure modes and the introduction of uncertainty variables such as material, design, load, and so on, the safety factor probabilistic Design(SFPD) method is proposed, in which taking the structural risk level as a constraint, the allowable failure probability is converted into a safety factor to break the correlation barriers between the safety index, safety factor, and structural design. First, the main failure modes of composite structures are considered to decompose the safety indexes, and the allowable failure probability is assigned to each failure mode; second, the reliability model of composite structures is constructed with the allowable failure probability as a constraint, combining the macro-and fine-specular failure criterion, and the ultimate load is inverted through structural optimization, to make the structure safety coefficient lower and reduce the weight of the structure under the condition of meeting the safety indexes; and finally taking the typical wall plate structure of civil aircraft as the case verification object, the weight reduction of 7% for the skin and 4% for the whole structure is realized under the premise of ensuring the structural safety, and the reasonableness and feasibility of the safety coefficient reduction from 1.5 to 1.4 are verified.

The angular motion of aircraft landing gear retraction and extension must be accurate to ensure flight safety. Therefore, this study experimentally evaluated the motion accuracy of the landing gear retraction and extension processes associated with a specific aircraft to construct a reliability evaluation model for the landing gear angle. Considering the limitations of data acquisition in practical applications, the Bayesian method, which combines prior knowledge with experimentally measured data to reasonably estimate the variable parameters in the evaluation model, was applied to obtain more accurate parameter distributions. The constructed Bayesian-updated iterative model was shown to effectively expand upon limited test data to provide a novel approach for accurately evaluating landing gear angle reliability. The results of this study not only enrich the theoretical basis underpinning aircraft landing gear reliability assessment but also provide a valuable reference for technical support and decision-making in related engineering practice.

This study presents a quasi- in situ observation of the fatigue crack growth behavior in a friction stir welded 2024-T4 joint. The microstructure and fatigue properties of the joint were investigated using electron backscatter diffraction (EBSD) technique, scanning electron microscopy (SEM), and fatigue crack growth tests. The fatigue crack growth behavior of the joint was examined by conducting fatigue crack growth tests with different notch locations. The results show that the sample with the notch in the stir zone (SZ) exhibited the highest resistance to fatigue crack growth, followed by the notched samples of the Advancing side (AS) and Retreating side (RS) weldments. Microstructural observations showed a homogeneous microstructure with a fine grain size in SZ and it was observed that this fine-grained structure significantly enhanced the material’s resistance to fatigue crack growth. The experimental results were further analyzed using the Paris model to provide a quantitative understanding of the crack growth behavior. The study underlines the impact of microstructural characteristics and notch location on the fatigue performance of the weldment. Overall, the quasi- in situ observations and experimental findings contribute to a comprehensive understanding of the fatigue crack growth behavior in friction stir welded 2024-T4 joints.

Due to the significant differences in aerodynamic loads offlaps at different positions, there are also significant differences in the loads borne by bearings at different flap angles. This leads to inconsistent wear depth of bearings at different angles. Therefore, the method of introducing uniform wear depth is difficult to apply to the dynamic characteristics analysis of flaps. To address this issue, a dynamic modeling method based on the least squares method is proposed. Firstly, based on the connection characteristics of the flap surface, the C-B method is used to make it flexible, and the RBE2 element is used to establish a rigid flexible coupling dynamic model. On this basis, combining with UAMP, DISP and UMESHMOTION subroutines, the uneven wear data of hinge bearings are obtained by using the wear evolution simulation. At the same time, the function relation among the wear depth, flap deflection angle, and friction coefficient is established via least squares fitting. Finally, the function relation is updated to the rigid-flexible coupling dynamic model by the offset of the hinge bearing center point and the friction coefficient of the ball pair, so as to obtain the dynamic response of the flap under the influence of wear, which verifies the applicability and effectiveness of the method. As wear progresses, the coaxiality of the inner and outer bearing shafts of the flaps decreases gradually, and the driving torque on the inner and outer sides increases accordingly. The maximum increase is 15.08%. This method can provide some support for designing the flap mechanism and bearing selection. 不同卡位的襟翼气动载荷差别很大, 使得轴承在不同襟翼偏角下所承受载荷也存在明显差异, 这导致在不同角度位置的轴承磨损深度不一致。因此, 引入均匀磨损深度的方法难以适用于襟翼的动力学特性分析。为解决这一问题, 提出了一种基于最小二乘法的动力学建模方法。根据襟翼翼面的连接特点利用C-B法对其进行柔性化, 并采用RBE2单元建立刚柔耦合动力学模型。联合UAMP、DISP、UMESHMOTION子程序进行磨损演化仿真，获取铰链轴承的非均匀磨损数据, 同时通过最小二乘拟合建立磨损深度和襟翼偏角角度以及摩擦因数的映射关系。将该映射关系以铰链轴承中心点的偏移量和轴承摩擦因数的方式更新刚柔耦合动力学模型, 以获取在磨损影响下的襟翼机构动力学响应, 验证了方法的适用性和有效性。结果表明, 随着磨损的进行，襟翼内外侧轴承转轴同轴度逐渐降低, 内外侧驱动力矩随之增加, 增加幅度最大为15.08%。该方法可为襟翼机构的设计及轴承选型提供一定支持。

It is significant to study the relationship between the stress triaxiality and the fracture behavior for analyzing the failure process of additive manufactured titanium alloy. This paper combined the tensile test of smooth round bar specimens and notched round bar specimens with the numerical simulation to obtain the stress triaxiality distribution and fracture strain in order to study fracture behavior of additive manufactured titanium under different stress triaxiality. Fracture analysis was proceeded by using scanning electronic microscope to analyze the correlation between the stress triaxiality and the fracture behavior. Results show that the fracture strain decreases while the stress triaxiality increases and the location of the crack initiation moves from the center to the edge of the minimum cross-section while the radius of the notch decrease. 研究应力三轴度与增材制造钛合金材料断裂行为的相关性, 对分析增材制造钛合金的断裂失效过程有着重要的作用和意义。对光滑圆棒和缺口圆棒试件在准静态下进行单轴拉伸试验, 结合数值仿真分析得到试件的应力三轴度分布和断裂应变, 研究了增材制造钛合金在不同应力三轴度下的韧性断裂行为。通过扫描电子显微镜观察试件断口表面的形貌, 分析不同应力三轴度下增材制造钛合金的断裂机理。研究发现, 在中高应力三轴度范围内, 增材制造钛合金的断裂应变随应力三轴度的升高而降低; 缺口圆棒试件的起裂位置随缺口半径的减小从最小截面中心处逐渐转移至边缘处。