Chinese Journal of Aeronautics最新文献

Passive binocular measurement systems are being increasingly utilized in the in-situ industries of automobiles, aviation, and aerospace, etc. due to their excellent qualities of accuracy, efficiency, and cost performance. Whereas the barrier of evaluating the accuracy of measured objects resulted from the unequal equivalent focal length and quantization of pixels, has limited their further development and application of high requirements for in-situ machining, e.g., the measurement of machining reference points for the positioning of robotic drilling in aerospace manufacturing. In this paper, an accuracy evaluation method is proposed to address the problem. Firstly, the unequal equivalent focal length is considered to improve the accuracy of 3D reconstruction. Next, the credibility probability model is developed to calculate the probability of the observed error in the public view of the binocular measurement system and indicates the direction of improvement. Finally, the in-situ experiment is carried out to validate the method within the effective public view range of 300 mm × 300 mm. The experiment results show that the RMSs of observed errors are superior to 0.035 mm, and the credibility probabilities are all higher than 0.91; the maximum 3D reconstruction accuracy improvement is 60.3%, with the error reduced from 0.078 mm to 0.031 mm.

In this paper, the influence of forced installation caused by a hole-location error on the 3D stress distribution and damage of a composite bolted joint is investigated. An analytical model of stress distributed on composite holes is promoted, in view of non-uniform extrusion caused by forced installation. At first, non-uniform extrusion of the hole edge caused by forced installation is analyzed. According to the contact state, expression of hole deformation is given. Then, based on Hertz theory, the maximum extrusion load is obtained with help of deformation expression. By constructing an elastic foundation beam model, 3D stress distributed on a hole could be analyzed according to the extrusion load. Then, stress distribution predicted by the above analytical method is compared with that provided by FE considering composite damage. Finally, a forced installation experiment is carried out to analyze the damage distribution of the joint. Results show that a central-symmetrically distributed stress is introduced by the hole-location error. With an increment of the error, strength of composite decreases due to extrusion damage. Therefore, stress presents a concave distribution on the hole. As the hole-location error exceeding 3%, stress decreases gradually due to failure of composite. Damage of holes does not exhibit a centrosymmetric distribution. Serious damage is mainly distributed on the entrance of the hole at the lower sheet.

Recognizing target intent is crucial for making decisions on the battlefield. However, the imperfect and ambiguous character of battlefield situations challenges the validity and causation analysis of classical intent recognition techniques. Facing with the challenge, a target intention causal analysis paradigm is proposed by combining with an Intervention Retrieval (IR) model and a Hybrid Intention Recognition (HIR) model. The target data acquired by the sensors are modelled as Basic Probability Assignments (BPAs) based on evidence theory to create uncertain datasets. Then, the HIR model is utilized to recognize intent for a tested sample from uncertain datasets. Finally, the intervention operator under the evidence structure is utilized to perform attribute intervention on the tested sample. Data retrieval is performed in the sample database based on the IR model to generate the intention distribution of the pseudo-intervention samples to analyze the causal effects of individual sample attributes. The simulation results demonstrate that our framework successfully identifies the target intention under the evidence structure and goes further to analyze the causal impact of sample attributes on the target intention.

The traditional clustering algorithm is difficult to deal with the identification and division of uncertain objects distributed in the overlapping region, and aimed at solving this problem, the Evidential Clustering based on General Mixture Decomposition Algorithm (GMDA-EC) is proposed. First, the belief classification of target cluster is carried out, and the sample category of target distribution overlapping region is extended. Then, on the basis of General Mixture Decomposition Algorithm (GMDA) clustering, the fusion model of evidence credibility and evidence relative entropy is constructed to generate the basic probability assignment of the target and achieve the belief division of the target. Finally, the performance of the algorithm is verified by the synthetic dataset and the measured dataset. The experimental results show that the algorithm can reflect the uncertainty of target clustering results more comprehensively than the traditional probabilistic partition clustering algorithm.

Using the plate/shell elements in commercial software, accurate analysis of interlaminar initial damage in typical composite structures is still a challenging issue. To propose an accurate and efficient model for analysis of interlaminar initial damage, the following work is carried out: (A) A higher-order theory is firstly proposed by introducing the local Legendre polynomials, and then a novel shell element containing initial damage prediction is developed, which can directly predict transverse shear stresses without any postprocessing methods. Unknown variables at each node are independent of number of layers, so the proposed model is more efficient than the 3D-FEM. (B) Compression experiment is carried out to verify the capability of the proposed model. The results obtained from the proposed model are in good agreement with experimental data. (C) Several examples have been analyzed to further assess the capability of the proposed model by comparing to the 3D-FEM results. Moreover, accuracy and efficiency have been evaluated in different damage criterion by comparing with the selected models. The numerical results show that the proposed model can well predict the initial interlaminar damage as well as other damage. Finally, the model is implemented with UEL subroutine, so that the present approach can be readily utilized to analyze the initial damage in typical composite structures.

A novel constant-pressure and constant-quenching distance Condensed Combustion Products (CCPs) collection system was developed, coupled with a timing control system, to collect the CCPs formed in the course of burning of aluminum-based composite propellants. The effects of adiabatic graphite plating, collection zone, quenching distance, time series of collection, and propellant burning rate on the microscopic morphology, particle size distribution and unburned aluminum content of CCPs were investigated. It was verified that the graphite plating can provide a high-fidelity high-temperature environment for propellant combustion. The combustion efficiency is improved by 2.44% compared to the bare propellant case. The time series of collection has a significant effect on the combustion efficiency of aluminum, and the combustion efficiency of aluminum in the thermal state (1.2–2.4 s) is 2.75% higher than that in the cold state (0–1.2 s). Similarly, the characteristics of the CCPs in different collection zones are different. At the quenching distance of 5 mm, the combustion efficiency of aluminum in the core zone (85.39%) is much lower than that in the outer zone (92.07%), while the particle size of the CCPs in the core zone (172 μm) is larger than that in the outer zone (41 μm). This indicates that the core zone is more likely to produce large-sized and incompletely burned agglomerates during the propellant combustion process. Different burning rates also lead to a significant difference in particle size distribution and combustion efficiency. High burning rates result in higher combustion efficiency. A detailed sequence of the elaborative collection process of CCPs is proposed, mainly including the setting of ignition delay time, burning rate, working pressure, plating length and time series of collection. The findings of this study are expected to provide a reliable tool for the evaluation of the combustion efficiency of solid propellants.

Previous Particle Boundary (PPB), as the detrimental structure in Powder Metallurgy (PM) components, should be eliminated by subsequent hot process to improve the mechanical properties. The objective is to investigate the Dynamic Recrystallization (DRX) nucleation mechanisms and grain growth behavior of the 3rd-generation PM superalloy with PPB structure. Microstructure observation reveals that PPB decorated with (Ti, Ta, Nb)C carbides belongs to the discontinuous chain-like structure. The elimination of PPB networks can be achieved effectively via hot deformation due to the occurrence of DRX. Four different DRX nucleation mechanisms were proposed and discussed in detail according to the special microstructure characteristics of the PM superalloy. Firstly, local lattice rotations can be detected in the vicinity of (Ti, Ta, Nb)C carbides during hot deformation and thus PPB structure serves as the preferential nucleation sites for DRX grains via Particle-Stimulated Nucleation (PSN). Then, Discontinuous-DRX (DDRX) characterized by grain boundary bulging dominates the microstructure refinement and Continuous-DRX (CDRX) operated by subgrain rotation can be regarded as an important assistant mechanism. At last, the initial Σ3 boundaries would lose their twin characteristics owing to the crystal rotation and then transform into the general High Angle Grain Boundaries (HAGBs). The distorted twins provide additional DRX nucleation sites, viz., twin-assisted nucleation. Particular attention was focused on the grain growth behavior of the PM superalloy in subsequent annealing process. The recrystallization temperature was determined to be about 1110 °C and 1140 °C can be considered as the critical temperature for grain growth. The findings would provide theoretical support for microstructure refinement of the 3rd-generation PM superalloy, which is of pivotal significance for improving the mechanical properties of aviation components.