Abstract:As a general quality characteristic with comprehensive feature, the Aircraft Structure Operational Integrity (ASOI) is the basis for aircraft structure to exert its operational applicability and effectiveness. The ASOI includes 6 characteristics，such as durability, supportability, safety, structural capability, survivability and recoverability. And even the same structural design techniques may have different effects on the 6 characteristics. In order to improve the ASOI, the development requirements of aircraft structural strength are discussed from the perspective of 6 characteristics of ASOI, based on the analysis of ASOI meaning and aircraft combat characteristics. In addition, the influence of typical structural design techniques on ASOI is also analyzed.

Abstract:Establishing testing pyramids with building blocks approach is a widely accepted process for the structural strength verification of large aircraft. This article briefly summaried the historial developments and trendencies of building block approach and testing pyramids. In the verification processes of aircraft structural strengthes, the building block approach is applied to construct various forms of testing pyramids with different verification objects. In order to verify various “New” related technologies, the objects can be materials, design configurations, design methods and calculation tools, manufacturing, assembly and maintenance processes, as well as the full scale componemts and whole aircraft. On this basis, the statistical results for the testing pyramids established in various US military aircraft developments are also presented with the numbers of ranges, the proportions of the amounts and costs. The presented results include four aspects: the level of experiment, the object, the aim and the type of experiments. These results can explain the importance and economy of the applications of the testing pyramids in the verifications for aircraft structural designs. The works in the basic levels of testing pyramids, not only provide solid design allowable values for related design methods / tools in multiple levels, but also provide reliable means of compliances to the developments of full scale components and whole aircraft. Finally, the application developments, trendencies and limitations of the virtual tests for aircraft developments are also introduced.

Abstract:AES(Airborne electronic suits)are carried in certain structures of military aircrafts, which contribute the relevant EMP／EMH(Electromagnetic Protection／Electromagnetic Hardening) characteristics for the AES. For military aircrafts, the EMP／EMH characteristics of aircraft structures have a great impact on the AES, so the EMP／EMH characteristics of aircraft structures is one of the important parts of its operational integrity. The EMP／EMH concept is attributed from perspectives of both EMC(Electro-Magnetic Compatibility) and the EW(Electromagnetic Warfare), which is followed the concept of electromagnetic hardening or reinforcement. The EMP／EMH of aircraft structures is combined engineering technology and operational tasks. Several typical EMP／EMH measures of aircraft structures are proposed based on the analysis of typical electromagnetic threats, the EMP／EMH characteristics of aircraft structure and the electromagnetic damage mechanism ware analyzed from aircraft structure, which was in order to improve the operational integrity of AES.

Abstract:Aero-engine is a device that provides power for aviation equipment. Maintenance is an important stage in the whole system and whole cycle of aero-engine. The development history of aero engine maintenance is introduced briefly. The aero-engine repair technology development is presented based on fault inspection, deposit washing, assembling and remanufacturing technology development is presented based on development history, key technologies and development process. Finally, the development prospect of aero-engine maintenance and remanufacturing is forecasted.

Abstract:Accurate prediction of fatigue crack growth serves as the cornerstone for aircraft component lifespan monitoring and residual life estimation. In this paper, a prediction method of structural crack propagation based on dynamic Bayesian network is proposed, which combines the prior knowledge and the posterior knowledge of fatigue crack propagation to accurately infer the crack length. The influence of different particle numbers on the inference accuracy of the dynamic Bayesian network was studied. Through the study of crack propagation of the single hole plate and the lug under random load spectrum, it is shown that the dynamic Bayesian network method can accurately predict the crack growth of structures, and the prediction accuracy is more than 50% higher than that of the traditional method.

Abstract:With the wide application of fibre-reinforced composites in aerospace, the fatigue problem of composites is becoming more and more prominent. In order to achieve efficient and accurate fatigue damage analysis, a data-mechanism driven method for the progressive analysis of fatigue damage in composites is proposed. The method utilizes a single-hidden-layer neural network as its fatigue constitutive law for simulations of fatigue delamination under cyclic loading. In order to achieve neural network training with a small quantity of samples, this paper uses a Paris-law-informed regulations to achieve data-mechanism fusion for neural network model training. The ability to analyze fatigue delamination is validated in in the full range of mode-I and mode-II as well as mixed modes of different mode ratios using double cantilever beam (DCB) and 4-point end flexure (4ENF), the paper further verifies the applicability of the cohesive model in the case of complex fatigue delamination front using an reinforced double cantilever beam (R-DCB) model. The numerical results of this paper show that the data-mechanism driven fatigue damage progressive analysis method for composites could rapidly and effectively simulate the composite delamination propagation with high fidelity, providing a new idea and method for composite structure design and safety assurance.

Abstract:Fatigue life scatter factor of aircraft damaged structures is an important parameter to analyze the fatigue life dispersion degree of damaged structures. In this paper, the fatigue test of prefabricated damage test pieces is carried out for aluminum alloy materials commonly used in aircraft. The distribution type of residual fatigue life of damaged structures is determined by correlation coefficient comparison method. The relationship between damage and fatigue life and the dispersion of residual fatigue life of damaged structures were analyzed through fracture observation and statistical data processing. The results show that the residual fatigue life of damaged structures is consistent with Weibull distribution. The fatigue life of the structure with preset damage decreases obviously compared with that without preset damage, and the residual fatigue life of the structure decreases gradually with the increase of preset damage size. With the increase of the preset damage size, the residual fatigue life dispersion increases, and the fatigue life dispersion of different structures with initial crack damage is different. The work in this paper provides a reference for establishing fatigue life scatter factor models of aluminum alloy structures with different damage sizes.

Abstract:It is of great practical significance for real-time health monitoring to reconstruct other position responses by using limited measuring point information of wing box structure in complex navigation with harsh bearing conditions In this paper, the nonlinear relationship between the responses is obtained by training the back propagation neural network, and the response reconstruction method based on neural network is established and verified by numerical simulation by finite element analysis. Finally, the method is applied to the response reconstruction, damage location and judgment analysis of typical load-bearing structures of wing boxes under measured random excitation environment The results show that the RMS relative error of the predicted response power spectral density reconstructed by this method is less than 1.90 dB and the main frequency error is less than 10%; The damage or fault of the key measuring point E of the wing box occurred 3s after the intercepted fragment data, and its fault characteristic frequency was about 240Hz, which indicated the feasibility of applying this method to response reconstruction prediction and health monitoring analysis.

Abstract:Aiming at various genetic algorithms commonly used in composite layer optimization, it is difficult to comprehensively consider complex engineering constraints such as surface 45 degrees, layering ratio, and continuous layer number limit, this paper proposes an isogenic sequence double random genetic algorithm for composite laminates, which can consider the layering in the optimization. Complex engineering constraints such as ratio, continuous layup limit, adjacent layup angle, surface laying ±45°, etc., the introduction of double random algorithms in the exchange and mutation operators ensures the strict equality of gene sequences in the optimization iteration, and based on the SABRE software The optimization method is realized, the results of calculation and application show that the proposed method can fit complex engineering constraints such as balance, symmetry, surface 45 degrees, continuous ply number limit, ply ratio, etc., and has high reliability and engineering applicability.

Abstract:As an important part of the fatigue load spectrum simplification of aircraft structures, small-load omission can significantly save the time and cost of fatigue tests. However, there is no widely accepted standard method for determining the small-load omission level. In this paper, the existing small load omission levels are collected and classified, and determination rules of small load omission levels are analyzed. Then, combined with the general characteristics of aircraft fatigue load spectrum and structural materials, the links between different determination methods of small-load omission levels are investigated, and the correlation model between small-load omission levels is established, providing suggestions and references for the determination of small-load omission levels in the engineering load spectrum simplification.

Abstract:This article conducts laboratory accelerated corrosion tests on simulated coastal atmospheric corrosion of 2A12-T4 aluminum alloy plates, simulating the impact of corrosion on the fatigue characteristics of aluminum alloy plates throughout the entire coastal atmospheric corrosion process from initial pitting to later erosion. Based on the principle of equivalent fatigue life degradation, an accelerated equivalent relationship between 2A12-T4 aluminum alloy plate accelerated corrosion and atmospheric corrosion is established. The research results show that the fatigue life degradation law of 2A12-T4 aluminum alloy after accelerated pre corrosion in laboratory is consistent with that of atmospheric pre Corrosion fatigue life degradation law, which is characterized by "rapid decline period"+"platform period". The first 144 hours of accelerated corrosion in the laboratory are approximately equivalent to the effect of corrosion on fatigue life in the first year of actual atmospheric environment; After 144 hours, every 36 hours of accelerated corrosion (3 cycles of immersion) is approximately equivalent to the effect of 2 years of corrosion on fatigue life in actual atmospheric environments.

Abstract:Weak honeycomb sandwich panels are used extensively in the structural design of small and medium-sized UAVs. Due to its life cycle in long-term storage status, and the state of the structure is difficult to determine after long-term natural aging. In this paper, the bending performance of weak honeycomb sandwich panels after natural ageing is investigated. Based on the Hashin failure criterion and the stiffness degradation model, a finite element analysis model was developed to study the mechanical response and failure forms of the honeycomb core layer and skin under bending. The results show that even after long-term natural aging, bending strength increase significantly; the experimental data have good stability and the main failure modes are consistent with expectations; the results of the simulations are in general agreement with the experimental results.

Abstract:The application of thin composite material laminate secondary bonding technology to the main load-bearing structure of small UAV wings has important engineering applications for reducing the manufacturing costs of wing box section. A single-lap structural tensile shear test was carried out using a 2mm sheet made of carbon fibre twill. The suitability of three different types of adhesive for the sheet was analysed, as well as the effect of adhesive thickness and laminate lay-up angle on the strength of the secondary glue joint, and the simulation was verified by ABAQUS software. The results show that: using SY-23B epoxy structural adhesive, the adhesive layer thickness is 0.2mm, the lay-up method is [(0/90)]8-[(0/90)]8, the bonding performance is optimal, the structural shear strength can reach 18.2MPa, to meet the small UAV stress box section bonding strength requirements, the secondary bonding formed wing stress box section has the advantages of light weight, low cost.

Abstract:In a high temperature service environment for a long time, coatings (TBCs) generate a double layer of thermally grown oxide (TGO) consisting of an Al₂O₃ layer and a mixed oxide layer (MO) between the internal top coat layer (TC) and the bond coat layer (BC). Among them, the late generated MO is highly susceptible to the formation and expansion of microcracks within the coating due to its looseness and porosity and brittleness, which leads to premature spalling of the coating. Therefore, in this paper, based on the diffusion-oxidation model of double-layer TGO growth, the failure and stress evolution process of the coating interface of the coating interface under the anisotropic growth of double-layer TGO within TBCs is investigated by using the birth-death cell method, considering the nonlinear deformation behavior of the material. The results show that: the growth of MO will significantly increase the level of tensile stress at the coating interface, which will easily lead to damage and failure of the MO/TC interface in the peak area at the high temperature stage and in the center of the slope at the cooling stage; failure of the MO/TC interface causes higher tensile stresses at the peak of the BC layer and promotes the destruction of the Al₂O₃/BC interface from the peak to the valley during the cooling stage; after the failure of the MO/TC interface, the increase of accelerates the damage of the Al₂O₃/BC interface.

Abstract:The high efficiency and low cost repair of perforation damage of aluminum honeycomb sandwich structure is of great significance to ensure the integrity of aviation equipment.In this paper, the intact and perforated aluminum honeycomb sandwich samples were designed and prepared. Four point bending failure test and finite element simulation analysis were carried out on intact, perforated and repaired composite material specimens. The experimental and simulation results show that the bending strength of aluminum honeycomb sandwich structure can be effectively restored by using composite materials bonding method . The results of finite element simulation are in good agreement with the experimental results. The simulation model can accurately calculate the ultimate load and failure mode of all kinds of samples. The simulation results show that when the damage range is ≤φ30mm (diameter to width ratio is less than 40%), the adhesive repair technology of composite materials can be applied to the damage repair of aluminum honeycomb sandwich structures of aircraft.

Abstract:As an important force in the three-dimensional combat of the Army, the Army Aviation Corps plays an important role in fire support, three-dimensional supply, and comprehensive service guarantee. However, its construction form and operational requirements, in low altitude ultra-low altitude and low speed to perform tasks, resulting in its service environment and combat environment is more severe. Therefore, it is necessary to ensure the integrity of helicopter operational and meet the operational requirements by rationally designing the fuselage structure, improving the ability to adapt to the marine environment, and establishing a complete battle injury repair capability.

Abstract:The echelon usage control of helicopters is one of the most import job in the aviation equipment support，aiming at the difficulty and lack of evaluation index in the echelon usage control, two methods of the echelon usage control are introduced, the way of echelon optimization control technology is mainly expatiated, the influences of different parameters in the echelon usage control are deduced and analyzed, and the evaluation indexes of echelon usage control are presented. Finally, a case study is carried out by using the method of echelon optimization technology, the results indicate that the method is more intuitive and more comprehensive than the ladder diagram method, and the evaluation indexes proposed are reasonable, and the research direction of the next step is clarified.

Abstract:Aiming at the fault of a helicopter tail rotor blade fracture, the fault cause analysis is carried out by fault tree analysis method, and the bottom event analysis results are obtained. By carrying out failure analysis of the blade, the results of macro and micro fractographic analysis shows that the fracture property of the blade is low-stress and high-cycle bidirectional bending fatigue fracture. The simulation analysis of the fractographic damage evolution of flexible beam shows that when the strength value of the fiber compression direction of the flexible beam is less than 700MPa, the fractographic type is similar to that of the faulty tail rotor flexible beam. Comprehensive analysis shows that the tail rotor will produce large vibration under large fatigue load condition, and the increase of vibration intensifies the load of the tail rotor, leading to the increase of load at the root of the flexible beam, exceeding the designed bearing capacity of the flexible beam, then fatigue fracture at the root of the flexible beam of the blade.

Abstract:The phenomenon of tire hydroplaning widely exists in aircraft and automobiles. Taking aircraft as an example, tire hydroplaning will lead to a sharp decrease in the friction between the tire and the ground, increase the distance between takeoff and landing of aircraft, and further affect the flight safety. Therefore, it is necessary to carry out research on airplane tire hydroplaning. Aiming at the tire hydroplaning problem of aircraft tires, a simplified tire model was established by FEM method and verified by experiments. A water model was established by SPH method, and finally a tire hydroplaning model with the interaction of tire, water and pavement was established. The influence of different influencing factors and different tire configurations on tire hydroplaning was analyzed. The results show that, the greater the water depth, the more likely occur the tire hydroplaning, but after the water depth is greater than 6mm, the water depth on the tire hydroplaning effect is small; The greater the tire speed, tire pressure and wheel load, the more likely the tire hydroplaning; With the increase of groove width, the tire hydroplaning speed increases, but the stability decreases. The more severe the tire abrasion, the more likely it is to tire hydroplaning; The greater the number of grooves, the greater the critical water skiing speed.

Abstract:Accurate fault diagnosis of electromechanical equipment under the condition of limited label samples is of great significance for improving the health management ability of complex electromechanical equipment. This article proposes a semi supervised bidirectional generative adversarial network (S-BIGAN) based on dual attention mechanism for mechanical and electrical equipment fault diagnosis. GAF is used to convert one-dimensional data into two-dimensional images, effectively utilizing a small amount of labeled data and a large amount of unlabeled data. Finally, bearing data is used as the validation object, and compared with algorithms such as CNN SVM and SGAN, the accuracy of fault diagnosis is greatly improved.