Abstract: The heat dissipation caused by internal friction plays an important role during fatigue property prediction based on self-heating data but it is still unclear for Carbon Fiber Reinforced Polymer (CFRP). In this paper, fatigue tests and thermal data analysis are carried out in order to investigate internal friction and Fracture Fatigue Entropy (FFE) of CFRP laminates with various stacking sequences. The fatigue limit is firstly estimated based on an improved graphic method developed by our previous study and then used to mark the beginning of fatigue damage occurs. It is found that the relationship between internal friction and applied stress amplitude is non-linear which is different from metals. Quadratic function is employed to characterize the internal friction region below fatigue limit and the trend line is used to separate heat dissipation related to damage and internal friction beyond fatigue limit. Results show that the internal friction effect of cross-ply laminates is significantly greater than that of unidirectional laminates. FFEs estimated by the heat dissipation related to damage are found to be independent of applied stress amplitude, which can be used to predict S–N curve of CFRP laminates efficiently and precisely.

Abstract: Experiments are performed in this study to investigate the influence of impact locations on the damage and compression behavior of stiffened composite panels with a single L-shaped stiffener. After the application of low-velocity impact to the flange tip or web from the outboard side with the same energy level, significant differences among the damage types in specimens are observed. The flange tip impact induces complex damage types including ply fracture, splitting, delamination, and stiffener/skin interface debonding. The stiffness discontinuity results in the extensive propagation of delamination along the longitudinal direction. In contrast, the web impact damage is minimal because of the web's high stiffness. The results of compression after impact reveal that these two types of damage lead to considerable differences in compression behavior. The severe damage caused by the former leads to a considerable reduction in buckling load; however, the buckling deformation drives the rapid propagation of damage without any constraint. As a result, no distinct post-buckling stage is observed, and the failure load is considerably reduced. On the other hand, the damage caused by the latter weakens the interaction between the stiffener and skin, thereby slightly reducing both buckling and failure loads. Based on these findings, several suggestions on aircraft structure design and inspection are proposed to avoid significant damage and rapid damage propagation.

Abstract: Three-dimensional braided composite has a unique spatial network structure that exhibits the characteristics of high delamination resistance, damage tolerance, and shear strength. Considering the characteristics of braided structures, two types of high-performance materials, namely, aramid and carbon fibers, were used as reinforcements to prepare braided composites with different hybrid structures. In this study, the longitudinal and transverse shear properties of 3D braided hybrid composites were tested to investigate the influences of hybrid and structural effects. The damage characteristics of 3D braided hybrid composites under short beam shear loading underwent comprehensive morphological analysis via optical microscopy, water-logging ultrasonic scanning, and X-ray micro-computed tomography methods. It is shown that the shear toughness of hybrid braided composite has been improved at certain degrees compared with the pure carbon fiber composite under both transverse and longitudinal directions. The hybrid braided composites with aramid fiber as axial yarn and carbon fiber as braiding yarn exhibited the best shear toughness under transverse shear loading. Meanwhile, the composites with carbon fiber as axial yarn and aramid fiber as braiding yarn demonstrated the best shear toughness in the longitudinal direction. Due to the different distribution of axial and braiding yarns, the transverse shear property of hybrid braided structure excels over the longitudinal shear property. The failure modes of the hybrid braided composite under the two loading directions are considerably different. Under transverse loading, the primary failure mode of the composites is yarn fracture. Under longitudinal loading, the primary failure modes are resin fracture and fiber slip. The extensive interfacial effects and the good deformation capability of the hybrid braided composites can effectively prevent the longitudinal development of internal cracks in the pattern, improving the shear properties of braided composites.

Abstract: The mechanical behavior of AZ31B magnesium alloy was studied through uniaxial tensile tests at strain rates of 0.001, 1, 100, and 1000/s. The results show that an increase in the strain rate results in a gradual increase in the flow stress. Considering that the original Johnson–Cook (J–C) model cannot adequately describe the flow stress of AZ31 magnesium alloy at different strain rates, a rate-dependent modified Johnson–Cook (M-J–C) model was proposed, and the coefficients were calibrated according to the experimental results. The calibration and validation show that the M-J–C model has a high accuracy in characterizing the flow stress of AZ31B magnesium alloy and can well predict the hardening curve of ZK60 and AM60 magnesium alloys at different strain rates in the literature. In addition, the variation in the fracture strain with different strain rates was characterized. The fractography was studied to reveal the mechanism of underlying fracture. The proposed M-J–C constitutive model combined with a failure criterion was developed and coded into LS-DYNA through the user subroutine UMAT. The comparison between the simulation and the experiment shows that the developed subroutine is accurate enough to simulate the plastic and fracture behaviors of AZ31B magnesium alloy at different strain rates.

Abstract: The free vibrations of nonlocal Euler and Timoshenko beams have been studied extensively, but there still remain some problems concerning boundary conditions and constitutive relations. For cantilever beams, a counterintuitive stiffening phenomenon is widely observed. And to the best of the authors’ knowledge, there is no work concerning about the Timoshenko beam with nonlocal shear force and local bending moment. This work reconsiders and explains these problems based on nonlocal differential theory. After obtaining the governing equation for nonlocal Euler beam, it is observed that the governing equation has the same form as that for the vibration of local beam with axial compressive force. Thus by comparing the nonlocal effects to the effects of end axial force, the stiffening phenomenon of cantilever beams is found to be caused by a meaningless term in boundary bending moment. This explanation is also suitable for nonlocal Timoshenko cantilever beams. Besides, for Timoshenko beams, the nonlocal effects on tensile and shear stress constitutive relations are considered separately. Three kinds of nonlocal Timoshenko beam models are solved. Numerical comparison shows that the effects of nonlocal tensile are bigger than that of nonlocal shear stress. Especially, for Timoshenko beams with nonlocal shear force only, the nonlocal effects lower the natural frequency for all boundary conditions. This finding can verify our explanation for the stiffening phenomenon of cantilever beams. In addition, it is also observed that, for both nonlocal beam theories, if all nonlocal internal forces are included in the governing equations, the eigenvalue equations and natural frequencies corresponding to local and nonlocal boundary conditions are the same.

Abstract: A type of gradient-degraded material-induced trigger has a greater potential to induce a progressive crushing mode in a controlled manner to reduce the initial crushing load and increase the specif...

Abstract: In this article, we propose a random fiber configuration method to set up quasi-realistic geometric models of the fibrous tow in reinforcement. Finite element method is applied to simulate the inje...

Abstract: Predictive maintenance is the novel development from the condition-based maintenance, which is being widely studied in various engineering systems. This paper proposed the integrated predictive maintenance framework for the aircraft system based on the existing maintenance management experience and the output result of prognostic and health management system (PHM).There are four aspects in this framework: historic data analysis, system health assessment, remaining useful life prediction and maintenance decision-making. The simulation study compares the predictive maintenance to the traditional preventive maintenance for the aircraft air-condition system(ACS), and selects the total maintenance cost and the mission reliability as the criteria. The results suggest that the proposed framework is a promising feature in maintenance management for the aircraft system.

Abstract: To better induce progressive collapse modes of composite corrugated plate, a novel multi-stage stacked structure is proposed. The multi-stage stacked triggering consists of stepped structures and sawtooth cutout that guides the progressive crushing load and failure mode. The different triggering configurations including non-sawtooth, partial sawtooth, overall evenly sawtooth and overall uneven sawtooth are discussed and compared. To better predict the progressive failure process, the material failure is initiated by the maximum-stress failure criterion and a stiffness degradation method. The traction-separation model is adopted to simulate inter-layer delamination failure. Under the validated model, the influences of geometrical parameters on the crushing responses are performed. Numerical simulation results show that a good agreement is exhibited between simulated and experimental results. The progressive failure behavior could be obtained by the stepped structures and sawtooth cutout. The initial loading responses highly depend on the gradient stacking methods. The initial peak load of proposed novel multi-stage stacked concepts is about 30% lower than that of traditional structure.

Abstract: Aims To investigate the impact of subchondral bone cysts (SBCs) in stress-induced osseous and articular variations in cystic and non-cystic knee models using finite element analysis. Materials and Methods 3D knee joint models were reconstructed from computed tomography (CT) and magnetic resonance imaging (MRI). Duplicate 3D models were also created with a 3D sphere mimicking SBCs in medial tibia. Models were divided into three groups. In group A, a non-cystic knee model was used, whereas in groups B and C, SBCs of 4 and 12 mm size were simulated, respectively. Cyst groups were further divided into three sub-groups. Each of sub-group 1 was composed of a solitary SBC in the anterior half of tibia adjacent to joint line. In sub-group 2, a solitary cyst was modeled at a lower-joint location, and in sub-group 3, two SBCs were used. All models were vertically loaded with weights representing double- and single-leg stances. Results During single-leg stance, increase in subchondral bone stress in sub-groups B-1 and B-3 were significant (p = 0.044, p = 0.026). However, in sub-group B-2, a slight increase was observed than non-cystic knee model (9.93 ± 1.94 vs. 9.35 ± 1.85; p = 0.254). All the sub-groups in group C showed significantly increased articular stress (p < 0.001). Conversely, a prominent increase in peri-cystic cancellous bone stress was produced by SBCs in groups B and C (p < 0.001). Mean cartilage shear stress in sub-groups B-1 and B-2 (0.66 ± 0.56, 0.58 ± 0.54) was non-significant (p = 0.374, p = 0.590) as compared to non-cystic model (0.47 ± 0.67). But paired cysts of the same size (B-3) produced a mean stress of 0.98 ± 0.49 in affected cartilage (p = 0.011). Models containing 12 mm SBCs experienced a significant increase in cartilage stress (p = 0.001, p = 0.006, p < 0.001) in sub-groups C-1, C-2, and C-3 (1.25 ± 0.69, 1.01 ± 0.54, and 1.26 ± 0.59), respectively. Conclusion The presence of large-sized SBCs produced an increased focal stress effect in articular cartilage. Multiple cysts further deteriorate the condition by increased osseous stress effect and high tendency of peripheral cyst expansion in simulated cystic knee models than non-cystic knee models.

Abstract: This paper presents a quantitative evaluation index efficiency of eddy current and defect interaction to evaluate the eddy current distribution induced by different planar eddy current probe. Effic...

Abstract: This study evaluated the effect of age and renal impairment on pharmacokinetics of trimetazidine (TMZ) in healthy elderly and renally impaired subjects and assess safety and tolerability. In this open-label, multi-dose study, 73 subjects were divided into six treatment groups: (1) 55-65 years; (2) 66-75 years; (3) >75 years (dosing for groups 1-3 [healthy]: B.D. for 4 days), (4) mild renally impaired (dosed B.D. for 8 days); (5) moderate renally impaired (dosed O.D. for 8 days); and (6) severe renally impaired-no dialysis (dosed once every 48 h for 8 days). Blood and urine samples were collected and analyzed. The geometric least squares mean ratios for; Group 2 and 1 of AUC(0-τ)ss was 112.2 (90% CI; 92.0-136.8) and Cmax,ss was 109.9 (89.6-134.8), Group 3 and 1 of AUC(0-τ),ss was 140.5 (115.9-170.3) and Cmax,ss was 137.8 (112.9-168.2), Group 4 and 1 of AUC(0-τ),ss was 114.2 (90.3-144.4) and Cmax,ss was 120.8 (92.5-157.8), Group 5 and 1 of; AUC(0-τ),ss was 213.0 (153.1-296.3) and Cmax,ss was 123.3 (92.2-164.7) and Group 6 and 1 of AUC(0-τ),ss was 247.4 (197.8-309.6) and Cmax,ss was 95.6 (73.0-125.1). Significant increase in systemic exposure of TMZ was observed in subjects; over 75 year's age and renally impaired compared to healthy subjects. TMZ was safe and well-tolerated.

Abstract: The fuselage frame, an apron construction of the typical transport aircraft fuselage, manufactured with carbon fibre/epoxy 2D triaxially braided composites, hinders the crashworthy aircraft analysi...

Abstract: The space–air–ground integrated network is an emerging network architecture integrated by satellite, aerial network, and ground communication, which can provide seamless connection on a global scale. However, the limited energy and spectrum resources cannot meet the growing communication needs, and its high heterogeneity, complex variability affect the reliable and efficient end-to-end transmission of services. In addition, machine learning is widely used. Using machine learning algorithms to solve problems in the space–air–ground integrated network is a new research idea for us. Therefore, this paper first introduces the concept and characteristics of apace–air–ground integrated network, summarizes, and analyzes the application of machine learning algorithms in solving the problems of resource allocation, attack detection, target recognition and location and security authentication of the space–air–ground integrated network, and looks forward to its prospects for development in space–air–ground integrated network.

Abstract: Based on three different angle of sideslip(AoS) measurement methods, which are nose boom with AoS vane, the fuselage-mounted AoS vane and differential static pressure methodology. This paper studies the flight test technique based on reconstruction of aircraft state methodology, analyzes the flight test data and calculates the measurement accuracy range after the reconstruction of true AoS.

Abstract: The civil aviation management department reviews airworthiness certification for aircraft products to ensure the airworthiness of aircraft products. The complexity of aircraft products and the characteristics of the airworthiness certification work determine that the airworthiness certification work requires that the certification reviewer need to have rich knowledge and experience in airworthiness domain. If these knowledges can be reused, it will effectively improve the airworthiness certification capability. Airworthiness compliance activities are the core of knowledge reuse. Therefore, in order to solve the problem of the accuracy of knowledge reuse in airworthiness compliance activities, based on the existing compliance activity ontology model, this paper further refines the model and constructs an attribute-oriented ontology model of airworthiness review compliance activity knowledge. At the same time, the attributes of compliance activities are introduced into the similarity measurement of compliance activities to form a new measurement method for calculating the similarity of compliance activities. This paper uses this model as a guide to construct a process-oriented airworthiness review compliance activity knowledge base and use it to recommend similar compliance activity cases. The test results show that this method can improve the judgment of the similarity of compliance activities and more effectively support the reuse of certification experience in the airworthiness certification process.

Abstract: The process of civil aircraft development is a complex system, where flight test is an extremely important process of the project. In the top-level planning of flight test, it is particularly important to determine the quantity of test aircraft, which is closely related to the total flight test period, cost, and resources. This paper analyzes and studies the number of test aircraft performing flight test missions, analyzes the related factors of the number of test aircraft, and proposes a reasonable calculation model with engineering operability based on flight test period and cost. It provides numerical data reference for overall planning of civil aircraft flight test during multi-objective optimization.

Abstract: Based on the civil aircraft hydraulic system, the typical slow-change fault injection is carried out in hydraulic system MWorks model, and the fault state assessment technology based on Gaussian mixture model is studied. The results show that the health curve of the Gaussian mixture model can truly reflect the system pressure abnormal deviation process, and the health confidence value obtained by the inverse tangent function normalization is more sensitive to the early failure process of the fault, which can better support the predictive maintenance.

Abstract: There is increasing concern about the design and evaluation of the human factors in the flight deck. The study was to propose a comprehensive evaluation method of the human factors in the flight deck, combing with multiple physiological signals. The proposed comprehensive evaluation method in the flight deck are composed with the evaluation of the operators' cognition, operational performance, control activities and workload. The cardiovascular signal, eye movement and flight parameters were recorded during task to conduct the evaluation. An experiment about the evaluation of the display elements in the flight deck was conducted to verify the proposed comprehensive method of the human factors. The results revealed the validity of the proposed method, which can give a detailed description of the operator's workload, operational performance and cognition during the flight task.

Abstract: Turbulence and windshear, especially low-altitude windshear, has great impact on successful flight. One of the most dangerous situations of low-altitude windshear associated with microburst phenomena. For the sake of avoiding or recovering microburst, we must know and study velocity trait of the wind profile. A downburst fluent dynamics is modeled using folded-line that is a closed vortex ring, establish a mathematical model of the microburst, and realized the different velocity profiles of the wind field when the microburst parameters are changed. it is more convenient that qualitative analysis microburst influences on aviation safety, for confirming exactly flight countermeasure.

Abstract: Visual ergonomics of modern civil flight deck is one of the most important aspects into which should be taken consideration. A subjective multi-stage evaluation method with two dimensions is proposed to evaluate the visual ergonomics design of flight deck, including lighting comfort, color collocation coordination and integrated visual environment in this paper. The evaluation results implies that the method proposed is effective and convenient, which is significantly applicable for engineering project.

Abstract: The large-scale reference system (LRS) based on multiple measuring stations is widely used to estimate the position and orientation of the aligned components of aircraft. The reference system consists of some enhanced reference system (ERS) points. However, the calibration accuracy of the reference system is prone to be degraded due to measurement systematic errors and environmental disturbance in the workshop. A novel nonlinear optimization method has been developed to reduce the overall calibration error of the LRS. First, the method focuses on analyzing the inhomogeneity and anisotropy of measurement errors of ERS points and establishing an improved weighting model for optimizing the coordinates of the points. Then, the measurement errors of each measuring station can be greatly reduced through a nonlinear unconstraint optimization method with redundant measurements. Thus, a more accurate LRS can be established. Finally, a field measurement experiment of ERS points in the reference system was conducted, and the results showed that the mean registration error of all ERS points was reduced from 0.058 to 0.014 mm and the standard deviation of registration error was reduced from 0.021 to 0.012 mm. Meanwhile, the measurement errors of each measuring station were also greatly reduced.

Abstract: 3D measurement plays an important role in the processing and assembling of large components in the aviation and aerospace industry. However, precision control is a challenging problem due to the complex on-site illumination environment and serious background interference. For the binocular stereovision measurement system based on auxiliary laser scanning, this paper proposes an extraction method of laser stripe for 3D reconstruction. First, an evaluation method for the laser stripe is proposed by analyzing the features of the stripe image. Then, a laser stripe extraction method based on self-adaptive threshold is proposed. To further improve the efficiency of image processing, an improved Kalman filter algorithm is adopted to fast-track and locate the region of interest of laser stripes in the sequence images. Finally, measurement experiments for a large-scale aircraft panel are carried out on-site. The results show that the center extraction error is less than 0.1 pixel and 3D reconstruction error is less than 0.06 mm. The proposed methods improve the efficiency and accuracy of 3D reconstruction of large components, and the feasibility of on-site application is also verified.