In this article, we investigate the safe trajectory tracking control problem of the unmanned helicopter (UH) subject to multisource disturbances and actuator faults. Firstly, by transforming the trajectory tracking problem into the commands tracking in position and attitude loops, a second-order fully actuated system model of the UH is established. Secondly, a high-gain input disturbance observer and a high-order sliding mode observer are adapted to estimate the lumped disturbances in position loop, the derivatives of the attitude angle tracking errors and the lumped disturbances in the attitude loop, respectively. And then, the composite tracking controller is designed by incorporating the estimation information. Moreover, considering the impact of disturbances and obstacles in the environment on system safety, an observer-based control barrier function is developed, and the corresponding quadratic programming problem is constructed to further obtain the closed-form solution of the safety controller. Finally, numerical simulations are performed to validate the effectiveness of the proposed approach.

Conventional vulcanized rubber elastic plates used in China’s high-speed railway turnouts frequently suffer from failure modes including surface cracking, material peeling, and iron-component corrosion. These defects impair elastic functionality, amplify wheel-rail dynamic forces, and degrade ride quality. To address this issue, a refined rigid-flexible coupling dynamic model was developed to accurately investigate wheel-rail high-frequency impacts induced by uneven stiffness distribution through implementation of optimized variable integration step sizes and advanced contact algorithms incorporating flexible deformation mechanics and nonlinear damping effects. Subsequently, optimized structure of rubber blocks implement three critical innovations: a dual-stage stiffness strategy where stiffness sharply rises at 1.5 mm compression, which overcomes the inherent deficiency in fixed stiffness designs by providing initial compliance for vibration isolation followed by high rigidity for load-bearing stability; vulcanized bonding coatings critically enhancing the rubber-iron interface strength; and a recessed surface design mitigating cyclic damage through optimized stress distribution. This integrated approach achieved precise stiffness control, targeting the identified optimal transition zone stiffness at 22 kN/mm. Simulations demonstrated substantial improvements: 7.62% reduction in wheel-rail force and 27.27% decrease in vehicle vertical acceleration. Finally, 1 year of field tests confirmed zero cracking or corrosion while validating significant performance gains: 28.03% lower the average of rail vibration acceleration, a 3.49% reduction in wheel-rail forces, and controlled structural deformations (Vertical: +9.23%; Lateral: +20.59%). Overall, the proposed structural optimization approach enables more uniform stiffness transitions and reduces mechanical impacts in turnout, thereby contributing to enhanced structural durability and running safety in high-speed railway infrastructure.

Fan and compressor blades are the critical components of aircraft engine. During flight operations, aircraft engines are inherently susceptible to ingesting debris, resulting in foreign object damage (FOD) that compromises structural integrity of fan and compressor blade assemblies. Accurately evaluating blades high cycle fatigue (HCF) strength after external damage is of great scientific significance and engineering value for the maintenance free/scrapping of blades in service. Among all the available prediction models, the theory of critical distances (TCD) model shows excellent potential due to its higher accuracy and simplicity. However, the model stability is a key factor for constraining its application. In the present work, the TCD model for fatigue strength prediction of FOD specimen was further investigated, and the model stability was in-depth discussed. The fatigue limit of 3 × 10⁷ cycles for titanium aerofoil specimens after FOD was evaluated using the TCD model. A total of 18 specimens after FOD were tested under first-order bending vibration fatigue conditions. Finite element analysis was employed to investigate the first-order bending vibration modes of notched samples featuring various semi-elliptical notch geometries, allowing the determination of the critical distance through a combination of experimental data and numerical simulations. Additionally, 9 further aerofoil specimens underwent both FOD and HCF testing, with fatigue limit predictions derived from the Peterson and Neuber formula as well as the TCD approach. The results indicate that TCD model provides significantly greater predictive accuracy compared to the conventional Peterson and Neuber models. The correction factor η has little influence on the model accuracy, indicating that an arbitrary value of η can be used for model prediction as long as its geometric features and surface roughness are identical. The distribution of weight function has little influence on the model accuracy, and the constant distribution f(r) = 1 is accurate enough for the model prediction. The TCD model built in the present work demonstrates excellent stability and provides significant convenience for engineering application.

Sandwich single-phase-driven piezoelectric actuators have attracted increasing interest owing to their simple control circuits, flexible designs, and high output forces. However, there are challenges in constructing a standing-wave driving mode for sandwich single-phase-driven rotary piezoelectric actuators and in achieving bidirectional driving as well as an integrated structural and functional design, which limit their applications. To address these issues and meet the demands of the joint drive, a novel sandwich single-phase-driven rotary piezoelectric actuator is proposed in this study. The actuator stator has a beam-ring configuration, with dual rotors effectively integrated with a preload adjustment mechanism to solve the contact-warping problem of the cantilever joint and achieve an integrated structural and functional design of the joint drive. The standing-wave rotation drive and steering functions are realized through the special design of modes and unique arrangement of the upper and lower driving teeth. To reveal the dynamic characteristics of the stator, a universal electromechanical coupling dynamic model for the torsional-bending composite vibration of sandwich piezoelectric actuators was developed for the first time using the transfer matrix method, and the correctness of the dynamic model was verified using a prototype of the proposed stator. Finally, the structural design feasibility of the proposed piezoelectric actuator was verified through performance evaluation experiments on the actuator prototype. The proposed sandwich single-phase-driven rotary piezoelectric actuator lays the technical and theoretical foundations for achieving simple, fast, efficient, and precise driving and control of robotic joints.

Bismaleimide (BMI) resin, a thermosetting material with superior heat resistance, mechanical strength, and environmental stability, is widely used in aerospace applications, especially in the military aircraft and turbofan engine characterized by high temperatures. While research has extensively covered the mechanical behavior of epoxy and thermoplastic composites, the effect of temperature on the BMI-based composites remains underexplored, especially within its service temperature range. Thus, a systematic study of the effects of temperature on mechanical properties and damage patterns of carbon fiber/bismaleimide resin composites was carried out through various experiments, ranging from quasi-static to dynamic and impact resistance. The test results of mechanical response curves, visual analysis, scanning electron microscopy, ultrasonic C-Scanning and X-ray tomography indicated that high temperatures reduce the interfacial properties, leading to diminished mechanical properties. The failure strain and modulus do not vary monotonically with temperature or strain rate, while the ballistic limit increases with temperature in general. These results provide valuable reference data and significant relevance of carbon fiber/bismaleimide resin composites in the aviation field.

Aircraft engine fans and compressor blades are inevitably subject to external damage during service. It's an important work to predict the high cycle fatigue limit of foreign object damaged blades. In this paper, machining aerofoil specimens were manufactured to simulate the foreign object damaged blade, and the high cycle fatigue limit of machining foreign object damaged TC17 titanium aerofoil specimen were tested at 3 × 107 cycles, and a high cycle fatigue limit prediction model of machining foreign object damaged TC17 titanium aerofoil specimen was built based on the theory of critical distances, and compared with the Peterson model. The prediction error is 9.56 ± 6.78% for theory of critical distance model and 59.76 ± 16.93% for Peterson model. The accuracy of fatigue limit prediction on notched samples using theory of critical distance model is much higher than that of Peterson model, and the theory of critical distances method model is more efficient to evaluate the fatigue strength of notched blade.

Foreign object damage (FOD) is a critical factor that impacts the operational safety of aero-engine fan blades and is both frequent and inevitable. Therefore, it is necessary to develop an accurate high cycle fatigue (HCF) limit prediction model to enhance the reliability of assessment criteria for fan blades after FOD. Notch and residual stress are the key factors affecting HCF performance. In this paper, FOD tests were conducted to obtain notched airfoil blades and tested their HCF limits. Furthermore, the residual and vibration stress near the aerofoil blade notch were obtained by combining numerical simulation and experiments. The evolution of the residual stress was determined so that the actual stress field near the notch was accurately reconstructed, and the location of the dangerous point was obtained then, based on the theory of critical distance (TCD), an HCF limit prediction model was established and compared with the current Peterson and TCD models without considering residual stress. The results show that the TCD model considering residual stress can accurately predict the HCF limit of FOD aerofoil blades, with an error of 9.70 % +8.66 %, which is lower than the Peterson model (19.60 %+17.56 %) and the TCD model without residual stress (16.58 %+11.62 %).

Flying wing UAVs are widely used in both civil and military areas and they are vulnerable to being affected by multi-source disturbances and actuator faults due to their unique aerodynamic configuration. This paper proposes composite continuous high-order nonsingular terminal sliding mode control controllers for the longitudinal command tracking control of flying wing UAVs. The proposed method guarantees not only the finite-time convergence of command tracking errors, but also the continuity of control actions. Simulation results validate the effectiveness of the proposed method.

This paper investigates the influence of laser cladding (LC) on the phase distribution, microstructure, residual stress, microhardness, and high-cycle fatigue performance of TC17 titanium alloy. The experimental results are analyzed through microscopic characterization and fatigue tests, and the fatigue fracture mechanism is discussed. The LC process transforms the dual-phase alpha + beta material containing stable beta phase into a microstructure composed entirely of beta phases. The beta phases exhibit a coarse grain size up to 200 mu m and numerous epitaxial columnar crystals in the additive direction. Near the laser cladding zone (LCZ), residual stress is in a tensile state, while the stress in the additive region relaxes to almost 0 after 106 cycles under a load of 300 MPa, without any change in the substrate's stress. Microhardness in the substrate, heat affected zone (HAZ), and LCZ shows a slight decrease trend, with only a 5 % drop. The fatigue limit of the TC17 repaired sample (309 MPa) decreases by approximately 45 % compared to the forging material (557 MPa) after 106 cycles at a stress ratio of 0.1. However, this result (309 MPa) is over 70 % higher than that of samples damaged by foreign objects (180 MPa), indicating a significant repair effect. Fatigue fracture observations reveal that cracks originate from additive manufacturing pores, and the crack propagation rate in the LCZ is significantly higher than that in the substrate. The characteristics of dimples in the final fracture region indicate a decrease in the plasticity of TC17 titanium alloy due to the additive repair.

Cross-type piezoelectric beams (CTPBs) have been widely employed in the fields of transducers, actuators, sensors, energy harvesters, and vibration control due to their unique vibration form. However, there is still a lack of electromechanical-coupling dynamic model for describing the two-dimensional out-of-plane bending vibration of CTPBs. The main reason is that the current mathematical modeling methods cannot accurately couple the dynamical parameters of beam vibrations in both directions. To solve this problem, a novel modeling method based on the transfer matrix method (TMM) is proposed in this paper. Initially, a new discretization concept is created to discretize the intersection of CTPBs into ordinary and massless elastic beams. Subsequently, the bending-torsional hybrid vibration transfer equations for discrete sub-elements are established. Finally, by deriving the two-dimensional transfer conditions of discrete sub-elements and combining the transfer equations, an electromechanical-coupling dynamic model of CTPBs is developed. In this study, the proposed modeling method is used to establish the electromechanical-coupling dynamic models of odd- and even-order out-of-plane bending vibrations of cross beams as case studies. And the validity of the models is verified through both finite element method and experimental study. Moreover, comparison results indicate that the established models can predict the impedance characteristics of the vibrators more accurately than finite element methods. The proposed modeling method fills the gap of the semi-analytical method in analyzing the two-dimensional out-of-plane vibration characteristics of CTPBs.

In the current study, limited research has been conducted on modelling high-velocity impacts and their effect on residual strength. Though the simulation of compression after low-velocity impact are mature, these methods still have some numerical issues when utilized in the case of high-velocity impacts. Thus, a brand-new method suitable for continuous simulation of compression after high-velocity impact was implemented. As for the modelling techniques for 2DTBC, both the research on the model structure and constitutive behavior is still crude and imprecise. To address this situation, a high fidelity multiscale approach which contains a more accurate RUC model, a strain rate sensitive viscoelastic constitutive model and a novel subcell model was established. The HVI and CAI examples were conducted based on this framework and most results showed an error of less than 5% in both the simulation of impact resistance and residual performance. Also, the damage morphologies of simulated results demonstrated its capability and effectiveness.

Considering the differences in damage mechanism between high-velocity impact (HVI) and low-velocity impact (LVI), this study conducted HVI tests and compression-after-impact (CAI) tests to reveal the post-impact compression behavior of laminates manufactured by unidirectional prepreg tape and exposed a completely different mechanical response in residual strength compared to that of LVI. By controlling the impact velocity within the range of 200 m/s ̃ 380 m/s, three kinds of impact results were obtained, including un-penetrated and penetrated conditions. Different CAI damage morphologies can be observed in these laminates. In order to fully understand the CAI damage mechanism induced by different HVI events, a surface-based cohesive behavior and a CDM intralaminar damage model were implemented. In addition, a more complete picture of the compression behavior after HVI was observed through the simulation results, which is of great help in estimating the residual strength of post-impact laminates. However, the HVI damage was introduced through the spherical steel projectiles, and the sample size was determined based on ASTM D7137, which might be different factors from the application conditions.

This paper presents a composite continuous fast nonsingular terminal sliding mode (CCFNTSM) trajectory tracking control method for Mars entry vehicle. Firstly, the trajectory tracking is transferred into the tracking of the pre-designed drag acceleration. Secondly, the finite-time disturbance observer (FTDO) is introduced to estimate the matched and mismatched disturbances. And then, the dynamical fast nonsingular terminal sliding mode manifold is designed based on the estimation information. Finally, the CCFNTSM controller is constructed and its continuity is guaranteed by employing the power function of sliding variable to replace the constant switching gain. Numerical simulation results validate the effectiveness of the proposed control method.

This paper investigates the attitude control problem of quadrotor UAVs with disturbances, actuator faults and measurement noises. Firstly, to avoid the noise amplification, the attitude system is transformed into a linear decoupled system, and the influences of uncertainties (including disturbances, actuator faults and nonlinearities) are regarded as lumped disturbances. Secondly, to handle the uncertainties and noises simultaneously, the combined Kalman filter generalized proportional integral observer (KFGPIO) is introduced to estimate the filtered states and lumped disturbances. And then, a composite controller is proposed based on the estimation of KFGPIO. Simulation results validate that the proposed method achieves good disturbance rejection and fault tolerance performance and guarantees the continuity of control action even under serious measurement noises.

Fiber-reinforced thermoset polymers are widely used in aerospace as a material with excellent performance. However, for the low-velocity impact damage to which they are most susceptible, existing repair methods are difficult to maintain the aerodynamic performance of the components (back to its pre-damage shape) after repair. In this study, the multiple impact deformation recovery, internal damage healing, and post-repair impact properties of epoxy-PCL (epsilon-caprolactone) 2D carbon fiber fabric-reinforced polymers with shape memory and self-healing properties were investigated. The material is manufactured using a hot press tank-prepreg process, curing at 160 degrees C for 3.5 h at 6 atmospheres. The results show that the incorporation of thermoplastic PCL into the composite matrix can enhance the self-healing ability and impact resistance of the material. Composites after lower energy impacts retain their structural integrity and mechanical properties after healing. Materials can recover effectively from a single impact, but repeated impacts can lead to more extensive damage, which makes healing more difficult and causes a decrease in Healing efficiency. The shape memory effect of composites can restore plastic deformation caused by impact, which highlights the potential of shape memory smart composites for aerospace applications.

In this paper, to address the shortcomings of the crossing structure design based on the elastic bending center method and the lack of related research, an optimization method for high-speed turnout crossing structures was proposed based on the actual elastic deformations of point and splice rails. Based on the finite element theory, the actual loading characteristics and spatial variable section characteristics of point and splice rails were fully considered, and a refined simulation analysis model of the switching system of point and splice rails in crossing areas was established. Moreover, the elastic deformation lines of point and splice rails in the nonworking state were obtained for the first time, which were consistent with actual situations. On this basis, system optimization was performed for the connecting parts of the crossing with a movable point in a high-speed turnout. In the crossing structure simulation model, the length adjustment values of the first–sixth spacer blocks between the branch line–wing and point rails and between the mail line–wing splice rails were ≤1 mm. Moreover, the lengths of the seventh–ninth spacer blocks decreased by gradually increasing amounts, and the length of the ninth spacer block decreased the most (∼6 mm). The length of the second spacer block between the point and splice rails slightly increased, but the length of the third spacer block significantly decreased by 6 mm. The length adjustment value of the distance block between the point and splice rails was smallest (0.7 mm). The calculated optimal lengths of the connecting parts of the crossing were found to be close to the empirical values used in actual manufacturing processes, and the dimension optimization patterns were completely consistent with actual situation, which validates the proposed optimization method. Thus, the proposed method can effectively improve the coordination between rails and connecting parts in crossing areas, substantially reduce internal stresses in crossing systems, and improve their assembly performance and service life. Moreover, the proposed optimization parameters can provide valuable references for the research on next-generation high-speed turnouts (400 km/h) and for improving the designs of existing high-speed turnouts.

Epoxy resin, as a crucial constituent of aerospace-grade composites, is an important consideration in designing composites for severing service conditions in terms of the hygrothermal environment (i.e. contains both temperature and moisture). In this work, a state-of-art elastoplastic-damage constitutive model is expanded to include the hygrothermal effects which are characterized by employing a glass transition temperature Tg as a bridge. The formulation of yield and fracture strengths with respect to hygrothermal effects demonstrates a high level of mathematical consistency. The model correctly captures the plastic flow and fracture initiation behavior with hygrothermal effects, as validated through quasi-static experiments. Subsequently, the application of this hygrothermal constitutive model for an epoxy resin on micro-mechanical analysis of carbon polymer composite materials is implemented. A representative volume element (RVE) is established with a random placement of fibers. Based on the commercial software ABAQUS, different loading scenarios are applied to evaluate the mechanical response and damage evolution of the composite in different hygrothermal conditions, enabling an initial understanding of the hygrothermal effects of epoxy resins on the mechanical performance of composite materials.

In this study, an evenness improvement method for new high-speed turnout crossing areas is proposed for the development of high-speed turnout and amplification of the wheel–rail dynamic impact in the crossing areas. A dynamic analysis model of the vehicle–turnout coupling system is established. In this model, the stock and switch rails as well as the wing and point rails are independent units. These independent units are connected using spring–damper units with variable parameters to accurately simulate the wheel-load transition process and the dynamic characteristics of the turnout. On this basis, an optimized scheme is developed for point rail–wing rail matching based on the center-of-mass oscillation compensation of wheelsets, and the rationality of the optimization method is verified via dynamic simulation evaluation at a high speed. Finally, the proposed method is validated through indoor actual-scale tests. The following are the results of this study. (1) As the vehicle passed over the crossing under the existing design scheme, the center-of-mass oscillation reached an oscillation length of 1.16–1.52 mm such that lifting the wing rail alone failed to eliminate the center-of-mass oscillation of the wheelsets. This is because the point and wing rails were incorrectly matched, leading to a backward shift in the wheel-load transition, thus causing a sharp drop of the wheelsets. Together with wing rail lifting, the longitudinal slope matching of the point rail effectively retained the wheel-load transition characteristics under the existing design scheme and eliminated the center-of-mass oscillation of the wheelsets. (2) As the train passed through the turnout crossing at a high speed, the optimized scheme substantially reduced the center-of-mass oscillation of the wheelsets, wheel–rail dynamic impact, and axle-box vibration while ensuring consistency of the wheel-load transition characteristics with the existing design scheme. (3) The maximum deflection change rate of the wing rail in the assembled crossing was only 1.67 mm/m, which could not meet the requirement of the theoretical longitudinal curve, and would cause the problem of turnout sleeper lifting, affecting the precision of laying turnouts on-site. Computer numerical control machining should be used to achieve the longitudinal curve requirement of the wing rail. The iron plate thickness should be increased gradually to 0.5 mm from the #82 sleeper to the #86 sleeper. Accordingly, the amount of machining of the wing rail should be increased from 0 mm to 2 mm. At the #92–#95 sleepers, this amount of machining should be decreased from 2 mm to 0.6 mm and then increased to 2 mm. This process would accurately realize the theoretical longitudinal slope curve.

This study improves the performance of piezoelectric inertial actuators by merging the benefits of inertial and inchworm drives and proposes a flexible actuator that utilizes elliptical drive mode (EDM) and stick-slip drive mode (SDM). Employing four piezoelectric stacks as the excitation source, the actuator transforms vertical motion into lateral motion through leaf-type flexible beams. The structure design, assembly, and drive principles of the proposed actuator are presented in detail, and its flexible stator structure is optimized using the finite element method. A dynamic model is established to analyze the step characteristics under both operational modes. The actuator prototype achieves a maximum velocity of 2.89mm/s and eliminates backward motion at 90Hz frequencies. The EDM mode shows improved load capacity, while the SDM mode provides faster speeds, indicating different performance characteristics depending on the drive methods. Ultimately, we successfully applied the proposed actuator in semiconductor inspection, demonstrating its application potential. This design surpasses current piezoelectric inertial actuators in speed, load, and resolution, facilitating performance optimization without structural alterations to accommodate diverse application requirements. This research offers valuable insights into optimizing actuator performance, with potential applications in high-precision scanning and optical system tracking for atomic force microscopy.