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Based on the long short-term memory (LSTM) neural network, an identification method is proposed to identify the support stiffness of an aero-engine at rotating state. First, the dynamic model of a whole aero-engine with nonlinear support was established. The displacement responses corresponding to different support stiffnesses at the target rotating speed were obtained. Then, the deep leaning neural network with LSTM as the core layer was established. The network was trained with the displacement responses as the inputs and the support stiffnesses as the outputs. The nonlinea relationship between the support stiffnesses and the displacement responses was constructed. Finally, the support stiffness was directly identified with the generalization of the deep leaning network. The support stiffness of an aero-engine was identified by the proposed method. Results show that the recognition error is less than 2%, and the recognition accuracy of LSTM is better than that of the radial basis function neural network and support vector machine. The proposed method can avoid the complex optimization process in inverse dynamic problems and realize the identification of dynamic parameters for complex nonlinear structures. [ABSTRACT FROM AUTHOR]

Modal parameter identification is adversely affected by the mass loading of the transducer in experiments, especially when multi-transducers are arranged on the lightweight structure. In order to remove the coupling effects of transducers on each measurement point, a hierarchical multi-transducers eliminations method based on Sherman–Morrison theory is investigated. The method consists of two steps: (1) Decomposition: multiple elimination is decomposed into multi-levels, the relationship of the frequency response functions between each level is illustrated in the tree diagram; (2) Elimination: according to the relationship between each level, the measured frequency response functions are modified level by level. Numerical simulation is conducted by employing a three-degrees-of-freedom spring-mass system and the robustness is verified in the noise case. Experimental investigations are undertaken by employing a lightweight cantilever beam: Laser Doppler vibrometer is adopted to obtain measured frequency response functions without transducer mass loading effect, which are regarded as the target data. The initial frequency response functions are obtained in the case, in which multi-accelerometers are arranged and the effects should be removed. The result shows that the method can effectively decouple the frequency response functions due to transducers. In the elimination process, it is necessary to delete duplicate information (frequency response functions), which can greatly reduce the amount of calculation. And the effects of multi-transducers mass can be removed and the corrected frequency response functions are in quite good agreement with the target values. [ABSTRACT FROM AUTHOR]

Random-vibration fatigue evaluation can be of considerable importance in the design phase of aerospace structures due to the severe dynamic loads in service. This paper presents the utilization of modal stress approach to the issue of structural random-vibration fatigue evaluation. Prognosis of random fatigue hotspots by using stress mode shapes is theoretically demonstrated. A two-step procedure is proposed for computational efficiency. Firstly, modal stress analysis is conducted to locate the fatigue hotspots in a dynamic structure. Secondly, the frequency domain-based approach for random fatigue evaluation is performed at these hotspots, as opposed to the computation of the entire structure as before. The capability of stress mode shapes to locate fatigue hotspots is verified by numerical investigations. The finite element model of a single-lap plate structure containing various opening holes was constructed for case study. Six elements were identified as hotspots by using modal stress distributions. Then, random responses and fatigue evaluation of the entire structure were carried out for verification. Good agreement was observed between the fatigue damage contour and the modal stress distributions, which can indicate that the critical positions predicted by stress mode shapes have good accuracy. The calculation time and storage space can be significantly reduced by means of the proposed evaluation procedure. Therefore, the accuracy and efficiency of utilization of modal stress approach in random fatigue evaluation can be ensured. [ABSTRACT FROM AUTHOR]

AbstractThe concept of both hierarchy and gradient are incorporated into thin-walled hexagonal tubes for a configuration with optimum crashworthiness and energy absorption. Graded hierarchical hexagonal (GHH) tubes are developed by replacing the corners of an original hexagonal tube with a series of micro hexagonal cells. The total net cross-sectional area as well as the mass are kept the same for all the GHH tubes. The axial crushing behavior of the GHH tubes is investigated in terms of deformation modes, crushing forces and energy absorption. Theoretical solutions are also derived to predict the mean crushing forces (MCFs) of the GHH tubes. Two deformation modes have been identified, a locally layer-by-layer folding deformation (Mode-L) and a globally buckling-like deformation (Mode-G). The hierarchical and graded parameters have significant but quite different influences on the crushing behavior of GHH tubes. The MCF and the specific energy absorption (SEA) can be significantly improved with reasonably hierarchical and graded arrangements, while the initial peak force (PF) remains almost constant. [ABSTRACT FROM AUTHOR]

Maneuverability is one of the important tactical and technical indexes of fighter aircraft. In this paper, the finite element method is used to establish a dynamic model of the rotor system that can consider arbitrary maneuvering flight form and rotor speed variation during the flight, and the vibration characteristic of the dynamic model is investigated in detail. In addition, the nonlinear forces caused by bearings and oil film are also considered. The Newmark-β method combined with Newton-Raphson method is adopted to solve the dynamic equations. The influences of speed variation, rolling, pitching, and yawing maneuver loads on the vibration responses of the rotor system are also evaluated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fatigue life at 600 °C was found to be approximately nine times higher than at 420 °C under identical stress conditions. • Multiple dynamic recrystallization (DRX) mechanisms, including continuous (CDRX) and discontinuous (DDRX), were identified. • Demonstrated that variation in fatigue life is attributed to different dominant DRX mechanisms at varying temperatures. High temperature low cycle fatigue (LCF) tests were conducted on the FGH95 nickel-based superalloy at temperatures of 420 °C and 600 °C. The experimental results indicate that the fatigue life of the FGH95 alloy at 600 °C is approximately nine times higher than that at 420 °C under identical stress conditions. This finding differs from the conclusions of previous studies on the effect of temperature on fatigue life. The microstructure of the alloy was characterised, and it was found that there were multiple dynamic recrystallisation (DRX) mechanisms present. Continuous dynamic recrystallisation (CDRX) and discontinuous dynamic recrystallisation (DDRX) were identified as the dominant mechanisms at different temperatures. These different dominant mechanisms contributed to the variation in the fatigue life of the alloys under different temperature conditions at the same stress level. [ABSTRACT FROM AUTHOR]

• The evolution mechanisms of out-of-plane performance in C/SiC riveted joint are demonstrated. • The refined simulation model considering deposited SiC matrix, mesoscale structural characteristics and interference fit is established. • The thermos-mechanical coupling effects on failure mechanisms of C/SiC riveted joints are illustrated by experiments and simulations. • Significant factors affecting jointed performance including deposition of SiC matrix and interference fit are revealed. The failure mechanisms of C/SiC riveted joints are complicated and unclear under thermo-mechanical coupling loading. This work numerically and experimentally examines the mechanical responses, failure evolutions and damage modes of C/SiC riveted joints subjected to push-out loading at room temperature and 800 ℃. The typical C/SiC riveted joints are fabricated by integrated manufacturing techniques based on CVI process, which are then adopted for push-out experiments through the combined mechanical and thermal loading system. To fully reveal the thermo-mechanical coupling damage mechanisms, a refined finite element (FE) model is established, considering deposited SiC matrix, structural characteristics of C/SiC composites and interference fit. The comprehensive results from FE model and experiments indicate the bearing capacity of C/SiC riveted joints could maintain within a certain deformation range even under broken interface between rivet and plate, which benefits from the designed interference fit. Furthermore, significant temperature-dependent mechanical responses and damage modes are observed and analyzed. This work could potentially provide the basis for designing reliable hot structures made of ceramic matrix composite. [ABSTRACT FROM AUTHOR]

• The unbalance responses of the rotor system are used to update the FE model. • Gaussian process (GP) model is used to describe the mapping relationship between the selected parameters and fusion features. • An adaptive sampling strategy is developed to reduce the computation cost of repeated finite element (FE) calculation. • Multi-channel data fusion is adopted to construct the objective function of the model updating. • The unbalance responses at different rotating speeds of the updated model are both close to the measured responses. • The modal frequencies of the updated FE model at different rotating speeds are both close to the measured model. For predicting the dynamic responses of rotor system with high accuracy, an adaptive Gaussian process model-based model updating method for rotor system using the unbalance responses is proposed. To utilize the data from multiple sensors, multi-channel data fusion is adopted to construct the objective function of the model updating. The fusion feature is the mean of the cumulative distribution function of the response errors of each channel. The Gaussian process model is used to describe the mapping relationship between the selected parameters and fusion features. An adaptive sampling strategy is developed to reduce the computation cost of repeated finite element calculation. Based on Sobol sequence sampling, new sampling parameters are added near the sample parameter with a larger error in the predicted value. The performance of the proposed method is validated by a gas-generator rotor and a dual-disks rotor. Results show that the unbalance responses of the updated model show good agreement with the exact responses and measured responses. The maximum error of the support parameters for the gas-generator rotor is 3.56%. For the dual-disks rotor, the discrepancies of the first three modal frequencies between the updated model and the measured model are below 1%, 2.5% and 5%. The proposed method is effective for model updating of the rotor system. [ABSTRACT FROM AUTHOR]

The residual stress generated from temperature changes and interference fit of rivet plays a significant role in the performance of C/SiC composites. To gain a thorough understanding of the residual stress evolution mechanisms and their influences on C/SiC composites, this work carries out comprehensive experimental research combined with simulation analyzes. The results of quasi-static tension tests present that as the environmental temperature rises from room temperature to 800 °C, the stiffness of structure increases a lot, while the strength of riveted joints significantly decreases. Furthermore, it is found that the microscopic failure modes are also changed. The cyclic unloading-reloading tests for calculating the residual stress quantitatively are conducted to explain the failure evolutions of structures. The obtained results reveal an important connection between the residual stress states and the microscopic failure modes of C/SiC composites. The environmental temperature and interference riveted joint both can affect stress state around the open hole, which are significant factors determining the damage modes and structural performance. In the process of C/SiC composites design, it is necessary to pay attention to the processing parameters of rivet interference fit to meet the performance optimization under service conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Wave Based Method (WBM) is an efficient method to analyze mid-frequency dynamic problems. This work extended the WBM to the transverse vibration analysis of a thermal beam with limited uncertain information. Novel wave functions and particular solution function for the thermal beam with deterministic parameters are derived to obtain the dynamic response. Then, by employing the interval perturbation method and sub-interval decomposition technique, the Sub-Interval Perturbation Wave Based Method (SIPWBM) is developed to analyze the uncertain propagation in thermal beams for the first time. Numerical simulations for thermal beams with deterministic parameters and interval parameters are conducted, respectively. The impacts of different thermal effects on deterministic dynamic response are investigated. Simulation results prove that the developed WBM could accurately predict the low- and mid-frequency transverse dynamic response of the thermal beam with deterministic parameters. The thermal stress effect plays a leading role in the low-frequency displacement frequency responses for beams under low-level temperature load. Whereas it is necessary to consider both the temperature-dependent material property effect and thermal stress effect in the mid-frequency transverse vibration analysis of thermal beams. By using the sub-interval decomposition technique and choosing a suitable sub-interval number, the SIPWBM could predict the bounds of the mid-frequency interval dynamic response accurately and efficiently. [ABSTRACT FROM AUTHOR]

The nonlinear behavior of the airfoil-store system introduces complexity to its mechanical characteristics, making it essential to identify the system's nonlinear features. This study presents a novel nonlinear subspace identification approach in combination with an aerodynamic force. Based on the dynamic modeling of the airfoil storage system with random force, a linear elastic contribution related to the wind speed is introduced to two sides of motion equations, thereby transforming the original asymmetric linearity into the symmetric stiffness. A nonlinear state-space representation of the airfoil-store system is established, and the nonlinear parameters are identified by the proposed approach. Simulation examples are conducted considering different levels of nonlinearity, measurement noise, and flow speeds. The results demonstrate that the proposed method exhibits strong flexibility and robustness across various wind speeds in the airfoil-store system. It effectively identifies nonlinear stiffness, nonlinear damping, and various types of nonlinearity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A reliability-guided frequency-domain-based digital image correlation method is proposed to solve the low computational efficiency caused by the amount of vibration collected data. • This method combines the advantages of a reliability-guided strategy and an integer-pixel search method based on the frequency domain to ensure that the seed point with the best matching effect in the calculation area is selected. • A multi-camera array system is established to obtain full-field modal anaysis. • The modal test of a solar panel is carried out by building four cameras system, which verifies the correctness of the proposed method and has certain engineering significance. A multi-camera array system was established to address the limitations of traditional measurement methods in full-field modal measurement. According to the principle of binocular vision, two cameras are utilized to form a set of three-dimensional measurement subsystems, and the subsystems are calibrated to establish unity in coordinates. To improve computational efficiency, a reliability-guided frequency-domain-based digital image correlation method is proposed to optimize pixel matching and calculation path. This method incorporates the benefits of a reliability-guided strategy and an integer-pixel search method based on the frequency domain to ensure that the seed point with the optimal matching effect in the calculation area is selected. The zero-mean normalized cross-correlation coefficient is used as the criterion for determining reliability. This approach effectively avoids the problem of error transmission and reduces the need for complex operations and repeated searches in the spatial domain, thus improving computational efficiency. The matching time is reduced, the calculation efficiency of displacement signal extraction under large data volume is improved, and the obtained response signal is substituted into the modal identification algorithm to obtain the modal parameters of the structure. Ultimately, the modal test of a solar panel is performed by constructing a four-camera system, which verifies the correctness of the proposed method and has practical engineering significance. [ABSTRACT FROM AUTHOR]