Labyrinthine ventilated acoustic metamaterials (LVAMs) offer great potential for applications requiring both strong sound insulation and efficient airflow, yet simultaneously optimizing these conflicting objectives remains a fundamental challenge. Unlike previous studies that directly regress the sound transmission loss (STL), this work introduces a novel deep-learning-assisted, transfer-matrix-based framework, enabling analytical STL computation for arbitrary serial combinations of unit cells. A forward predictor network (FPN) is trained to predict the four components of the transfer matrix for a single unit cell, enabling analytical computation of the STL of arbitrary serial combinations of unit cells. To enhance robustness, a peak-softening preprocessing strategy and a value-weighted loss function are introduced, yielding predictions that better align with experimentally realizable performance. The FPN is integrated with the NSGA-II algorithm to jointly optimize STL and ventilation capacity, quantified by the open area ratio, thereby obtaining Pareto-optimal designs that balance these objectives. Numerical studies demonstrate the scalability and flexibility of the proposed method across various frequency ranges and STL thresholds. Experimental validation of 3D-printed prototypes confirms close agreement between predictions, simulations, and measurements, with the proposed framework outperforming direct STL prediction, particularly near resonance frequencies. This work highlights the potential of using intermediate physical representations in deep-learning-assisted optimization of multifunctional acoustic metamaterials.

Labyrinthine ventilated acoustic metamaterials (LVAMs) enable simultaneous sound insulation and air ventilation but remain difficult to design due to their geometric complexity. This study develops a surrogate-guided inverse design framework for LVAMs with target phononic bandgaps. A parametric LVAM model is constructed, and a large finite element dataset is generated to link geometry with band structure. The framework integrates a finite-element-trained forward predictor with an inverse generator, allowing feasible designs to be directly generated from target bandgaps without repeated simulations during inverse training. Numerical and experimental results show high design accuracy, with R2=0.9975 and 0.9908 for the lower and upper bandgap bounds, respectively, surpassing a baseline inverse model. The results demonstrate that the proposed framework provides an efficient surrogate-guided approach for the parametric inverse design of complex acoustic metamaterials.

Negative Poisson's Ratio (NPR) structures have attracted considerable attention in impact protection and energy absorption applications. However, many existing NPR designs rely on complex geometries and additive manufacturing, which limits their large-scale engineering applications. In this study, a self-locking NPR energyabsorbing structure inspired by the conventional re-entrant honeycomb configuration is proposed and fabricated using a sheet-based manufacturing process. The mechanical response and deformation mechanisms of both the internal unit cell and the assembled structure are systematically investigated through theoretical modeling, finite element simulations, and quasi-static compression experiments. The results demonstrate that the proposed structure exhibits a significant NPR effect, and a stable self-locking mechanism is gradually formed during compression. The theoretical model based on plastic hinge theory accurately predicts the plateau stress of the internal cell, showing good consistency with experimental and numerical results. Parametric studies reveal that increasing the cell wall thickness and the hypotenuse angle significantly enhances the specific energy absorption of the structure. In addition, topology optimization improves material utilization by redistributing regions with low energy absorption contribution. The proposed structure provides a feasible design strategy for developing lightweight, low-cost, and high-efficiency energy-absorbing systems.

Quasi-zero stiffness (QZS) vibration isolators are widely used in low-frequency applications for their superior vibration attenuation. However, strong nonlinearity leads to complex, non-Gaussian steady-state responses, particularly near resonance, challenging conventional uncertainty quantification (UQ) methods. In this study, a Mixture Density Network (MDN) is introduced to the UQ of QZS systems, enabling direct learning of the conditional probability distribution of the steady-state peak displacement response given uncertain input parameters. This approach accurately predicts response distributions across the full frequency range while requiring approximately 15

Faithful replication of far-field pyroshock environments is essential for the qualification of aerospace systems in system-level testing. Electrodynamic shakers are well-suited for this purpose because of their controllability and cost-effectiveness. Current shaker testing practices, however, are largely limited to matching the shock response spectrum (SRS) at a single control point. This single-point approach can lead to significant distortion at other critical response points within the integrated structure, thereby compromising the validity of the system-level qualification. To address this system-level fidelity challenge, this paper introduces a multi-location compatibility assessment framework specifically designed for shaker-based pyroshock testing. The framework enables a priori quantitative evaluation of multi-point reproducibility, via a compatibility matrix, of the feasibility of simultaneously replicating the multi-point environment. Furthermore, the framework provides a systematic methodology to identify an optimal set of target response points and determine the corresponding optimal shaker shock loads. A numerical study on a representative aerospace nested structure demonstrates that the framework effectively guides the successful, simultaneous replication of the far-field pyroshock environment across all target response points. This approach transforms test design from a single-point, trial-and-error practice into a predictive and optimized process.

Existing nonlinear model updating predominantly relies on a constant-force level swept frequency test, which captures only stable solutions. Recently, shaker voltage-based fixed frequency continuation has been proposed as an experimental method capable of acquiring unstable responses without additional feedback devices. However, current research has not thoroughly investigated its underlying dynamical mechanisms, treating it merely as an experimental technique with limited unstable solution regions. To probe the deeper principles of shaker voltage-based fixed-frequency continuation and expand its applicability, this paper proposes a stability-switch analysis framework. This framework enables quantitative analysis of this continuation method and enhances optimization efficiency. Virtual testing is conducted on a single-degree-of-freedom (SDOF) system with nonlinear stiffness coupled to a shaker, replicating fixed frequency voltage continuation. The coupled system exhibits a characteristic force drop-out phenomena and is validated against published experimental literature, showing excellent agreement with published experimental trends. Subsequently, stability-switch analysis elucidates stability differences and connections between the shaker-coupled system and the SDOF system. Crucially, this study reveals that adjusting stinger stiffness expands the range of force levels over which multi-valued responses are all stable in the SDOF system. This adjustment transforms previously unstable responses into stable states. Under these conditions, new force jump and force drop-out phenomena emerge during voltage continuation. This research provides valuable references for designing nonlinear dynamic experiments.

Aerospace structures operating in wide-temperature environments are frequently subjected to coupled thermal and vibrational loads, which introduce significant uncertainties into fatigue life prediction. This study investigates the cross-temperature random vibration fatigue behavior through an integrated approach of experimental testing and numerical simulation. A novel damage-equivalent stress amplitude probability density function (PDF) model is developed to account for temperature effects. By extracting statistical features from the stress power spectral density (PSD) and incorporating a temperature-dependent spectral bandwidth correction term, the model effectively captures the temperature-induced narrow-band attenuation and broad-band enhancement effects. This allows for the precise characterization of the statistical response and damage distribution variations at elevated temperatures. After validating the model's superiority in rainflow stress range PDF reconstruction and life prediction, random vibration fatigue tests were conducted on TA15 titanium alloy thin-walled structures at room temperature (RT), 300 degrees C, and 500 degrees C. Calibrated finite element (FE) model was further utilized to simulate the thermalvibrational responses under both broadband stepped and flat spectrum excitations. The results reveal that an inherent competitive coupling mechanism between stress response attenuation and material fatigue resistance degradation dictates the non-linear and non-monotonic evolution of fatigue life with increasing temperature. Compared to traditional frequency-domain models, the proposed method effectively characterizes the temperature-induced energy redistribution of structural dynamic responses, demonstrating higher predictive fidelity and robustness across the investigated temperature range. This research provides a new perspective on failure mechanisms under high-temperature random vibration and offers a reliable theoretical foundation and engineering reference for the durability design and life assessment of aerospace components in extreme environments.

This paper presents a novel bionic hexagonal conical tube with a stiffness gradient, inspired by the microstructure of horsetail stems. The structural energy dissipation mechanisms were analytically derived using the Simplified Super Folding Element (SSFE) theory. Following experimental validation, numerical simulations were employed to compare the crashworthiness of Double-Hexagonal Tubes (DHT) across varying rib topologies, establishing the edge-connected configuration (E-DHT-2) as the superior base design. A parametric study was then conducted to assess the influence of taper angle, hierarchical ratio, and wall thickness on Energy Absorption (EA). Furthermore, multi-objective optimization was executed by combining Latin Hypercube Sampling (LHS), a Kriging surrogate model, and the NSGA-II algorithm. The optimized E-DHT-2 achieved a 15.16% increase in Specific Energy Absorption (SEA) and an 8.78% reduction in Initial Peak Crushing Force (IPCF). These findings provide an effective design and optimization paradigm for advancing lightweight and high-safety structural energy absorbers.

Thin-walled tubular structures play a significant role in energy absorption owing to their lightweight nature, low cost, and high specific energy absorption, which are widely applied in crash resistance in aerospace and vehicle fields. However, the structures always denote a high initial peak force; thus, triggers have attracted tremendous attention. In this study, a chamfer trigger has been presented to decrease the peak crushing force, and a thin-walled structure has been designed to absorb energy. First, the proposed trigger has been verified by finite element analysis. Then, a square conical thin-walled multi-cell structure is designed and analyzed by experimental tests and finite element analysis. Moreover, the parametric analysis and multi-objective optimization design have been applied to figure out the influences of structural parameters on the energy-absorbing performance. Finally, a horizontal crash test has been carried out to verify the availability of the designed structure. The chamfer trigger proposed can be used in thin-walled tubular structures to decrease the initial peak force, and the designed structure can be utilized in high-speed helicopter and automotive fields.

High-temperature random vibration fatigue is a critical cause of aerospace structural failure, while obtaining high-temperature fatigue curves (S-N curves) remains time-consuming and costly. Thus, a novel and engineering-oriented estimation approach is proposed to predict fatigue strength and high-cycle S-N curves of metallic materials over a wide temperature range. The method requires only room-temperature S-N curve data and limited tensile and yield strengths at multiple temperatures, to establish a direct quantitative relationship between mechanical property degradation and fatigue behavior. The approach was validated through literature data and high-temperature random vibration fatigue tests on TA15 titanium alloy. The results confirm its accuracy and generality, demonstrating that fatigue strength decreases non-linearly with temperature and is strongly correlated with mechanical properties. The predicted high-temperature S-N curves of TA15, applied to fatigue life prediction, showed good agreement with experimental data, confirming the method’s predictive reliability. Further investigations reveal that, under high-temperature random vibration, both stress and velocity response power spectral densities shift toward lower frequencies while maintaining their overall spectral shapes. The combined effects of temperature-dependent stiffness degradation, modal damping, and excitation spectrum distribution lead to a non-monotonic variation in fatigue life with temperature. A moderate temperature rise improves fatigue life owing to higher damping, whereas further heating reduces it as stiffness degradation dominates. This paper presents an efficient, experimentally validated framework for estimating temperature-dependent S-N curves that markedly reduces high-temperature fatigue testing costs. It provides theoretical and engineering guidance for fatigue design and durability assessment of aerospace structures under thermal-vibrational coupling conditions.

Conventional uniform-thickness expansion-tube energy-absorbing structures suffer from excessively high initial peak crushing forces (IPCFs) and sub-optimal energy absorption efficiency. Inspired by the gradient stiffness characteristics of the inter node-to-node structure in Buddha’s Belly Bamboo, this study proposed an expansion-tube energy-absorbing structure design featuring a gradient stiffness. An LS-DYNA finite element simulation model was first established, validated through experimental results, and subsequently subjected to multi-objective optimization. The analysis results demonstrate that the stiffness-gradient expansion-type energy-absorbing structure designed in this study not only effectively reduces the IPCF during energy absorption but also further enhances its buffering and specific energy absorption (SEA).

In previous designs, energy-absorbing structures typically relied on plastic deformation to absorb the energy generated by impacts, which means that such structures could only be used as single-use energy absorption solutions. Therefore, the development of reusable energy-absorbing structures has become a focus of current research. Due to their unique properties, multistable mechanical metamaterials have emerged as one of the materials capable of achieving this goal. This paper proposes a snap-fit mechanical metamaterial with programmable and reusable features. The mechanical performance of the snap-fit structure is studied through theoretical and numerical simulation. The results indicate that the designed structure exhibits excellent energy absorption performance. Additionally, multi-objective optimization is conducted using the Response Surface Method and the Non-dominated Sorting Genetic Algorithm (NSGA-II), resulting in optimal design parameters obtained through the Pareto solution set. By adjusting the structural parameters, programmable design can be carried out, offering new design approaches for applications such as robotics, impact protection devices, and instrument packaging.

In practical engineering, thin plates or stiffened plates with too small thicknesses due to machining technology limits may not be scaled accurately. Therefore, independent scaling of thickness can be considered. To overcome the shortcoming of the traditional dimension systems that use a single geometric scaling factor to relate the prototype and scaled models, the DLT- Lz dimension basis is proposed, which reflects the effect of thickness on the similarity law by introducing the dimension Lz, and the similarity framework of thickness distorted thin plates in the elastic-plastic phase is established. Afterwards, we propose the loss function method based on the DLT- Lz basis to obtain optimal scaling factors directly. In order to verify the validity of the method, numerical simulations are carried out on the distorted circular thin plate and stiffened plate. With the responses of distorted models inverted by the proposed similarity law, for the circular thin plate under impulses, the displacement, stress and strain responses show good consistency with those of the prototype in the spatial and temporal fields. For the stiffened plate impacted by a hammer, distorted models are equally capable of predicting the responses of the prototype with high accuracy. The mechanism of the effect of stiffeners on temporal similarity is further revealed, and the applicability of the proposed method for thin-walled stiffened plates is demonstrated.

The quasi-zero stiffness (QZS) isolator exhibits significantly better isolation capability than traditional isolators in the low-frequency range due to its lower natural frequency in the working range. Currently, most studies on the response of QZS vibration isolators are based on a single-periodic excitation, which does not simulate realistic and complex environments well. This paper focuses on the response of QZS system under quasi-periodic (QP) excitation, establishes a dynamics model under quasi-periodic excitation for a class of classical QZS vibration isolator configurations, obtains the response of the system under quasi-periodic excitation by using the MHBM method, analyzes the effects of different structural parameters and excitation parameters on the final response of the system, and investigates the distribution of the frequency components in the response and their influence on the frequency-response curves. On this basis, the bifurcation phenomenon and chaotic motion of the QZS system under QP excitation were discussed. The results show that QP excitation makes the nonlinear response of the QZS isolator more complicated and more sensitive to the changes in parameters, especially to the changes in the external excitation amplitude. It leads to the appearance of more unstable regions before the resonance peak of the system response, which may result in chaotic motion. QP excitation also increased the force transfer rate of QZS isolators before the resonance peak and reduced the isolation frequency band, resulting in a decrease in the isolation performance of QZS isolators.

The arresting cable is one of the key factors to ensure the safe landing of carrier-based aircraft. The accurate measurement of arresting cable tension force can provide useful information for overall condition assessment of the arrested landing system. Most cable tension force estimation methods focus on fixed-length cable. However, the arresting cable will be extended from the arresting gear during arrested landing, which is a length-varying system. In this study, a new vibration-based technique for the identification of the arresting cable tension forces is proposed. First, a cable model is established and the acceleration responses for the transverse motion of the cable can be obtained. Second, the relationship between the acceleration response signal and the instantaneous frequency of the cable was derived based on the Hilbert–Huang transform (HHT). Next, a formulation specially developed for the arresting cables is used to calculate the cable force. Finally, the effectiveness of the presented methodology is demonstrated by numerical simulations, proving its potential for the estimation of the arresting cable structures.

Ensuring rotor stability is a major concern in engineering, as instabilities can lead to catastrophic failures. Existing literature shows that anisotropic boundary conditions significantly affect the parametric instability characteristics of rotors under periodical axial loads. However, there is little literature systematically analyzing the formation mechanism of parametric resonance under these boundary conditions or providing a detailed classification of the parametric instability regions. Therefore, this paper presents a comprehensive parametric instability analysis of a rotor subjected to periodic axial loads under anisotropic boundary conditions. A novel approach based on the multiple scales method is proposed to address anisotropy in the boundary conditions. Using this approach, the analytical boundaries of the parametric instability regions are derived, and a proof regarding the absence of certain parametric resonances is presented. These analytical solutions are validated by numerical results obtained from the discrete transition matrix method, which form the basis for systematically investigating the effects of anisotropy in direct or cross-coupling stiffness/damping coefficients on the rotor instability. The key scientific contributions of this work include: Deriving analytical instability boundaries, providing a more efficient alternative to purely numerical methods while maintaining high accuracy; Demonstrating the absence of parametric resonance of difference type under both isotropic or anisotropic boundary conditions; Discovering that anisotropy in stiffness coefficients can induce self-interaction within a given forward or backward whirl mode, as well as interaction between two forward or two backward whirl modes, leading to additional instability regions; Reducing anisotropy in direct damping coefficients may increase critical dynamic load coefficients, potentially enhancing rotor safety; If the cross-coupling stiffness coefficients exceed the threshold for triggering intrinsic instability, the rotor may become unstable in all operating conditions. All these findings offer insights into the stability management of rotors under various operating conditions and provide valuable guidance for designing and operating safer, more efficient rotor systems.

This research aims to seek a suitable way for analyzing the time-varying characteristics of some engineering phenomena such as the fuel consumption of flying rockets, the movement process of control rods used to regulate the reaction rate in nuclear reactors, etc. To address this problem, a simulated procedure containing modeling and response solving is proposed. A common variable cross-section pipeline with time-varying mass is designed as a practical time-varying system. A simplified segmented beam model with a moving interface is proposed to simulate the pipe's time-varying behavior. Then the Wentzel-Kramers-Brillouin (WKB)-recursive method is proposed to solve this time-varying problem. A two-segmented beam example is used to verify its computability. The computational efficiency is greatly improved in comparison with the conventional numerical integration methods. To validate this proposed procedure, numerical simulation is carried out and an experiment is specially designed and implemented. In the experiment, many cases of different rates of mass variation and excitation forces are carried out. Overall, the numerical dynamic responses match well with the experimental ones, which indicates that the proposed procedure is suitable for analyzing the system's time-varying characteristics.

In the process of developing floating reactor systems, their operation in the marine environment needs to be simulated to ensure the reliability of the safe design of nuclear reactors. Scaling test is a potential option for computer model validation by virtue of its low cost and flexibility. This study first gives the similarity law for dynamic tests of the reactor system in high-temperature environments by dimensional analysis. Then we focus on analyzing the jamming phenomenon that may occur during the similarity design process and provides a solution for realizing the contact state of the prototype in the scaled model. This study also analyzes the dynamic response of a floating reactor system under extreme operating conditions by combining numerical simulations and scaling tests. By comparing the response results predicted by the scaled model with the prototype response, it is further demonstrated that the feasibility of scaling test as an alternative to full-size test to provide a reference for realizing low-cost, accurate and safe design for reactor system.