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.

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.

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.

Dynamic force reconstruction theory has been developed for many years, generating numerous effective methods. However, the applications of engineering structures are relatively rare, owing to the difficult experiment, low accuracy and noise disturbance, among others. Aiming at the support platform structure commonly used in engineering, we propose the complete dynamic force reconstruction process based on the direct inversion method in frequency domain. The dynamic calibration methods of experiment and simulation are both analyzed in this case. In order to improve identification accuracy, the Tikhonov regularization is introduced. The results validate the reliability of our proposed method in real scenarios and the necessity of regularization method. Moreover, dynamic load identification method of structural variable stiffness is derived by the four-terminal parameter method. This work provides engineering application–a reference for the engineering of dynamic load identification technology.

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.

Abstract This paper presents an analytical solution for the free vibration of functionally graded material (FGM) sandwich plates in a thermal environment. An equivalent‐single‐layer (ESL) plate theory with four variables is used to obtain the solution. Two types of sandwich plates are examined in this study: one with FGM face sheets and a homogeneous core and the other with an FGM core and homogeneous face sheets. The governing equations of motion are derived based on Hamilton's principle and then solved using the Navier method. The results of natural frequencies of simply supported FGM sandwich plates are compared with the available solutions in the literature. The effects of volume fraction distribution, geometrical parameters, and temperature increments on the free vibration characteristics are discussed in detail.

基于含双边裂纹梁的振动行为,本文提出一种含双边呼吸式裂纹悬臂梁自由振动的理论分析方法.考虑裂纹的倾斜角度,将裂纹模块转化成悬臂梁的局部柔度;根据双边裂纹的呼吸行为,建立含双边呼吸式裂纹悬臂梁的刚度模型;采用Galerkin方法,将梁结构的振动微分方程简化为多个单自由度系统的振动微分方程组,推导含双边呼吸式裂纹梁的固有频率和振型;通过ANSYS开展含双边呼吸式裂纹悬臂梁模态的数值分析,验证本文提出的理论方法.算例分析结果表明:与张开时裂纹模型相比,呼吸式裂纹模型更加接近工程实际;裂纹的倾斜角度是影响梁结构固有频率的重要因素,而裂纹对梁结构固有振型的影响很小.

Based on the band structure theory of phononic crystals,combined with the elastic wave equation and the Bloch theorem,the dynamic equation of the unit cell is established.The band gap of star-shaped periodic grid structure with negative Poisson′s ratio is studied,including in-plane longitudinal vibration and out-of-plane bending vibration.It is found that the structure has rich band gap characteristics,and the lower frequency band gap is stable and wide.Band gaps of the two vibration modes are compared,and the influence of geometric parameters,such as the concave angle and slenderness ratio,on the equivalent elastic parameters and band gap is studied.It also analyses the vibration modes of the unit cell at the gap frequency.Results show that there is a complete band gap in which two vibrations are both suppressed.Concave angle and geometric parameters of the oblique beam are keys to the low-order band gap.The appearance of the rotating resonance mode leads to the lowest band gap.Band gap characteristics of the star-shaped periodic grid structure make it potentially valuable in engineering vibration and noise reduction.

The deep learning methods have been extensively studied in the field of dynamic load identification, due to their strong direct modeling ability between vibration response and external excitation. Dynamic load identification is a complicated inverse problem, which extremely relies on the solution of the structural model parameter. Nevertheless, the accurate computation of model parameters is always a challenge, small errors in model parameters will lead to inaccuracy of dynamic load identification. This brings various hardships to engineering applications. To achieve this problem, we propose a novel method based on a deep dilated convolution neural network (DCNN) for dynamic load identification, directly constructing the inverse model between vibration response and excitation, avoiding solving the model parameter. A dynamic load identification model, which contains two 1-D dilated convolution layers, one pooling layer, and two fully connected layers, is constructed to estimate the sinusoidal, impact, and random dynamic loads of a simply supported beam. We also appraise the anti-noise ability of the proposed method for load identification. Moreover, a vibration test is carried out to further evaluate this algorithm in the experimental aspect. Additionally, we analyze the comparison of the proposed method along with the Green kernel function method, and the dynamic system with uncertain model parameters is also analyzed. Besides, the operation of the convolution layer for response input is studied, and the applicability to different distributions of measurement points and the adaptability for frequency domain data are investigated. Ultimately, we find this method has a strong anti-noise ability due to its convolution layer, which can be regarded as a filter in dynamic load identification. Furthermore, the proposed method is of great practical for engineering applications owing to its satisfying applicability for systems with uncertain parameters, distributions of measurement points, and frequency data. All the results reveal the advantages of the identification method based on DCNN, consisting of good accuracy, reliability, and robustness. These results can be favorable for many applications.

The rotor unbalance is a major source of rotor vibrations. Rotor vibrations often produce many undesired effects like noise, wear and fatigue, etc. In this paper, we try to seek the benchmark solutions for the unbalance responses of complex rotor-bearing system. The presented approach could be seen as the extension of transfer matrix method (TMM) in some sense. For the TMM, a disk or supporting structure cut off one uniform shaft el-ement into two and someone must use the compatibility condition between these two new elements to derive the transitive matrix. However, for the presented approach, it di-rectly solves the governing equations of uniform shaft elements with consideration of the effects of disks and supporting structures. Thus, this analytical approach is advantageous in reducing the times of matrix multiplication between state matrices and field matrices. One only needs to calculate the inversion of 16 x 16 dynamic stiffness matrix to find the steady state response. It saves the computer memory and is easy to be programmed. In addition, this analytical approach avoids the problems of selecting optimal discretization mesh densities in the case of FEM applications. For arbitrary linear boundary condition, the benchmark solutions are always easy to be obtained. The numerical simulation is car-ried out and two numerical examples are given to validate the new solutions. In which the finite element method is used as the numerical approach. Simulation results show that the benchmark solutions match very well with the FEM results. The effects of anisotropy in the supporting structures on the rotor's dynamic behavior, which are observed in this work, are also in accordance with many references. This validates the benchmark solutions further.(c) 2023 Elsevier Inc. All rights reserved.

考虑振动环境中斜裂纹的呼吸行为,文中提出一种理论方法开展含呼吸式斜裂纹梁的模态和非线性振动分析.在双线性弹簧模型的基础上,建立含呼吸式斜裂纹梁的理论模型.根据虚功原理,将斜裂纹转化为梁结构的局部柔度.通过Galerkin方法,将含呼吸式斜裂纹梁的弯曲振动微分方程简化为多个单自由度系统.在方波激励作用下,采用精细积分方法的衍生格式——精细库塔法,研究裂纹倾角和裂纹尺寸对含呼吸式斜裂纹梁非线性振动响应的影响.算例表明:斜裂纹倾角是影响梁结构模态的一个重要因素,呼吸行为使得梁结构振动响应呈现非线性.含呼吸式斜裂纹梁理论模型实现斜裂纹倾角和呼吸行为的引入,与工程实际更为接近.

This work proposes a new parameter identification method based on the Wentzel-Kramers-Brillouin (WKB) approximation for slow linear time-varying (LTV) dynamic systems. The considered time period is divided into a series of short time windows. In each time window, the assumption of “short time linearly varying” parameters is employed, and a nonlinear optimization problem is solved using the WKB results for the slow LTV dynamic system. A search algorithm is developed to find the optimal solution. In the identification process, only one type of response signal (displacement, velocity or acceleration) is required. Thus, numerical differentiation or integration of the measured signal, which leads to truncation or cumulative errors in noise environment, is avoided. The accuracy and robustness of the new identification method are validated by applying it to a particular LTV system with time-varying stiffness.

This study proposes a continuous convolution method combined with memoryless nonlinear transformation for multi-input multi-output stationary non-Gaussian random vibration tests. The challenge of the multi-shaker non-Gaussian random vibration test lies in the coupling problems that are manifested in the inherent physical system and in the existence of cross-spectral densities. In the presented method, the independent stationary Gaussian random signals pass through a designed finite impulse response filter with a convolution manipulation first, and then the resulting signals are transformed to the non-Gaussian random signals by the memoryless nonlinear transformation method. The desired drive signals are obtained by the input–output relationship in the frequency domain. The finite impulse response filter is constructed by the frequency sampling technique in which the amplitude characteristics of the filter are determined by the predefined reference power spectral densities. A new monotonic nonlinear transformation function with an approximate kurtosis solution is provided. It only contains one parameter for kurtosis control both in sub-Gaussian and super-Gaussian cases. The memoryless nonlinear transformation is used to maintain the cross-spectral densities, although some distortions are introduced to the power spectra during the transformation process. The inverse system method is used to overcome the coupling problem caused by the inherent physical system. A simulation example and a triaxial vibration test are carried out, and the results indicate the validity and feasibility of the proposed method.

目的 使用简谐激励替代随机平直谱激励进行振动疲劳试验.方法 利用有限元仿真计算某典型铝合金试验件在简谐激励和随机平直谱激励下的疲劳寿命,分析2种工况下试验件寿命相等时激励的等效关系.进行一组定频激励试验和一组谱激励试验,对比试验结果,验证在某典型铝合金试验件上利用简谐激励替代随机平直谱激励进行振动疲劳试验的可行性.结果 通过试验与仿真技术,对2024-T4铝合金试验件在一定频率非共振简谐激励和随机平直谱激励作用下的振动疲劳寿命规律进行研究,得出了不同激励作用下试验件寿命相同时载荷的等效关系.结论 基于损伤等效,工程中可以使用简谐激励代替随机平直谱激励进行振动疲劳试验,从而解决了一类振动疲劳试验加载困难的问题,实现振动疲劳的试验加速.

目的 评估在下肢深静脉血栓治疗中应用阿加曲班抗凝对预防Ⅱ型肝素诱导的血小板减少症(HIT)的疗效.方法 回顾性分析2018年5月至2019年6月于南京市第一医院治疗的下肢深静脉血栓患者285例的临床资料,根据治疗初始阶段使用的抗凝药物分为阿加曲班组(n=84)和低分子肝素组(n=201),比较两组患者Ⅱ型HIT的发病率,并通过二元logistic回归分析影响Ⅱ型HIT发病的危险因素.结果 阿加曲班组Ⅱ型HIT发病率为1.2％(1/84),低分子肝素组为9.0％(18/201),差异有统计学意义(x2=5.740,P=0.017).二元logistic回归分析显示,低分子肝素抗凝相对于阿加曲班抗凝,是Ⅱ型HIT的独立危险因素(OR=7.963,95％CI:1.042-60.281,P=0.045).结论 低分子肝素抗凝相比于阿加曲班抗凝其Ⅱ型HIT发病率更高,是Ⅱ型HIT发生的独立危险因素.应用阿加曲班抗凝治疗下肢深静脉血栓,或可能预防Ⅱ型HIT的发生.

Our work investigates a tunable multilayer composite structure for applications in the area of low-frequency absorption. This acoustic device is comprised of three layers, Helmholtz cavity layer, microperforated panel layer, and the porous material layer. For the simulation and experiment in our research, the absorber can fulfill a twofold requirement: the acoustic absorption coefficient can reach near 0.8 in very low frequency (400 Hz) and the range of frequency is very wide (400–3000 Hz). In all its absorption frequency, the average of the acoustic absorption coefficient is over 0.9. Besides, the absorption coefficient can be tunable by the scalable cavity. The multilayer composite structure in our article solved the disadvantages in single material. For example, small absorption coefficient in low frequency in traditional material such as microperforated panel and porous material and narrow reduction frequency range in acoustic metamaterial such as Helmholtz cavity. The design of the composite structure in our article can have more wide application than single material. It can also give us a novel idea to produce new acoustic devices.

In order to realize the accurate prediction of the vibration fatigue life of the beam in service, a loose coupling analysis method is proposed to carry out vibration fatigue analysis of a beam with an initial crack. In modal analysis, the initial crack segment is replaced with a torsion spring, and the damping loss factor is introduced by the complex modulus of elasticity; for the simply supported beam, the inherent vibration characteristic equation of the cracked beam is derived. In vibration fatigue analysis, the interaction between the crack’s growth and vibration analysis is considered, and a loose coupling analysis method is proposed to conduct modal dynamic response and vibration fatigue analysis simultaneously. Results indicate that the crack’s relative location and depth determine the modal of the cracked beam, and crack parameters, damping loss factor and external excitation frequency are important factors for the vibration fatigue life of the beam.

拦阻索的安全性是舰载机在航母上安全着舰的关键因素之一.针对舰载机拦阻着舰过程,提出了一种通过舰载机着舰拦阻过程中机体加速度求解拦阻索张力的方法.首先,根据舰载机拦阻钩挂索后的受载情况,确定拦阻索载荷的传力路径,实现拦阻索索力的间接识别.然后,通过考虑拦阻索的弯折波特性,对索力识别方法进行了改进和优化.最后,采用多体动力学软件MSC.ADAMS建立了离散拦阻索模型,对基于加速度的索力识别方法进行了分析和验证.分析结果显示,拦阻索索力识别的平均误差可以控制在5％以内.

当多跨结构受到横向载荷产生振动时,支承与基座衔接处往往产生较大的支反力.针对该问题,以双支承的梁系统为例,基于压电换能原理,采用柱状压电陶瓷支承作为减振元件,并对其减振效果进行了理论分析.利用Hamilton原理推导了压电机电耦合边界条件下该系统的振动微分方程.结合有限元法和偏微分方程数值计算方法,对不同种类压电材料的机电耦合系统进行了模态分析和动力学响应计算.计算结果表明,压电陶瓷支承可以有效抑制多跨结构中支承传递到基座的振动和支反力.

为确保水陆两栖飞机尾翼结构的抗鸟撞性能,针对其不同结构部位提出不同的抗鸟撞设计思路.耦合SPH方法建立了尾翼结构的鸟撞数值模型,采用实验方法获得了结构铝合金材料的准静态和中低应变率拉伸实验数据以及不同冲击速度下带母材铆钉的极限拉伸载荷和极限剪切载荷数据.进一步开展了尾翼结构抗鸟撞分析,并通过鸟撞实验对数值分析结果进行验证.结果表明,针对水陆两栖飞机尾翼前缘结构提出的两种抗鸟撞设计思路合理,且具有较好的抗鸟撞性能;结构采用的3种铝合金存在较为明显的应变硬化效应,但应变率敏感性较弱;随着加载速度的增大,结构采用的4种铆钉拉伸载荷呈下降趋势,但总体幅度并不大,而剪切载荷变动较小;建立的尾翼结构鸟撞数值分析模型准确,较好预测了结构的破坏模式和鸟体冲击分散过程.