今日更新:Mechanics of Materials 1 篇,Thin-Walled Structures 4 篇
In-plane elastic waves in piezoelectric metamaterials with Parity–Time symmetry
Peng-Hui Li, Zi-Hao Miao, Yi-Ze Wang
doi:10.1016/j.mechmat.2024.105005
具有奇偶-时间对称性的压电材料中的面内弹性波
The propagation of in-plane waves in piezoelectric metamaterial involves the coupling of longitudinal (i.e. quasi–pressure), transverse (i.e. quasi–shear) and electric potential waves, which can result in different exotic phenomena. In this study, the stiffness matrix method is used to analyze the dispersion relation, which contains anomalous propagation characteristics. With the coupling of electric potential, the frequency spectrum of in–plane wave shows new characteristics. The exceptional point caused by non–Hermitian operator that does not exist before also appears when the vertical wave number is imaginary. The oblique incidence of the in–plane wave at the interface between a homogeneous medium and phononic crystal can excite multiple refraction modes which include the negative refraction. The normal mode decomposition is developed to study the in-plane incidence of piezoelectric metamaterial and then the averaged Poynting vector is applied to obtain the refraction angle. Moreover, the defect layer is introduced into the phononic crystals to study the transmission coefficients with two different symmetrical arrangements. When the balanced gain and loss are considered in the metamaterial, the Parity–Time symmetry appears and brings in pairs of exceptional points to achieve a complete transmission with a unidirectional zero reflection.
平面波在压电超材料中的传播涉及到纵波(即准压力波)、横波(即准剪切波)和电位波的耦合,从而导致不同的奇异现象。本文采用刚度矩阵法分析了包含异常传播特性的色散关系。随着电势的耦合,面内波的频谱呈现出新的特征。当纵波数为虚数时,以前不存在的非厄米算子引起的异常点也会出现。平面波在均匀介质和声子晶体界面处的斜入射可以激发包括负折射在内的多种折射模式。采用正交模态分解方法研究了压电材料的面内入射,并利用平均坡印亭矢量计算了折射角。此外,在声子晶体中引入缺陷层,研究了两种不同对称排列方式下的透射系数。当在超材料中考虑平衡增益和损耗时,奇偶-时间对称性出现并引入对异常点,从而实现单向零反射的完全传输。
Buckling strengths of Cold-Formed Built-up Cruciform Section Columns under axial compression
Jelena Dobrić, Nina Gluhović, Nenad Fric, Xiongfeng Ruan, Marina Bock, Barbara Rossi
doi:10.1016/j.tws.2024.111879
冷弯组合十字形截面柱轴压屈曲强度研究
This paper describes experiments addressing the buckling and collapse behaviour of cold-formed stainless steel cruciform section columns. Doubly symmetrical flanged cruciform section columns were built using six individual press-braked plain channels made of austenitic grade EN 1.4307 assembled back-to-back. Three different column lengths were tested – namely, short (600 mm), intermediate (1200 mm) and long (2400 mm) lengths, and two channel geometries were used in all tests – with cross-section depths of 200 mm and 100 mm. Tests were carried out under pure axial compression and with fixed end support conditions. Tests were repeated two times for each length. It was observed that the buckling patterns were affected both by the global slenderness and by the spacing between the fasteners. Stocky columns experienced local buckling of the individual channel sections. The plastic failure mechanism was dependent on the fasteners spacing. Intermediate slenderness columns were characterised by interaction between global torsional buckling and local buckling whereas more slender columns failed predominantly through torsional buckling. For the latter, the spacing between the fasteners had a minor influence on the ultimate capacity.
本文介绍了冷弯不锈钢十字形截面柱的屈曲和破坏行为的实验研究。双对称法兰十字形截面柱由6个独立的压制动平面通道组成,这些通道由奥氏体等级EN 1.4307背对背组装而成。测试了三种不同长度的柱子——即短(600毫米)、中间(1200毫米)和长(2400毫米)长度,所有测试中都使用了两种通道几何形状——横截面深度分别为200毫米和100毫米。试验是在纯轴向压缩和固定端支条件下进行的。每个长度重复测试两次。结果表明,屈曲模式受整体长细和紧固件间距的影响。粗壮柱经历了个别通道段的局部屈曲。塑性破坏机制与紧固件间距有关。中等细度柱的破坏主要是整体扭转屈曲和局部屈曲的相互作用,而较细度柱的破坏主要是扭转屈曲。对于后者,紧固件之间的间距对极限承载力的影响较小。
Improvement of interfacial thermal contact conductance and mechanical performance of metal-composite joint via controlling anchoring structures
Ziwei Feng, Xueyan Zhang, Chunlin Qin, Jianhui Su, Caiwang Tan, Hongyun Zhao, Bo Chen, Xiaoguo Song
doi:10.1016/j.tws.2024.111882
通过控制锚固结构改善金属复合材料接头的界面热接触导率和力学性能
This study discussed the interfacial heat conduction in depth during the laser welding of metal to composite by constructing rough morphologies adopting the laser ablation method. Results revealed the interface temperature was significantly elevated, reaching 375°C under a line spacing of 0.4mm, which was higher 45°C than without treatment. For one thing, the increased surface roughness reduced the heat loss and caused the heat concentration at the interface. For another thing, the expanded contact area improved the wettability and strengthened the physical adsorption, and the highest work of adhesion was increased to 49mJ/mm2, reaching 1.3 times of those without treatment. The thermal contact resistance was thus decreased, which was confirmed by finite element analysis. Finally, the maximum tensile-shear force and strength of joints were 4171N and 23MPa, which was 3.7 times and 3.9 times of those joints without treatment. Additionally, the fatigue life and anti-salty corrosion of joints were improved, providing an effective method for further application.
本文采用激光烧蚀的方法,对金属与复合材料激光焊接过程中的界面热传导进行了深入的研究。结果表明,在线间距为0.4mm时,界面温度显著升高,达到375℃,比未处理时高45℃。一方面,表面粗糙度的增加减少了热损失,引起了界面处的热集中。另一方面,接触面积的扩大提高了润湿性,增强了物理吸附,最高粘附功提高到49mJ/mm2,达到未处理的1.3倍。通过有限元分析证实了接触热阻的减小。最后,节理的最大拉剪力和强度分别为4171N和23MPa,分别是未处理节理的3.7倍和3.9倍。提高了接头的疲劳寿命和抗盐腐蚀性能,为进一步推广应用提供了有效的方法。
Coupled vibration analysis of partially liquid-filled cylindrical shells with internal horizontal plates
Songhao Chen, Yueyang Han, Xiang Zhu, Tianyun Li, Kexin Zhong
doi:10.1016/j.tws.2024.111884
内水平板部分充液圆柱壳的耦合振动分析
A semi-analytical method is proposed to analyze the coupling vibration characteristics of a partially liquid-filled cylindrical shell with an internal horizontal plate, considering the sloshing effect of the free liquid surface. Two coordinate systems are set at the midpoint of the free surface and the geometric center of the cylindrical shell's cross-section, respectively. The Flügge shell and Kirchhoff-love theories are adopted to establish the motion equations of the cylindrical shell and the plate on the structural coordinate system, respectively, in which the displacement functions are expressed with the wave propagation method. The liquid velocity potential functions are described in the symmetrical/anti-symmetrical forms based on the liquid coordinate system, which satisfies Laplace's equation. The coupling governing equations are deduced by the continuous conditions of force and displacement on the fluid-shell interface. After that, the coupling vibration responses can be solved. The accuracy of the present method is verified by the comparison with the finite element method. The influences of the structures’ parameters and liquid effect on the coupling system's free and forced vibration behaviors are discussed, and the sloshing behaviors of the internal fluid are also discussed under different parameters.
考虑自由液面晃动效应,提出了一种半解析法分析内水平板部分充液圆柱壳的耦合振动特性。在自由表面的中点和圆柱壳截面的几何中心分别设置两个坐标系。采用fl<s:1> gge壳理论和Kirchhoff-love理论分别建立了柱壳和板在结构坐标系上的运动方程,其中位移函数用波传播法表示。在满足拉普拉斯方程的液体坐标系下,以对称/反对称形式描述了液体的速度势函数。根据流壳界面上力和位移的连续条件,推导了耦合控制方程。然后求解耦合振动响应。通过与有限元法的比较,验证了该方法的准确性。讨论了结构参数和液体效应对耦合系统自由和强制振动特性的影响,并讨论了不同参数下内部流体的晃动特性。
High-frequency vibration analysis of panels under aerothermoelastic effects in supersonic airflow by an energy finite element method
Zhaolin Chen, Zhichun Yang, Yingsong Gu, Xiaochen Wang
doi:10.1016/j.tws.2024.111885
超声速气流中热弹性作用下面板高频振动的能量有限元分析
Vibration analysis of heated panels in supersonic airflow under aerothermoelastic effects has attracted wide attention, but the high-frequency vibration characteristics have not yet been thoroughly studied. A novel energy finite element method (EFEM), which can consider the aerothermoelastic effects, is proposed to investigate the high-frequency vibration response of heated panels in supersonic airflow. By separating the high-frequency response from the static or low-frequency aerothermoelastic response, a linearized high-frequency forced vibration equation is derived from the nonlinear motion equation of the panel. On this basis, the effects of in-plane and aerodynamic forces on the propagation properties of elastic waves in the panel are analyzed theoretically. By introducing these effects and the equivalent loss factors of elastic waves into EFEM theory, the energy density governing equation and the corresponding energy finite element model are established. Through numerical comparative studies, it is demonstrated that the proposed EFEM can well capture the aerothermoelastic effects and efficiently predict the high-frequency vibration response of heated panels in supersonic airflow. Particularly, the present EFEM is valid for panels in different aerothermoelastic states such as thermal buckling and flutter. In addition, the effects of aerothermoelasticity on the high-frequency vibration response are studied in detail, and the corresponding effect mechanism is revealed.
热弹性作用下加热板在超声速气流中的振动分析已引起广泛关注,但其高频振动特性尚未得到深入研究。提出了一种考虑气动热弹性效应的能量有限元方法来研究加热板在超声速气流中的高频振动响应。通过将面板的高频响应与静态或低频气动热弹性响应分离,从面板的非线性运动方程推导出线性化的高频强迫振动方程。在此基础上,从理论上分析了面内力和气动力对弹性波在面板中传播特性的影响。将弹性波的这些影响和等效损失因子引入有限元理论,建立了弹性波的能量密度控制方程和相应的能量有限元模型。数值对比研究表明,本文提出的有限元方法能够很好地捕捉到热弹性效应,并能有效地预测加热板在超声速气流中的高频振动响应。特别地,本有限元法适用于不同气动热弹性状态下的板,如热屈曲和颤振。此外,还详细研究了气动热弹性对高频振动响应的影响,揭示了其影响机理。