今日更新:Journal of the Mechanics and Physics of Solids 1 篇,Mechanics of Materials 1 篇,Thin-Walled Structures 6 篇
Mechanical forces quench frontal polymerization: Experiments and theory
Xuanhe Li, Tal Cohen
doi:10.1016/j.jmps.2023.105517
机械力淬灭正面聚合:实验与理论
Frontal polymerization is a promising energy-saving method for rapid fabrication of polymer components with good mechanical properties. In these systems, a small energy input is sufficient to convert monomers, from a liquid or soft solid state, into a stiff polymer component. Once the reaction is initiated, it propagates as a self-sustaining front that is driven by the heat released from the reaction itself. While several studies have been proposed to capture the coupling between thermodynamics and extreme chemical kinetics in these systems, and can explain experimentally observed thermo-chemical instabilities, only few have considered the potential influence of mechanical forces that develop in these systems during fabrication. Nonetheless, some experiments do indicate that local volume changes induced by the competing effects of thermal expansion and chemical shrinkage, can lead to significant deformation or even failure in the resulting component. In this work, we present a unique experimental approach to elucidate the effect of mechanics on the propagation. Our experiments reveal that residual stresses that arise in frontal polymerization are not only a potential cause of undesired deformations in polymer products, but can also quench the reaction front. This thermo-chemo-mechanically coupled effect is captured by our theoretical model, which explains the mechanical limitations on frontal polymerization and can guide future fabrication. Overall, the findings of this work suggest that mechanical coupling needs to be taken into consideration to enable industrial applications of frontal polymerization at large scales.
正面聚合是一种快速制备具有良好力学性能的聚合物构件的节能方法。在这些系统中,一个小的能量输入就足以将单体从液体或软固体状态转化为坚硬的聚合物组分。一旦反应开始,它就像一个由反应本身释放的热量驱动的自我维持的锋面一样传播。虽然已经提出了一些研究来捕捉这些系统中热力学和极端化学动力学之间的耦合,并且可以解释实验观察到的热化学不稳定性,但只有很少的研究考虑了在制造过程中这些系统中产生的机械力的潜在影响。尽管如此,一些实验确实表明,由热膨胀和化学收缩的竞争效应引起的局部体积变化可能导致产生的部件发生重大变形甚至破坏。在这项工作中,我们提出了一种独特的实验方法来阐明力学对传播的影响。我们的实验表明,在正面聚合中产生的残余应力不仅是聚合物产品中不期望变形的潜在原因,而且还可以淬灭反应前沿。我们的理论模型捕捉到了这种热-化学-机械耦合效应,这解释了正面聚合的机械局限性,并可以指导未来的制造。总的来说,这项工作的发现表明,需要考虑机械耦合,以实现大规模正面聚合的工业应用。
Metamaterial invisibility of a corner target with proportional integral active control
Jing-Wei Jiang, Yi-Ze Wang
doi:10.1016/j.mechmat.2023.104883
比例积分主动控制拐角目标的超材料不可见性
Wave invisibility in confined space has been proved practical significance in mechanical engineering and military fields. In this work, a flexural wave cloak of a corner-domain target in a metamaterial plate with proportional integral (PI) active control circuit is proposed. According to the double reflection principle and mechanical characteristic at the boundary, wave fields for a corner-domain target are defined as a collection of incident, scattering and three mirror domains. The unknown scattering mode coefficients are determined by the image method and boundary conditions. The dynamic stress concentration, scattering amplitude and scattering cross-section for the corner-domain target are obtained. The cloaking configuration is composed of multiple equally spaced concentric layers, which are filled with piezoelectric (PZT) patches. In addition, these PZT patches are connected to the active control circuit with proportional integral (PI) control module. The results indicate that the flexural wave cloak can reduce the dynamic stress concentration, scattering amplitude and scattering cross-section in corner domain. Compared to the original structure without PI active control, the effective frequency range of the active cloak can be extended by 20%.
密闭空间波隐身技术在机械工程和军事领域具有重要的现实意义。本文提出了一种基于比例积分有源控制电路的超材料板角域目标的弯曲波斗篷。根据双反射原理和边界处的力学特性,将角域目标的波场定义为入射域、散射域和三个镜像域的集 合。利用图像法和边界条件确定了未知的散射模式系数。得到了角域目标的动应力集中、散射幅值和散射截面。该隐形结构由多个等间距的同心层组成,其中填充了压电片。此外,这些PZT贴片与比例积分(PI)控制模块连接到有源控制电路。结果表明,弯曲波包覆可以减小角域的动应力集中、散射幅值和散射截面。与无PI主动控制的原结构相比,该主动斗篷的有效频率范围可延长20%。
Generalized Rayleigh waves in a multi-layered structure of porous piezoelectric materials overlying a functionally graded porous piezoelectric base
Anil K. Vashishth, Vishakha Gupta, Umang Bareja
doi:10.1016/j.tws.2023.111448
多孔压电材料多层结构中的广义瑞利波覆盖在功能梯度多孔压电基上
Functionally graded materials (FGM) are materials in which there is a gradual variation in functional properties of the material so as to make it useful for different purposes. The life span and efficiency of Surface Acoustic Waves (SAW) devices can be increased by taking FGM into consideration. Further, FGM as a substrate can help to improve the structural integrity of a component or device. FGM substrates offer flexibility in design, enabling engineers to tailor the substrate’s characteristics for specific functions within a device or system. Rayleigh-type surface waves, known for their numerous advantageous attributes, find extensive applications in various functional devices, and Rayleigh waves in functionally graded porous piezoelectric medium have not been studied so far and for more accurate simulation of field conditions, porous layers should be taken into account when determining the excitation and propagation processes of Rayleigh surface waves. Taking these considerations into account, this paper introduces a new model of composites of ‘n’ porous piezoelectric layers over functionally graded porous piezoelectric half-space (FGPPHS) and different characteristics of generalized Rayleigh waves in this model are studied. The material properties of the FGPPHS are taken to vary along the vertical direction (thickness). Closed form frequency equations are obtained for electrically short and open boundaries. Computing the model numerically, the impacts of gradation and wavenumber on the phase velocity and group velocity of generalized Rayleigh waves are examined. Also, lateral and vertical fluctuations of the electric potentials, stresses, mechanical displacements and electrical displacements are depicted by plotting 3D surface and contour graphs. In acoustic devices, a crucial measure that reflects the impact of piezoelectricity on wave phase velocity is the electromechanical coupling factor, therefore, the numerical analysis in terms of the electromechanical coupling factor is done and it is observed that the gradation coefficient can be adjusted to produce fairly high electromechanical coupling factor for the structure at a particular wave number. Numerical results are presented for alternating layers of Barium Titanate Crystal, PZT-5H, and PZT-7H and it is found that phase velocity decreases as the number of porous piezoelectric layers above FGPPHS increases for a particular wavenumber. The particle motion, in the layers and the half-space, is also determined and is found to be elliptic, in general, but its eccentricity changes with layer to FGPPHS and with depth. The outcome of the study provides a deeper understanding of the nature of generalized Rayleigh wave propagation in non-homogeneous functionally graded porous materials and may find applications in designing high performance SAW devices and also in the optimization of Rayleigh wave based devices for engineering applications.
功能梯度材料(FGM)是一种材料的功能特性逐渐变化,从而使其可用于不同目的的材料。考虑女性生殖器切割可以提高表面声波(SAW)器件的寿命和效率。此外,FGM作为衬底可以帮助提高组件或器件的结构完整性。FGM基板在设计上具有灵活性,使工程师能够根据器件或系统中的特定功能定制基板的特性。瑞利型表面波以其众多的优势属性在各种功能器件中得到了广泛的应用,而瑞利波在功能梯度多孔压电介质中的应用至今尚未得到研究,为了更精确地模拟现场条件,在确定瑞利表面波的激发和传播过程时应考虑到多孔层。考虑到这一点,本文提出了一种基于功能梯度多孔压电半空间(FGPPHS)的“n”多孔压电层复合材料的新模型,并研究了该模型中广义瑞利波的不同特性。FGPPHS的材料性能沿垂直方向(厚度)变化。得到了电短边界和开边界的闭型频率方程。通过数值计算,考察了梯度和波数对广义瑞利波相速度和群速度的影响。此外,电势、应力、机械位移和电位移的横向和垂直波动通过绘制3D表面和等高线图来描述。在声学器件中,反映压电性对波相速度影响的关键指标是机电耦合系数,因此,本文从机电耦合系数的角度进行了数值分析,发现通过调整级配系数可以使结构在特定波数下产生较高的机电耦合系数。对钛酸钡晶体与PZT-5H和PZT-7H交替层进行了数值计算,发现在一定波数下,相速度随FGPPHS以上多孔压电层数的增加而减小。粒子在层和半空间内的运动也被确定为椭圆运动,但其偏心率随层至FGPPHS和深度的变化而变化。该研究结果为非均匀功能梯度多孔材料中广义瑞利波传播的本质提供了更深入的理解,并可能在设计高性能SAW器件以及优化基于瑞利波的工程应用器件方面找到应用。
Unveiling the Mechanics of Deep-Sea Sponge-Inspired Tubular Metamaterials: Exploring Bending, Radial, and Axial Mechanical Behavior
Zhennan Zhang, Lei Liu, Jordan Ballard, Fatih Usta, Yanyu Chen
doi:10.1016/j.tws.2023.111476
揭示深海海绵启发的管状超材料的力学:探索弯曲,径向和轴向力学行为
Strengthened tubular structures have had a significant impact on various industries. Advancements in aircraft, construction, medical implants, robotics, and renewable energy have improved safety, efficiency, and durability in multiple sectors. This section explores the practical applications of medical health, using Nasal Swabs as an example, under different loading scenarios. The study focuses on incorporating bioinspired structural elements, drawing inspiration from the skeletal lattice of sea sponges. By utilizing the sea sponge's process of trial and error in evolution, this bioinspired approach provides a promising perspective on enhancing the mechanical performance of tubular structures. To evaluate the mechanical advantages of the bioinspired design approach, we conducted 3-point bending, radial, and axial compression tests on 3D printed tubular lattice structures. The tests showed that the tubular structure, inspired by sponges, displayed improved bending properties and was approximately twice as stiff as traditional tubular designs. Furthermore, the sponge-inspired design exhibits significantly higher strength and toughness compared to traditional designs, with approximate improvements of 3 and 4 times, respectively. Numerical simulations revealed that these enhancements are attributed to the strengthening effect of diagonally double diagonal struts, which distribute stress evenly and allow for bending without excessive stress concentration. The bio-inspired design shows improved resistance to radial and axial loading, with approximately 1.3/3 times greater radial/axial compression stiffness compared to unreinforced designs. These improved mechanical properties of sea sponge-inspired tubular metamaterials make them suitable for a wide range of applications.
强化管状结构对各行各业产生了重大影响。飞机、建筑、医疗植入物、机器人和可再生能源的进步提高了多个领域的安全性、效率和耐用性。本节以鼻腔拭子为例,探讨医疗卫生在不同负载场景下的实际应用。该研究的重点是结合生物启发的结构元素,从海绵的骨骼晶格中汲取灵感。通过利用海绵在进化过程中的反复试验,这种受生物启发的方法为提高管状结构的机械性能提供了一个有希望的前景。为了评估生物启发设计方法的机械优势,我们对3D打印的管状晶格结构进行了三点弯曲、径向和轴向压缩测试。试验表明,受海绵启发的管状结构显示出更好的弯曲性能,并且刚度大约是传统管状设计的两倍。此外,与传统设计相比,海绵设计的强度和韧性显著提高,分别提高了约3倍和4倍。数值模拟表明,这些增强是由于对角双对角支柱的强化作用,它均匀分布应力,允许弯曲而不会过度集中应力。仿生设计提高了抗径向和轴向载荷的能力,与未加固设计相比,径向/轴向压缩刚度提高了1.3/3倍。海绵启发的管状超材料的这些改进的机械性能使它们适用于广泛的应用。
Nonlinear Vibration of the Sandwich Beam with Auxetic Honeycomb Core under Thermal Shock
P.Q. Li, K.F. Wang, B.L. Wang
doi:10.1016/j.tws.2023.111479
热冲击作用下蜂窝芯夹层梁的非线性振动
The nonlinear thermally induced vibration (TIV) characteristics of sandwich beams with auxetic honeycomb cores under general boundary conditions are studied. Based on first-order shear deformation theory, the dynamic governing equations are obtained through Hamilton principle, in which geometric nonlinearity and temperature dependence are considered. The temperature field along the thickness is calculated by finite element method and nonlinear TIV responses are solved via Newton-Raphson-Newmark method. The effects of temperature dependency, thermal shock forms, geometric nonlinearity, thicknesses of beam and face-sheet, boundaries and honeycomb geometrical parameters are studied. Results show that the reduction of the absolute inclined angle of the auxetic honeycomb can weaken the TIV responses. The influence of geometric nonlinearity on quasi-static and dynamic responses depends on the thermal shock form. Thermal buckling is the necessary condition for the occurrence of the TIV in clamped beams with immovable ends. Moreover, the research provides some design references to suppress the TIV responses of the sandwich beam with auxetic honeycomb core.
研究了一般边界条件下蜂窝芯夹层梁的非线性热激振动特性。基于一阶剪切变形理论,利用Hamilton原理得到了考虑几何非线性和温度依赖性的动力控制方程。采用有限元法计算了沿厚度方向的温度场,采用newton - rapson - newmark法求解了非线性TIV响应。研究了温度依赖性、热冲击形式、几何非线性、梁和面板厚度、边界和蜂窝几何参数的影响。结果表明,减小消声蜂窝的绝对倾斜角可以减弱TIV响应。几何非线性对准静态和动态响应的影响取决于热冲击的形式。热屈曲是端部不动的固支梁发生TIV的必要条件。研究结果为抑制蜂窝芯夹层梁的TIV响应提供了一定的设计参考。
Numerical investigation of cold-formed steel channels with edge-stiffened and unstiffened elongated web holes under shear
Dinesh Lakshmanan Chandramohan, Krishanu Roy, Zhiyuan Fang, G Beulah Gnana Ananthi, James B.P. Lim
doi:10.1016/j.tws.2023.111472
剪切作用下带边加筋和未加筋细长腹板孔冷弯型钢通道的数值研究
Over the past decade, cold-formed steel (CFS) channel sections having edge-stiffened circular web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened web holes, while still allowing full building service integration. In the case of shear, previous research has found that the use of edge-stiffened web holes significantly improves the shear strength of such channel sections. However, no studies are available in the literature investigating the shear strength of CFS channel sections with edge-stiffened elongated web holes. The issue is addressed herein. Non-linear finite element (FE) analyses are used to investigate the shear strength of CFS channel sections with a shear span aspect ratio of 2.0. The FE models were validated against the experimental test results of sections having unstiffened elongated web holes and edge-stiffened circular web holes; good agreement in terms of the load-displacement curves and failure behaviour was shown. Using the validated FE models, a parametric study was conducted, comprising 2,124 finite element analyses (FEA) results. The parametric results were then compared to the design predictions of the American Iron and Steel Institute (AISI 2016), and Australia/New Zealand Standards (AS/NZS 2018) and Wanniarchchi et al. (2017) for unstiffened elongated web holes, showing that the design predictions are unconservative in comparison results. Moreover, the direct strength method (DSM) approach of Pham et al. (2020a and 2023) provides conservative results for channels with unstiffened elongated web holes. It was also found that the design equations proposed by Chen et al. (2018) for edge-stiffened circular web holes were unconservative in predicting the shear strength of channels having edge-stiffened elongated web holes. Therefore, design equations in the form of a shear reduction factor and a modified DSM approach for CFS channel sections having unstiffened and edge-stiffened elongated web holes were proposed. Finally, a reliability analysis was carried out to ensure that the proposed equations are reliable to predict the shear strength of CFS channel sections with edge-stiffened and unstiffened web holes.
在过去的十年中,冷弯型钢(CFS)槽段的边缘加劲圆形腹板孔已在新西兰开发。与具有未加劲腹板孔的等效截面相比,这种边缘加劲孔增加了CFS通道截面的强度,同时仍然允许完整的建筑服务集成。在剪切的情况下,先前的研究发现,使用边加筋腹板孔可以显著提高这类通道截面的抗剪强度。然而,目前文献中还没有关于带边加劲细长腹板孔的CFS通道截面抗剪强度的研究。这里讨论这个问题。采用非线性有限元法研究了剪跨比为2.0的CFS通道截面的抗剪强度。对比未加筋细长腹板孔和边缘加筋圆形腹板孔截面的试验结果,对有限元模型进行了验证;在荷载-位移曲线和破坏行为方面表现出良好的一致性。利用验证的有限元模型,对2,124个有限元分析结果进行了参数化研究。然后,将参数化结果与美国钢铁协会(AISI 2016)、澳大利亚/新西兰标准(AS/NZS 2018)和Wanniarchchi等人(2017)对非加筋细长腹板孔的设计预测进行比较,表明设计预测在比较结果中具有非保守性。此外,Pham等人(2020a和2023)的直接强度法(DSM)方法对于具有未加筋的细长腹板孔的通道提供了保守的结果。研究还发现,Chen等人(2018)提出的边缘加劲圆形腹板孔的设计方程在预测具有边缘加劲细长腹板孔的通道的抗剪强度方面是不保守的。因此,提出了以剪切折减因子形式的设计方程和改进的DSM方法,用于具有未加筋和边加筋的细长腹板孔的CFS通道截面。最后,进行了可靠性分析,以确保所提出的方程能够可靠地预测具有边加劲和未加劲腹板孔的CFS通道截面的抗剪强度。
Modeling the joint rotational stiffness of a radial-type flight intersection joint: an analytical approach, numerical simulation, and experimental validation
R. Mohapatra, S. Palathingal, V. Narayanamurthy, M. Ramji
doi:10.1016/j.tws.2023.111473
径向型飞行交会关节转动刚度建模:解析方法、数值模拟和实验验证
Joint rotational stiffness (JRS) of a flight intersection joint (FIJ) and its accurate quantification plays an essential role in studying the dynamic modal characteristics of a flight vehicle. This JRS of a FIJ is mostly determined through elaborate experiments due to the non-availability of a reliable predictive model. Therefore, in this paper, an analytical model is proposed to evaluate JRS of a radial type FIJ when subjected to external bending moment. In this model, at first, the tensile and compressive part of the FIJ section is identified by determining the neutral axis position. The respective part's contributing stiffness is then estimated by employing a spring-mass model. Later, the JRS expression is derived from the moment equilibrium condition and expressed as a function of the stiffness of the tensile and compressive part and neutral axis position. Subsequently, finite element analysis (FEA) is conducted with different numbers of screws, followed by detailed experimental investigations. The proposed analytical model is validated with the results from FEA and experiments for different screw configurations of FIJ. Further, the proposed model is extended to account for the effect of joint clearances on the JRS and the corresponding moment-rotation characteristics of the FIJ.
飞行交节的关节转动刚度(JRS)及其精确量化是研究飞行器动态模态特性的关键。由于没有可靠的预测模型,因此FIJ的JRS主要是通过精心设计的实验来确定的。因此,本文提出了一种分析模型来评估径向型光纤接头在受外部弯矩作用下的JRS。在该模型中,首先通过确定中性轴位置来识别FIJ截面的拉伸和压缩部分。然后通过采用弹簧-质量模型估计各部分的贡献刚度。随后,由力矩平衡条件导出JRS表达式,并将其表示为拉伸、压缩部分刚度和中性轴位置的函数。随后,对不同数量螺钉进行了有限元分析,并进行了详细的实验研究。采用有限元分析和实验结果验证了该分析模型的正确性。此外,所提出的模型进行了扩展,以考虑关节间隙对JRS的影响以及FIJ的相应力矩旋转特性。
Nonlinear Forced Vibration Analysis of PFG-GPLRC Conical Shells under Parametric Excitation Considering Internal and External Resonances
Reza Saboori, Majid Ghadiri
doi:10.1016/j.tws.2023.111474
考虑内外共振的PFG-GPLRC锥形壳参数激励下的非线性强迫振动分析
Comprehending the vibration dynamics of porous functionally graded-graphene platelet reinforced composite (PFG-GPLRC) structures is vital for accurate predictions and reliability in practical applications. This study addresses gaps in nonlinear dynamics, instability, and frequency response research within truncated PFG-GPLRC conical shells under parametric loading and ½ subharmonic and 1:1 internal resonance. To achieve this, three porosity distributions in metal foam (uniform, non-uniform symmetric, and non-uniform asymmetric) are considered, along with various graphene platelet dispersion patterns (GPL-O, GPL-V, GPL-U, GPL-A, and GPL-X) within the matrix. These considerations lead to a comprehensive conical shell model. Utilizing the first-order shear deformation theory and von-Karman's assumptions, stress-strain relations are extracted, yielding nonlinear motion equations for the truncated conical shell. Employing Galerkin's method and considering simply supported boundaries, two-degree-of-freedom equations of motion are derived. The research culminates in steady state frequency responses obtained through perturbation theory and the multiple scales method, encompassing ½-subharmonic excitation resonance and 1:1 internal resonance. Bifurcation points are analysed to highlight the influence of parametric excitation and system instabilities. A parametric study underscores the significance of porosity and graphene platelets within the metal foam in relation to system instability, revealing their intricate impact on PFG-GPLRC structure behavior.
了解多孔功能梯度-石墨烯血小板增强复合材料(PFG-GPLRC)结构的振动动力学对于在实际应用中准确预测和可靠性至关重要。本研究解决了截断PFG-GPLRC锥形壳在参数加载和1 / 2次谐波和1:1内共振下的非线性动力学、不稳定性和频率响应研究的空白。为了实现这一目标,研究人员考虑了金属泡沫中的三种孔隙率分布(均匀、非均匀对称和非均匀不对称),以及基体内各种石墨烯血小板分散模式(GPL-O、GPL-V、GPL-U、GPL-A和GPL-X)。这些考虑导致了一个全面的锥形壳模型。利用一阶剪切变形理论和von-Karman假设,提取应力-应变关系,得到截顶圆锥壳的非线性运动方程。采用伽辽金法,考虑简支边界,导出了两自由度运动方程。研究最终通过微扰理论和多尺度方法获得稳态频率响应,包括1 / 2 -次谐波激励共振和1:1内共振。对分岔点进行了分析,以突出参数激励和系统不稳定性的影响。一项参数研究强调了金属泡沫中的孔隙率和石墨烯薄片对系统不稳定性的重要性,揭示了它们对PFG-GPLRC结构行为的复杂影响。