今日更新:International Journal of Solids and Structures 1 篇,Journal of the Mechanics and Physics of Solids 1 篇,Mechanics of Materials 1 篇,Thin-Walled Structures 3 篇
Design and study of novel Nested auxetic lattices with tunable and enhanced in-plane elastic properties
Antu Acharya, Anirvan DasGupta, Atul Jain
doi:10.1016/j.ijsolstr.2024.112749
设计和研究具有可调和增强面内弹性特性的新型嵌套辅助晶格
Auxetic lattices are interesting engineering materials due to Negative Poisson’s Ratio (NPR). However, auxetic lattices usually have extremely low stiffness and exhibit high anisotropy (E1/E2>>1), severely limiting their application in high-loading environments. Attempts at increasing the stiffness of lattices typically lead to a decrease in auxeticity and an increase in anisotropy. In the current study, using novel nesting strategies, modified Sinusoidal Re-entrant Honeycomb (SRH) microstructures are developed to enhance stiffness, retain the auxeticity and introduce nearly isotropic characteristics (E1/E2 ∼ 1). Different Nested n-type (n = 0, 1,2, 3 and 4) microstructures have been studied. Translation studies involving 90° and 0° oriented lattices are undertaken to find the effect of these nesting along different lengths and combinations leading to enhanced stiffness with minor loss in auxeticity. The possibility of attaining a stiffness at least 1500 % greater than the empty lattices, while retaining significant auxeticity (Poisson’s ratio < -1) has been showcased. The proposed approach can also lead to the development of lattices that exhibit nearly isotropic characteristics. The proposed approach can be realized using the state-of-art capabilities of modern 3D printers. The proposed methods and modifications are simple yet very substantial in terms of property enhancement and can be extended to almost all types of lattices.
由于具有负泊松比(NPR),磁性晶格是一种有趣的工程材料。然而,辅助晶格通常具有极低的刚度和较高的各向异性(E1/E2>>1),严重限制了其在高负载环境中的应用。提高晶格刚度的尝试通常会导致辅助性降低和各向异性增加。本研究采用新颖的嵌套策略,开发出改进的正弦再入蜂窝(SRH)微结构,以提高刚度、保留辅助性并引入近乎各向同性的特性(E1/E2 ∼ 1)。对不同的嵌套 n 型(n = 0、1、2、3 和 4)微结构进行了研究。涉及 90° 和 0° 方向晶格的平移研究旨在发现这些嵌套沿不同长度和组合的影响,从而在提高刚度的同时略微降低辅助性。结果表明,在保持显著辅助eticity(泊松比<-1)的同时,刚度比空网格至少高出 1500%。所提出的方法还可以开发出具有近乎各向同性特征的晶格。所提出的方法可以利用现代三维打印机的先进功能来实现。所提出的方法和修改虽然简单,但却能极大地提高性能,并可扩展到几乎所有类型的晶格。
Fully optimized second-order estimates for the macroscopic behavior and field statistics of particle-reinforced viscoplastic composites
Christoph Kammer, Pedro Ponte Castañeda
doi:10.1016/j.jmps.2024.105598
对颗粒增强粘塑性复合材料的宏观行为和场统计进行全面优化的二阶估算
This paper is concerned with the characterization of the macroscopic behavior and statistics for the distribution of the stress and strain-rate fields in composites consisting of random and isotropic suspensions of rigid spherical particles in a power-law viscoplastic material. For this purpose, use is made of the Fully Optimized Second-Order (FOSO) homogenization method (Ponte Castañeda, 2016) in combination with recently developed estimates (Kammer and Ponte Castañeda, 2022) for the macroscopic properties of the associated ‘linear comparison composite’ (LCC). Special attention is devoted to the method’s ability to account for the dependence of the homogenized properties of the nonlinear composite on the Lode angle (third invariant) of the applied loading. It is found that, while, for large particle volume fractions c, the effective flow stress is only weakly dependent on the Lode angle, for dilute volume fractions, the dependence on the Lode angle becomes more pronounced. In the ideally plastic limit, as c tends to zero, the effective yield stress is shown to depend linearly on c for axisymmetric shear, while this dependence becomes weaker with a non-analytic leading-order correction of O(c/ln c) for pure shear loading. This strong dependence on the Lode angle at dilute concentrations is shown to be due to significant differences in the local deformation patterns, which become strongly anisotropic and localize for pure shear conditions, but do not for axisymmetric shear. In turn, the FOSO homogenization method is able to capture the statistical features of these different deformation patterns by providing consistent estimates for the covariance tensor of the strain-rate field fluctuations in the matrix phase, which tend to become more strongly anisotropic for the pure shear case. As c increases, the shear bands are deflected by the randomly dispersed spheres leading to a more isotropic distribution of the stress and strain-rate fields, which is consistent with a weaker Lode angle effect. The estimates can also capture the effect of strong particle interactions, including the existence of a rigidity threshold where the macroscopic flow stress and field fluctuations blow up.
本文关注的是由幂律粘塑性材料中刚性球形颗粒的随机和各向同性悬浮液组成的复合材料中应力场和应变率场分布的宏观行为和统计特征。为此,我们采用了完全优化二阶(FOSO)均质化方法(Ponte Castañeda, 2016),并结合最近开发的相关 "线性比较复合材料"(LCC)宏观特性的估计值(Kammer 和 Ponte Castañeda, 2022)。特别关注的是该方法能否解释非线性复合材料的均质化特性与所施加载荷的洛德角(第三不变量)之间的关系。研究发现,当颗粒体积分数 c 较大时,有效流动应力与洛德角的关系较弱,而当颗粒体积分数较小时,与洛德角的关系则更为明显。在理想塑性极限中,当 c 趋近于零时,对于轴对称剪切,有效屈服应力与 c 呈线性关系,而对于纯剪切加载,这种依赖性在 O(c/ln c)的非解析前阶修正下变得更弱。稀释浓度下对 Lode 角的这种强烈依赖性被证明是由于局部变形模式的显著差异造成的,在纯剪切条件下,局部变形变得强烈各向异性,而在轴对称剪切条件下则不然。反过来,FOSO 均质化方法能够捕捉到这些不同变形模式的统计特征,为矩阵相中应变率场波动的协方差张量提供一致的估计值,而在纯剪切情况下,这些应变率场波动往往变得更加强烈各向异性。随着 c 的增大,剪切带被随机分散的球体偏转,导致应力场和应变率场的分布更加各向同性,这与较弱的洛德角效应相一致。估计值还能捕捉到强粒子相互作用的影响,包括存在一个刚性阈值,在该阈值下宏观流动应力和场波动会爆发。
Explicating tensile response of AA6061-T6 sheet post single point incremental forming: Two camera-DIC strain measurement and texture analysis
Mohit Sharma, Anirban Bhattacharya, Surajit Kumar Paul
doi:10.1016/j.mechmat.2024.104963
解释单点增量成形后 AA6061-T6 板材的拉伸响应:双摄像头-DIC 应变测量和纹理分析
Incremental sheet forming (ISF) produces 3D components imposing localized deformation by spherical-ended tool moving on a predefined path without requiring component-specific die/punch. The formability achieved in ISF is much higher than the conventional sheet forming processes; however, the deformation imposed during ISF alters the mechanical properties of the component. The present work investigates the tensile behavior and strain localization during the uniaxial tensile test of the AA6061-T6 component after single point incremental forming (SPIF). The influence of incremental depth (Δz) and tool diameter (dt) on the tensile response and strain localization is illustrated by a digital image correlation setup with two cameras. The tensile strength of SPIF components increases with Δz and mildly decreases with dt. The changes in scallop heights/undulations formed due to tool movement at higher Δz and dt influence the localized strain accumulation. Regions of localized strain are more when Δz is high, but strain accumulation is more even with an increase in dt. Texture analysis showed increased dislocation density due to the strain hardening after SPIF. The presence of brass {011}<211>, copper {112}<111>, and S {123}<634> texture indicates the plane-strain deformation in the wall region of the component formed by SPIF.
增量式板材成形(ISF)通过在预定路径上移动的球形端部工具施加局部变形来生产三维部件,而无需特定的部件模具/冲头。ISF 所实现的成型性远远高于传统的板材成型工艺;然而,ISF 过程中施加的变形会改变部件的机械性能。本研究对单点增量成形(SPIF)后的 AA6061-T6 部件进行单轴拉伸试验时的拉伸行为和应变定位进行了研究。通过使用两台相机的数字图像相关装置,说明了增量深度(Δz)和工具直径(dt)对拉伸响应和应变定位的影响。SPIF 组件的拉伸强度随 Δz 增大,随 dt 减小。在较高的 Δz 和 dt 条件下,由于工具移动而形成的扇贝高度/凹陷的变化会影响局部应变的累积。当 Δz 较高时,局部应变区域较多,但随着 dt 的增加,应变累积更为均匀。纹理分析表明,由于 SPIF 后的应变硬化,位错密度增加。黄铜{011}<211>、铜{112}<111>和S{123}<634>纹理的存在表明 SPIF 所形成的部件壁区存在平面应变变形。
Linear active disturbance rejection control algorithm for active vibration control of piezo-actuated beams: theoretical and experimental studies
Xian Guang Sun, Wei Chao Chi, Yan Qing Wang
doi:10.1016/j.tws.2024.111782
压动梁主动振动控制的线性主动干扰抑制控制算法:理论与实验研究
The active vibration control (AVC) of lightweight thin-walled structures on spacecraft has been a proven solution for vibration suppression. In this study, a linear active disturbance rejection control (LADRC) algorithm is presented for vibration suppression of piezo-actuated beams. Firstly, the governing equation of a piezo-actuated beam is obtained by using the Euler-Bernoulli beam theory and the Lagrange equation. The LADRC algorithm is designed for the piezo-actuated beam based on the governing equation. Then, the accuracy of the piezo-actuated beam model is confirmed by comparison with ANSYS and experiments. Finally, numerical simulations and experiments are carried out on the active vibration suppression of the piezo-actuated beam under the fixed harmonic excitation, variable harmonic excitation, and fixed harmonic excitation with measuring noise, respectively. The results show that the LADRC algorithm has an excellent control effect on structural vibration suppression, strong adaptability to various external excitations, and anti-noise ability.
航天器轻质薄壁结构的主动振动控制(AVC)是一种行之有效的振动抑制解决方案。本研究针对压动梁的振动抑制提出了一种线性主动干扰抑制控制(LADRC)算法。首先,利用欧拉-伯努利梁理论和拉格朗日方程得到压动梁的支配方程。根据支配方程设计了压动梁的 LADRC 算法。然后,通过与 ANSYS 和实验的对比,确认了压动梁模型的准确性。最后,分别对固定谐波激励、可变谐波激励和带测量噪声的固定谐波激励下压动梁的主动振动抑制进行了数值模拟和实验。结果表明,LADRC 算法对结构振动抑制具有良好的控制效果,对各种外部激励具有较强的适应性和抗噪声能力。
Vibration frequency and mode localization characteristics of strain gradient variable-thickness microplates
Tao Deng, Bo Zhang, Juan Liu, Huoming Shen, Xu Zhang
doi:10.1016/j.tws.2024.111779
应变梯度可变厚度微孔板的振动频率和模式定位特性
Based on the modified strain gradient theory and Kirchhoff-Love assumptions, a free vibration model is established for variable-thickness microplates with three material length scale parameters, and the corresponding Euler-Lagrange equation is derived. Keeping the microplate volume constant, three kinds of thickness variations along the X-direction are considered: linear, parabolic, and cubic variations. Further, a C2-type four-node 36-degree-of-freedom variable-thickness differential quadrature finite element is developed to solve the resulting variable-coefficient boundary value problem by combining the Gauss-Lobatto and differential quadrature rules. Galerkin approximate solution for fully simply supported microplates is provided as a benchmark for numerical method verification. The convergence and accuracy of the model are verified through several examples. Finally, the vibration frequencies of the microplates under different thickness variation types, taper ratios, thickness ratios, material length scale parameters, and boundary conditions are examined through parametric analysis. Also, the influence of each factor on the mode localization of the microplates is quantitatively characterized by the modal assurance criterion (MAC) for the first time. The numerical results show that the thickness variation has a minor effect on the vibration frequency but a significant influence on the mode shape when the volume of the microplate is constant. The strain gradient, taper ratio, and discontinuous boundary have a remarkable effect on the distribution of higher-order mode shape contour lines and the regions where vibration localization occurs.
基于修正的应变梯度理论和基尔霍夫-洛夫假设,建立了具有三个材料长度尺度参数的变厚度微板自由振动模型,并推导出相应的欧拉-拉格朗日方程。在保持微孔板体积不变的情况下,考虑了三种沿 X 方向的厚度变化:线性变化、抛物线变化和三次方变化。此外,一个 C2 型四节点 36 自由度可变厚度微分正交有限元,通过结合高斯-洛巴托规则和微分正交规则来解决由此产生的可变系数边界值问题。提供了完全简单支撑微板的 Galerkin 近似解作为数值方法验证的基准。通过几个实例验证了模型的收敛性和准确性。最后,通过参数分析研究了不同厚度变化类型、锥度比、厚度比、材料长度尺度参数和边界条件下微板的振动频率。同时,通过模态保证准则(MAC)首次定量分析了各因素对微板模态定位的影响。数值结果表明,当微孔板的体积不变时,厚度变化对振动频率的影响较小,但对模态振型的影响很大。应变梯度、锥度比和不连续边界对高阶模态振型轮廓线的分布和发生振动局部化的区域有显著影响。
Enhancing the reliability of laser welded-brazed aluminum/stainless steel joints via laser-chemical hybrid surface texturing
Haoyue Li, Hongbo Xia, Liqun Li, Longqiu Li, Xuan Su, Jin Peng, Yunwu Ma, Caiwang Tan, Xiaoguo Song, Tao Wu
doi:10.1016/j.tws.2024.111780
通过激光-化学混合表面纹理处理提高激光焊接-钎焊铝/不锈钢接头的可靠性
Surface microtexture is a promising technique for enhancing the quality of heterogeneous joints. This study developed a novel surface texturing method to improve the reliability of laser welded-brazed aluminum/stainless steel joints. The method combined laser etching and chemical etching to create high-quality multi-scale surfaces with large grooves and small wrinkles. The designed microtexture promoted atomic transfer and induced the generation of nanoscale η-Fe2(Al,Si)5 phases during the welding-brazing process. It reduced the spreading activation energy along the groove direction, which enlarged the joining area. It also optimized the strain-stress distribution to enhance the deformation tolerance of the bonding interface throughout the structural strengthening mechanism. Through the synergistic regulation, the joint achieved a maximum line load of 495.9 N/mm, which was 61% higher than the untextured joint of 307.5 N/mm. The joint performance reached 95% of the Al/Al lap joint (519.3 N/mm) with the same welding parameters. This study provided new insights into the high-quality joining of aluminum/steel systems or other heterogeneous materials.
表面微纹理是提高异质接头质量的一种有前途的技术。本研究开发了一种新型表面纹理处理方法,以提高激光焊接-钎焊铝/不锈钢接头的可靠性。该方法结合了激光蚀刻和化学蚀刻技术,可制造出具有大凹槽和小皱纹的高质量多尺度表面。设计的微纹理促进了原子转移,并在焊接-钎焊过程中诱导生成了纳米级的 η-Fe2(Al,Si)5 相。它降低了沿沟槽方向的扩展活化能,从而扩大了接合面积。它还优化了应变应力分布,在整个结构强化机制中提高了结合界面的变形容限。通过协同调节,接头的最大线荷载达到了 495.9 牛顿/毫米,比无纹理接头的 307.5 牛顿/毫米高出 61%。在相同的焊接参数下,接头性能达到了铝/铝搭接接头(519.3 N/mm)的 95%。这项研究为铝/钢系统或其他异质材料的高质量焊接提供了新的见解。