今日更新:International Journal of Solids and Structures 1 篇,Journal of the Mechanics and Physics of Solids 1 篇,International Journal of Plasticity 2 篇,Thin-Walled Structures 1 篇
Contact formulations for analysis of micropolar media with finite continuum beam elements
L. Obrezkov, B. Bozorgmehri, R. Kouhia, M.K. Matikainen
doi:10.1016/j.ijsolstr.2024.112880
用有限连续光束单元分析微极介质的接触公式
Microscale beam-like structures are standard components of micromechanical systems in many devices. However, the small dimensionality affects their deformation characteristics and leads to misinterpretations of the results. Presenting such size dependency is possible with advanced continuum descriptions via introducing additional variables compared to the classical one. Hence, the problems where contact occurs require the readjustment of boundary conditions considering these extra parameters. That burdens the already challenging task of contact problem calculations and restricts most demonstration examples to two-dimensional problems and geometrical linearity. The resolution of the imposed restrictions within finite element modeling further emphasizes the usage of advanced media in design and facilitates its application to various problems, which is the aim of this paper. The delivery of that task is as follows. Firstly, we present the kinematics and material descriptions for the micropolar media. The authors propose to use a newly developed continuum-based micropolar beam formulation to avoid an overwhelming computational burden and, at the same time, deal with nonlinear stress–strain relations. Secondly, the work develops a contact approach within the micropolar theory from two-dimensional to three-dimensional elasticity, although the contact is considered frictionless. Finally, it compares two existing contact formulations, including the developed one, for the contact beam problems, using the examples of two collinear sliding beams’ bending.
在许多设备中,微尺度梁状结构是微机械系统的标准部件。然而,小维度影响了它们的变形特性,导致了对结果的误读。与经典的连续体相比,通过引入额外的变量,先进的连续体描述可以呈现这种大小依赖关系。因此,发生接触的问题需要考虑这些额外的参数重新调整边界条件。这增加了接触问题计算的难度,并限制了大多数的演示例子只能解决二维问题和几何线性问题。解决有限元建模中所施加的限制,进一步强调了先进介质在设计中的使用,并促进了其在各种问题中的应用,这是本文的目的。该任务的交付如下。首先,我们给出了微极介质的运动学和材料描述。作者建议使用新开发的基于连续体的微极梁公式,以避免压倒性的计算负担,同时处理非线性应力-应变关系。其次,该工作在微极理论中发展了从二维到三维弹性的接触方法,尽管这种接触被认为是无摩擦的。最后,以两根共线滑动梁的弯曲为例,比较了现有的两种接触公式,包括所开发的接触公式。
An interpenetrating-network theory of the cytoskeletal networks in living cells
Haiqian Yang, Thomas Henzel, Eric M. Stewart, Ming Guo
doi:10.1016/j.jmps.2024.105688
活细胞中细胞骨架网络的互穿网络理论
Cells undergo dramatic deformations during many physiological and pathological processes such as division and migration, and their mechanical integrity is supported by cytoskeletal networks (i.e. intermediate filaments, F-actin, and microtubules). Recent observations of cytoplasmic microstructure indicate interpenetration among different cytoskeletal networks, and micromechanical experiments have shown evidence of complex characteristics in the mechanical response of the interpenetrating cytoskeletal networks of living cells, including viscoelastic, nonlinear stiffening, microdamage, and healing characteristics (Hu et al., 2019). However, a theoretical framework describing such a response is missing, and thus it is not clear how different cytoskeletal components with distinct mechanical properties come together to build the overall complex mechanical features of the cytoskeletal networks. In this work, we address this gap by developing a finite-deformation continuum-mechanical theory with a multi-branch visco-hyperelastic constitutive relation coupled with phase-field damage and healing. The proposed interpenetrating-network model elucidates the coupling among interpenetrating cytoskeletal components, and the roles of finite elasticity, viscoelastic relaxation, damage, and healing in the experimentally-observed mechanical response of interpenetrating cytoskeletal networks in living eukaryotic cells.
细胞在分裂和迁移等生理和病理过程中会发生剧烈变形,其机械完整性由细胞骨架网络(即中间丝、f -肌动蛋白和微管)支持。最近对细胞质微观结构的观察表明,不同的细胞骨架网络之间存在相互渗透,微力学实验表明,活细胞相互渗透的细胞骨架网络的机械响应具有复杂的特征,包括粘弹性、非线性硬化、微损伤和愈合特征(Hu等人,2019)。然而,缺乏描述这种反应的理论框架,因此尚不清楚具有不同机械性能的不同细胞骨架成分如何聚集在一起以构建细胞骨架网络的整体复杂机械特征。在这项工作中,我们通过发展具有多分支粘-超弹性本构关系的有限变形连续力学理论,结合相场损伤和愈合来解决这一差距。提出的互穿网络模型阐明了互穿细胞骨架组分之间的耦合,以及实验观察到的真核细胞互穿细胞骨架网络力学响应中有限弹性、粘弹性松弛、损伤和愈合的作用。
Constitutive modelling of glassy polymers considering shear plasticity and craze yielding
Zhouzhou Pan, Huanming Chen, Laurence Brassart
doi:10.1016/j.ijplas.2024.103996
考虑剪切塑性和开裂屈服的玻璃聚合物本构模型
The inelastic behaviour of thermoplastic polymers below the glass transition temperature can involve shear plasticity or crazing, depending on the strain rate and temperature. Shear plasticity is driven by local shear stresses and is essentially volume preserving. In contrast, crazing is a failure phenomenon occurring under tension and causes significant volume change. In some cases, crazing can also result in large inelastic deformations at macroscopic scale, referred to as craze yielding. The aim of this study is to propose a thermodynamically-consistent constitutive framework that accounts for both shear plasticity and craze yielding in glassy polymers. The main assumption is that shear plasticity and craze yielding occur exclusively from each other, depending on the local stress state. Both are modelled as thermally-activated processes with different activation stresses and flow rules. The theory is validated against experimental data for polylactic acid (PLA). Our model is capable of reproducing the stress–strain response including yielding, softening, and drawing under both shear plasticity and craze yielding, and also accurately predicts the volumetric deformation under tension. In particular, our simulations well capture the interesting phenomenon that craze yielding stabilises localised deformations and prevents necking. Our model can also simulate complex scenarios where both mechanisms occur simultaneously at different locations of the specimen.
热塑性聚合物在玻璃化转变温度以下的非弹性行为可能涉及剪切塑性或裂纹,这取决于应变速率和温度。剪切塑性是由局部剪应力驱动的,本质上是保持体积的。相比之下,起皱是一种在张力作用下发生的破坏现象,会导致显著的体积变化。在某些情况下,开裂也会导致宏观尺度上的大的非弹性变形,称为开裂屈服。本研究的目的是提出一个热力学一致的本构框架,该框架考虑了玻璃聚合物的剪切塑性和开裂屈服。主要假设是剪切塑性和开裂屈服只发生在彼此之间,取决于局部应力状态。两者都被建模为具有不同激活应力和流动规则的热激活过程。用聚乳酸(PLA)的实验数据对理论进行了验证。该模型能够再现剪切塑性和开裂屈服下的屈服、软化和拉伸等应力应变响应,并能准确预测拉伸作用下的体积变形。特别是,我们的模拟很好地捕获了一个有趣的现象,即裂纹屈服稳定了局部变形并防止了颈缩。我们的模型还可以模拟两种机制同时发生在试件不同位置的复杂情况。
Unraveling the Hall-Petch to Inverse Hall-Petch Transition in Nanocrystalline High Entropy Alloys under Shock Loading
Wanghui Li, Meizhen Xiang, Zachary Howard Aitken, Shuai Chen, Yilun Xu, Xinyu Yang, Qingxiang Pei, Jian Wang, Xiaoyan Li, Guglielmo Vastola, Huajian Gao, Yong-Wei Zhang
doi:10.1016/j.ijplas.2024.104010
冲击载荷下纳米晶高熵合金中Hall-Petch向逆Hall-Petch转变的研究
The transition from Hall-Petch (HP) to inverse Hall-Petch (IHP) behaviors associated with grain size reduction has been recognized for over two decades. However, the underlying mechanisms for such transition in high entropy alloys (HEAs) under dynamic loading, in which abundant deformation mechanisms could be activated either sequentially or simultaneously, remain unclear. Here, we investigate the HP to IHP transition in nanocrystalline CoCrFeMnNi HEAs under shock loading by examining their deformation mechanisms and flow stresses using large-scale molecular dynamics (MD) simulations. It is found that this transition is strongly dependent on the shock pressure as a result of the complex interplay among multiple competing deformation mechanisms, including the hardening mechanisms such as dislocations interactions and grain boundary (GB) blocking, as well as the softening mechanisms like phase formation, amorphization, GB thickening, and grain rotation. Moreover, there exists a critical shock pressure, which corresponds to the largest critical grain size for the HP-IHP transition. Below the critical shock pressure, the critical grain size increases with pressure due to a stronger hardening effect in grain interior (GIs), while above the critical pressure, the critical grain size first decreases and then undergoes a pressure-insensitive plateau before further decrease due to softening effects in GIs. A theoretical model that includes different deformation mechanisms is proposed for the first time to capture the shock pressure-dependent HP-IHP transition. Our work provides valuable guidance for optimizing the grain size of nanocrystalline HEAs for applications involving dynamic loadings.
从霍尔-佩奇(HP)到与晶粒尺寸减小相关的逆霍尔-佩奇(IHP)行为的转变已经被认识了二十多年。然而,在动态载荷下,高熵合金(HEAs)的这种转变的潜在机制尚不清楚,其中大量的变形机制可以顺序或同时激活。本文采用大尺度分子动力学(MD)模拟方法,研究了CoCrFeMnNi纳米晶HEAs在冲击载荷下从HP到IHP的转变过程。研究发现,这种转变强烈依赖于冲击压力,这是多种竞争变形机制复杂相互作用的结果,包括位错相互作用和晶界阻塞等硬化机制,以及相形成、非晶化、晶界增厚和晶粒旋转等软化机制。此外,存在一个临界冲击压力,该压力对应于HP-IHP相变的最大临界晶粒尺寸。当冲击压力低于临界冲击压力时,由于晶粒内部的硬化作用更强,临界晶粒尺寸随压力增大而增大;而当冲击压力高于临界冲击压力时,由于晶粒内部的软化作用,临界晶粒尺寸先减小,然后进入一个压力不敏感的平台期,再进一步减小。一个理论模型,包括不同的变形机制,首次提出捕捉冲击压力相关的HP-IHP转换。我们的工作为动态加载应用中纳米晶HEAs的晶粒尺寸优化提供了有价值的指导。
Local damage and imperfection sensitivities of pyramidal core sandwich cylinders
Shuai Kang, Wu Yuan, Hongwei Song
doi:10.1016/j.tws.2024.112020
锥心夹层柱的局部损伤及缺陷灵敏度
Local damage and imperfections may affect the loading capacity of truss core sandwich cylinders. This study develops a numerical model to investigate the effects of missing lattice struts, unbound nodes, openings, and eigenmode-shape imperfections on the buckling and post-buckling behavior of pyramidal core sandwich cylinders. Results from the numerical model show that the pyramidal core sandwich cylinder is sensitive to missing struts and unbound nodes when local buckling is the main failure model. Critical loads show a gradual decrease as the opening damage increases. Pyramidal core sandwich cylinders are not sensitive to eigenmode-shape imperfections compared to the equivalent single-walled shells.
局部损伤和缺陷会影响桁架芯筒的承载能力。本研究建立了一个数值模型来研究缺失的晶格支柱、未绑定节点、开口和特征模态缺陷对锥形芯芯夹层柱屈曲和后屈曲行为的影响。数值模拟结果表明,当局部屈曲为主要破坏模式时,锥体芯芯夹层柱对缺失支撑和未绑定节点敏感;随着开口损伤的增加,临界载荷逐渐减小。与等效的单壁筒壳相比,锥形芯芯夹芯筒对本征模态缺陷不敏感。