【新文速递】2023年10月9日固体力学SCI期刊最新文章

今日更新：International Journal of Solids and Structures 3 篇，International Journal of Plasticity 2 篇，Thin-Walled Structures 1 篇

International Journal of Solids and Structures

Investigation of the compressive properties of three-dimensional Voronoi reticula

Colamartino Ivan, Anghileri Marco, Boniardi Marco

doi:10.1016/j.ijsolstr.2023.112501

研究三维 Voronoi 网状结构的抗压性能

With the rise of additive manufacturing technologies, artificial production of stochastic cellular materials is becoming increasingly more feasible and convenient, exposing the need of accurate models able to predict their mechanical properties. However, the construction of generalized predictive models for stochastic structures is non-trivial: on the one hand, this is due to the several potential base materials, and on the other it is because of the difficulty in implementing geometrically accurate numerical models. In light of these considerations, the present work presents a systematic analysis of one the most known – and commonly used – stochastic cellular structure, the Voronoi three-dimensional lattices; the aim is providing simple empirical relations between the main properties of a generic base material and the compressive properties of the related additively manufactured stochastic Voronoi reticulum as a function of its geometry. The investigation provides novel insights on the mechanical properties of Voronoi reticula, highlighting superior efficiency with respect to their natural counterpart, the open-cell foams, and exposing unsuitability of classical equations for accurate prediction of their mechanical properties.

随着增材制造技术的兴起，人工制造随机蜂窝材料变得越来越可行和方便，这暴露出对能够预测其机械性能的精确模型的需求。然而，为随机结构构建通用预测模型并非易事：一方面，这是由于存在多种潜在的基础材料，另一方面，这也是由于难以实施几何精确的数值模型。鉴于这些考虑因素，本研究对一种最著名和最常用的随机蜂窝结构--沃罗诺伊三维网格--进行了系统分析；目的是提供通用基础材料的主要特性与相关加成制造随机沃罗诺伊网状结构的压缩特性之间的简单经验关系，作为其几何形状的函数。这项研究为 Voronoi 网状结构的机械特性提供了新的见解，突出了其相对于天然材料（开孔泡沫）的优越性，并揭示了经典方程在准确预测其机械特性方面的不适用性。

A metamaterial with sign-programmable thermal expansivity and Poisson’s ratio constructed from a hybrid of rotating and non-rotating rigid units

Lim Teik-Cheng

doi:10.1016/j.ijsolstr.2023.112510

由旋转和非旋转刚性单元混合构建的热膨胀率和泊松比符号可编程超材料

A 2D mechanical metamaterial is introduced herein using a hybrid of rotating parallelograms and non-rotating rhombi. The in-plane Poisson’s ratio under on-axes loading were derived by considering the rotation of the parallelograms. The on-axes coefficients of thermal expansion were extracted by matching the simple harmonic motion energy with the principle of energy equipartition, while the on-axes Young’s moduli were formulated by equating the total stored rotational spring potential energy at the connecting points with the strain energy of deformation for the equivalent continuum of the metamaterial. Results indicate that the Poisson’s ratio and CTE are primarily governed by the separation angles between the rigid units and, to a smaller extent, by the shapes of the rotating rigid units. In addition to the aforementioned parameters, the effective Young’s moduli of this metamaterial is directly proportional to the rotational elastic restraint at the hinges that connect adjacent rigid units. Due to the instability of the metamaterial under a specific geometrical condition, charges are incorporated into the rhombi in order to programme the sign of the Poisson’s ratio.

本文利用旋转平行四边形和非旋转菱形的混合体，介绍了一种二维机械超材料。通过考虑平行四边形的旋转，得出了轴向负载下的面内泊松比。轴向热膨胀系数是通过将简谐运动能量与能量等分原理相匹配而提取的，而轴向杨氏模量则是通过将连接点处存储的总旋转弹簧势能与超材料等效连续体的变形应变能相等分而得出的。结果表明，泊松比和 CTE 主要受刚性单元之间的分离角影响，其次受旋转刚性单元形状的影响。除上述参数外，这种超材料的有效杨氏模量还与连接相邻刚性单元的铰链处的旋转弹性约束成正比。由于超材料在特定几何条件下的不稳定性，为了调节泊松比的符号，在菱形中加入了电荷。

Dual-band topological states in actively convertible metamaterials with parallel platforms

Cui Ling-Fan, Wang Yi-Ze

doi:10.1016/j.ijsolstr.2023.112511

具有平行平台的主动可转换超材料中的双波段拓扑状态

Topological propagation in elastic wave metamaterials is widely investigated due to the superior transmission performance but most studies are focused on a single frequency range. This work proposes the elastic wave metamaterial composed of parallel platforms with active control, which illustrates topological interface states in two separate frequency ranges. In order to show basic features, band gap properties and localized modes in the rectilinear structure are considered at first. Then, the honeycomb system is investigated to present dynamic behaviors with two Dirac cones which belong to two frequency regions. The topological phase transition is identified by the eigenstates and topological invariants, respectively. Based on the k·p perturbation method, the effective Hamiltonian of two Dirac degeneracies is derived. Due to different stiffness of two platforms within a unit cell, two nontrivial degeneracies will be destroyed. Two band gaps support the interface states with topological protection and robust characteristic between lattices with different valley Hall phases. In addition, the topological transmission can be flexibly tuned by the active control system, which is supported by experiments. This work wishes to provide new designs of mechanical metamaterial with multiple functions.

弹性波超材料中的拓扑传播因其卓越的传输性能而被广泛研究，但大多数研究都集中在单一频率范围。本研究提出了一种由具有主动控制功能的平行平台组成的弹性波超材料，它展示了两个不同频率范围内的拓扑界面状态。为了展示基本特征，首先考虑了矩形结构的带隙特性和局部模式。然后，对蜂窝系统进行研究，以呈现出属于两个频率区域的两个狄拉克锥的动态行为。拓扑相变分别由特征状态和拓扑不变式确定。基于 k-p 扰动方法，推导出了两个狄拉克退化的有效哈密顿。由于单位晶胞内两个平台的刚度不同，两个非难性将被破坏。两个带隙支持具有拓扑保护的界面态，以及不同谷霍尔相晶格之间的稳健特性。此外，拓扑传输可通过主动控制系统灵活调整，这一点已得到实验的支持。这项工作希望为具有多种功能的机械超材料提供新的设计。

International Journal of Plasticity

Exploring structural origins responsible for the exceptional mechanical property of additively manufactured 316L stainless steel via in-situ and comparative investigations

An Dayong, Zhou Yuhao, Liu Xinxi, Wang Haoliang, Li Shilei, Xiao Yao, Li Rui, Li Xifeng, Han Xianhong, Chen Jun

doi:10.1016/j.ijplas.2023.103769

通过原位研究和比较研究，探究加成型 316L 不锈钢优异机械性能的结构根源

The laser beam powder-bed-fusion (PBF-LB) technique offers the possibility to fabricate metallic materials with unparalleled mechanical properties. However, due to the complexity of nonequilibrium solidification structures, untangling the role of specific structural features in influencing mechanical properties through post-mortem analysis remains a significant challenge. Here, we tracked the complete evolution of deformation microstructures in PBF-LB 316L stainless steel (SS) and conventionally manufactured (CM) counterparts using in-situ electron channeling contrast imaging (ECCI) in conjunction with high-angular resolution electron backscatter diffraction (HR-EBSD). Our findings underscore the importance of the intrinsic dislocation configuration, i.e., faulted dipole, in modulating the plastic deformation behaviors of the PBF-LB sample. The periodic arrangement of faulted dipoles triggers a widespread activation of stacking faults (SFs) with extremely fine spacing at the yielding stage, resulting in a high passing stress (∼433 MPa) that is responsible for the high yield strength. Meanwhile, such configuration facilitates uniform plastic deformation and mediates twinning propensity, thereby alleviating stress concentrations and enhancing ductility. Moreover, by correlating the mechanical response with microstructural evolution, we establish a modified model for multiple strengthening mechanisms in the PBF-LB sample. Additionally, we examine the effect of nonequilibrium solidification structures on the strain rate sensitivity of PBF-LB samples. Taking 316L SS as an exemplar, our results extend the current understanding of the structural origins responsible for the exceptional mechanical properties of metals manufactured by PBF-LB.

激光束粉末床熔融（PBF-LB）技术为制造具有无与伦比的机械性能的金属材料提供了可能。然而，由于非平衡凝固结构的复杂性，通过死后分析来揭示特定结构特征在影响力学性能方面的作用仍然是一项重大挑战。在这里，我们使用原位电子通道对比成像（ECCI）结合高角分辨率电子反向散射衍射（HR-EBSD）技术，跟踪了 PBF-LB 316L 不锈钢（SS）和传统制造（CM）不锈钢中变形微结构的完整演变过程。我们的研究结果强调了内在位错配置（即断层偶极子）在调节 PBF-LB 样品塑性变形行为方面的重要性。断层偶极子的周期性排列在屈服阶段引发了间距极小的堆积断层（SFs）的广泛激活，从而产生了高通过应力（∼433 兆帕），这就是高屈服强度的原因。同时，这种构造有利于产生均匀的塑性变形并促进孪生倾向，从而缓解应力集中并增强延展性。此外，通过将机械响应与微结构演变联系起来，我们建立了 PBF-LB 样品中多种强化机制的修正模型。此外，我们还研究了非平衡凝固结构对 PBF-LB 样品应变速率敏感性的影响。以 316L SS 为例，我们的研究结果拓展了目前对 PBF-LB 制造的金属具有优异机械性能的结构根源的理解。

A robust and efficient hybrid solver for crystal plasticity

Hardie Chris, Long Daniel J., Demir Eralp, Tarleton Edmund, Dunne Fionn P.E.

doi:10.1016/j.ijplas.2023.103773

稳健高效的晶体塑性混合求解器

Conventional crystal plasticity (CP) solvers are based on a Newton-Raphson (NR) approach which use an initial guess for the free variables (often stress) to be solved. These solvers are limited by a finite interval of convergence and often fail when the free variable falls outside this interval. Solution failure results in the reduction of the time increment to be solved, thus convergence of the CP solver is a bottleneck which determines the computational cost of the simulation. The numerical stability of the slip law in its inverted form offers a solver that isn't vulnerable to poor pre-conditioning (initial guess) and can be used to progress to a solution from a stable starting point (i.e., from zero slip rate γpk = 0). In this paper, a novel formulation that enables the application of the slip law in its inverted form is introduced; this treats all slip systems as independent by approximating the Jacobian as a diagonal matrix, thus overcomes ill-defined and singular Jacobi associated with previous approaches. This scheme was demonstrated to offer superior robustness and convergence rate for a case with a single slip system, however the convergence rate for extreme cases with several active slip systems was relatively poor. Here, we introduce a novel ‘hybrid scheme’ that first uses the reverse scheme for the first stage of the solution, and then transitions to the forward scheme to complete the solution at a higher convergence rate. Several examples are given for pointwise calculations, followed by CPFEM simulations for FCC copper and HCP Zircaloy-4, which demonstrated solver performance in practise. The performance of simulations using the hybrid scheme was shown to require six to nine times fewer increments compared to the conventional forward scheme solver based on a free variable of stress and initial guess based on a fully elastic increment.

传统的晶体塑性（CP）求解器基于牛顿-拉斐森（NR）方法，使用自由变量（通常是应力）的初始猜测来求解。这些求解器受到有限收敛区间的限制，当自由变量超出该区间时，求解器往往会失效。求解失败会导致求解时间增量的减少，因此 CP 求解器的收敛性是决定模拟计算成本的瓶颈。反转形式滑移定律的数值稳定性提供了一种求解器，它不会受到不良预设条件（初始猜测）的影响，并可用于从稳定的起点（即从零滑移率）开始求解。本文引入了一种新的表述方法，可以应用反转形式的滑移定律；这种方法通过将雅各布近似为对角矩阵，将所有滑移系统视为独立系统，从而克服了以往方法中雅各布定义不清和奇异的问题。该方案已被证明在单一滑移系统的情况下具有优异的鲁棒性和收敛速度，但在有多个主动滑移系统的极端情况下收敛速度相对较差。在这里，我们引入了一种新的 "混合方案"，首先在求解的第一阶段使用逆向方案，然后过渡到正向方案，以更高的收敛率完成求解。我们举了几个点式计算的例子，然后对 FCC 铜和 HCP Zircaloy-4 进行了 CPFEM 模拟，展示了求解器的实际性能。与基于自由应力变量和基于全弹性增量的初始猜测的传统前向方案求解器相比，使用混合方案进行模拟所需的增量减少了 6 到 9 倍。

Thin-Walled Structures

Influence of post-expansion residual stress on the fatigue life of the supercharged boiler

Zeng Qingpeng, Li Yanjun, Gong Sungen, Chen Xu, Sun Baozhi, Cao Yuanwei, Shi Jianxin

doi:10.1016/j.tws.2023.111246

膨胀后残余应力对增压锅炉疲劳寿命的影响

The stress distribution on boiler tubesheets becomes very complex due to the combined effects of thermal-mechanical load and residual stress from expansion in numerous expanded joints. This study determined the residual stress distribution generated by the expansion process on the boiler drum, which was used as the initial stress state boundary to simulate continuous steam charging and discharging cycles. Different fatigue assessment methods were employed to evaluate the impact of residual stress on fatigue life. The results indicated that the residual stress exhibited higher values in the central region and lower values on the sides. When considering the post-expansion residual stress, there was a reduction of 10.4%/20% and 8.9% in the permissible number of cycles based on the maximum shear stress and distortion energy theories, respectively. It is crucial to account for the fatigue weakening caused by the expansion process in the fatigue evaluation of pressure vessels.

由于热机械载荷和众多膨胀接头膨胀产生的残余应力的共同作用，锅炉管板上的应力分布变得非常复杂。本研究确定了膨胀过程在锅炉汽包上产生的残余应力分布，并将其作为初始应力状态边界来模拟连续的蒸汽充放电循环。采用不同的疲劳评估方法来评估残余应力对疲劳寿命的影响。结果表明，残余应力在中心区域的数值较高，而在两侧的数值较低。在考虑膨胀后残余应力时，根据最大剪应力和变形能理论，允许的循环次数分别减少了 10.4%/20% 和 8.9%。在压力容器的疲劳评估中，考虑膨胀过程造成的疲劳削弱至关重要。