今日更新：International Journal of Solids and Structures 2 篇，Mechanics of Materials 1 篇，Thin-Walled Structures 2 篇International Journal of Solids and StructuresA stable numerical framework for long-time dynamic crack analysisWenzhen Qu, Yan Gu, Chia-Ming Fandoi:10.1016/j.ijsolstr.2024.112768用于长时间动态裂纹分析的稳定数值框架This paper introduces a stable numerical framework designed to address dynamic crack problems over long-time intervals. The initial step involves the temporal discretization of the governing dynamic equilibrium equations using the arbitrary order Krylov deferred correction method. To ensure precise boundary condition matching, a novel numerical implementation is incorporated into the Krylov deferred correction technique. Subsequently, the resulting system of spatial partial differential equations at each time node is solved using the meshless generalized finite difference method with 4th-order expansions in regions close to the crack-tips and 2nd-order expansions in areas far from the crack-tips. This combined approach capitalizes on the strengths of both the Krylov deferred correction technique and the generalized finite difference method, enabling stable simulations of dynamic cracks with the large time step and without the need for mesh generation. Notably, we refine the collocation nodes near crack tips to attain accurate numerical results for displacement and stress field. Several numerical experiments involving diverse impact loadings are conducted to validate the developed framework. Furthermore, a comparison is made between the dynamic stress intensity factors obtained using our approach and those from existing methods.本文介绍了一种稳定的数值框架，旨在解决长时间跨度上的动态裂缝问题。第一步是使用任意阶克雷洛夫延迟修正法对支配动态平衡方程进行时间离散化。为了确保精确的边界条件匹配，在克雷洛夫延迟修正技术中加入了一种新的数值实现方法。随后，利用无网格广义有限差分法对每个时间节点上的空间偏微分方程系进行求解，在靠近裂缝尖端的区域采用四阶展开法，在远离裂缝尖端的区域采用二阶展开法。这种组合方法充分利用了克雷洛夫延迟校正技术和广义有限差分法的优点，能够在大时间步长下稳定模拟动态裂缝，且无需生成网格。值得注意的是，我们改进了裂纹尖端附近的配位节点，以获得位移和应力场的精确数值结果。为了验证所开发的框架，我们进行了多次涉及不同冲击载荷的数值实验。此外，我们还比较了使用我们的方法和现有方法获得的动态应力强度因子。Shape morphing of 2D lattice structures from localized contra-rotationsKenichiro Yokota, Francois Barthelatdoi:10.1016/j.ijsolstr.2024.112771从局部反旋转看二维晶格结构的形状变形The morphing of structure and materials from localized, self-equilibrated actuation loads is limited by Saint-Venant’s principle: Deformations typically decay rapidly from the actuation region, so that changes in shape for the entire structure are negligible. Materials and structures with unusual combinations of elastic properties may induce competitions between different deformation modes over longer decay distances, thereby overcoming this limitation. Here we push this principle to the extreme to generate shape morphing in large 2D lattice structures. We consider planar triangular lattice made of “meta-elements” with unusual combinations of axial, shear and flexural stiffness. We show, using finite element models, that localized contra-rotations on the center nodes can morph the entire structure in bending, provided that adequate combinations of elastic properties are selected. We use the global curvature as measure of this deformation to establish precise design guidelines for morphing. We finally propose physical embodiments of these meta-elements and lattice structures which we fabricated using laser cutting, and which tested using servo-motors to impose contra-rotations on the two center nodes. The results validate our models and the design guidelines: planar lattice can morph in bending with significant curvatures, especially when the size of the structure is small. In comparison, similar lattice structures made of regular beams show no morphing, with all the deformation localized near the center nodes. These findings may lead to new strategies to actuate morphing materials and structures, with applications in aerospace or robotics.结构和材料在局部自平衡致动载荷作用下的变形受到圣-韦南原理的限制：变形通常会从致动区域迅速衰减，因此整个结构的形状变化可以忽略不计。具有不同寻常弹性特性组合的材料和结构可能会在较长的衰减距离内引起不同变形模式之间的竞争，从而克服这一限制。在这里，我们将这一原理发挥到极致，在大型二维晶格结构中产生形状变形。我们考虑的是由 "元元元 "组成的平面三角形晶格，其轴向、剪切和挠曲刚度具有不同寻常的组合。我们利用有限元模型证明，只要选择适当的弹性特性组合，中心节点上的局部反旋转就能使整个结构在弯曲时变形。我们使用全局曲率来衡量这种变形，从而为变形制定精确的设计准则。最后，我们提出了这些元元件和晶格结构的物理实施方案，我们使用激光切割技术制造了这些元元件和晶格结构，并使用伺服电机对两个中心节点施加反向旋转进行了测试。测试结果验证了我们的模型和设计准则：平面晶格在弯曲时可以产生明显的曲率变形，尤其是在结构尺寸较小时。相比之下，由规则梁构成的类似晶格结构不会发生变形，所有变形都集中在中心节点附近。这些发现可能会带来驱动变形材料和结构的新策略，并应用于航空航天或机器人领域。Mechanics of MaterialsShear bands occurrence in collapsing thick-walled cylinders: Role of user-defined perturbationsM. Xavier, M. Reynauddoi:10.1016/j.mechmat.2024.104960厚壁圆柱体坍塌时产生的剪切带：用户定义的扰动的作用Self-organization of multiple adiabatic shear bands (ASB) is often investigated through collapsing thick-walled cylinders (TWC). In the present work, the material behaviour is described by a thermoviscoplastic constitutive law with a strain energy based failure model. Inhomogeneities in the specimen are somehow represented using Voronoi cells. In addition, a user-defined perturbation is imposed in the numerical perturbation to each Voronoi cell. Therefore, a mesh independent perturbation is obtained. Several draws of initial perturbation are considered to investigate variability in shear band patterns. The numerous realizations are analyzed through an algorithm to track and count shears bands providing statistically significant results. The influence of the failure model and perturbation parameters on shear bands number and length is studied. While short bands are affected by the size of the cells, it is shown that the self-organized pattern of developed bands is relatively independent of the imposed Voronoïcell structure. The amplitude of the perturbation affects neither the pattern nor the length of bands (within the considered range of amplitude of the user-defined perturbation).多绝热剪切带（ASB）的自组织通常通过厚壁圆柱体（TWC）的坍塌进行研究。在本研究中，材料行为由热粘塑性构成定律和基于应变能的失效模型来描述。试样中的非均质性以某种方式用 Voronoi 单元表示。此外，在对每个 Voronoi 单元进行数值扰动时，会施加用户定义的扰动。因此，可以获得与网格无关的扰动。为了研究剪切带模式的变化，考虑了几种初始扰动。通过跟踪和统计剪切带的算法分析了大量的实现情况，并得出了具有统计意义的结果。研究了破坏模型和扰动参数对剪切带数量和长度的影响。虽然短剪切带会受到单元尺寸的影响，但研究表明，已形成剪切带的自组织模式相对独立于所施加的 Voronoïcell 结构。扰动的振幅既不会影响剪切带的形态，也不会影响剪切带的长度（在用户定义的扰动振幅范围内）。Thin-Walled StructuresExperimental and Numerical Investigation of Square Concrete-Filled Double-Skin Steel Stiffened Tubular Stub Columns with CHS Inner Tubes under Axial CompressionWei-Feng Huang, Yong-Bo Shao, M.F. Hassanein, Marijana Hadzima-Nyarko, Dorin Radu, K.A. Cashelldoi:10.1016/j.tws.2024.111792带 CHS 内管的方形混凝土填充双层钢加劲管式支柱在轴向压缩下的实验和数值研究This paper explores the performance of concrete-filled double-skin (square stiffened hollow sections (SHS) outer and circular hollow sections (CHS) inner) steel tubular (CFDSST) stub columns under axial compression through experimental research and finite element analysis. The static axial compression experiments of six concrete-filled stiffened steel tubular (CFST) stub columns and fifteen CFDSST stub columns were conducted. The test method, process, phenomena and results are introduced in detail. The results indicated that compared with conventional CFST stub columns, CFDSST stub columns with reasonable hollow ratio can maintain load-carrying capacity, increase ductility and reduce self-weight. Increasing the strength of concrete is the most effective way to increase the load-carrying capacities of specimens when other variables remain constant. Finite element (FE) software was then utilised to generate the models of current specimens. The simulation results showed reasonableness and accuracy compared to the experimental results. Based on the validated models, parameter analysis was performed to reveal the influence of concrete strength, width-to-thickness ratio of the outer steel tube, stiffener depth, hollow ratio and yield strength of the outer steel tube on the ultimate strengths of the specimens. In addition, compared with test and FE strengths, the ultimate strengths predicted by available international codes were found to be quite conservative. Consequently, a formula was proposed to predict the load-carrying capacity of CFDSST stub columns considering the effective cross-sectional areas of the outer steel tubes and the strength of the confined concrete. The formula has been shown to provide the best prediction with acceptable reliability.本文通过实验研究和有限元分析，探讨了混凝土填充双层（外层为方形加劲空心截面（SHS），内层为圆形空心截面（CHS））钢管桩柱（CFDSST）在轴向压缩下的性能。对六根混凝土填充加劲钢管（CFST）短柱和十五根 CFDSST 短柱进行了静态轴向压缩实验。详细介绍了试验方法、过程、现象和结果。结果表明，与传统 CFST 存根柱相比，合理空心率的 CFDSST 存根柱可保持承载能力、增加延性并减轻自重。在其他变量不变的情况下，提高混凝土强度是提高试件承载能力的最有效方法。然后利用有限元（FE）软件生成当前试样的模型。与实验结果相比，模拟结果显示出合理性和准确性。在验证模型的基础上，进行了参数分析，以揭示混凝土强度、外钢管宽厚比、加劲件深度、空心率和外钢管屈服强度对试件极限强度的影响。此外，与试验和 FE 强度相比，发现现有国际规范预测的极限强度相当保守。因此，考虑到外钢管的有效截面积和受限混凝土的强度，提出了一个公式来预测 CFDSST 存根柱的承载能力。结果表明，该公式可提供最佳预测，且可靠性可接受。On the collapse stress of tubular enhanced anti-tetra-missing rib structureChuanbiao Zhang, Fucong Lu, Tinghui Wei, Xiangyu Ling, Beicheng Lin, Yilin Zhudoi:10.1016/j.tws.2024.111801论管状增强型抗四漏筋结构的坍塌应力In the contemporary landscape of engineering, escalating demands for advanced material and structural performance have brought metamaterials to the forefront. Among them, the enhanced anti-tetra-missing rib structure has gained prominence owing to its auxetic behavior under significant strain. However, the lack of research on its quasi-static and dynamic mechanical performance have hindered its practical application. To address this, we introduce the tubular enhanced anti-tetra-missing rib structure (TEATMRS) and derive its collapse stress expression under various conditions. Through extensive simulations and experiments, we explore its deformation mechanisms and assess the influence of the structural geometric parameters and impact velocity on collapse stress. The results demonstrate excellent agreement among theoretical description, numerical analysis, and experimental tests, establishing the feasibility of the proposed collapse stress expression. These findings provide a theoretical foundation and design guidance for TEATMRS in engineering applications.在当代工程领域，人们对先进材料和结构性能的要求不断提高，超材料也随之进入人们的视野。其中，增强型抗四漏肋结构因其在巨大应变下的辅助行为而备受瞩目。然而，由于缺乏对其准静态和动态机械性能的研究，阻碍了其实际应用。针对这一问题，我们引入了管状增强型抗四漏肋结构（TEATMRS），并推导出其在各种条件下的塌陷应力表达式。通过大量的模拟和实验，我们探索了其变形机制，并评估了结构几何参数和冲击速度对坍塌应力的影响。结果表明，理论描述、数值分析和实验测试之间存在极好的一致性，从而确定了所提出的坍塌应力表达式的可行性。这些发现为 TEATMRS 的工程应用提供了理论基础和设计指导。来源：复合材料力学仿真Composites FEM
