【新文速递】2024年3月19日固体力学SCI期刊最新文章

今日更新：Journal of the Mechanics and Physics of Solids 1 篇，Mechanics of Materials 1 篇，Thin-Walled Structures 1 篇Journal of the Mechanics and Physics of SolidsTop-down constitutive modelling to capture nanoscale shear localizationJici Wen, Yujie Weidoi:10.1016/j.jmps.2024.105629 捕捉纳米级剪切定位的自顶向下构造模型Deformation localization as exemplified by earthquakes, landslides, shear banding in solids, and failure of engineering components is of utmost importance. In practice, differentiating the mechanical behavior in such generative narrow bands from the rest part, with difference by orders of magnitude in characteristic size, flow strength, temperature, and shearing rate, is both experimentally and computationally formidable. Here we propose a machine-learning-based constitutive modeling framework to overcome this barrier borne from conventional top-down continuum modelling approach. The model enables us to realize ultra-fine resolutions for deformation in those narrow bands with high efficiency. Taking metallic glasses (MGs) as an example, our model captures well shear localization in BMGs across a broad range of temperatures (0 K to its melting point of ∼1000 K) and strain rates (10^−4 to 10^8/s). We verify through this model the width of shear bands (SBs) in MGs is on the order of 5 to 8 nanometers, which is resulted from a cascade of (intervening) events, from localized shearing to plastic heating, subsequent temperature rise to thermal softening, and accelerated flow rate to strain-rate hardening. Temperature rise in SBs is a resultant of heat flow and plastic dissipation, but strongly depend on thermal conductivity: Low thermal conductivity facilitates strain localization and great temperature rise. It explains the current controversy upon experimentally measured temperature rise ranging from several K to ∼1000 K. Lastly, strain rates within SBs are approximately one to two orders of magnitude higher than externally applied strain rates, and in general shearing in adiabatic SBs is faster than that in isothermal condition.地震、山体滑坡、固体中的剪切带以及工程部件的失效所体现的变形局部化至关重要。在实践中，要将这种产生窄带的机械行为与其他部分区分开来，在特征尺寸、流动强度、温度和剪切速率等方面存在数量级的差异，这在实验和计算上都是非常困难的。在此，我们提出了一种基于机器学习的结构建模框架，以克服传统的自上而下连续建模方法所带来的障碍。该模型使我们能够高效地实现窄带变形的超精细分辨率。以金属玻璃（MGs）为例，我们的模型能很好地捕捉到 BMGs 在宽温度范围（0 K 至其熔点 ∼1000 K）和应变速率（10^-4 至 10^8/s）内的剪切定位。我们通过该模型验证了MGs中剪切带（SBs）的宽度约为5至8纳米，它是由一连串（相互干扰的）事件造成的，从局部剪切到塑性加热，随后的温度上升到热软化，以及流速加快到应变速率硬化。SB 中的温升是热流和塑性耗散的结果，但在很大程度上取决于热传导率： 低导热率有利于应变局部化和大幅温升。最后，SBs 内部的应变速率比外部施加的应变速率高出约一到两个数量级，一般来说，绝热 SBs 中的剪切比等温条件下的剪切更快。Mechanics of MaterialsMolecular insights into reversible and irreversible kinks formed in nanocelluloseRongZhuang Song, YuanZhen Hou, ZeZhou He, HengAn Wu, YinBo Zhudoi:10.1016/j.mechmat.2024.104986 对纳米纤维素中形成的可逆和不可逆扭结的分子认识Kink defects in nanocellulose are common, yet questions remain open regarding the unclear microstructure-mechanical property relationship. Various kink patterns without molecular-scale resolution cause confusion about how nanocellulose forms different kinks and what the fundamental mechanisms of reversible and irreversible kinks are. In atomic force microscopy images, bent nanofibrils usually exhibit small curvatures, while kinked nanofibrils feature sharp bends, in which kinks are notable due to their distinct disordered configurations. To identify the incipient kink defects formed in nanocellulose, molecular dynamics simulations of cellulose nanocrystals (CNCs) under curvature-dependent bending were subsequently carried out. Five typical bending/kinking modes were found, depending on the anisotropic microstructure and size of CNCs. More importantly, two contrasting cases of kinks were demonstrated, providing evidence that kink defects in nanocellulose depend mainly on the microstructure at the molecular scale. Kinks in CNCs with the (100) and (11¯0) crystal plane are recoverable with a few residual defects. While kinks in CNCs with the (010) crystal plane are irreversible with permanent microstructural damage. Compressive stresses accumulated in the bottom chains of CNC contribute to the main mechanism for forming incipient kinks in nanocellulose. The results can fundamentally answer the confusion in recent experiments why bond breakage did not necessarily occur even at high kink angles. The insights present intrinsic deformation mechanisms for understanding the widespread but mysterious kinks arising in nanocellulose.纳米纤维素中的扭结缺陷很常见，但微观结构与力学性能之间的关系尚不明确，因此问题仍然存在。没有分子尺度分辨率的各种扭结模式使人们对纳米纤维素如何形成不同的扭结以及可逆和不可逆扭结的基本机制感到困惑。在原子力显微镜图像中，弯曲的纳米纤维通常表现出较小的曲率，而扭结的纳米纤维则以急剧弯曲为特征，其中扭结因其独特的无序构型而引人注目。为了确定纳米纤维素中形成的初期扭结缺陷，随后对纤维素纳米晶体（CNC）在曲率依赖性弯曲条件下进行了分子动力学模拟。根据各向异性的微观结构和 CNC 的尺寸，发现了五种典型的弯曲/扭结模式。更重要的是，研究发现了两种截然不同的扭结情况，从而证明纳米纤维素中的扭结缺陷主要取决于分子尺度上的微观结构。晶面为 (100) 和 (11¯0) 的 CNC 中的扭结可恢复，但残留缺陷较少。而(010) 晶面的 CNC 中的扭结是不可逆的，会造成永久性的微观结构破坏。在 CNC 底链中积累的压应力是纳米纤维素形成初期扭结的主要机制。这些结果从根本上解答了近期实验中的一个困惑，即为什么即使在高扭结角下也不一定会发生键断裂。这些见解提出了内在的变形机制，有助于理解纳米纤维素中广泛存在但却神秘莫测的扭结现象。Thin-Walled StructuresExperimental and numerical study of impact resistance and compression properties after impact of none-felt needled compositesTianlei Yao, Jiao Li, Xiaoming Chen, Diansen Li, Lei Jiangdoi:10.1016/j.tws.2024.111807非毛毡针 刺复合材料抗冲击性和冲击后压缩性能的实验与数值研究In this paper, the impact and after-impact compression (CAI) properties of new none-felt needled composites were investigated by finite element and experimental methods. Micro-CT and digital image correlation (DIC) were used for structural characterization and recording surface strains in CAI specimens. The impact and CAI finite element models of needled composites were developed, and the damage mechanisms were analyzed. The results showed that the impact and CAI properties of none-felt needled composite were substantially improved. In the impact experiments, the failure firstly occurred in the interlayer and gradually extended to the fiber layer. In the CAI experiment, the damage gradually extended from the impact damage region to the specimen edges, and the specimen finally failed when the damage with the specimen edges extended together. The established finite element model agreed well with both the impact and CAI tests, and the errors were less than 5% and 10%.本文采用有限元和实验方法研究了新型非毛毡针 刺复合材料的冲击和冲击后压缩（CAI）性能。微计算机断层扫描和数字图像相关（DIC）被用于 CAI 试样的结构表征和表面应变记录。建立了针 刺复合材料的冲击和 CAI 有限元模型，并分析了其损伤机理。结果表明，非毛毡针 刺复合材料的冲击和 CAI 性能得到了显著改善。在冲击实验中，破坏首先发生在夹层，然后逐渐扩展到纤维层。在 CAI 实验中，损伤从冲击损伤区域逐渐扩展到试样边缘，当损伤与试样边缘一起扩展时，试样最终失效。建立的有限元模型与冲击试验和 CAI 试验结果吻合良好，误差分别小于 5%和 10%。来源：复合材料力学仿真Composites FEM