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 1 篇，Thin-Walled Structures 2 篇International Journal of Solids and StructuresA combined displacement discontinuity-interaction integral method for computing stress intensity factors and T-stressKe Li, Fei Wangdoi:10.1016/j.ijsolstr.2024.112964计算应力强度因子和 T 应力的位移不连续-相互作用积分组合法In this paper, the displacement discontinuity method (DDM) is combined with interaction integral to simultaneously evaluate stress intensity factors and T-stress for analyzing two-dimensional mixed-mode crack problems. The displacement discontinuity method has been proved to be one of the most efficient boundary element methods for solving crack problems with boundary-only discretization character. However, there is a lack of efficient methods collaborating with the displacement discontinuity method to evaluate fracture parameters. The available geometrical extrapolation method and J-integral technique for calculating fracture parameters in combination with the displacement discontinuity method are imprecise and difficult to be implemented into mixed-mode crack analysis. The present combined displacement discontinuity method and interaction integral approach can easily extract stress intensity factors and T-stress for mixed-mode crack problems without needing any decomposition of elastic field into symmetric and antisymmetric components. The fundamental basis lies in introducing auxiliary fields for the proper defined single mode crack, then calculating fracture parameters by evaluating the formulated interaction integral in terms of displacement discontinuity solutions and auxiliary elastic fields. In this paper, the basis of the displacement discontinuity method is illustrated firstly, then the explicit expressions for auxiliary fields of displacement gradients are derived. Next, the interaction integral can be determined by being converted to an equivalent area integral. Finally, several numerical examples are examined to demonstrate the correctness of the present method.本文将位移不连续法（DDM）与相互作用积分相结合，同时评估应力强度因子和 T 应力，用于分析二维混合模式裂纹问题。位移不连续法已被证明是解决仅边界离散化特征的裂纹问题的最有效边界元方法之一。然而，目前还缺乏与位移不连续法相结合的高效方法来评估断裂参数。现有的几何外推法和结合位移不连续法计算断裂参数的 J-积分技术不够精确，难以应用于混合模式裂纹分析。本研究采用位移不连续法和相互作用积分相结合的方法，无需将弹性场分解为对称和非对称分量，即可轻松提取混合模式裂纹问题的应力强度因子和 T 应力。其基本原理在于为适当定义的单模裂纹引入辅助场，然后通过评估位移不连续解和辅助弹性场的相互作用积分来计算断裂参数。本文首先说明了位移不连续法的基础，然后推导出位移梯度辅助场的明确表达式。接着，通过转换为等效面积积分，可以确定相互作用积分。最后，通过几个数值实例来证明本方法的正确性。Journal of the Mechanics and Physics of SolidsDuctility of a nanocomposite of glassy and rubbery polymersChristine Heera Ahn, Guogao Zhang, Zhigang Suodoi:10.1016/j.jmps.2024.105760玻璃态和橡胶态聚合物纳米复合材料的延展性A brittle glassy polymer can be made ductile by forming a nanocomposite with a rubbery polymer. This paper investigates a nanocomposite of poly(methyl methacrylate) (PMMA) and poly(ethyl acrylate) (PEA). Pure PMMA is a brittle glass, pure PEA is a rubber, and a PEA-PMMA nanocomposite is ductile. We fabricate the nanocomposite by swelling PEA with MMA monomer, followed by polymerizing MMA. We prepare nanocomposites of various weight fractions of PMMA and measure their properties, including modulus, yield strength, fracture strain, fracture strength, work of fracture, and toughness. Whereas bulk PMMA fractures at a strain of ∼0.05 by localizing inelastic deformation in crazes, the PEA-PMMA nanocomposite can be stretched several times its original length with homogeneous deformation. The nanocomposite separates into a glassy phase and a rubbery phase. For a nanocomposite of 45% weight fraction of PMMA, the atomic force microscopy shows that the two phases are bicontinuous and the phase size is at ∼20 nanometers. For the nanocomposite to undergo large deformation, the continuous glassy phase must accommodate. Our experiments exclude the mechanism that the glassy phase in the nanocomposite breaks into small pieces. Rather, the glassy phase in the nanocomposite is itself ductile. We discuss the molecular picture of this ductility.通过与橡胶聚合物形成纳米复合材料，可使脆性玻璃聚合物具有延展性。本文研究了聚甲基丙烯酸甲酯（PMMA）和聚丙烯酸乙酯（PEA）的纳米复合材料。纯 PMMA 是一种脆性玻璃，纯 PEA 是一种橡胶，而 PEA-PMMA 纳米复合材料则具有延展性。我们用 MMA 单体溶胀 PEA，然后聚合 MMA，制备出纳米复合材料。我们制备了不同重量分数的 PMMA 纳米复合材料，并测量了它们的性能，包括模量、屈服强度、断裂应变、断裂强度、断裂功和韧性。虽然块状 PMMA 在应变为 0.05 ∼ 0.05 时会因局部裂纹的非弹性变形而断裂，但 PEA-PMMA 纳米复合材料可在均匀变形的情况下拉伸其原始长度的数倍。纳米复合材料会分离成玻璃相和橡胶相。原子力显微镜显示，PMMA 重量分数为 45% 的纳米复合材料的两相是双连续的，相尺寸为 20 纳米。要使纳米复合材料发生大变形，必须容纳连续的玻璃相。我们的实验排除了纳米复合材料中玻璃相破碎成小块的机制。相反，纳米复合材料中的玻璃相本身具有延展性。我们将讨论这种延展性的分子结构。International Journal of PlasticityEffects of intergranular deformation incompatibility on stress state and fracture initiation at grain boundary: Experiments and crystal plasticity simulationsJiawei Chen, Tsuyoshi Furushimadoi:10.1016/j.ijplas.2024.104052 晶间变形不相容性对晶界应力状态和断裂起始的影响：实验和晶体塑性模拟The heterogeneous deformation of polycrystalline metals inherently originates from the intergranular deformation incompatibility. This paper proposes physical parameters related to the crystal orientations, the Schmid factor of the most activated slip system, and the misorientation angle to characterize the deformation incompatibility between the adjacent grains couple. A comprehensive multiscale investigation is conducted to reveal the mechanism from intergranular deformation incompatibility to fracture initiation at grain boundaries. At the specimen scale, experimental and numerical uniaxial tensile tests are performed on smooth and pre-notched dog-bone specimens to achieve different loading paths on the materials. The heterogeneous fields of stress triaxiality explains the heterogeneous size of the dimples observed in fractography. At the grain scale, electron backscatter diffraction analysis is conducted to characterize the microstructural properties around the nucleated voids within the materials. Voids are captured at the grain boundaries with directions parallel to the loading direction and intergranular deformation incompatibility is characterized using the proposed parameters. Simulations on the plastic deformation of realistic microstructures are performed to clarify the phenomenon. The results reveal that the fluctuation in stress triaxiality at grain boundaries is ascribed to intergranular deformation incompatibility, leading to fracture initiation at these sites. The relationships between the proposed physical parameters of intergranular deformation incompatibility and fluctuation in stress triaxiality are summarized in all circumstances. Finally, the ductile damage at the grain scale is predicted by the Rice-Tracey model, and the results show that the effects of microstructures on heterogeneous plastic deformation and stress state can be well considered.多晶金属的异质变形本质上源于晶粒间的变形不相容性。本文提出了与晶体取向、最活跃滑移系统的施密特因子和错位角相关的物理参数，以表征相邻晶粒间的变形不相容性。通过全面的多尺度研究，揭示了从晶间变形不相容性到晶界断裂引发的机理。在试样尺度上，对光滑和预缺口狗骨试样进行了实验和数值单轴拉伸试验，以实现材料的不同加载路径。应力三轴性的异质场解释了分形图中观察到的凹痕的异质大小。在晶粒尺度上，通过电子反向散射衍射分析来确定材料内成核空洞周围的微观结构特性。在与加载方向平行的晶界处捕捉空洞，并利用所提出的参数表征晶间变形不相容性。对现实微结构的塑性变形进行了模拟，以阐明这一现象。结果表明，晶界处应力三轴性的波动归因于晶间变形不相容性，从而导致在这些部位发生断裂。总结了所提出的晶间变形不相容性物理参数与各种情况下应力三轴度波动之间的关系。最后，利用 Rice-Tracey 模型预测了晶粒尺度上的韧性破坏，结果表明可以很好地考虑微结构对异质塑性变形和应力状态的影响。Thin-Walled StructuresEfficient graph representation in graph neural networks for stress predictions in stiffened panelsYuecheng Cai, Jasmin Jelovicadoi:10.1016/j.tws.2024.112157 用于加劲板应力预测的图形神经网络中的高效图形表示法Machine learning (ML) and deep learning (DL) techniques have gained significant attention as reduced order models (ROMs) to computationally expensive structural analysis methods, such as finite element analysis (FEA). Graph neural network (GNN) is a particular type of neural network which processes data that can be represented as graphs. This allows for efficient representation of complex geometries that can change during the conceptual design of a structure or a product. In this study, we propose a novel graph embedding for the efficient representation of 3D stiffened panels by considering separate plate domains as vertices. This approach is considered using Graph Sampling and Aggregation (GraphSAGE) to predict stress distributions in stiffened panels with varying geometries. A comparison between a finite element-vertex graph representation is conducted to demonstrate the effectiveness of the proposed approach. A comprehensive parametric study is performed to examine the effect of structural variables on stress predictions. A wide range of geometries is considered, material nonlinearity, a few boundary conditions, together with uniform and patch loading at various positions. The study involves straight and curved panels with uni- and bi-directional stiffeners. The proposed unit-vertex representation of the panel requires only about 2% of GPU memory and about 4% of training time in comparison to a finite element-vertex embedding. The GraphSAGE model with the proposed unit-vertex representation accurately captures stress distribution across all panels, achieving an average prediction accuracy of 92.3% for the maximum von Mises stress. Our results demonstrate the immense potential of graph neural networks with the proposed graph embedding as a robust reduced-order model for 3D structures.机器学习（ML）和深度学习（DL）技术作为计算成本高昂的结构分析方法（如有限元分析（FEA））的降阶模型（ROM），受到了广泛关注。图神经网络（GNN）是一种特殊类型的神经网络，可处理以图表示的数据。这样就能有效地表示复杂的几何形状，而这些几何形状在结构或产品的概念设计过程中可能会发生变化。在本研究中，我们提出了一种新颖的图嵌入方法，通过将独立的板域视为顶点来有效表示三维加劲板。我们使用图形采样和聚合（GraphSAGE）对这种方法进行了研究，以预测具有不同几何形状的加劲板的应力分布。对有限元-顶点图表示法进行了比较，以证明所提方法的有效性。进行了全面的参数研究，以检查结构变量对应力预测的影响。研究考虑了多种几何形状、材料非线性、一些边界条件，以及不同位置的均匀加载和贴片加载。研究涉及带有单向和双向加强筋的直线和曲线面板。与有限元顶点嵌入相比，所提出的面板单元顶点表示法只需要约 2% 的 GPU 内存和约 4% 的训练时间。采用拟议单元顶点表示法的 GraphSAGE 模型准确捕捉了所有面板的应力分布，最大 von Mises 应力的平均预测准确率达到 92.3%。我们的研究结果表明，图形神经网络与所提出的图形嵌入作为三维结构的稳健降阶模型，具有巨大的潜力。Hybrid isogeometric-based analysis and experimental investigation on the dynamic response characteristics of a clamped circular plate partially in contact with fluidI. Tugrul Ardic, M. Erden Yildizdag, Ahmet Ergindoi:10.1016/j.tws.2024.112171对部分与流体接触的夹紧圆板的动态响应特性进行基于等距测量的混合分析和实验研究The aim of this study was to analyze the effect of fluid presence on the dynamic response characteristics of the thin circular plate and the distortions associated with the wet mode shapes. To this end, series of numerical calculations and experimental measurements were performed to investigate the free vibration characteristics of clamped circular plate under in-vacuo conditions and when it is partially in contact with fluid. In the experimental studies, the clamped boundary conditions are imposed on the circular end plate of the horizontal rigid cylindrical tank by closely-spaced bolts, and measurements were performed based on roving hammer impact technique. The proposed numerical approach was divided into two parts based on linear hydroelasticity theory. In the first stage, the thin circular plate is considered to be under in-vacuo conditions, and the mathematical model for this problem is developed based on the isogeometric finite element method (IGAFEM). The fluid environment is introduced in the second stage of the study in which the generalized in-vacuo modal displacements constitute the boundary conditions of the potential flow problem. The influence of fluid medium is incorporated in the system of equations in the form of fluid added mass, and the corresponding fluid forces are calculated by the isogeometric boundary element method (IGABEM). It is observed that the fluid presence has significant effects on the dynamic response characteristics of the test structure, and the specifically, the distortions of wet mode shapes were noticeable due to presence of free surface of the water. Overall, it is found that the natural frequencies and corresponding mode shapes obtained by conducted experiments and adapted numerical framework are in favourable agreement.本研究旨在分析流体存在对薄圆板动态响应特性的影响以及与湿模态振型相关的变形。为此，进行了一系列数值计算和实验测量，以研究夹紧圆板在空腔条件下和部分接触流体时的自由振动特性。在实验研究中，通过间距较近的螺栓对水平刚性圆柱形水箱的圆形端板施加了夹紧边界条件，并基于巡回锤冲击技术进行了测量。根据线性流体弹性理论，提出的数值方法分为两个部分。在第一阶段，将薄圆板视为处于空泡条件下，并基于等几何有限元法（IGAFEM）建立了该问题的数学模型。研究的第二阶段引入了流体环境，其中广义虚空模态位移构成了潜在流动问题的边界条件。流体介质的影响以流体附加质量的形式被纳入方程系统，相应的流体力通过等距边界元法（IGABEM）进行计算。结果表明，流体的存在对测试结构的动态响应特性有显著影响，特别是由于水的自由表面的存在，湿模态形状发生了明显的扭曲。总之，通过试验和调整数值框架获得的固有频率和相应的模态振型非常吻合。来源：复合材料力学仿真Composites FEM
