今日更新：Mechanics of Materials 1 篇，Thin-Walled Structures 3 篇Mechanics of MaterialsMicrostructure characterization and dynamic recrystallization behavior of Ni–Cu alloy during hot deformationA. Momeni, G.R. Ebrahimi, M. Jahazi, H.R. Ezatpourdoi:10.1016/j.mechmat.2024.105002Ni-Cu合金热变形过程的显微组织表征及动态再结晶行为Flow curve and microstructure of Ni–30Cu alloy were studied after hot compression at 1150 °C and strain rate of 0.01 s−1. The stress-strain and work hardening rate curves showed a weak peak at strain of 0.32, followed by a slight dynamic softening. The dominant microstructural mechanisms in low (0.1–0.23) and medium strains (0.23–0.32) were dynamic recovery and dynamic recrystallization, respectively. Microstructural characterizations by electron back scattered diffraction (EBSD) showed that continuous dynamic recrystallization brings about after the peak strain (ε = 0.32) and leads to grain refinement. It was found that the twin boundaries help to activate a grain dissociation mechanism which works as a new variant of continuous dynamic recrystallization. The grain boundary maps developed by EBSD showed that new twin boundaries form through the evolution of low angle grain boundaries. This step, named as “recovery twinning”, was identified as the origin for the observed twinning-assisted continuous dynamic recrystallization (TCDRX). The Kocks-Mecking dislocation evolution model was modified in order to take the dynamic softening by TCDRX into account and describe the variation in the frequency of high angle grain boundaries with strain. Model predictions were validated and confirmed by the experimental results.研究了Ni-30Cu合金在1150 ℃、应变速率为0.01 s−1的热压缩条件下的流变曲线和显微组织。应力-应变和加工硬化速率曲线在应变为0.32时出现弱峰值，随后出现轻微的动态软化。低应变(0.1 ~ 0.23)和中应变(0.23 ~ 0.32)的主要显微组织机制分别为动态恢复和动态再结晶。电子背散射衍射(EBSD)的显微组织表征表明，在峰值应变(ε = 0.32)之后，晶粒发生了连续的动态再结晶，导致晶粒细化。发现孪晶界有助于激活晶粒解离机制，这是连续动态再结晶的一种新变体。EBSD绘制的晶界图显示，低角度晶界的演化形成了新的孪晶界。这一步骤被称为“恢复孪晶”，被认为是观察到的孪晶辅助连续动态再结晶(TCDRX)的起源。修正了Kocks-Mecking位错演化模型，考虑了TCDRX的动态软化作用，并描述了高角晶界频率随应变的变化规律。实验结果验证了模型预测的正确性。Thin-Walled StructuresStacking effects on dynamic mechanical behavior of bilayer hexagonal boron nitride under impactXiaodong Qian, Fang Li, Hong Tiandoi:10.1016/j.tws.2024.111866 冲击作用下双层六方氮化硼动态力学行为的叠加效应Hexagonal boron nitride (h-BN) is a promising material for ballistic armor due to its excellent mechanical properties, enriched by different bilayer stacking arrangements. Molecular dynamics methods are used to study the stacking effects on the static and dynamic mechanical properties of bilayer h-BN. The AB (nitrogen) stacked bilayer structure attracts our attention because of its superior interlayer synergistic ability to resist projectile indentation up to a maximum force of 152.89 nN, which is about 22.9% higher than the average value of other stacked bilayers. The impact response of bilayer h-BN with AB (nitrogen) stacking arrangement is then investigated at velocities of 2-4 km/s, which has the highest critical perforation velocity of 3.075 km/s, increased by 36.7% compared to monolayer h-BN. At a low impact velocity of 2.5km/s, the AB (nitrogen) stacked h-BN bilayer spends the shortest time to dissipate the impact energy of projectile and remains intact, while the top layers of other stacked bilayers are penetrated. At high impact velocities, a perforation event occurs, accompanied by multiple deflections of crack tips from zigzag to armchair to zigzag again, which intrinsically enhances the toughness of material. This study provides more understanding of the dynamic mechanical behavior of bilayer h-BN, as well as the design of armor structures based on stacking arrangements of 2D materials.六方氮化硼(h-BN)由于其优异的力学性能和不同的双层堆叠方式而成为一种很有前途的弹道装甲材料。采用分子动力学方法研究了叠层效应对双层h-BN静态和动态力学性能的影响。AB(氮)堆叠双层结构因其优异的层间协同抗弹射压痕能力而引起了我们的关注，其抗弹射压痕力最大可达152.89 nN，比其他堆叠双层结构的平均值高出约22.9%。在2 ~ 4 km/s速度下，研究了AB(氮)堆砌双层h-BN的冲击响应，其最高临界射孔速度为3.075 km/s，比单层h-BN提高了36.7%。在2.5km/s的低冲击速度下，AB(氮)堆叠的h-BN双分子层耗散弹丸冲击能的时间最短，且保持完整，而其他堆叠双分子层的顶层被击穿。在高冲击速度下，穿孔事件发生，伴随着裂纹尖端从之字形到扶手形再到之字形的多次偏转，这从本质上提高了材料的韧性。本研究为进一步了解双层h-BN的动态力学行为，以及基于二维材料堆叠排列的装甲结构设计提供了依据。Nonlinear forced vibration of functionally graded hybrid three-phase nanocomposite toroidal shell segments reinforced by carbon nanotubes (CNTs) and graphene nanoplatelets (GPLs)Ahmed S. Khalaf, Hamad M Hasandoi:10.1016/j.tws.2024.111876碳纳米管和石墨烯纳米片增强功能梯度杂化三相纳米复合材料环形壳段的非线性强迫振动This study proposes a unique three-phase functionally graded (FG) hybrid nanocomposite material reinforcing the toroidal shell segments to investigate the nonlinear forced vibration using Reddy's higher-order shear deformation theory, von Karman geometrical nonlinearity and Stein-McElman's assumption along with the Hamilton principle. The examined toroidal shell's material consists of polymeric resin, carbon nanotubes (CNTs), and graphene platelets (GPLs) as nanocomposites. The material properties have been derived based on a modified Halpin-Tsai micromechanical model. Four distribution patterns have been studied: uniform (UD), FG-X, FG-O, and FG-V. The continuous distribution of GPLs and CNTs leads to inhomogeneous position-dependent properties throughout the shell thickness. The obtained differential equations of motion have been reduced to ordinary equations using Galerkin's technique. A multi-scales method (MSM) is used to estimate a closed-form solution representing the frequency-amplitude relation, and the state space representation is used along with numerical fourth-order Runge Kutta method (RK4) to obtain the nonlinear dynamic response of the toroidal shell. The accuracy of the current results obtained has been verified by comparing them with the relevant literature and numerical results using (RK4). In addition, the influence of both GPLs and CNTs weight fractions, nanofillers’ distribution types, longitudinal and circumferential wave numbers, elastic foundation parameters, static axial compression load, transverse excitation load, damping ratio, geometrical characteristics of the toroidal shell on the dimensionless natural frequency, nonlinear primary resonance (frequency-amplitude curve), and nonlinear dynamic response are carefully studied. The results found that combining (GPLs & CNTs) into the shell's matrix improves performance, especially in concave shells compared to convex ones. The FG-X pattern reduces peak resonance amplitude and improves natural frequency. A reduction of 12.3% is observed for convex shells, and 21.5% for concave shells compared to FG-O.利用Reddy的高阶剪切变形理论、von Karman几何非线性、Stein-McElman假设和Hamilton原理，提出了一种独特的三相功能梯度(FG)杂化纳米复合材料增强环面壳段来研究非线性强迫振动。所研究的环形壳体材料由聚合物树脂、碳纳米管(CNTs)和石墨烯片(GPLs)作为纳米复合材料组成。基于改进的Halpin-Tsai微力学模型推导了材料的性能。研究了四种分布模式:均匀分布(UD)、FG-X、FG-O和FG-V。gpl和碳纳米管的连续分布导致了整个壳体厚度的不均匀位置依赖性质。利用伽辽金技术将得到的运动微分方程化为普通方程。采用多尺度法(MSM)估计频率-幅度关系的封闭解，并结合四阶数值龙格库塔法(RK4)进行状态空间表示，得到环面壳的非线性动力响应。通过与相关文献和使用(RK4)的数值结果进行比较，验证了当前所得结果的准确性。此外，还仔细研究了gpl和CNTs重量分数、纳米填料分布类型、纵波数和周向波数、弹性基础参数、静态轴向压缩载荷、横向激励载荷、阻尼比、环形壳几何特性对无量纲固有频率、非线性主共振(频幅曲线)和非线性动力响应的影响。结果发现，与凸壳相比，将(gpl和CNTs)结合到壳的基体中可以提高性能，特别是在凹壳中。FG-X模式降低了峰值共振幅度，提高了固有频率。与FG-O相比，凸壳减少了12.3%，凹壳减少了21.5%。Cross-section behaviour and capacity of cold-formed austenitic stainless steel flat-oval hollow sections under combined compression and bendingShuai Li, Ke Jiang, Man-Tai Chen, Andi Su, Tong Guo, Ou Zhaodoi:10.1016/j.tws.2024.111877冷弯奥氏体不锈钢扁椭圆形空心截面在压缩和弯曲联合作用下的截面行为和性能Flat-oval hollow section is composed of two semi-circular elements and two flat elements, with the semi-circular elements (exposed to wave and wind) offering a low level of hydrodynamic and aerodynamic drag and the flat elements facilitating connections with other members perpendicular to the wave and wind directions. This paper presents an experimental and numerical study of the cross-section behaviour and resistance of cold-formed austenitic stainless steel flat-oval hollow section stub columns under combined compression and bending. An experimental programme, including initial local geometric imperfection measurements and ten major-axis and minor-axis eccentric compression tests, was firstly carried out, with the test setups, procedures and results fully reported. Following the experimental programme, a numerical modelling programme was performed, with finite element models developed and validated against the eccentric compression test results and then used to conduct parametric studies to generate additional numerical data. Based on the test and numerical results, the relevant codified design interaction curves for cold-formed austenitic stainless steel rectangular hollow sections were evaluated for the applicability to their flat-oval hollow section counterparts. It was found from the evaluation results that the codified design interaction curves led to inaccurate resistance predictions, mainly due to the conservative end points (i.e. cross-section resistances under pure compression and pure bending) and inefficient shapes. Finally, a new design interaction curve was proposed through the use of more accurate end points and more efficient shape and offered more accurate and consistent resistance predictions for cold-formed austenitic stainless steel flat-oval hollow sections under combined loading than the codified design interaction curves.扁平椭圆形中空截面由两个半圆单元和两个平面单元组成，半圆单元(暴露在波浪和风中)提供低水平的流体动力和空气动力学阻力，平面单元促进与垂直于波浪和风向的其他构件的连接。本文对冷弯奥氏体不锈钢扁椭圆形空心截面短柱在压缩和弯曲联合作用下的截面性能和阻力进行了试验和数值研究。首先进行了一项实验方案，包括初步的局部几何缺陷测量和十次大轴和小轴偏心压缩试验，并全面报告了试验装置、程序和结果。在实验程序之后，进行了数值模拟程序，开发了有限元模型，并根据偏心压缩试验结果进行了验证，然后用于进行参数研究，以生成额外的数值数据。根据试验结果和数值计算结果，评价了冷弯奥氏体不锈钢矩形空心截面的相关规范设计相互作用曲线对扁椭圆形空心截面的适用性。从评价结果中发现，规范的设计交互曲线导致了不准确的阻力预测，主要是由于端点保守(即纯压缩和纯弯曲下的截面阻力)和低效的形状。最后，通过使用更精确的端点和更有效的形状，提出了一种新的设计交互曲线，并提供了比编码设计交互曲线更准确和一致的冷弯奥氏体不锈钢扁椭圆形空心截面在组合载荷下的阻力预测。来源：复合材料力学仿真Composites FEM
