今日更新：International Journal of Solids and Structures 3 篇，Journal of the Mechanics and Physics of Solids 1 篇，Thin-Walled Structures 1 篇International Journal of Solids and StructuresSynergistic effect of interface and agglomeration on Young's modulus of graphene-polymer nanocompositesJie Wang, Liangfei Gong, Shangbin Xi, Chao Li, Yu Su, Lina Yangdoi:10.1016/j.ijsolstr.2024.112716界面和团聚对石墨烯-聚合物纳米复合材料杨氏模量的协同效应Filler agglomeration can severely hinder the stress transfer at the graphene-polymer interface, leading to deterioration of the interfacial properties and the overall mechanical performance of graphene nanocomposites. However, the correlation between the agglomeration and the interface effect was rarely investigated in the past. We hereby propose a novel and efficient approach to accurately obtain the effective Young’s modulus of graphene nanocomposites. We first introduced Cauchy's cumulative probability function to describe the progressive deterioration of the filler-matrix interface as the graphene’s volume concentration increases. Then, via the shear-lag approach, we developed a modified Halpin-Tsai model to take into account the effects of the agglomeration threshold, the filler-matrix interfacial moduli, and the surfactant treatment. The entire approach was validated by comparing the predicted results with five groups of experimental data. It was found that the interfacial properties are roughly linearly related to the matrix-to-nanofiller modulus ratio, which illustrates that a severer interfacial modulus mismatch leads to poorer interfacial bonding quality, and thus to a lower overall elastic modulus. The interfacial coefficient can also quantitatively characterize the enhancement effect of surfactant treatment. Besides, the synergistic effect of filler-matrix interface and filler agglomeration in the overall Young's modulus of composites was confirmed by comparison between theoretical and experimental results, and the latter becomes increasingly dominant as the graphene volume concentration increases.填料团聚会严重阻碍石墨烯-聚合物界面的应力传递，导致界面性能和石墨烯纳米复合材料的整体机械性能下降。然而，过去很少有人研究团聚与界面效应之间的相关性。在此，我们提出了一种新颖、高效的方法来精确获得石墨烯纳米复合材料的有效杨氏模量。我们首先引入考奇累积概率函数来描述随着石墨烯体积浓度的增加，填料-基体界面逐渐恶化的过程。然后，通过剪切滞后方法，我们建立了一个改进的 Halpin-Tsai 模型，以考虑团聚阈值、填料-基质界面模量和表面活性剂处理的影响。通过将预测结果与五组实验数据进行比较，验证了整个方法。结果发现，界面特性与基体-纳米填料模量比大致呈线性关系，这说明界面模量失配越严重，界面结合质量越差，从而导致整体弹性模量越低。界面系数还可以定量表征表面活性剂处理的增强效果。此外，通过比较理论和实验结果，证实了填料-基体界面和填料团聚在复合材料整体杨氏模量中的协同效应，而且随着石墨烯体积浓度的增加，后者变得越来越主要。Size-dependence of fracture processes in intact rocksAleksander Zubelewiczdoi:10.1016/j.ijsolstr.2024.112699完整岩石断裂过程的尺寸依赖性In brittle heterogeneous materials, the ultimate stress carries information on the material’s load-bearing capacity and, for this reason, this stress is an important engineering quantity. However, this stress is just a point in the sequence of stress–strain responses, each of them reflects the current state of damage in the material. Initially, isolated cracks grow, sense each other, and form multiple crack networks. The networks enable dilatational shear and facilitate further growth of damage. Large samples contain a broad spectrum of the crack-enabling defects and, therefore, the sample size becomes an irrelevant factor. However, when the defect population is limited, the damage process is constrained and, as a result, the peak stress is rising. According to the central limit theorem, the defect’s propensity for generating cracks should obey the rules of normal distribution. It turns out that the normal distribution of defects becomes a Weibull-like distribution of strength, where shape of the distribution is affected by the sample size and, also, is sensitive to hydrostatic pressure. The size-dependence of fracture processes is the main objective of the study.在脆性异质材料中，极限应力包含了材料承载能力的信息，因此，极限应力是一个重要的工程量。然而，该应力只是应力-应变反应序列中的一个点，每个应力-应变反应序列都反映了材料当前的损坏状态。起初，孤立的裂缝会逐渐扩大，相互感应，并形成多个裂缝网络。这些裂纹网络能够产生扩张剪切，并促进损伤的进一步发展。大样本中包含了广泛的裂纹致能缺陷，因此样本大小成为一个无关紧要的因素。然而，当缺陷数量有限时，损伤过程受到限制，因此峰值应力不断上升。根据中心极限定理，缺陷产生裂纹的倾向应遵守正态分布规则。结果发现，缺陷的正态分布变成了类似于 Weibull 的强度分布，分布的形状受样本大小的影响，而且对静水压力也很敏感。研究的主要目标是断裂过程的尺寸依赖性。Green’s functions for the isotropic planar relaxed micromorphic model — Concentrated force and concentrated couplePanos Gourgiotis, Gianluca Rizzi, Peter Lewintan, Davide Bernardini, Adam Sky, Angela Madeo, Patrizio Neffdoi:10.1016/j.ijsolstr.2024.112700各向同性平面松弛微观模型的格林函数 - 聚力和聚偶We derive the Green’s functions (concentrated force and couple in an infinite space) for the isotropic planar relaxed micromorphic model. Since the relaxed micromorphic model particularises into the micro-stretch, Cosserat (micropolar), couple-stress, and linear elasticity model for certain choices of material parameters, we recover the fundamental solutions in all these cases.我们推导出了各向同性平面松弛微形态模型的格林函数（无限空间中的集中力和耦合力）。由于松弛微形态模型在某些材料参数的选择下会具体化为微拉伸、Cosserat（微极性）、耦合应力和线性弹性模型，因此我们恢复了所有这些情况下的基本解。Journal of the Mechanics and Physics of SolidsAnomalous tension–compression asymmetry in amorphous silicon: insights from atomistic simulations and elastoplastic constitutive modelingBin Ding, Liang Hu, Yuan Gao, Yuli Chen, Xiaoyan Lidoi:10.1016/j.jmps.2024.105575非晶硅中反常的拉伸-压缩不对称现象：原子模拟和弹塑性结构建模的启示Recent experiments observed an inherent, anomalous tension-compression (T-C) asymmetry with T>C in microscale amorphous silicon (a-Si), which is free of dominant microcracks or dislocations. However, quantifying the disordered structure of a-Si and correlating it with T-C asymmetry remains mysterious. Here, we first conduct a series of atomistic simulations to explore this anomaly in a-Si. Results reveal a positive correlation between cooling rate q and fraction of liquid-like phase ϕll, suggesting that higher cooling rates trap more atoms in liquid-like phase. Uniaxial tension and compression tests reveal that T-C asymmetry with T>C persists across all cooling rates, where the physical origin is attributed to variations in initial ϕll and its subsequent spatial and temporal evolutions during loading. A physics based, Mohr-Coloumb type elastoplastic constitutive model, determining cohesion c by the content of liquid-like component ϕll, successfully reproduces the observed anomalous T-C asymmetry and its dependence on the initial structure in a-Si. Furthermore, the degree of asymmetry tends to diminish with an increase in initial ϕll, a trend general to both amorphous Si and CuZr metallic glass (MG). While the contrasting atomic volumes of the liquid-like phase in a-Si and MG explain their differing T-C asymmetries, with a-Si exhibiting T>C and CuZr exhibiting T< C. These insights enhance the fundamental understanding of processing-structure-property relationship in amorphous materials, which benefits for designing amorphous with desired asymmetry in practical applications.最近的实验观察到，在微尺度非晶硅（a-Si）中存在固有的反常拉伸-压缩（T-C）不对称现象，T>C。然而，量化非晶硅的无序结构并将其与 T-C 不对称相关联仍是一个谜。在此，我们首先进行了一系列原子模拟，以探索非晶硅中的这一反常现象。结果表明，冷却速率 q 与类液相的比例 ϕll 之间存在正相关，这表明较高的冷却速率会将更多原子捕获到类液相中。单轴拉伸和压缩测试表明，在所有冷却速率下，T-C 不对称与 T>C 都持续存在，其物理原因可归结为初始 ϕll 的变化及其随后在加载过程中的空间和时间演变。基于物理学的莫尔-科鲁姆（Mohr-Coloumb）型弹塑性构成模型，通过类液体成分ϕll的含量来确定内聚力c，成功地再现了观察到的反常T-C不对称现象及其与a-Si初始结构的依赖关系。此外，不对称的程度往往会随着初始 ϕll 的增加而减小，这是无定形硅和 CuZr 金属玻璃 (MG) 的普遍趋势。这些见解加深了人们对非晶材料的加工-结构-性能关系的基本认识，有利于在实际应用中设计出具有所需不对称性的非晶材料。Thin-Walled StructuresInvestigation on shock wave mitigation performance of modified polyurea coated helmetShengpeng Xue, Wenlong Xu, Cheng Wang, Xuefang Li, Shiyu Jiadoi:10.1016/j.tws.2024.111704改性聚脲涂层头盔的冲击波减缓性能研究In recent years, traumatic brain injury caused by explosive blast has become the leading cause of death in current military conflicts. However, as for the existing battlefield protection equipment, most of them focus on how to protect against infered injury caused by high-speed shrapnel. Accordingly, there is a lack of systematic research based on shock wave protection. In this work, a new modified polyurea is designed by adding SiO2 nanoparticles filler firstly. The effects of different proportions of SiO2 nanoparticles on the thermodynamic, quasi-static and dynamic mechanical properties of matrix are investigated. In recent years, traumatic brain injury caused by explosive blast has become the leading cause of death in current military conflicts. However, as for the existing battlefield protection equipment, most of them focus on how to protect against infered injury caused by high-speed shrapnel. Accordingly, there is a lack of systematic research based on shock wave protection.. The protection property of the material under shock wave is tested by the shock tube. Based on the above test results, the full-size shock wave protection test model of human head is developed, and the measurement of overpressure and acceleration peak of several key positions of head is realized. Finally, a new type of shock wave protection helmet is developed, which realizes efficient protection against shock wave. Under quasi-static loading conditions, the yield stress of PU-SiO2 decreases gradually with the increase of the content of SiO2 nanoparticles. Under high strain rate conditions, the strain hardening characteristic of PU-SiO2 increases gradually with the increase of SiO2 content. In the shock mitigation experiment, the peak overpressure and peak acceleration of shock wave decrease by 32.60% and 50.90%, respectively. The peak overpressure decreases again by 11.20% when the protective material is PU-SiO2, indicating that the SiO2 particles can improve the shock mitigation of PU. In the brain protection experiment, the changes in peak overpressure and peak acceleration at the three monitoring sites of the prefrontal lobe, posterior skull, and head reflect the degree of protection of the new material against shock wave.近年来，爆炸造成的脑外伤已成为当前军事冲突中的主要死亡原因。然而，就现有的战场防护装备而言，它们大多侧重于如何防护高速弹片造成的脑损伤。因此，缺乏基于冲击波防护的系统研究。本研究首先通过添加 SiO2 纳米粒子填料设计了一种新型改性聚脲。研究了不同比例的 SiO2 纳米粒子对基体热力学、准静态和动态力学性能的影响。近年来，爆炸造成的脑外伤已成为当前军事冲突中的主要死亡原因。然而，就现有的战场防护装备而言，它们大多侧重于如何防护高速弹片造成的脑损伤。因此，目前还缺乏基于冲击波防护的系统研究。通过冲击管测试材料在冲击波作用下的防护性能。在上述试验结果的基础上，开发了全尺寸的人体头部冲击波防护试验模型，并实现了对头部几个关键位置的超压和加速度峰值的测量。最后，研制出一种新型冲击波防护头盔，实现了对冲击波的有效防护。在准静态加载条件下，随着纳米二氧化硅含量的增加，聚氨酯二氧化硅的屈服应力逐渐减小。在高应变速率条件下，随着 SiO2 含量的增加，PU-SiO2 的应变硬化特性逐渐增强。在减震实验中，冲击波的峰值过压和峰值加速度分别降低了 32.60% 和 50.90%。当保护材料为 PU-SiO2 时，过压峰值又降低了 11.20%，这表明 SiO2 颗粒可以改善 PU 的减震性能。在脑保护实验中，前额叶、后颅骨和头部三个监测点的峰值过压和峰值加速度的变化反映了新材料对冲击波的保护程度。来源：复合材料力学仿真Composites FEM
