【新文速递】2024年1月23日固体力学SCI期刊最新文章

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今日更新：Journal of the Mechanics and Physics of Solids 1 篇，Mechanics of Materials 1 篇

Journal of the Mechanics and Physics of Solids

A continuous phase-evolution model for cold and strain-induced crystallization in semi-crystalline polymers

Ming Lei, Shuailong Ren, Yulin Xiong, Jinyou Xiao, Lihua Wen, Haibao Lu, Xiao Hou

doi:10.1016/j.jmps.2024.105550

半结晶聚合物中低温和应变诱导结晶的连续相演化模型

The dynamic crystallization during extreme thermomechanical history under producing or service strongly influences the dimensional stability of the semi-crystalline thermoplastic polymers. To produce high-precision structural components, the proper thermomechanical history needs to be carefully designed to eliminate the crystallization-induced shrinkage. On the contrary, the rapidly developed four-dimensional (4D) printing technology tries to amplify the crystallization-induced shrinkage to directly produce the complex curvatures without supporting materials. However, the crystals formed at different deformation states might have different orientations, leading to an anisotropic residual deformation. Therefore, tracing of all crystals formed with different initial configurations is the key issue to ensure the geometric accuracy of both the high-precision and the deformable components. In this study, we developed a continuous phase-evolution model for both the cold and the strain-induced crystallization in semi-crystalline thermoplastics. The irreversible cold crystallization is analogized as the raindrop falling into the pool, and the reversible strain-induced crystallization is analogized as the nonequilibrium liquid-gas phase transformation. Using the continuous phase-evolution concept, the crystal growth is described by a series of continuously formed crystal phases sequentially added into the initial amorphous medium. Each newly formed crystal phase is in a stress-free state at the formation moment, and therefore the crystallization history coupled with the whole deformation history can be memorized. By introducing the oriented growth tensor representing the stress-free state of all formed crystals, the deformation-history dependent anisotropic crystallization and the corresponding residual deformation can be traced. The developed model is validated by comparing with the experimental data of the dynamic crystallization in amorphous poly l-lactide polymers under thermomechanical loading cycles. Finally, the predictive capability of the model is illustrated by several demonstrations, to show the influences of deformation-history dependent crystallization orientations and the corresponding anisotropic residual deformation.

在生产或使用过程中，极端热机械过程中的动态结晶对半结晶热塑性聚合物的尺寸稳定性有很大影响。为了生产高精度的结构部件，需要仔细设计适当的热机械历史，以消除结晶引起的收缩。相反，快速发展的四维(4D)打印技术试图放大结晶引起的收缩，直接产生复杂的曲率，而不需要支撑材料。然而，在不同变形状态下形成的晶体可能具有不同的取向，导致各向异性残余变形。因此，以不同初始构型形成的所有晶体的示踪是保证高精度和可变形部件几何精度的关键问题。在这项研究中，我们建立了半结晶热塑性塑料的冷结晶和应变诱导结晶的连续相演化模型。不可逆冷结晶被类比为雨滴落入池中，可逆应变结晶被类比为非平衡气液相变。利用连续相演化的概念，晶体生长是通过一系列连续形成的晶体相依次加入到初始非晶介质中来描述的。每个新形成的晶相在形成时刻都处于无应力状态，因此可以记忆结晶历史和整个变形历史。通过引入代表所有形成的晶体无应力状态的取向生长张量，可以追踪变形历史相关的各向异性结晶和相应的残余变形。通过与热载荷作用下非晶态聚l-丙交酯聚合物动态结晶实验数据的对比，验证了所建立的模型的有效性。最后，通过几个实例说明了该模型的预测能力，以显示变形历史相关的结晶取向和相应的各向异性残余变形的影响。

Mechanics of Materials

Emerging anisotropy and tethering with memory effects in fibrous materials

Antonino Favata, Andrea Rodella, Stefano Vidoli

doi:10.1016/j.mechmat.2024.104928

纤维材料中出现的各向异性和记忆效应

Fibrous materials may undergo an internal reorganization, which turns out in the emergence of preferential directions. This is a peculiar behavior of many biological tissues, which drive reorientation by external stimuli at chemo-mechanical levels. In particular, it is detected that contractile cells can reorganize fibrous extracellular matrices and form dense tracts of aligned fibers (tethers), that guide the development of tubular tissue structures and may provide paths for the invasion of cancer cells. Tether formation is caused by buckling instability of network fibres under cell-induced compression. We present a simple mechanical model within a variational framework that captures the essential aspects of these phenomena. The model qualitatively describes: (i) the emergence, induced by local compressive strain, of anisotropy, where fibrous materials exhibit directional preferences; (ii) the occurrence of micro-buckling, which leaves a lasting plastic deformation in the material; and (iii) the formation of localized field patterns, which contribute to the overall behavior of the material. By considering these fundamental aspects, our model provides insights into the mechanical response of fibrous materials and sheds light on the underlying mechanisms driving their behavior.

纤维材料可能经历内部重组，这表现为优先方向的出现。这是许多生物组织的一种特殊行为，它在化学机械水平上通过外部刺激驱动重新定向。特别是，研究发现，收缩细胞可以重组纤维细胞外基质，形成密集的排列纤维束(系索)，引导管状组织结构的发展，并可能为癌细胞的侵袭提供途径。绳系的形成是由网状纤维在细胞诱导的压缩作用下的屈曲失稳引起的。我们在变分框架内提出一个简单的力学模型，该模型捕捉了这些现象的基本方面。该模型定性地描述了:(i)由局部压缩应变引起的各向异性的出现，其中纤维材料表现出方向偏好;(ii)发生微屈曲，在材料中留下持久的塑性变形;(iii)局部场模式的形成，这有助于材料的整体行为。通过考虑这些基本方面，我们的模型提供了对纤维材料的机械响应的见解，并阐明了驱动其行为的潜在机制。

来源：复合材料力学仿真Composites FEM

【新文速递】2024年1月6日复合材料SCI期刊最新文章

今日更新：Composite Structures 3 篇，Composites Part A: Applied Science and Manufacturing 1 篇，Composites Science and Technology 1 篇Composite StructuresPlanar-thick panels and 3D-printed gap fillers: A hybrid digital fabrication approach to curved surface approximationsTing-Uei Lee, Yuanpeng Liu, Yi Min Xiedoi:10.1016/j.compstruct.2024.117875平面厚板和 3D 打印间隙填充物：曲面近似的混合数字制造方法Curved surfaces may be approximated using polygonal panels to simplify complex architectural designs, yet their constructions can be expensive due to single-use moulds producing unique panels. To reduce costs, strategies like planarizing and reducing the number of different panels have been suggested, which are increasingly achievable with advancing digital fabrication technologies. However, current subtractive and additive manufacturing techniques face challenges in producing complex 3D shapes and large volumes, respectively. Combining these two techniques has been attempted, mainly with small 3D-printed nodes, leaving the direct realization of curved surface approximations unexplored. This paper extends the thick-panel origami theory to introduce planar-thick panels and 3D-printed gap fillers for cost-effective constructions. It presents a computational workflow to transform meshes into non-intersecting panels while preserving edge connectivity and frame-like gap fillers with minimized volumes. Physical prototypes demonstrate significant cost savings compared to direct 3D printing. All prototypes are accurate within a 10 mm material thickness due to the guidance of the gap fillers. The finite element analysis shows that structural performance is greatly influenced by the material properties, especially of panels, due to their relatively larger volume. Numerical examples are also presented using the k -means clustering-optimization method to reduce the number of different panels.曲面可以使用多边形面板来近似，以简化复杂的建筑设计，但由于生产独特面板的模具是一次性使用的，其建造成本可能很高。为了降低成本，有人提出了平面化和减少不同面板数量等策略，随着数字制造技术的发展，这些策略越来越容易实现。然而，目前的减法和增法制造技术分别在生产复杂的三维形状和大批量产品方面面临挑战。将这两种技术结合在一起的尝试主要是使用小型三维打印节点，而直接实现曲面近似的技术尚未得到探索。本文扩展了厚板折纸理论，引入了平面厚板和三维打印间隙填充物，以实现具有成本效益的结构。它提出了一种计算工作流程，可将网格转化为不相交的面板，同时保留边缘连接和体积最小的框架式间隙填充物。与直接三维打印相比，物理原型展示了显著的成本节约。由于间隙填充物的引导作用，所有原型的材料厚度都精确到 10 毫米以内。有限元分析表明，结构性能在很大程度上受到材料特性的影响，尤其是面板，因为其体积相对较大。此外，还介绍了使用 k -means聚类优化法减少不同面板数量的数值示例。Shear strength damage model and damage removal FE modeling of stud shear connectors embedded in UHPCJianan Qi, Weihao Zou, Jie Liu, Shuai Li, Jingquan Wangdoi:10.1016/j.compstruct.2024.117880嵌入超高强度混凝土中的螺柱剪切连接件的剪切强度损伤模型和损伤消除有限元模型The study conducted a series of push-out tests to study the shear strength of studs as shear connectors in steel-UHPC (ultra high-performance concrete) composite structures. The damage removal modeling was developed and utilized to simulate stud damage caused by welding defects, concrete cracking, and lifting effects. The study investigated the impact of stud damage on the static performance and shear strength of studs. Results indicated that when the root area of the stud was damaged, the shear strength and stiffness of the stud decreased with the damage degree. When the stud root was damaged within 5%h (h is the height of stud shank), it had a significant effect on the shear strength of the stud. Damage outside the 5%h range of the stud root had no significant effect on the shear strength of the stud. And a shear strength damage model was firstly proposed to reveal the damage mechanism of studs. A reduction factor K was proposed to account for the loss in shear strength caused by stud damage. Two methods for calculating K, namely the area reduction method and the equivalent area method, were developed. The calculated values of shear strength considering stud damage were obtained and verified by comparing the calculated values with the test results. The proposed method offers a better prediction of shear strength for damaged studs in UHPC.该研究进行了一系列推出试验，以研究钢-UHPC（超高性能混凝土）复合结构中作为剪切连接件的螺柱的剪切强度。开发并使用了损伤消除模型来模拟由焊接缺陷、混凝土开裂和提升效应造成的螺柱损伤。研究调查了螺柱损坏对螺柱静态性能和抗剪强度的影响。结果表明，当螺柱根部区域受损时，螺柱的剪切强度和刚度会随着受损程度的增加而降低。当螺柱根部的损坏程度在 5%h（h 为螺柱柄的高度）范围内时，对螺柱的抗剪强度有显著影响。在螺柱根部 5%h范围之外的损坏对螺柱的抗剪强度没有明显影响。为了揭示螺柱的损坏机制，首先提出了一个剪切强度损坏模型。并提出了一个折减系数 K 来计算因螺栓损坏而造成的剪切强度损失。提出了两种计算 K 的方法，即面积缩减法和等效面积法。通过将计算值与测试结果进行比较，获得了考虑到螺柱损坏的剪切强度计算值，并对其进行了验证。所提出的方法能更好地预测超高强度混凝土中受损螺柱的抗剪强度。Three-dimensional finite element modelling OF the fire response of passive and prestressed near-surface mounted (NSM)–cfrp-strengthened reinforced concrete slab stripsAdriana S. Azevedo, João P. Firmo, João R. Correiadoi:10.1016/j.compstruct.2023.117872 被动和预应力近表面安装（NSM）-cfrp 加固钢筋混凝土板条火灾响应的三维有限元建模This paper presents a numerical study about the fire behaviour of reinforced concrete (RC) slab strips strengthened with passive and prestressed carbon fibre reinforced polymer (CFRP) laminates installed according to the Near-Surface Mounted (NSM) technique. 3D finite element models were developed to simulate fire resistance tests in which the NSM-CFRP-strengthened-RC slab strips were simultaneously subjected to a service load and the ISO834 fire. The CFRP-concrete interface was modelled through temperature-dependent bi-linear bond-slip laws. In addition to the prestress levels applied to the CFRP (0%, 25% and 50% of their tensile strength), the presence/geometry of fire protection (calcium silicate boards) was also assessed. The comparison between numerical and previous experimental results showed the models accuracy in predicting the thermo-mechanical response of fire exposed passive and prestressed NSM-CFRP-strengthened-RC slab strips, presenting a fire resistance decrease when the prestress increased from 0% to 50%, from 13to 6min when no fire protection was used, and from 152to 127min with fire protection. The numerical results allowed predicting the decrease of critical temperature in the CFRP anchorages with the prestress increase: 3.4-3.6Tg, 3.0Tg , and 2.1-2.4Tg respectively for prestress levels of 0%, 25% and 50% (Tg– adhesive’s glass transition temperature).本文对采用近表面安装（NSM）技术安装的被动和预应力碳纤维增强聚合物（CFRP）层压板加固的钢筋混凝土（RC）板条的火灾行为进行了数值研究。开发了三维有限元模型来模拟耐火试验，在试验中，NSM-CFRP 加固的 RC 板条同时承受使用荷载和 ISO834 火灾。CFRP - 混凝土界面通过与温度相关的双线性粘结滑移定律进行建模。除了应用于 CFRP 的预应力水平（拉伸强度的 0%、25% 和 50%）外，还评估了防火保护（硅酸钙板）的存在/几何形状。数值结果与之前实验结果的对比显示，模型在预测受火的无源和预应力 NSM-CFRP 加固 RC 板条的热机械响应方面非常准确，当预应力从 0% 增加到 50%，耐火性下降；在未使用防火保护时，耐火性从 13 分钟下降到 6 分钟；在使用防火保护时，耐火性从 152 分钟下降到 127 分钟。数值结果可以预测 CFRP 锚固件的临界温度会随着预应力的增加而降低：在预应力水平为 0%、25% 和 50% 时，临界温度分别为 3.4-3.6Tg、3.0Tg 和 2.1-2.4Tg（Tg为粘合剂的玻璃转化温度）。Composites Part A: Applied Science and ManufacturingPseudo-ductile behaviour of fibrous composite Z-pinsE. Santana de Vega, G. Allegri, B. Zhang, I. Hamerton, S.R. Hallettdoi:10.1016/j.compositesa.2024.108009纤维状复合材料 Z 形销的伪电导行为This paper describes the development and characterisation of a novel type of composite Z-pin able to accommodate large deformation without exhibiting fibre failure. Three types of pseudo-ductile Z-pins are fabricated by means of micro-pultrusion of polybenzoxazole (PBO) fibres. Namely, unidirectional PBO fibre (uPBO) Z-pins in combination with a ductile (uPBO/DCT) and a brittle (uPBO/BT) matrix system are developed, together with a twisted PBO fibre Z-pin in combination with a ductile matrix (tPBO/DCT). Single pin bridging tests are carried out across the full mode mixity range from mode I (Φ= 0) to mode II (Φ = 1). The tests reveal that uPBO-based pins are able to pull out throughout the full mode mixity range, regardless of the ductility of the pin matrix. uPBO/DCT pins exhibit a 20-fold increase in energy dissipation per pin than traditional carbon fibre/bismaleimide (CF/BMI) pins at load mode mixities higher than Φ = 0.9. The mode I behaviour of all pins considered is comparable. All PBO pins exhibit an apparent delamination toughness enhancement superior to CF/BMI at mode mixities above Φ = 0.2, with a ductile matrix increasing the average energy dissipated per pin by a further 2-8%.本文介绍了一种新型复合材料 Z 形销的开发和特性分析，这种销能够承受大变形而不会出现纤维断裂。通过对聚苯并恶唑（PBO）纤维进行微拉伸，制造出了三种假韧性 Z 形销。即，结合韧性（uPBO/DCT）和脆性（uPBO/BT）基体系统的单向 PBO 纤维（uPBO）Z 形销，以及结合韧性基体的扭曲 PBO 纤维 Z 形销（tPBO/DCT）。在从模式 I（Φ= 0）到模式 II（Φ= 1）的整个混合模式范围内进行了单针桥接测试。测试结果表明，无论插针基体的延展性如何，基于 uPBO 的插针都能在整个混合模式范围内拔出。当负载模式混合度高于 Φ = 0.9 时，uPBO/DCT 插针的单位能量耗散比传统碳纤维/双马来酰亚胺（CF/BMI）插针增加了 20 倍。所有引脚的模式 I 行为都具有可比性。所有 PBO 销针在模式混合度超过 Φ = 0.2 时，分层韧性明显优于 CF/BMI，韧性基体使每个销针的平均耗散能量再增加 2-8%。Composites Science and TechnologyEpoxy composites with satisfactory thermal conductivity and electromagnetic shielding yet electrical insulation enabled by Al2O3 platelet-isolated MXene porous microsphere networksFanjun Guo, Yuying Wang, Kangle Xue, Li Liu, Jun Li, Yudong Huangdoi:10.1016/j.compscitech.2023.110425 通过 Al2O3 板块隔离 MXene 多孔微球网络实现具有令人满意的导热性、电磁屏蔽性和电气绝缘性的环氧树脂复合材料The development of highly integrated electronic devices has placed higher demands on the thermal conductivity, electromagnetic interference (EMI) shielding, and electrical insulation properties of electronic packaging materials. In this work, a facile strategy for the fabrication of epoxy composites with Al2O3 platelet-isolated MXene porous microsphere networks was proposed. The composites were prepared by a simple salt-template method under vortex conditions and showed effective electric insulation as well as satisfactory EMI shielding and thermal conductivity properties. Particularly, the EMI shielding performance is enhanced by MXene porous microspheres with multi-interfacial conductive networks. Moreover, Al2O3 platelets (Al2O3p) with shell-like arrangement enrich the thermal conductivity paths on one hand and synergistically interact with the epoxy matrix to intercept the electron transfer between the MXene porous microspheres on the other hand. As a result, the obtained MXene/Al2O3p/Epoxy composites exhibit excellent thermal conductivity (2.1 W/mK) and satisfactory EMI shielding performance (22.3 dB at 8.6 GHz), while maintaining high electrical insulation (1.2 × 109 Ωcm). This paper provided a new idea to synergistically improve the electrical insulation, thermal conductivity and EMI shielding properties of epoxy composites.高度集成电子设备的发展对电子封装材料的导热性、电磁干扰（EMI）屏蔽和电绝缘性能提出了更高的要求。本研究提出了一种简便的环氧树脂与 Al2O3 板状隔离 MXene 多孔微球网络复合材料的制备方法。复合材料是在涡流条件下通过简单的盐模板法制备的，具有有效的电绝缘性能、令人满意的电磁干扰屏蔽性能和导热性能。特别是，具有多界面导电网络的 MXene 多孔微球增强了 EMI 屏蔽性能。此外，具有贝壳状排列的 Al2O3 小板（Al2O3p）一方面丰富了导热路径，另一方面与环氧基质协同作用，拦截了 MXene 多孔微球之间的电子转移。因此，所获得的 MXene/Al2O3p/Epoxy 复合材料具有优异的导热性（2.1 W/mK）和令人满意的电磁干扰屏蔽性能（8.6 GHz 时为 22.3 dB），同时还保持了较高的电绝缘性（1.2 × 109 Ωcm）。本文为协同改善环氧树脂复合材料的电绝缘性、导热性和 EMI 屏蔽性能提供了一个新思路。来源：复合材料力学仿真Composites FEM