今日更新:Composite Structures 3 篇,Composites Part B: Engineering 1 篇,Composites Science and Technology 1 篇
Waterborne polyurethane aerogel with asymmetric gradient structure formed by density-induced self-stratification for absorption-dominated electromagnetic interference shielding
Meng Ma, Xiao Liang, Wenting Tao, Qiang Peng, Wenqin Shao, Si Chen, Yanqin Shi, Huiwen He, Yulu Zhu, Xu Wang
doi:10.1016/j.compstruct.2024.118259
采用密度诱导自分层形成不对称梯度结构的水性聚氨酯气凝胶,用于吸收型电磁干扰屏蔽
The issues of electromagnetic (EM) emission and its secondary contamination have prompted significant concern among individuals. Hence, the development of efficient absorbing electromagnetic interference (EMI) shielding materials are urgent. Herein, silver-coated and foamed temperature-sensitive microspheres (Ag@FTSM) were synthesized by electroless silver plating. Subsequently, the Ag@FTSM/Fe3O4/waterborn polyurethane (WPU) composite aerogels with a porous and asymmetric gradient structure were prepared via freeze-drying process based on the principle of density difference. The introduction of the porous structure can reduce the material density and filler addition, augment the loss interface, and prolong the conduction path resulting in the enhancement of the EM wave absorption property. Through the loss mechanism of “absorption-reflection-reabsorption” and the longer loss path of the aerogels, the EMI shielding efficiency (SE) of the composites reached 48.7 dB with excellent absorption efficiency (46.5dB) and high absorption coefficient (0.60) when the electromagnetic waves hit the magnetic layer.
电磁辐射及其二次污染问题引起了人们的广泛关注。因此,开发高效吸收电磁干扰的屏蔽材料迫在眉睫。本文采用化学镀银法制备了包银泡沫温敏微球(Ag@FTSM)。随后,基于密度差原理,通过冷冻干燥法制备了具有多孔和不对称梯度结构的Ag@FTSM/Fe3O4/水性聚氨酯(WPU)复合气凝胶。多孔结构的引入可以降低材料密度和填料的添加量,增大损耗界面,延长传导路径,从而增强电磁波吸收性能。通过“吸收-反射-重吸收”的损耗机制和气凝胶较长的损耗路径,复合材料的电磁干扰屏蔽效率(SE)达到48.7 dB,电磁波撞击磁层时具有良好的吸收效率(46.5dB)和较高的吸收系数(0.60)。
Shear strengthening of RC beams with prestressed NSM CFRP: Influencing factors and analytical model
Hengliang Guo, HaoHan Liao, Miao Su, Bai Zhang, Shaofang Li, Hui Peng
doi:10.1016/j.compstruct.2024.118262
预应力NSM碳纤维布加固混凝土梁的影响因素及分析模型
This study proposes the application of prestressed near-surface-mounted (NSM) carbon-fiber-reinforced polymer (CFRP) technique in the field of the shear-strengthening of bridges for the first time. Fourteen reinforced concrete (RC) beams shear strengthened with prestressed NSM CFRP were tested under static load. The effect of the CFRP prestressing level, spacing, angle, and end-anchorage measures on the shear-strengthening behavior was evaluated. The experimental results demonstrate that the ultimate shear capacity of prestressed NSM CFRP shear-strengthened beams increased by 65–127% when compared to that of the reference beams, and the width of shear cracks was effectively suppressed. The failure mode of prestressed NSM CFRP shear-strengthened beams without end-anchorage measures was web concrete cover separation, which can be suppressed using a CFRP U-jacket and through-beam screw. Increasing the CFRP prestressing level and percentage enhanced the ultimate shear capacity and cracking resistance of the strengthened beams. However, an excessively high CFRP percentage and prestress level combination resulted in large shear crack angles and decreased the shear contribution of CFRP and concrete. Finally, an analytical model based on the modified compression field theory (MCFT) was proposed to predict the flexural-shear load response of strengthened beams, which was in agreement with the experimental results.
本研究首次提出了预应力近表面贴装碳纤维增强聚合物(CFRP)技术在桥梁剪切加固领域的应用。对14根钢筋混凝土(RC)梁进行了静载试验。评价了CFRP预应力水平、间距、角度和端固措施对抗剪加固性能的影响。试验结果表明:预应力NSM CFRP抗剪加固梁的极限抗剪能力比对照梁提高65 ~ 127%,抗剪裂缝宽度得到有效抑制;无端部锚固措施的预应力NSM CFRP剪力加固梁的破坏模式为腹板混凝土盖板分离,可采用CFRP u型护套和贯通梁螺钉进行抑制。增加CFRP预应力水平和比例,增强梁的极限抗剪能力和抗裂能力均有所提高。然而,过高的CFRP掺量和预应力水平组合导致CFRP和混凝土的剪切裂缝角较大,降低了CFRP和混凝土的剪切贡献。最后,提出了基于修正压缩场理论(MCFT)的加固梁弯剪响应分析模型,该模型与试验结果吻合较好。
Study on isotropic design of triply periodic minimal surface structures under an elastic modulus compensation mechanism
Jing Zhang, Suchao Xie, Kunkun Jing, Hao Wang, Tao Li, Guandi He
doi:10.1016/j.compstruct.2024.118266
弹性模量补偿机制下三周期最小表面结构各向同性设计研究
The energy absorption characteristics of the triply periodic minimal surfaces (TPMS) structure may vary significantly due to the anisotropy under multi-directional loading conditions. To address this issue effectively, an isotropic design strategy based on a precise elastic modulus compensation mechanism for different TPMS lattices is proposed. This strategy involves combining a TPMS lattice with a high elastic modulus in the axial direction with another TPMS lattice featuring a low elastic modulus in the same direction, leveraging the complementary effects of elastic modulus to achieve isotropy. The relationship between the relative density and the elastic modulus of six types of TPMS lattices is analyzed through homogenization simulation and finite element analysis. Mathematical expressions are then fitted using the Gibson-Ashby model. Additionally, a Kriging model is employed to establish the relationship between the Zener anisotropy values of hybrid TPMS structures and the relative density of their component lattices. This enables the precise complementary effect of elastic modulus in different TPMS lattice structures, providing a widely applicable selection rule for achieving isotropy. Using the Primitive-Diamond hybrid lattice as an example, the Zener anisotropy index after hybridization is reduced by 65.2% and 31.37% compared to single Primitive and Diamond lattices, respectively.
在多向加载条件下,三周期最小表面(TPMS)结构的能量吸收特性会因各向异性而发生显著变化。为了有效地解决这一问题,提出了一种基于精确弹性模量补偿机制的各向同性设计策略。该策略涉及将轴向高弹性模量的TPMS晶格与同一方向低弹性模量的TPMS晶格相结合,利用弹性模量的互补效应来实现各向同性。通过均匀化模拟和有限元分析,分析了六种TPMS晶格的相对密度与弹性模量的关系。然后用Gibson-Ashby模型拟合数学表达式。此外,采用Kriging模型建立了杂化TPMS结构的齐纳各向异性值与其组成晶格相对密度之间的关系。这使得不同TPMS晶格结构的弹性模量具有精确的互补效应,为实现各向同性提供了广泛适用的选择规则。以原始-金刚石杂化晶格为例,杂化后的齐纳各向异性指数比单一原始晶格和金刚石晶格分别降低了65.2%和31.37%。
Chiral-assisted geometrically phased metasurfaces: manipulating orbital angular momentum for efficient and stable microwave attenuation
Yupeng Shi, Yuping Duan, Lingxi Huang, Wei Chen, Jiangyong Liu, Meng Wang
doi:10.1016/j.compositesb.2024.111614
手性辅助几何相位超表面:控制轨道角动量以实现高效稳定的微波衰减
Chiral wave-absorbing metamaterials can enhance microwave attenuation performance by converting linearly polarized waves into circularly polarized waves. However, the mechanism for transforming incident waves into vortex waves to overcome the angular momentum mismatch to satisfy broadband stealth is unclear. This work proposes a chiral-assisted geometrically phase (CAGP) metasurfaces that utilizes the Pancharatnam-Berry (PB) phase concept to convert incident plane waves into reflected vortex waves. Such metamaterials demonstrate adaptive transformation capabilities under the incidence of electromagnetic (EM) waves with multi-polarization modes, providing an effective absorption bandwidth(≥ 90% absorptivity, reflection loss ≤ −10 dB) reaches 6.92 GHz (9.16 -16.08 GHz) at a thickness of 2.48 mm. Based on an orbital angular momentum (OAM) phase and amplitude analysis, the mode purity of the generated vortex waves is discussed in detail, and the mechanisms are analyzed and verified by simulation models to confirm their effectiveness and practicability. Additionally, the metamaterials exhibit excellent radar cross-section (RCS) reduction properties and stable polarization insensitivity properties. In short, this work presents a tailorable metasurface to manipulate the OAM spectrum and achieve broadband microwave attenuation, which holds great potential for various applications in chiral wave-absorbing metamaterials.
手性吸波材料通过将线极化波转换成圆极化波来增强微波衰减性能。然而,将入射波转化为涡旋波以克服角动量失配以满足宽带隐身的机制尚不清楚。本研究提出了一种手性辅助几何相位(CAGP)超表面,该超表面利用Pancharatnam-Berry (PB)相位概念将入射平面波转换为反射旋涡波。该材料在多极化模式电磁波入射下表现出自适应变换能力,在厚度为2.48 mm时,有效吸收带宽(吸收率≥90%,反射损耗≤- 10 dB)达到6.92 GHz (9.16 -16.08 GHz)。基于轨道角动量(OAM)相位和振幅分析,详细讨论了产生的涡旋波的模式纯度,并通过仿真模型分析和验证了其机理,验证了其有效性和实用性。此外,该材料还具有优异的雷达截面(RCS)还原性能和稳定的极化不敏感性能。简而言之,本工作提出了一种可定制的超表面来操纵OAM频谱并实现宽带微波衰减,这在手性吸波超材料的各种应用中具有很大的潜力。
Electric-field-induced assists fabrication of micro-SiC/Epoxy coating with low additive amount to improve surface insulating performance of HVDC insulator
Shiyi Mao, Zijun Pan, Yuhan Ye, Pu Han, Ju Tang, Cheng Pan
doi:10.1016/j.compscitech.2024.110696
电场诱导制备低掺量的微sic /环氧涂层,提高高压直流绝缘子的表面绝缘性能
The micro-SiC/Epoxy composite coating has huge potential for application in the insulator of high voltage direct current (HVDC) gas insulated switchgear (GIS) since it can effectively suppress charge accumulation at gas-solid interface and adaptively regulate resistive electric field distribution. However, achieving stable and fruitful properties often requires high filler concentrations, which can compromise processability and long-term stability. Thus, a new method is proposed for preparing SiC/Epoxy composite coatings based on in-situ electric-field-induced assist (EFIA). The alignment process of SiC induced by the in-situ electric field, the effects of in-situ field on the physical and chemical properties of cured composites were studied. Even at concentrations far below the percolation threshold, the alignment of SiC particles along the in-situ electric field direction can induce significant non-linear conductive properties along that specific direction in the composite. Furthermore, the EFIA-coating leads to a 59.43% reduction in surface charge accumulation, more than a 50% decrease in charge dissipation time, and a 17.3% increase in surface flashover voltage. The coating discussed in this paper will be helpful in insulation design of DC components.
微sic /环氧复合涂层能有效抑制气固界面电荷积聚,自适应调节电阻电场分布,在高压直流气体绝缘开关设备绝缘子中具有巨大的应用潜力。然而,要获得稳定和富有成效的性能,通常需要较高的填料浓度,这可能会损害可加工性和长期稳定性。因此,提出了一种基于原位电场诱导辅助(EFIA)制备SiC/环氧复合涂层的新方法。研究了原位电场诱导SiC的取向过程,以及原位电场对固化复合材料理化性能的影响。即使在远低于渗透阈值的浓度下,SiC颗粒沿着原位电场方向排列也会在复合材料中沿该特定方向产生显著的非线性导电性能。此外,efia涂层导致表面电荷积累减少59.43%,电荷耗散时间减少50%以上,表面闪络电压增加17.3%。本文所讨论的涂层将有助于直流元件的绝缘设计。