首页/文章/ 详情

【新文速递】2023年11月22日固体力学SCI期刊最新文章

19天前浏览955

今日更新:International Journal of Solids and Structures 1 篇,International Journal of Plasticity 1 篇,Thin-Walled Structures 6 篇

International Journal of Solids and Structures

The lateral confinement effect on the interfacial crack in hybrid composites under uniaxial compression

Cheryala Sneha B., Yerramalli Chandra S.

doi:10.1016/j.ijsolstr.2023.112589

单轴压缩下混合复合材料界面裂纹的横向约束效应

The effect of hybridization on the interface crack growth along the fiber is predicted from numerical and analytical modelling approaches. A three-phase hybrid composite representative volume element (RVE) with an adjustable hybrid ratio and an initial interfacial crack is modelled. The fracture parameters and composite strength are computed from finite element analysis using VCCT approach in Ansys Workbench. A fracture energy-based mathematical model with a steady state crack growth is implemented to compute the hybrid composite splitting failure strength. The results show an enhancement in the compressive splitting strength with hybridization due to lateral confinement effect on the interfacial crack.

通过数值和分析建模方法预测了杂化对界面裂纹沿纤维生长的影响。对具有可调混合比和初始界面裂纹的三相混合复合材料代表体积元素(RVE)进行了建模。通过在 Ansys Workbench 中使用 VCCT 方法进行有限元分析,计算了断裂参数和复合材料强度。在计算混合复合材料的分裂破坏强度时,采用了基于断裂能量的数学模型,该模型具有稳定的裂纹生长状态。结果表明,由于界面裂纹的横向约束效应,混合后的压缩劈裂强度有所提高。


International Journal of Plasticity

An extended M-K model under surface traction with adjustable gradient distribution

Ma Li, Zheng Lihuang, Wang Zhongjin

doi:10.1016/j.ijplas.2023.103817

可调节梯度分布的地表牵引力下的扩展 M-K 模型

The forming limit of sheets usually corresponds to the strain accumulation before localized necking and is closely related to the loading state. In the viscous pressure forming (VPF) method, the surface traction generated by the force-transmitting medium with high-viscosity fluid-flow characteristics on the sheet exhibits the obvious gradient distribution near the necking region. However, existing necking instability theories have not factored in the surface traction gradient distribution (STGD) and can't accurately explain the inherent mechanism of the VPF method with this loading state to improve the forming limit. To deal with the issue, STGD-related ‘stress balance’ equations are established and an extended M-K model with STGD response under 3D stress state (STGD-3D-MK model) is proposed, based on the analysis of the adjustable STGD generated in the VPF method during the necking development. The proposed model is used to explore the influence and mechanism of the STGD on the forming limit, as well as to provide suggestions on how to achieve the full positive effect of tangential surface traction. This research demonstrates that the forming limit is sensitive to the STGD, which affects the ability of surface traction to improve the forming limit. The STGD changes the stress path of the groove, affecting the development of necking. In addition, the critical STGD that can increase the limit strain is also provided and its magnitude is related to the strain path. Finally, the VPF-based experimental results are provided to support the effectiveness of the analysis of the STGD-3D-MK model. This work provides a new perspective on the loading method to improve the forming limit.

板材的成形极限通常对应于局部缩颈前的应变累积,与加载状态密切相关。在粘性压力成形(VPF)方法中,具有高粘度流体流动特性的传力介质在薄片上产生的表面牵引力在颈缩区域附近呈现明显的梯度分布。然而,现有的缩颈不稳定性理论并未将表面牵引梯度分布(STGD)考虑在内,无法准确解释 VPF 法在这种加载状态下提高成形极限的内在机理。为了解决这个问题,我们建立了与 STGD 相关的 "应力平衡 "方程,并根据对 VPF 方法在颈部发展过程中产生的可调节 STGD 的分析,提出了一个在三维应力状态下具有 STGD 响应的扩展 M-K 模型(STGD-3D-MK 模型)。该模型用于探讨 STGD 对成形极限的影响和机理,并就如何充分发挥切向表面牵引的积极作用提出建议。研究表明,成形极限对 STGD 非常敏感,STGD 会影响表面牵引改善成形极限的能力。STGD 会改变沟槽的应力路径,影响颈缩的发展。此外,还提供了能增加极限应变的临界 STGD,其大小与应变路径有关。最后,提供了基于 VPF 的实验结果,以支持 STGD-3D-MK 模型分析的有效性。这项工作为改善成形极限的加载方法提供了一个新的视角。


Thin-Walled Structures

Mechanically induced electric potential and charge redistribution in laminated composite piezoelectric semiconductor circular cylindrical thin shells

Cao Yong, Guo Ziwen, Qu Yilin

doi:10.1016/j.tws.2023.111372

层压复合压电半导体圆柱薄壳中的机械感应电动势和电荷再分布

We study electromechanical effects and piezotronic behaviors in a Kirchhoff-Love laminated composite piezoelectric semiconductor circular cylindrical thin shell, which is composed of a non-piezoelectric semiconductor core and two piezoelectric dielectric layers. A second-order assumption for electric potentials and carrier concentration perturbations is utilized to capture accurate descriptions of the electric field and charge distributions within the composite shell, where the zeroth-order, first-order, and second-order forms represent constant, antisymmetric, and symmetric distributions along the thickness, respectively. The field equations and boundary conditions are simultaneously derived through a principle of virtual work and the fundamental lemma of the calculus of variation. The new governing equations derived show a new coupling relation between mechanical deformation and charge behavior in the composite shell, where all mechanical deformations (extension, bending of the shell) and all distribution forms of electric potential (zeroth-, first-, second-order electric potentials) are coupled, which is different from piezoelectric semiconductor beams and plates. Then, the numerical results of electromechanical effects and piezotronic behaviors in static bending and forced vibration problems of the shell are conducted with the derived theoretical model. Numerical studies of static bending graphically show some fundamental coupling relations between mechanical forces and charge distributions in deformed piezoelectric semiconductor shells. The new results from the forced vibration analysis given by the current model show that the deflection amplitude and the electric potential distribution in the thin shell are frequency-dependent and can be adjusted by controlling the excitation frequency. In addition, the semiconducting properties (dependence of mechanical behavior on doping level) are studied in both static and dynamic problems. The mechanically controlled charge distribution suggests that shell-shaped piezoelectric semiconductor shells could serve as an effective means of sensing or energy harvesting by converting mechanical energy into electricity.

我们研究了基尔霍夫-洛夫层压复合压电半导体圆柱薄壳中的机电效应和压电行为,该薄壳由一个非压电半导体芯和两个压电介质层组成。利用电势和载流子浓度扰动的二阶假设来捕捉复合外壳内电场和电荷分布的精确描述,其中零阶、一阶和二阶形式分别代表沿厚度方向的恒定、非对称和对称分布。场方程和边界条件是通过虚功原理和变分微积分基本定理同时导出的。推导出的新控制方程显示了复合材料壳体中机械变形和电荷行为之间的新耦合关系,即所有机械变形(壳体的延伸、弯曲)和所有电动势分布形式(零阶、一阶、二阶电动势)都是耦合的,这与压电半导体梁和板不同。然后,利用推导出的理论模型对壳体静态弯曲和受迫振动问题中的机电效应和压电行为进行了数值计算。静态弯曲的数值研究以图形方式显示了变形压电半导体壳体中机械力和电荷分布之间的一些基本耦合关系。当前模型给出的受迫振动分析的新结果表明,薄壳中的偏转振幅和电动势分布与频率有关,可通过控制激励频率进行调整。此外,还研究了静态和动态问题中的半导体特性(机械行为与掺杂水平的关系)。受机械控制的电荷分布表明,壳形压电半导体外壳可以通过将机械能转化为电能,成为传感或能量收集的有效手段。


Experimental and numerical research on the analysis methods for buckling and post-buckling of inclined stiffened panel under shear load

Lian Chenchen, Wang Peiyan, Chen Xin, Liu Fuchao, Yuan Kangbo, Zheng Jie, Yue Zhufeng

doi:10.1016/j.tws.2023.111374

剪切荷载下倾斜加劲板屈曲和后屈曲分析方法的实验和数值研究

The purpose of this paper is to investigate the buckling and post-buckling behavior of inclined stiffened composite panels under shear load. Two types of stiffened composite panels were manufactured and tested. The buckling load, ultimate load and other required structural properties of the inclined stiffened composite panels were obtained. The test results show that the failure load of the two types of panels are 5.79 times and 11.2 times of the buckling load, respectively, indicating that such inclined stiffened panels have a large post-buckling capacity. The damage modes of the panel are tearing around the skin near the clamps and debonding of the stringers from the skin. The combination of Hashin failure criterion, Cohesive model and nonlinear connection of clamp was used to conduct finite element modeling, which effectively predicts the buckling, post-buckling and damage modes of the structure. The buckling and post-buckling behavior of stiffened panels with different stinger configurations were discussed based on finite element analysis. The results show that when the initial buckling occurs between the stringers, the buckling and failure load of the stiffened panel become larger as the equivalent skin thickness between the stringers become larger. The research in this paper can provide reference for aircraft structural design.

本文旨在研究倾斜加劲复合板在剪切载荷作用下的屈曲和屈曲后行为。我们制造并测试了两种加劲复合板。获得了倾斜加劲复合板的屈曲载荷、极限载荷和其他所需的结构特性。试验结果表明,两种板材的破坏荷载分别是屈曲荷载的 5.79 倍和 11.2 倍,这表明这种倾斜加劲板材具有较大的屈曲后承载能力。面板的破坏模式为夹具附近表皮的撕裂和 弦杆与表皮的脱粘。采用哈申失效准则、内聚模型和夹具非线性连接相结合的方法进行有限元建模,可有效预测结构的屈曲、后屈曲和损坏模式。基于有限元分析,讨论了不同激振杆配置的加劲板的屈曲和后屈曲行为。结果表明,当初始屈曲发生在弦杆之间时,随着弦杆之间等效表皮厚度的增大,加劲板的屈曲和破坏载荷也随之增大。本文的研究可为飞机结构设计提供参考。


Life-cycle Assessment and Prediction on Ultimate Capacity of Corroded Q690 Steel Columns with H-section under Bi-directional Cyclic Loading

Zhang Qiang, Wen Jianian, Han Qiang, Zhuge Hanqing, Zhou Yulong

doi:10.1016/j.tws.2023.111391

双向循环荷载下腐蚀的 H 型截面 Q690 钢柱的生命周期评估和极限承载力预测

The structures or structural members made of high-strength steel may have time-varying mechanical properties in whole life-cycle due to the ageing effects. In particular, the corroded steel structures in high-seismicity regions could have unexpected failure modes when subjected multi-directional excitations. Therefore, in this study, the mechanical properties of Q690 steel H-section columns during the life-cycle under bi-directional cyclic loads are investigated. Firstly, a refined finite element (FE) model is built, which takes the time-varying of corrosion characteristics into consideration. Then, the degradations of mechanical property and failure mechanisms of steel columns with different design parameters at whole life-cycle are analyzed by the FE models. Finally, a quantitative calculation method of ultimate resistance and damage index of steel columns considering ageing effects is proposed. The findings demonstrate that several factors affect the ultimate strength of steel columns during the life-cycle stage, with the axial compression ratio and flange width-thickness ratio having the greatest impacts on the ultimate capacity. The ageing effect decreases the plastic flow capacity of steel columns, increases the stress concentration, and induces the failure mode transition from plastic flow to buckling failure. The ageing effect may be accurately estimated by the suggested calculation method for the ultimate capacity and damage index of steel columns at the life-cycle stage. The findings of this study highlight the significance of taking into account the ageing effects of steel columns in the seismic design.

由于老化效应,由高强度钢材制成的结构或结构部件在整个生命周期内可能具有随时间变化的机械性能。特别是在高震地区的锈蚀钢结构,在受到多向激励时可能会出现意想不到的破坏模式。因此,本研究对 Q690 钢 H 型截面柱在双向循环荷载作用下全生命周期的力学性能进行了研究。首先,建立了一个考虑了腐蚀特性时变的精细有限元(FE)模型。然后,通过有限元模型分析了不同设计参数的钢柱在全寿命周期内的力学性能退化和破坏机理。最后,提出了考虑老化效应的钢柱极限抗力和损伤指数的定量计算方法。研究结果表明,钢柱在全寿命周期阶段的极限强度受多种因素影响,其中轴向压缩比和翼缘板宽厚比对极限承载力的影响最大。老化效应降低了钢柱的塑性流动能力,增加了应力集中,并导致失效模式从塑性流动过渡到屈曲失效。老化效应可通过建议的计算方法准确估算钢柱在生命周期阶段的极限承载力和损伤指数。本研究的结果凸显了在抗震设计中考虑钢柱老化效应的重要意义。


Experimental and numerical investigation into hysteretic performance of orthogonal double corrugated steel plate shear wall

Zhu Bo-Li, Bai Wen-Hua, Wen Chen-Bao, Zuo Jia-Qi, Sun Hao-Jun, Wang Xiong, Guo Yan-Lin

doi:10.1016/j.tws.2023.111392

正交双波纹钢板剪力墙滞回性能的实验和数值研究

The orthogonal double corrugated steel plate shear wall (ODC-SPSW) is comprised of two identical corrugated plates that are arranged orthogonally and interconnected through high-strength bolts located at the valleys of the corrugations. Due to the strong axis of one corrugated plate coinciding with the weak axis of the other corrugated plate, the flexural rigidity of each plate can be significantly enhanced in its weak axis, thereby improving its shear resistance. The ODC-SPSW has itself boundary elements in two side and connected only with frame beams at its top and bottom, leading to conveniently moving within the frame. This paper presents experimental and numerical analyses of the shear resistance and the hysteretic performance of ODC-SPSW. Two experimental specimens subjected to cyclic loading were tested, and accordingly finite element (FE) simulations were conducted, both reaching an excellent agreement. Firstly, the test results of two ODC-SPSW specimens under cyclic loading are reported and analyzed. Second, FE models are established to simulate the hysteretic energy-dissipation performance of the test specimens. The numerical results from FE Model agree well with the test results, thus validating the FE models. Moreover, a parametric study was conducted using the validated FE model through changing various geometrical parameters, such as aspect ratio, bolt number and arrangement, corrugation depth, corrugated steel plate thickness, boundary element dimensions of the ODC-SPSWs. It is found that these parameters affect significantly the ultimate shear resistance and hysteretic energy-dissipation capacity of the ODC-SPSW. The numerical result obtained indicated the dimensions of the boundary elements have little effect on the shear resistance and hysteresis performance of the ODC-SPSWs. Finally, some design recommendations are concluded which can provide valuable references for the practical design of ODC-SPSWs.

正交双波纹钢板剪力墙(ODC-SPSW)由两块相同的波纹板组成,两块波纹板正交排列,并通过位于波纹谷处的高强度螺栓相互连接。由于一块波纹板的强轴线与另一块波纹板的弱轴线重合,因此每块波纹板的挠曲刚度都能在其弱轴线上得到显著增强,从而提高其抗剪性能。ODC-SPSW 两侧均有边界元素,仅在其顶部和底部与框架梁连接,因此可方便地在框架内移动。本文对 ODC-SPSW 的抗剪性能和滞后性能进行了实验和数值分析。对两个承受循环荷载的实验试样进行了测试,并相应地进行了有限元(FE)模拟,结果均非常吻合。首先,报告并分析了两个 ODC-SPSW 试样在循环加载下的测试结果。其次,建立了 FE 模型来模拟试样的滞后能量耗散性能。FE 模型的数值结果与试验结果吻合良好,从而验证了 FE 模型。此外,通过改变 ODC-SPSW 的各种几何参数,如长宽比、螺栓数量和排列、波纹深度、波纹钢板厚度、边界元素尺寸等,利用验证后的 FE 模型进行了参数研究。结果发现,这些参数对 ODC-SPSW 的极限抗剪能力和滞后耗能能力有很大影响。数值结果表明,边界元素的尺寸对 ODC-SPSW 的抗剪性能和滞后性能影响不大。最后,总结出了一些设计建议,可为 ODC-SPSW 的实际设计提供有价值的参考。


Experimental study on Q355 steel T-stubs connected through high-strength ring groove rivets

Gao Fei, Wang Zongyi, Zhu Rui, Chen Zhenming, Ye Quanxi, Duan Yaqi, Jia Yunlong, Zhang Qin

doi:10.1016/j.tws.2023.111399

通过高强度环槽铆钉连接 Q355 钢 T 型管的实验研究

High-strength ring groove rivet connections have several advantages over bolt connections, including anti-loosening performance and high fatigue resistance. This research aims to investigate the mechanical properties of high-strength ring groove rivet assemblies and load resistances of riveted T-stubs. Experimental tests on high-strength ring groove rivet assemblies were firstly carried out, including coupon tests, preload measurements, and load-bearing tests. Q355 steel T-stubs connected through ring groove rivets were subsequently tested. The effects of certain geometrical parameters and material grades of the rivets on the performance of the T-stubs were analyzed. The applicability of the Eurocode 3 and Demonceau methods to the T-stubs was discussed. The results show that the Grade 10.9 rivet possesses higher yield strength and strain, and lower ultimate strain, in comparison to the Grade 8.8 rivet. Increasing the diameter of the rivet is beneficial for the T-stubs, whereas increasing the flange thickness is not always advantageous. The Eurocode 3 method is unsuitable for the T-stubs connected through ring groove rivets, whereas the Demonceau method is conservative. The findings of this research provide guidance for engineering designs of high-strength ring groove rivet assemblies and steel T-stubs connected through ring groove rivets.

与螺栓连接相比,高强度环槽铆钉连接具有防松性能和高抗疲劳性等优点。本研究旨在探讨高强度环槽铆钉组件的力学性能和铆接 T 形管的抗负载能力。首先对高强度环槽铆钉组件进行了实验测试,包括试样测试、预紧力测量和承载测试。随后对通过环槽铆钉连接的 Q355 钢 T 形管进行了测试。分析了铆钉的某些几何参数和材料等级对 T 型管性能的影响。讨论了欧洲规范 3 和 Demonceau 方法对 T 型管的适用性。结果表明,与 8.8 级铆钉相比,10.9 级铆钉具有更高的屈服强度和应变,而极限应变较低。增加铆钉直径对 T 型管有利,而增加凸缘厚度则不一定有利。欧洲规范 3 方法不适合通过环槽铆钉连接的 T 型管,而 Demonceau 方法则比较保守。研究结果为高强度环槽铆钉组件和通过环槽铆钉连接的钢 T 型管的工程设计提供了指导。


Web crippling behaviour of cold-formed steel channels with elongated un-stiffened and edge-stiffened web holes under end-two-flange loading condition

Wang Wei, Roy Krishanu, Fang Zhiyuan, Beulah Gnana Ananthi G, Lim James B.P.

doi:10.1016/j.tws.2023.111398

在两端法兰加载条件下,带有拉长的未加固和边缘加固腹板孔的冷弯型钢槽钢的腹板瘸腿行为

Over the last decade, cold-formed steel (CFS) channels with circular edge-stiffened web holes have been widely used in New Zealand. In the case of web crippling, previous studies have revealed that the use of an edge-stiffened hole almost results in the same strength as an equivalent channel-section having a plain web. Such circular edge-stiffened web holes could be extended to elongated holes. In terms of web crippling, however, no experimental or numerical works on such elongated holes were reported in the literature. In this paper, a numerical investigation was carried out to investigate the web crippling behaviour of CFS channels with elongated un-stiffened and edge-stiffened web holes under the end-two-flange (ETF) loading condition. The finite element (FE) models were validated against the test results of CFS channels with circular edge-stiffened web holes; good agreement in terms of the load-displacement relationships and failure modes was shown. A parametric study was then conducted, comprising 1,536 FE models. Compared to CFS channels with a plain web, for the case of channels with an elongated un-stiffened web hole, the average web crippling strength reduction for sections with an aspect ratio of two and three was 21% and 36%, respectively. However, for an elongated edge-stiffened hole, the reduction in the web crippling strength was only 5% and 8%, respectively. Finally, design equations in the form of the web crippling reduction factor (Rp) and the equations based on the direct strength method (DSM) for CFS channels with elongated web holes under ETF loading conditions were recommended.

在过去十年中,新西兰广泛使用了带有圆形边缘加固腹板孔的冷弯型钢(CFS)槽钢。以前的研究表明,在腹板脆化的情况下,使用边缘加固孔几乎可以获得与具有普通腹板的等效槽钢截面相同的强度。这种圆形边缘加固腹板孔可以扩展到细长孔。然而,在腹板跛行方面,文献中没有关于此类细长孔的实验或数值研究报告。本文进行了数值研究,以探讨在端部-两法兰(ETF)加载条件下,带有未加固和边缘加固细长腹板孔的 CFS 槽钢的腹板脆化行为。有限元(FE)模型与带有圆形边缘加固腹板孔的 CFS 槽钢的测试结果进行了验证,结果表明两者在载荷-位移关系和破坏模式方面具有良好的一致性。随后进行了参数研究,包括 1,536 个 FE 模型。与带有普通腹板的 CFS 槽道相比,对于带有拉长的未加固腹板孔的槽道,纵横比为 2 和 3 的截面的平均腹板破坏强度分别降低了 21% 和 36%。然而,对于边缘加固的细长孔,腹板挠曲强度的降低幅度分别仅为 5%和 8%。最后,腹板跛行降低系数(Rp)形式的设计方程和基于直接强度法(DSM)的方程,适用于 ETF 荷载条件下带有细长腹板孔的 CFS 渠道。





来源:复合材料力学仿真Composites FEM
ACTMechanicalWorkbenchDeform振动疲劳断裂复合材料非线性半导体ADS裂纹理论材料螺栓
著作权归作者所有,欢迎分享,未经许可,不得转载
首次发布时间:2024-11-03
最近编辑:19天前
Tansu
签名征集中
获赞 3粉丝 0文章 690课程 0
点赞
收藏
作者推荐

【新文速递】2023年11月23日复合材料SCI期刊最新文章

今日更新:Composite Structures 2 篇,Composites Part A: Applied Science and Manufacturing 2 篇,Composites Part B: Engineering 1 篇,Composites Science and Technology 6 篇Composite StructuresFlexural behaviors and failure mechanisms of CFRP sandwich structures with enhanced dual-phase lattice coresWang Yihao, Han Guangchao, Liu Xincheng, Ren Yiru, Jiang Hongyongdoi:10.1016/j.compstruct.2023.117724带有增强型双相晶格芯材的 CFRP 夹层结构的挠曲行为和破坏机制Inspired by bionic/metallurgical microstructures, novel dual-phase lattice/ Carbon Fiber Reinforced Polymer (CFRP) composite sandwich structures are proposed to improve the energy absorption (EA). The composite sandwich structures for different dual-phase strengthening strategies are designed, where the topology optimization is used to yield efficient lattice distribution configurations. The experimental samples are fabricated by 3D-printing and three-point bending tests are conducted. The flexural failure process and failure modes are observed and analyzed to reveal the failure mechanisms. Results show that DPL-1-CFRP and DPL-2-CFRP have higher peak load (+24.8% and 18.0%), post-peak average load (42.6% and 20.8%) and specific energy absorption (+7.8% and +21.1%) compared to SPL-1-CFRP. It is indicated that the interactive failure mechanism of dual-phase lattice is effective in improving the mechanical properties of sandwich structure. It represents the occurrence of synergistic deformation between struts rather than a single brittle fracture. Finally, several potential failure mechanisms for the separation of the core and end faces are revealed. This novel concept and structural design greatly contribute to improve mechanical properties of sandwich structure.受仿生/冶金微结构的启发,提出了新型双相晶格/碳纤维增强聚合物(CFRP)复合材料夹层结构,以改善能量吸收(EA)。设计了不同双相强化策略的复合材料夹层结构,并通过拓扑优化获得了高效的晶格分布配置。通过三维打印技术制作了实验样品,并进行了三点弯曲试验。通过对弯曲破坏过程和破坏模式的观察和分析,揭示了破坏机理。结果表明,与 SPL-1-CFRP 相比,DPL-1-CFRP 和 DPL-2-CFRP 具有更高的峰值载荷(+24.8% 和 18.0%)、峰值后平均载荷(42.6% 和 20.8%)和比能量吸收(+7.8% 和 +21.1%)。这表明双相晶格的交互破坏机制能有效改善夹层结构的机械性能。它代表了支柱之间发生的协同变形,而不是单一的脆性断裂。最后,还揭示了芯材和端面分离的几种潜在失效机制。这种新颖的概念和结构设计大大有助于提高夹层结构的机械性能。High-fidelity computational micromechanics of composite materials using image-based periodic representative volume elementHiguchi R., Yokozeki T., Nishida K., Kawamura C., Sugiyama T., Miyanaga T.doi:10.1016/j.compstruct.2023.117726利用基于图像的周期代表体积元素对复合材料进行高保真微观力学计算This study presents numerical investigations into the progressive damages in unidirectional carbon fiber reinforced plastics (CFRP) using computational micromechanics with an image-based periodic representative volume element (RVE). This RVE modeling approach combines the methodologies of image-based RVE and artificial periodic RVE to reflect the actual fiber packing while retaining geometrical periodicity. For high-fidelity modeling, the RVE model is prepared with more than 200 carbon fibers extracted from X-ray computed tomography images. Both homogenization simulation for elastic properties and unidirectional loading simulations for plastic and fracture properties are carried out. The constitutive model parameters are identified and verified by comparing the experimental and predicted effective (spatially averaged) elastic and plastic properties, and ultimate strength. Then, with the identified parameters, the local damage initiation and propagation mechanism, and their influence on the macroscopic nonlinear stress–strain behaviors are discussed. Finally, the influences of fiber packing on the predicted accuracy of computational micromechanics are discussed by comparing the results between the proposed image-based RVE and simple RVEs with the square and hexagonal arrays.本研究利用基于图像的周期性代表体积元素(RVE)计算微观力学,对单向碳纤维增强塑料(CFRP)的渐进损伤进行了数值研究。这种 RVE 建模方法结合了基于图像的 RVE 和人工周期 RVE 的方法,在保留几何周期性的同时反映了实际的纤维堆积。为了进行高保真建模,RVE 模型是用从 X 射线计算机断层扫描图像中提取的 200 多根碳纤维制作的。对弹性特性进行了均质化模拟,对塑性和断裂特性进行了单向加载模拟。通过比较实验和预测的有效(空间平均)弹性和塑性以及极限强度,确定并验证了构成模型参数。然后,根据确定的参数,讨论了局部损伤的引发和传播机制,以及它们对宏观非线性应力应变行为的影响。最后,通过比较所提出的基于图像的 RVE 与方形和六角形阵列的简单 RVE 的结果,讨论了纤维堆积对计算微观力学预测精度的影响。Composites Part A: Applied Science and ManufacturingNanocomposites of polyethylene with Fe3O4 nanoparticles via surface-initiated ROMP: Thermomechanical, shape memory and photothermal propertiesGao Yuan, Hu Jiawei, Wang Huaming, Liu Liyue, Li Lei, Zheng Sixundoi:10.1016/j.compositesa.2023.107923 聚乙烯与 Fe3O4 纳米粒子通过表面引发的 ROMP 纳米复合材料:热力学、形状记忆和光热特性The nanocomposites of polyethylene with Fe3O4 nanoparticles (NPs) were synthesized via surface-initiated ring-opening metathesis polymerization (SI-ROMP). First, the surfaces of pristine Fe3O4 NPs were functionalized with (5-nicyclo[2.2.1]hept-2-enyl)ethyl]triethoxylsilane. The as-obtained Fe3O4 NPs functionalized with norbornene were used to mediate the ROMP of cyclooctene (COE). By controlling the mass ratios of COE to the surface-functionalized Fe3O4 NPs, the polycyclooctene-grafted Fe3O4 NPs (denoted PCOE-g-Fe3O4 NPs) were obtained with variable contents of Fe3O4 NPs. Finally, these PCOE-g-Fe3O4 NPs were hydrogenated into the corresponding polyethylene-grafted Fe3O4 NPs (PE-g-Fe3O4 NPs). The nanocomposites of PE with Fe3O4 NPs were successfully synthesized as evidenced by the morphologies that the Fe3O4 NPs were well dispersed in PE matrix at the scale of nanometer. The nanocomposites displayed the mechanical properties superior to plain PE. More importantly, the nanocomposites were capable of displaying superparamagnetic, thermally-induced shape memory and photothermal properties. Furthermore, the photothermal behavior can be utilized to trigger the shape memory properties in a non-contact fashion.通过表面引发的开环偏聚聚合(SI-ROMP)合成了聚乙烯与 Fe3O4 纳米粒子(NPs)的纳米复合材料。首先,用(5-二环[2.2.1]庚-2-烯基)乙基]三乙氧基硅烷对原始的 Fe3O4 NPs 表面进行官能化。得到的与降冰片烯官能化的 Fe3O4 NPs 被用于介导环辛烯(COE)的 ROMP。通过控制 COE 与表面功能化 Fe3O4 NPs 的质量比,得到了不同 Fe3O4 NPs 含量的聚环辛烯接枝 Fe3O4 NPs(称为 PCOE-g-Fe3O4 NPs)。最后,这些 PCOE-g-Fe3O4 NPs 被氢化成相应的聚乙烯接枝 Fe3O4 NPs(PE-g-Fe3O4 NPs)。从形态上看,Fe3O4 NPs 在纳米级的聚乙烯基体中分散良好,成功合成了聚乙烯与 Fe3O4 NPs 的纳米复合材料。纳米复合材料的机械性能优于普通聚乙烯。更重要的是,纳米复合材料还具有超顺磁性、热诱导形状记忆和光热特性。此外,光热行为可用于以非接触方式触发形状记忆特性。Mechanical property enhancement of graphene-kenaf-epoxy multiphase composites for automotive applicationsMalik Khurshid, Ahmad Faiz, Shaik Dawood MSI, Islam Mohammad S., Ali Saad, Raza Ali, Ahmed Shahed Chowdhurydoi:10.1016/j.compositesa.2023.107916 提高石墨烯-kenaf-环氧多相复合材料在汽车应用中的机械性能Kenaf composites have a high strength-to-weight ratio, but weak fiber-matrix interface bonding limits their automotive use. To address this, a novel technique was developed to fabricate multiphase composites using graphene nanoplatelets (GNPs), kenaf fibers, and an epoxy matrix. The composites were made using vacuum infusion molding, with the GNPs exfoliated using a bath sonicator for uniform dispersion. The composites modified with 0.2 wt.% GNP showed the most significant improvement in mechanical properties. Specifically, these composites exhibited a 30.5% increase in tensile strength, a 61.5% increase in tensile modulus, a 17.6% increase in flexural strength, a 22.7% increase in flexural modulus, a 35.1% increase in interlaminar shear strength, and a 17.1% increase in fracture toughness. Additionally, the water absorption resistance of the multiphase composites improved by up to 7%. These improvements were attributed to the uniform dispersion of GNPs and improved interlocking with the fiber surface. The developed composite has the potential for interior parts (such as dashboards, interior walls, and luggage compartments) in the automotive vehicle.Kenaf复合材料具有很高的强度重量比,但纤维与基体界面粘合力较弱,限制了其在汽车上的应用。为了解决这个问题,我们开发了一种新技术,使用石墨烯纳米片(GNPs)、Kenaf 纤维和环氧基质制造多相复合材料。复合材料采用真空灌注成型法制造,使用水浴式超声波仪对 GNPs 进行剥离,使其均匀分散。使用 0.2 wt.% GNP 改性的复合材料在机械性能方面的改善最为显著。具体来说,这些复合材料的拉伸强度提高了 30.5%,拉伸模量提高了 61.5%,弯曲强度提高了 17.6%,弯曲模量提高了 22.7%,层间剪切强度提高了 35.1%,断裂韧性提高了 17.1%。此外,多相复合材料的吸水性也提高了 7%。这些改进归功于 GNPs 的均匀分散以及与纤维表面更好的互锁。所开发的复合材料有望用于汽车内饰件(如仪表板、内壁和行李箱)。Composites Part B: EngineeringEffect of fibre concentration on the mechanical properties of welded reinforced polypropyleneMofakhami E., Gervat L., Fayolle B., Miquelard-Garnier G., Ovalle C., Laiarinandrasana L.doi:10.1016/j.compositesb.2023.111111 纤维浓度对焊接增强聚丙烯机械性能的影响The effects of fibre concentration on the mechanical response of welded glass-fibre-reinforced polypropylene (GF-PP) were studied in-depth. The weld ratio is defined as the ratio between the strength of the welded material and that of the bulk material. Experimental observations during tensile tests of unwelded and welded GF-PP have shown a weld ratio reduction as high as 60%. For all conditions studied, no significant change in the polymer matrix was observed. Increasing the fibre content on the welded material was additionally associated with a decrease in the stress at break and the strain at the maximum stress, respectively 68 and 84% for 50 wt% GF-PP. The DIC technique was used to retrieve the local response in the welded zone, showing local strain as high as 19.5 times the macroscopic strain. Using X-ray microtomography, the strain magnification could be explained by the significant increase of the fibre density at the welded zone. It was also shown that at least 2/3 of the fibres were orientated within the weld plane limiting the transverse strain, favouring void nucleation and embrittlement of the material. As a consequence, the rupture can be explained by the amplification of the strain linked with the fibre concentration and orientation of the welded material.深入研究了纤维浓度对焊接玻璃纤维增强聚丙烯(GF-PP)机械响应的影响。焊接率的定义是焊接材料的强度与主体材料的强度之比。在对未焊接和已焊接的 GF-PP 进行拉伸试验时进行的实验观察表明,焊接比的降低幅度高达 60%。在所有研究条件下,都没有观察到聚合物基体发生明显变化。此外,焊接材料纤维含量的增加还与断裂应力和最大应力应变的降低有关,50 wt% GF-PP 的断裂应力和最大应力应变分别降低了 68% 和 84%。DIC 技术用于检索焊接区的局部响应,显示局部应变高达宏观应变的 19.5 倍。利用 X 射线显微层析技术,焊接区纤维密度的显著增加可以解释应变放大的原因。研究还表明,至少有 2/3 的纤维在焊接平面内定向,限制了横向应变,有利于空洞成核和材料脆化。因此,断裂可通过与焊接材料的纤维浓度和取向有关的应变放大来解释。Composites Science and TechnologyComparative study of different bonding interactions on the interfacial adhesion and mechanical properties of MXene-decorated carbon fiber/epoxy resin compositesHu Shaokai, Han Ping, Meng Chao, Yu Ying, Han Shaolong, Wang Haoyu, Wei Gang, Gu Zhengdoi:10.1016/j.compscitech.2023.110352 不同粘合相互作用对 MXene 装饰碳纤维/环氧树脂复合材料界面粘合力和机械性能的比较研究Interfacial adhesion determines the mechanical performance of the carbon fibers-reinforced polymers composites (CFRPs), and different bonding interactions could lead to different degrees of interfacial adhesion and mechanical properties of CFRPs. In order to survey specific influence of different bonding interactions on the interface bonding, further boost the mechanical properties of CFRPs, MXene is decorated onto carbon fiber (CF) surface via Van der Waals force or hydrogen bonds (CF-v-MXene), ionic bonds (CF-i-MXene), and covalent bonds (CF-c-MXene), respectively. Besides, detailed interaction mechanisms of various bonding interactions are also comprehensively investigated. The results indicate that the introduction of MXene is obviously efficient for improving the interface adhesion and mechanical properties of CF/epoxy (CF/EP) composites, and the composites reinforced by CF-c-MXene exhibit the optimal properties. Tremendous improvements of 90.1 % and 110.3 % for the impact strength and interfacial shear strength (IFSS) are achieved compared with the composites reinforced by the unsized CF. The microscopic interfacial structure and fracture failure mode are further observed and analyzed to explore the enhancement mechanisms. This work provides effective guidance and reference for the application of MXene and other similar 2D layered materials, such as Transition Metal Dichalcogenides (TMDCs), to design and manufacture high-quality interface for CFRPs with excellent interfacial and mechanical properties.界面粘附力决定了碳纤维增强聚合物复合材料(CFRP)的力学性能,而不同的键合作用会导致不同程度的界面粘附力和碳纤维增强聚合物复合材料的力学性能。为了研究不同结合相互作用对界面结合的具体影响,进一步提高 CFRP 的力学性能,研究人员分别通过范德华力或氢键(CF-v-MXene)、离子键(CF-i-MXene)和共价键(CF-c-MXene)将 MXene 装饰到碳纤维(CF)表面。此外,还全面研究了各种键的详细相互作用机理。结果表明,引入 MXene 能明显有效地改善 CF/EP 复合材料的界面粘附性和力学性能,而 CF-c-MXene 增强的复合材料则表现出最佳性能。与使用非尺寸 CF 增强的复合材料相比,冲击强度和界面剪切强度(IFSS)分别提高了 90.1% 和 110.3%。此外,还进一步观察和分析了微观界面结构和断裂失效模式,以探索增强机制。这项工作为应用 MXene 和其他类似的二维层状材料(如过渡金属二卤化物)设计和制造具有优异界面和力学性能的 CFRP 的高质量界面提供了有效的指导和参考。Acoustic emission-based failure load prediction for plain woven laminates under quasi-static indentationLiu Yuhang, Huang Kai, Ding Junfeng, Yu Shangyang, Li Zhixing, Zhang Li, Guo Lichengdoi:10.1016/j.compscitech.2023.110355 基于声发射的平纹编织层压板在准静态压痕作用下的破坏载荷预测Composites are widely used in engineering applications, and their penetration resistance is critical for performance and safety. However, testing the failure load of composites directly leads to component failure, making it challenging to evaluate the expected residual capacity. To address this issue, this study proposes an artificial neural network (ANN) method that accurately predicts the penetration failure load of composites using acoustic emission (AE) data. A cyclic loading test schedule is designed to capture the AE data during each cycle, and a relationship between AE data and load ratio (LR) is established. To predict the failure load, an extrapolation method (EM) based on uncertainty is proposed in this paper. This approach enables the prediction of failure load intervals when LR equals 1, with relative errors of less than 7.66 %. In cases where multiple loads are not feasible, the single-point prediction method (SPM) can be used instead of the extrapolation method. However, it is crucial to avoid training AE data during the initial loading stage for accurate predictions. This study recommends a loading ratio of more than 0.1 for optimal results with this approach.复合材料广泛应用于工程领域,其抗穿透性对性能和安全性至关重要。然而,测试复合材料的失效载荷会直接导致部件失效,因此评估预期剩余能力具有挑战性。为了解决这个问题,本研究提出了一种人工神经网络(ANN)方法,利用声发射(AE)数据准确预测复合材料的穿透失效载荷。设计了一个循环加载测试时间表,以捕获每个循环中的声发射数据,并建立了声发射数据与负载率(LR)之间的关系。为了预测失效载荷,本文提出了一种基于不确定性的外推法(EM)。这种方法可以预测 LR 等于 1 时的失效载荷区间,相对误差小于 7.66%。在多负载不可行的情况下,可以使用单点预测法 (SPM) 代替外推法。不过,要想获得准确的预测结果,关键是要避免在初始加载阶段训练 AE 数据。本研究建议加载比应大于 0.1,以获得该方法的最佳结果。Improving delamination resistance of 3D printed continuous fiber-reinforced thermoset composites by multi-scale synergistic toughening of mono-component polyetherketone-cardoWang Feng, Ming Yueke, Yang Fuhong, Xiao Hong, Liu Tianqi, Zhang Chenping, Zhu Yansong, Wang Jie, Duan Yugang, Wang Bendoi:10.1016/j.compscitech.2023.110358 通过单组分聚醚酮-卡多的多尺度协同增韧改善 3D 打印连续纤维增强热固性复合材料的抗分层性能Continuous fiber-reinforced thermoset composites (CFRTCs) 3D printing offers a promising solution to fabricate lightweight, high-strength sophisticated composite structures. However, the delamination resistance of 3D printed CFRTCs is decreased by the weak fiber-matrix and interlayer adhesion caused by the process principle. To increase the interlayer toughness of 3D printed CFRTCs, this study developed a printing matrix toughened by various polyetherketone-cardo (PEK-C) forms by modulating its dissolution state. The results showed that the interlaminar toughening effects of the particle dispersion and dissolved dual form of PEK-C were superior to the insoluble particles or the dissolved PEK-C. As a result, the mode I and mode II interlaminar fracture toughness increased by 112.38 % and 189.01 %, respectively. And the synergistic effect of dual-form PEK-C was determined. Fractographic investigation revealed that the dissolved PEK-C experienced the reaction-induced phase separation initiating a nanoscale thermoplastic phase and developing a multi-scale PEK-C toughening system with the microscale PEK-C particles. Moreover, morphological observation of the particle and PEK-C phases demonstrate multi-scale synergistic toughening mechanisms of mono-component PEK-C. This study presents an innovative technique for interlayer toughening applicable to the CFRTCs 3D printing, illustrates the toughening principle, and shows its promise as a general strategy.连续纤维增强热固性复合材料(CFRTCs)三维打印技术为制造轻质、高强度的精密复合材料结构提供了一种前景广阔的解决方案。然而,由于工艺原理导致纤维基体和层间粘附力较弱,三维打印 CFRTC 的抗分层能力有所下降。为了提高三维打印 CFRTC 的层间韧性,本研究开发了一种通过调节聚醚酮-卡多(PEK-C)的溶解状态来增韧各种聚醚酮-卡多形态的打印基体。结果表明,颗粒分散型和溶解型双形态 PEK-C 的层间增韧效果优于不溶解颗粒或溶解型 PEK-C。因此,模式 I 和模式 II 层间断裂韧性分别提高了 112.38 % 和 189.01 %。并确定了双形态 PEK-C 的协同效应。断裂学研究表明,溶解的 PEK-C 经历了反应诱导的相分离,引发了纳米级热塑性相,并与微尺度 PEK-C 颗粒形成了多尺度 PEK-C 增韧体系。此外,颗粒和 PEK-C 相的形态观察证明了单组分 PEK-C 的多尺度协同增韧机制。本研究提出了一种适用于 CFRTC 三维打印的创新层间增韧技术,说明了增韧原理,并展示了其作为通用策略的前景。Analysis of interfacial characteristics in polymer nanocomposites via visual particle recognition methodology and micromechanical predictive modelsMohsenzadeh R., Soudmand B.H., Najafi A.H., Fattahi M., Uyen D.P.doi:10.1016/j.compscitech.2023.110360 通过视觉颗粒识别方法和微机械预测模型分析聚合物纳米复合材料的界面特性This study examines the morphological features of nano-zeolite nanoparticles incorporated into ultra-high molecular weight polyethylene nanocomposites, known for their excellent biocompatibility and significant potential in structural biomedical applications. The analyses involved qualitative assessments and a statistical approach based on visual particle recognition technique. Scanning electron microscopy was adopted for morphological assessments of impact-fractured surfaces. The scanning electron microscopy observations unveiled the improved dispersion of nanoparticles within the polymer matrix following nano-zeolite incorporation. In the quantitative approach, the nanoparticles size and distribution were systematically determined through tailored histograms, utilizing the customized particle recognition strategy applied to images. This analysis yielded average particle sizes for each composite, further used for calculating the effective elastic moduli of nanocomposites by employing a two-fold micromechanics-based homogenization technique, accounting for interfacial effects. The computation of average particle size based on visual measurements substantially improved the accuracy regarding the quantitative analysis of interphase effects on macroscopic properties, marking a departure from the conventional practice of conducting such calculations by relying on unrealistic particle sizes based on their as-received values before compounding with the polymer.本研究探讨了超高分子量聚乙烯纳米复合材料中纳米沸石纳米颗粒的形态特征,众所周知,超高分子量聚乙烯纳米复合材料具有极佳的生物相容性,在结构性生物医学应用方面潜力巨大。分析包括定性评估和基于视觉颗粒识别技术的统计方法。采用扫描电子显微镜对冲击断裂表面进行形态学评估。扫描电子显微镜观察结果表明,纳米沸石加入后,纳米粒子在聚合物基质中的分散性得到了改善。在定量方法中,利用应用于图像的定制颗粒识别策略,通过定制直方图系统地确定了纳米颗粒的尺寸和分布。这一分析得出了每种复合材料的平均粒度,并通过采用基于微观力学的两重均质化技术,进一步用于计算纳米复合材料的有效弹性模量,同时考虑到界面效应。根据目测结果计算平均粒度大大提高了定量分析相间效应对宏观特性影响的准确性,这标志着该方法已摆脱了传统的计算方法,即根据与聚合物复合前的实际粒度值进行计算。Design and preparation of ternary polymer nanocomposites for high energy density film capacitorsCai Jinxia, Xie Bing, Jiang Yunliang, Lu Jinshan, Li Zeyu, Mao Pu, Marwat Mohsin Ali, Zhang Haibodoi:10.1016/j.compscitech.2023.110361 设计和制备用于高能量密度薄膜电容器的三元聚合物纳米复合材料High discharge energy density (Ue) film capacitors are important for miniaturization and integration in power electronic applications. The Ue of a polymer film is mainly dependent on Weibull's breakdown strength (Eb) and dielectric constant (εr). This work aims to develop ternary nanocomposites composed of polycarbonate (PC), Al2O3 nanoparticles (Al2O3 NPs) and BaTiO3 nanowires (BT NWs) for capacitive energy-storage. Al2O3 NPs have a wide bandgap and are expected to enhance Eb owing to their insulating nature, while BaTiO3 nanowires (BT NWs) are ferroelectric and are expected to provide a high εr. To overcome local electric-field distortion at the interface due to the mismatch in εr, core-shell structured BT@SiO2 NWs are prepared. The Eb of the composite containing 1.0 wt.% Al2O3 NPs and 6.0 wt.% BT@SiO2 NWs can reach 626 MV/m while that of the pure PC is 465 MV/m. As a result, its Ue reaches 12.12 J/cm3, which is improved by 211 % that of the pure PC. Its discharge efficiency is 83.5 %. A finite element analysis corroborates the superiority of the ternary polymer nanocomposites for dielectric energy-storage.高放电能量密度(Ue)薄膜电容器对于电力电子应用的微型化和集成化非常重要。聚合物薄膜的 Ue 主要取决于威布尔击穿强度(Eb)和介电常数(εr)。本研究旨在开发由聚碳酸酯(PC)、Al2O3 纳米粒子(Al2O3 NPs)和 BaTiO3 纳米线(BT NWs)组成的三元纳米复合材料,用于电容储能。Al2O3 NPs 具有宽带隙,由于其绝缘性能,有望提高 Eb 值,而 BaTiO3 纳米线 (BT NWs) 具有铁电性,有望提供较高的εr 值。为了克服εr 不匹配导致的界面局部电场畸变,制备了核壳结构的 BT@SiO2 纳米线。含有 1.0 wt.% Al2O3 NPs 和 6.0 wt.% BT@SiO2 NWs 的复合材料的 Eb 可达到 626 MV/m,而纯 PC 的 Eb 为 465 MV/m。因此,其 Ue 达到 12.12 J/cm3,比纯 PC 提高了 211%。其放电效率为 83.5%。有限元分析证实了三元聚合物纳米复合材料在电介质储能方面的优越性。High-performance carbon fiber reinforced polyether-ether-ketone composite pellets 3D-Printed via screw-extrusion additive manufacturingHu Zhonglue, He Jiawen, Chen Wei, Liu Wei, Ding Jietai, He Chang, Wang Sisi, Ning Fuda, Li Xipingdoi:10.1016/j.compscitech.2023.110362 高性能碳纤维增强聚醚醚酮复合材料颗粒通过螺旋挤出增材制造技术实现 3D 打印The lightweight and high-strength carbon-fiber reinforced polyether-ether-ketone composites (PEEK-CF) are highly favorable for a plethora of strength-demanding and weight-sensitive applications. Yet, the traditional filament-based three-dimensional (3D) printing approaches are limited both in throughput and reinforcement content, leaving a wide gap between the service requirement and attainable strength. In this study, pelletized PEEK-CF composites with high CF content (up to 30 wt%), are successfully printed with a custom-designed screw-extrusion 3D-printer. Microstructural characterization reveals the CFs, averaging around 226 μm long, are generally well aligned along the printing direction. The printed PEEK-CF composites exhibit an outstanding tensile strength, reaching over 190 MPa. Post-print treatment, such as hot compression, can further enhance the strength over 200 MPa. Addtionally, those printed specimens also exhibit superior thermal stability, the tensile strength of which reaches 64 MPa at 250 °C. Overall, the tensile strength of the composites agrees well with the Kelly-Tyson equation. The results of this study may incentivize new strategies for designing and optimizing the performance of 3D-printed PEEK-CF composites.轻质、高强度的碳纤维增强聚醚醚酮复合材料(PEEK-CF)非常适用于大量对强度和重量敏感的应用。然而,传统的基于长丝的三维(3D)打印方法在产量和增强材料含量方面都受到限制,因此在使用要求和可达到的强度之间存在很大差距。在本研究中,使用定制设计的螺旋挤出三维打印机成功打印出了高 CF 含量(高达 30 wt%)的粒状 PEEK-CF 复合材料。微观结构表征显示,平均长度约为 226 μm 的 CF 沿打印方向排列整齐。打印出的 PEEK-CF 复合材料具有出色的拉伸强度,超过 190 兆帕。印刷后处理(如热压)可进一步提高强度,超过 200 兆帕。此外,这些印刷试样还表现出卓越的热稳定性,在 250 °C 时的拉伸强度达到 64 兆帕。总体而言,复合材料的抗拉强度与凯利-泰森方程十分吻合。这项研究的结果可能会促进设计和优化三维打印 PEEK-CF 复合材料性能的新策略。 来源:复合材料力学仿真Composites FEM

未登录
还没有评论
课程
培训
服务
行家
VIP会员 学习 福利任务 兑换礼品
下载APP
联系我们
帮助与反馈