The strength of metallic nanocomposites structures can be greatly improved by adding nanofillers to the matrix. However, there is a discrepancy between the conventional theories and the experimental evidence on the effect of nanofiller loading on the strength of the nanocomposite. The conventional theories predict that the strength increases with the nanofiller loading, but the experimental evidence shows that there is an optimal nanofiller loading beyond which the strength does not improve much. This discrepancy, especially at high filler loadings, is due to the neglect of the agglomeration and the interphase region formation in the composite structure modeling. In this paper, we propose a new micromechanical model based on mean-field theory to examine how the agglomeration and the interphase region influence the elastic modulus of metal/graphene nanocomposites (MGNs). We also explore how other factors, such as interphase region thickness and strength, graphene size, and metallic matrix elastic modulus, influence the elastic modulus of MGNs. We present a mathematical model that describes how the thickness and modulus of the interphase layer of graphene nanoplatelets change due to agglomeration. This model allows us to reproduce the parabolic behavior of the elastic modulus of the composite, which is consistent with the experimental results.
Continuous fiber reinforced meta-composites with tailorable Poisson’s ratio and effective elastic modulus: Design and experiment
Guixing Li, Yuan Chen, Guangkai Wei
doi:10.1016/j.compstruct.2023.117768
具有可定制泊松比和有效弹性模量的连续纤维增强元复合材料：设计与实验
Auxetic metamaterials, i.e., with negative Poisson’s ratio are attracting increasing attention. This study develops a novel method to design and investigate continuous fiber-reinforced meta-composites with tailorable negative Poisson’s ratio and effective elastic modulus. First, the design scheme based on parametric level set method, is proposed by combining fast marching method, filtering technology and matrix rotation for attaining the two-dimensional isotropic composites. A novel objective function considering both negative Poisson’s ratio and effective elastic modulus is introduced and the result demonstrate that it is effective to not only accelerate the numerical convergence but also achieve a larger negative Poisson’s ratio when compared with that using the currently-used objective function. By tailoring a weight ratio for balancing the negative Poisson’s ratio and effective elastic modulus, a general contradictive trend was captured. Experimentally, the specimens are accordingly fabricated via 3D printing. Then, the axial compression tests are performed with the aid of digital image correlation technology to characterize the deformation behaviors and evaluate the mechanical properties of the designed meta-composites. Experimental results show that, as the weight ratio increases from 0.02 to 1.57, the effective elastic modulus increases from 180.5 MPa to 310.3 MPa (enhanced by 71.9%) while the negative Poisson’s ratio decreases from −0.41 to −0.036 (reduced by 91.4%), proving the effectiveness of the design method. The design methods and experimental results can provide effective approaches and important information for designing novel continuous fiber reinforced meta-composites with tailorable mechanical performance.
Femtosecond laser drill high modulus CFRP multidirectional laminates with a segmented arc-based concentric scanning method
Chunyang Zhao, Zhenhua Ma, Jiayan Sun, Likuan Zhu
doi:10.1016/j.compstruct.2023.117769
利用基于分段圆弧的同心扫描方法，用飞秒激光钻削高模量 CFRP 多向层压板
High modulus carbon fiber reinforced plastic multidirectional laminates (HM-CFRP-MDL) are widely employed in the aerospace industry as crucial structural materials for satellites, rockets, and aircraft. However, it is difficult for the femtosecond laser to drill holes on HM-CFRP-MDL with the traditional concentric scanning method (CSM). To improve drilling quality and precision, this study proposes a segmented arc-based concentric scanning method (SAB-CSM) and investigates the interaction mechanisms between femtosecond lasers and CFRP. By adopting the proposed scanning method with optimized parameters, the overall average HAZ width can be decreased to 10 μm in different regions on the surface of the drilled hole, the hole taper can be reduced significantly, and the consistency across different layers can be improved. Compared to CSM, the HAZ width can be decreased by 40.8% (12.597μm to 7.464μm) and 50.3% (15.585μm to 7.748μm) in the regions where the angles between fiber direction and scanning direction are 45° and 90° respectively, and the taper can be reduced by 34.5% (0.084 to 0.055). Moreover, the SAB-CSM approach effectively decreases quality discrepancies between different layers, and substantially reduces those defects which results in smooth and uniform hole walls, facilitating synergistic removal of multidirectional carbon fibers and resin matrix.
Electrochemical reduction and oxidation reactions of vanadium ions can enable efficient power management by a secondary battery, such as a vanadium redox flow battery (VRFB). To increase the energy efficiency of a VRFB system, the electrical resistance of the cell component, such as a bipolar plate, should be reduced. In this study, particles of polyaniline (PANI), a conductive polymer, were embedded in a carbon/epoxy composite by spraying on the prepreg surface to increase the electrical conductivity of the bipolar plate. The effect of the PANI particles on the electrical and mechanical properties was investigated. Furthermore, the optimum PANI content of 3 wt.% achieved an area-specific resistance of 16.7 mΩ·cm2, 55.2% lower than that of the neat specimen. The tensile strength was improved to 586 MPa, a 13.8% increase compared with the neat specimen. Finally, the cell performance of the fabricated bipolar plate was verified via permeability and single-cell charge/discharge tests.
钒离子的电化学还原和氧化反应可使钒氧化还原液流电池（VRFB）等二次电池实现高效的电源管理。为了提高钒氧化还原液流电池系统的能量效率，应降低电池组件（如双极板）的电阻。在本研究中，通过在预浸料表面喷涂的方式，将导电聚合物聚苯胺（PANI）颗粒嵌入碳/环氧树脂复合材料中，以提高双极板的导电性。研究了 PANI 粒子对电气和机械性能的影响。此外，3 wt.% 的最佳 PANI 含量可实现 16.7 mΩ-cm2 的面积特定电阻，比纯试样低 55.2%。拉伸强度提高到 586 兆帕，比纯试样提高了 13.8%。最后，通过渗透性和单电池充放电测试验证了制作的双极板的电池性能。
Vibration-based prediction of residual fatigue life for composite laminates through frequency measurements
Fiber reinforced polymer (FRP) structures may experience cumulative fatigue damage during their service life which can lead to structural failure. This paper focuses on predicting the residual fatigue life of FRP structures using vibration parameters. The relationship between residual fatigue life and natural frequencies is examined through modal testing and fatigue measurements on FRP beam specimens. Two prediction methods; semi-empirical models and machine learning (ML) algorithms, are utilized. The semi-empirical models are derived from existing “residual stiffness” models based on the relationship between bending stiffness and flexural frequencies. ML algorithms Support Vector Machine (SVM) and Artificial Neural Network (ANN), are developed for fatigue life prediction. Experimental validation is performed using measured frequencies during fatigue testing of FRP beams. The ML algorithms can use multimode frequencies unlike single mode of semi-empirical models. The verification results show that the ML algorithms can be used to predict the residual fatigue life with the selection of the appropriate mode of frequency. The results show that ML algorithms outperform single-mode frequency inputs, and the use of higher modes of measured frequencies improves the precision of fatigue life prediction. An inverse algorithm based on SVM exhibits higher prediction accuracy and stability, even with limited training samples.
Composites Part A: Applied Science and Manufacturing
Significantly Enhanced Tribological Properties of PTFE/PEEK Fabric Composites by Macroporous Metal−Organic Frameworks with Solid–Liquid Synergistic Lubrication
Mingkun Xu, Jing Zhang, Song Li, Tingmei Wang, Qihua Wang, Liming Tao, Peng Liu
doi:10.1016/j.compositesa.2023.107935
大孔金属有机框架固液协同润滑显著增强 PTFE/PEEK 织物复合材料的摩擦学性能
In this work, a macroporous oil-containing metal-organic framework material (CuBTCO) was prepared by a solvothermal method and vacuum impregnation. The tribological behaviors of PTFE/PEEK fabric composites (PFC) filled with CuBTCO were evaluated by the pin-on-disk tribometer under different loads. The coefficient of friction and mass wear rate of PFC containing 6 wt% CuBTCO (PFC-CuBTCO-6%) were 0.017 and 1.1×10-9 g/(Nm), respectively, which were reduced by 63.8% and 76.3% in comparison to PFC containing 6 wt% CuBTC under the same conditions. The excellent tribological properties of PFC-CuBTCO-6% are attributed to the solid–liquid synergistic lubrication between the adsorption film formed by the oleylamine released from CuBTCO and the PTFE-based transfer film. This work provides a novel approach for the structural design of solid–liquid synergistic lubrication of fabric liner composites.
Mechanism-based damage and failure of fused filament fabrication components
Iván Rivet, Narges Dialami, Miguel Cervera, Michele Chiumenti
doi:10.1016/j.compositesb.2023.111119
基于机理的熔融长丝制造组件的损坏和失效
Fused Filament Fabrication (FFF) is a polymer-based Additive Manufacturing (AM) technology that produces complex layered components. The characterization of the inherited orthotropic properties of FFF components and their failure analysis is a challenging endeavor. In this paper, the failure mechanics of FFF parts are studied via a Mechanism-Based (MB) damage material model. A MB damage criterion is developed by considering that the damage is driven by different failure modes identified according to the printing pattern. The developed criterion is compared to the Tsai–Wu (TW) criterion, which is commonly used for orthotropic materials with different strengths in tension and compression. Also, a MB cracking model that incorporates the orthotropic brittleness of FFF components is developed. The application of this cracking model requires solely two parameters to be defined. Numerical predictions of the cracking of two different experimental tests illustrate the similarities and the differences between the MB and TW damage criteria. The results demonstrate that the MB damage criterion can accurately match the experimental results, while the TW criterion fails to describe correctly the failure modes in complex 3D stress states.
