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Elsevier Science
Composite structures

Elsevier Science

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0263-8223

Composite structures/Journal Composite structuresSCIISTPEI
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    Ultrasonic reconsolidation of separated CF-PEEK composite layers at 20 kHz — An experimental study on parameter optimization and Ex-situ characterization

    Ragupathi B.Rotzinger L.Rienks M.Balle F....
    1.1-1.14页
    查看更多>>摘要：© 2024 The Author(s)Ultrasonic-assisted joining can replace the current repair strategies, such as adhesive bonding, to join the repair patches onto the damaged aerospace composite structures due to their energy and time efficiency. This work reports on the process optimization of repairing separated carbon fiber reinforced (CF)/ poly-ether-ether-ketone (PEEK) layers through ultrasonic reconsolidation at 20 kHz and its influence on the mechanical performance. The results showed that weld force and weld time dominate the temperature evolution, which was used to set the ultrasonic process window. Repairing CF-PEEK layers to different laminate architecture exhibited a 15% deviation from the reference repair. Compared with quantitative results, the ex-situ investigation showed that excessive holding force caused fiber–matrix debonding, leading to a cohesive failure inside the composite laminate. An optimal holding force, approximately 25% of the used weld force, is recommended to alleviate these damages.
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    Low-velocity impact damage characteristics of flax/glass epoxy hybrid laminates on the influence of different temperatures: Experimental and numerical analysis

    Musthaq Ahamed M.A.Dhakal H.N.Zhang Z.Barouni A....
    1.1-1.23页
    查看更多>>摘要：© 2024 The Author(s)This study investigated the effects of different temperatures on the low-velocity impact damage behaviour of flax fibre-reinforced epoxy composites and their glass/flax hybrids. Composites reinforced with flax, glass, and hybrid flax/glass onto epoxy matrix Subjected to low-velocity drop weight impact tests at 5 J of incident impact energy at sub-zero temperatures (−10 °C and −20 °C) and at room temperature (RT) are presented. Under the different temperatures, the experimental findings showed a beneficial hybrid effect where the temperature played a significant role. At RT, the Lam-GFGFGFG exhibit improved impact resistance, with enhanced energy absorption capabilities compared to glass-only laminates (Lam-G). Besides, Lam-GFFFFG laminates exhibit a significant difference in the force–displacement curves at − 20 °C, with a maximum load of 801.95 N in contrast to RT and − 10 °C resulting in a gradual increase in force with increasing displacement. This indicates that Lam-GFFFFG laminates can resist the impact and maintain structural integrity at sub-zero temperatures. The alternation of glass and flax layers in the hybrid structure contributes to the synergistic effects, resulting in improved damage resistance and tolerance. Also, the highest impact tolerance in a laminate is achieved through the hybridisation of flax fibre-reinforced composites with glass-reinforced layers on the outer surfaces (Lam-GFFFFG) at − 10 °C. Subsequently, experimental results were compared with finite element analysis (FEA) results, derived from a model built using a VUMAT subroutine integrated with ABAQUS/Explicit for a more accurate representation of the damage characterisation of the composite laminates under low-velocity impact.
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    Three-dimensional graded metamaterials with customizable thermal responses under space-variant temperature stimuli

    Wang K.Gao X.-L.Han Z.Lin F....
    1.1-1.18页
    查看更多>>摘要：© 2024 Elsevier LtdMetamaterials with customizable thermal expansions are desirable for important engineering applications. However, existing metamaterials were designed by considering uniform temperature distributions. In the current study, a new design strategy is proposed to develop metamaterials with customizable thermal deformations under space-variant temperature (SVT) stimuli which are non-uniform. Three types of bi-material pyramidal units are first devised through using different material distributions and geometrical configurations. The coefficients of thermal expansion (CTEs) of these units are derived in closed-form expressions. Graded metamaterials are then constructed from the pyramidal units through combined periodic and graded tessellations. Based on targeted thermal deformations under prescribed stimuli, geometrical parameters are identified, and the thermal strains are determined using the newly derived analytical formulas and finite element simulations. The two sets of predictions are found to agree well, which indicates the effectiveness of the new design strategy for the graded metamaterials. The numerical results reveal that the graded metamaterials exhibit customizable uniform deformations under the SVT stimuli. In addition, targeted customizable thermal deformations with quadric-shape strain profiles are achieved in the graded metamaterials. Compared with the conventional design with uniform temperature distributions, the newly proposed design of metamaterials under non-uniform SVT stimuli is more versatile and flexible, thereby providing a systematic strategy for developing graded metamaterials.
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    Lamb wave S0/A0 mode conversion for imaging the internal structure of composite panel

    Wandowski T.Radzienski M.Kudela P.
    1.1-1.13页
    查看更多>>摘要：© 2024 Elsevier LtdStiffened structures are utilised in various industries and their structural assessment is of paramount importance. In this paper, a novel, automated algorithm for internal structure imaging based on S0/A0 mode conversion effect is proposed. Moreover, a contrast indicator for the quantitative characterisation of structure imaging results was introduced. The research is exclusively experimental and focuses on fibre-reinforced, stiffened aerospace composite panel. Both non-contact (air-coupled transducer-ACT) and contact (piezoelectric transducer-PZT) methods of elastic wave generation were investigated. Low-frequency (40 kHz) wave generation was applied to ACT and PZT, while high-frequency excitations (100 kHz and 180 kHz) were analysed for the PZT. The results obtained for both excitation methods were compared. Full wavefield signals of elastic wave propagation were registered with a scanning laser Doppler vibrometer. The S0/A0 mode conversion observed on the specimens stiffeners led to the development of a new algorithm based on time–space guided wave signal filtering, which enables the imaging of the internal structure of the stiffened panel. The efficacy of the developed algorithm was proved to be higher than conventional weighted RMS (WRMS) and wave irregularity mapping (WIM) algorithms. The proposed method allows for the generation of easily interpretable maps illustrating discontinuities in the examined structure. The contrast indicator is two times higher for the proposed MCWA than for WRMS and WIM for wave frequency 100 kHz and three times higher for frequency 180 kHz.
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    Bi-directional homogenization method for the design of multi-scale mechanical metamaterials

    Huo S.Du B.Zhao Y.Chen X....
    1.1-1.14页
    查看更多>>摘要：© 2024 Elsevier LtdInverse Homogenization (IH) is a classical concept for the Topology Optimization (TO) of metamaterials. Traditional IH design methods are mainly the single-scale TO within a Representative Volume Element (RVE), suffering from challenges like design inefficiency and under-utilization of the design space. To address the problems, a Bi-Directional Homogenization (BDH) method based on the multi-scale TO principle is proposed for the design of mechanical metamaterials. The general design framework includes a forward homogenization process from the microscale to the mesoscale, and an inverse design process from the macroscale to the mesoscale. Firstly, at the microscale, the Graded Microstructures (GMs) are generated via a multi-cut level set method. Then, by varying the relative densities, the microstructure instances are sampled and the mesoscopic equivalent properties are computed using the homogenization method. After that, a spectral decomposition-based interpolation model is used to predict the relationship between the relative densities and the elastic tensors. These preparations allow for the mesoscopic optimization of the GMs distribution, and the reconstruction of the graded multi-scale metamaterial structures by using a mapping transformation on the density field. Various types of auxetic metamaterials are performed to demonstrate the effectiveness and versatility of the proposed method.
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    Fatigue life prognosis of composite structures using a transferable deep reinforcement learning-based approach

    Liu C.Chen Y.Xu X.
    1.1-1.18页
    查看更多>>摘要：© 2024 Elsevier LtdAccurately predicting the remaining useful life (RUL) of Carbon Fiber Reinforced Polymer (CFRP) structures under fatigue loading is crucial for enhancing safety and minimizing maintenance costs, especially in industries like aerospace and automotive. However, the complex physical properties of CFRP, combined with the scarcity of real-world damage-condition data, make this task extremely challenging. To address these issues, we propose a novel deep reinforcement learning (DRL)-based prognostic method. Our approach integrates Denoising Autoencoder (DAE) and Transformer architectures to construct a powerful DRL Policy Network, capable of extracting high-quality features from X-ray records to capture the subtle progression of damage in CFRP structures. Additionally, we employ advanced data augmentation techniques to overcome the limitations of small datasets and introduce transfer learning to extend the model's generalization capabilities across different CFRP structures. By pre-training on diverse CFRP datasets, our model achieves highly accurate RUL predictions for new designs, even with minimal labeled data from the target structure. Experimental results demonstrate that our method significantly outperforms current state-of-the-art (SOTA) techniques, offering a scalable, efficient, and practical solution for the real-world monitoring and prognostics of CFRP structures, with broad potential for industrial applications.
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    Numerical prediction of impact damage in thick fabric composite laminates

    van Hoorn N.van den Brink W.Turteltaub S.Kassapoglou C....
    1.1-1.15页
    查看更多>>摘要：© 2024 The AuthorsA simulation methodology for assessing the damage in thick fabric Carbon Fibre Reinforced Polymer (CFRP) composite laminates under low- and high-velocity impacts is presented. It encompasses steps for calibration, verification, and validation of the elastic and fracture material properties as well as determination of model parameters for the numerical simulations. Damage is modelled using a discrete fracture approach with cohesive interface elements that capture individual cracks occurring in and between plies. For computational efficiency, the method is implemented in a two-dimensional (2D) axi-symmetric model. Results from double-cantilever beam, end-notched flexure, and quasi-static indentation experiments align well with numerical simulations and serve to calibrate and verify the implementation of the discrete fracture approach. The methodology is extended to dynamic impact analysis to predict damage mechanisms, force–displacement histories, and is validated using test results. This methodology combines meaningful insight in the failure mechanisms with a manageable computational effort, achieving a factor 50 improvement compared to a benchmark. A parametric analysis summarised in failure maps relates damage mechanisms to impact energy, mass, and laminate thickness. The proposed methodology strikes a balance between computational efficiency and accuracy, making it a valuable tool for optimum design and certification of thick CFRP composite laminates under impact.
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    A multi-scale uncertainty analysis method based on the Hermite–Chebyshev polynomials for dynamic responses of FRP composite structures with hybrid uncertainties

    Qian S.-Y.Zhou X.-Y.Wang N.-W.
    1.1-1.16页
    查看更多>>摘要：© 2024 Elsevier LtdMulti-scale hybrid uncertainties in material properties of FRP composites stemming from their manufacturing processes present significant challenges for dynamic analysis and reliability assessment. This paper proposes a multi-scale uncertainty surrogate model based on Hermite–Chebyshev polynomials. The relationship between micro- and macro-scale material properties is established using the Mori–Tanaka method. To demonstrate the efficacy of the proposed method, case studies are conducted on both a FRP wide-flange I-beam structure and a FRP truss bridge. Results indicate that this method accurately determines the probability density functions and cumulative distribution functions of natural frequencies and mode shapes. Notably, the method efficiently computes the upper and lower bounds of dynamic failure probability of FRP truss bridge with high numerical efficiency.
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    Experimental study on the electrical conductivity and strain sensitivity of fibre-reinforced thermoplastic for structural health monitoring

    Ciampaglia A.Roccia S.Ciardiello R.
    1.1-1.16页
    查看更多>>摘要：© 2024 Elsevier LtdThis experimental study explores the mechanical, electrical, and piezometric characteristics of conductive thermoplastic polymers reinforced with short carbon and glass fibres. The work investigates how the local anisotropy induced during the manufacturing injection process impacts the properties of the composite. Tensile tests showed that the material orientation respect to the injection flow direction significantly affects the mechanical properties due to the alignment of the fibres with the injection flow, as shown through microscopy analysis. Contrarily, electrically conductive tests showed that the influence of the orientation on the conductive properties of the material is negligible. The study also unveils the difference in the surface and bulk conductivity with the increasing distance of the electrodes. Tensile tests with in-situ electrical measurements were conducted to assess strain sensitivity by correlating stress–strain curves with changes in material conductivity. The results demonstrate the predominant impact of local anisotropy on piezometric response. Finally, a model for the piezometric response of the material is proposed and applied for the structural health monitoring of a tensile specimen, revealing its ability to detect local damage before final failure. This application underscores the prognostic capabilities of this material and its potential significance in ensuring structural integrity.
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    A transparent multifunctional integrated meta-window with excellent sound insulation and vibration reduction performance

    Tang Z.Wang X.Li S.Li H....
    1.1-1.11页
    查看更多>>摘要：© 2024 Elsevier LtdAs the speed of transportation vehicles such as high-speed train continues to increase, there has been a significant rise in both noise and vibration levels, substantially compromising passenger comfort and overall travel experience. In transportation vehicles, the necessity for transparency in windows poses a challenge in incorporating high sound-insulating or vibration-damping materials, rendering windows vulnerable in sound isolation and vibration attenuation. This study employs an integrated material-structural design concept to develop a multifunctional meta-window, which ensures optimal lighting transmission while achieving outstanding sound-insulating and vibration-damping capabilities. Two distinct structures, named ultra-lightweight thin plate-type metamaterial and high-stability thick plate-type metamaterial, are precisely designed to adapt to varied application scenarios. Utilizing a gradient parameter multi-cell parallel synergetic coupling design method broadens the working bandwidth for sound insulation. The meta-window incorporates localized resonance units, enabling acoustic and vibrational energy dissipation through low-frequency resonance, effectively enhancing the window's sound-insulating and vibration-damping capabilities. Comprising a composite of various transparent materials, the design amalgamates sound insulation, vibration reduction, and light transmission, eliminating the need for opaque sound-insulating or damping materials. Consequently, it holds substantial potential for applications across sectors, including train, aircraft, and architectural domains.
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