Composite Structures最新文献

This paper investigates delamination detection in composite pipes using higher harmonic generation technique for the first time. The semi-analytical finite element (SAFE) method is developed to analyze the dispersion characteristics of the composite pipe. Then, a flexural mode at low frequency is selected to detect delamination. The three-dimensional (3D) finite element (FE) model is developed to simulate the flexural mode propagating in the composite pipe and its interaction with delamination. By comparing the simulated radial displacement signals with and without delamination, it is observed that the delamination can contribute to the higher harmonic generation. Subsequently, the ultrasonic measurements are conducted to demonstrate the numerical results. Using a relatively simple piezoelectric transducer (PZT) configuration, an almost pure flexural mode can be excited in the experiment. More importantly, experimental results indicate the higher harmonics induced by the delamination can be observed obviously. Finally, extensive parametric studies are performed to reveal the sensitivity of higher harmonics to the delamination with various sizes and at different interface. The proposed higher harmonic generation of flexural waves is promising for the practical application of delamination detection in composite pipes.

Plain-woven composites are extensively utilized across various fields; however, it exhibits significant shear nonlinearity, especially at high temperatures. This study aims to propose a machine learning (ML) based constitutive model using Gaussian Process Regression (GPR), which is able to effectively characterize the shear nonlinearity of plain-woven composites at different temperatures. The shear nonlinearity of T800 carbon fiber-reinforced epoxy-based plain-woven composites are investigated by carrying out in-plane shear experiments, and the data sets considering temperature effects are established accordingly. Compared with traditional constitutive models, the proposed ML-based model excels in predicting shear nonlinearity, even at temperatures not included in the training set. The integration of this ML-based constitutive model into the finite element (FE) simulation framework achieves high consistency between simulation and experimental results, thereby validating the significant application of ML in complex material behavior modeling and FE analysis.

Numerous works in both recent and historical literature have concentrated on formulating theories to perform static analysis on simply-supported shell structures. However, it is worth noting that obtaining analytical solutions for clamped boundary conditions presents a strong challenge. In this paper, closed-form solutions for clamped cross-ply laminated and sandwich shells are achieved by employing a robust and hybrid methodology not previously reported in the literature. The high versatility of the Carrera Unified Formulation (CUF), based on the Equivalent-Single-Layer (ESL) description, is utilized to implement several refined shell theories. The Principle of Virtual Displacements (PVD) is utilized to derive the strong form of the governing equations in terms of displacement variables. As the main novelty, these equations are solved by the Boundary Discontinuous Fourier-based method (BDM) which provides highly accurate analytical solutions. The validity and robustness of the proposed methodology are assessed through a detailed comparison with references available in the open literature, as well as with FEM 3D results obtained with commercial software. Furthermore, the stress recovery technique is exploited to fulfill zero-stress and interlaminar continuity (IC) conditions. The findings might be useful in training artificial intelligence (AI) models, which, for instance, could facilitate the development of digital twin structures.

This paper evaluated the influence of filling rate and printing direction on the mechanical properties of composite metastructure via experimental and numerical approaches. A representative volume element (RVE) and finite element method were adopted to estimate the tensile and flexural properties and verify the applicability of these methods in the 3D printing of composite metastructure. Results showed that apparent tensile and flexural properties drop with decreasing filling rates. The tensile and flexural strength reached 70.7 MPa and 131.1 MPa for solid specimens. The bending test for samples with different printing directions showed that the printing direction of the core has no noticeable effect on flexural strength, but the +45°/-45° sample exhibited the highest modulus. The numerical estimation showed similar trend compared to experimental results for both tensile and flexural properties. Such an attempt indicates the feasibility of designing a composite metastructure with an optimum weight-strength relationship.

Many biological materials such as tendons and muscles contain helical fibers. In this paper, the fracture behavior of such chiral composites is investigated through a combination of theoretical analysis and finite element simulations. A mesoscopic fracture mechanics model of helical fiber-reinforced biological composites is presented, with the effects of interfacial damage and fiber breakage. A cohesive law is adopted to characterize the interfacial damage induced by the relative slipping between the fibers and the matrix. The theoretical model agrees well with the numerical results. The optimized fiber radius that can maximize the fracture toughness of the composites is determined. The effects of interfacial (e.g., bonding strength and energy dissipation) and material properties (e.g., strength and elastic modulus) on the resistance to crack propagation are revealed. Our results show that the composites reinforced by helical fibers exhibit comprehensively excellent mechanical properties, e.g., simultaneous high strength, stiffness, and fracture toughness. This work not only helps understand the structure–property interrelations of biological chiral composites, but also provides inspirations for designing high-performance engineering materials.

Replacing steel reinforcing bars in reinforcing concrete (RC) structures with fibre-reinforced polymer (FRP) bars is an effective approach to avoid problems associated with corrosion of steel bars due to external chloride ions and humid environments. Recently, thermoplastic FRP bar has attracted much attention due to its advantages such as recyclability and on-site workability. In particular, bendable FRP threaded bars made of thermoplastic composites are very easy to be processed on-site due to their flexibility when heated. A number of studies have been conducted on recyclable thermoplastic FRP bars for reinforced concrete structures. This article provides a comprehensive overview of the benefits associated with thermoplastic FRP bars. The basic properties of thermoplastic FRP bars (including mechanical properties, durability properties and creep properties, etc.) are reviewed and summarized, and the comparisons between them and thermosetting FRP bars are conducted. Opportunities for further research on thermoplastic FRP bars in terms of material properties and structural engineering applications are finally identified.

Pentamodes are known for their almost zero shear modulus. Polymer Matrix Composites are renowned for multiple advantages, such as their ability to withstand harsh conditions and prolonged usage. In the current study, a combination of these two technologies, i.e. Pentamode-based Polymer Matrix Composites (PPMCs) are proposed for application in seismic isolation. Bearings composed of pentamode layers embedded into polymer matrices are proposed. It is demonstrated that PPMCs feature a shear response improved up to 33 % compared to conventional pentamode specimens. By adding stiffening plates to PPMCs their compressive response can be improved up to 24 %. PPMCs with layers rotated every 45° are suggested to overcome the pentamodes’ anisotropy and their shear stiffness is proved to be increased by up to 26 %. The bearings’ failure mechanisms confirm the aforementioned findings. Real-life seismic excitations illustrate the applicability of PPMCs in seismic isolation and highlight the shear response improvement of up to 39 % offered by PPMCs compared to conventional pentamode devices.

By integrating structural steel with Fiber-Reinforced Polymer (FRP) and Ultra-High Performance Concrete (UHPC), FRP-UHPC-steel tubular columns (FUSTs) emerge as innovative composite members that offer exceptional corrosion resistance and lightweight properties. FUSTs hold significant potential for use as thin-walled tubular columns working in harsh environments, such as wind turbines and high-voltage transmission towers. To obtain in-depth understanding of key parameters including the steel fiber ratio of UHPC, the specimen void ratio and the FRP thickness, this paper tested 24 specimens to evaluate their compressive behaviour, including 18 FUSTs and 6 UHPC-filled FRP tubes (UCFFTs). Experimental results showed that: (1) FUSTs demonstrated ductile behavior with significant strain enhancement and notable strength improvement; (2) the steel fibers in UHPC had marginal influences on the ultimate condition of FUSTs; (3) a larger inner void had a general effect to lead to more localized rupture for the FRP tube; (4) the FRP thickness was the predominant influencing factor on both the general shape and the ultimate point of the normalized axial stress–strain curves. Finally, a design model was proposed, which was able to capture the general shape of the axial load–strain curves, and could generate reasonably accurate predictions for the peak load.

This work investigates the static and fatigue degradation after low-velocity impact (LVI) and the corresponding mechanisms of 3D woven carbon/epoxy composites with a fiber volume fraction of 53 %. Drop weight tests employing impact energies ranging from 6 J to 20 J are performed to introduce damage to the specimens. Quasi-static tensile tests after impact (TAI) and tension–tension fatigue tests after impact (FAI) are then carried out to study the post-impact behaviors. The results of TAI tests show that the residual strength decreases linearly by up to 62 % as impact energy increases to 20 J. Similarly, residual stiffness shows a linear decline with increasing impact energy until 15 J. However, as the impact energy increases to 20 J, the residual stiffness decreases significantly and deviates from linear decreasing trend due to the impact causing fiber breakage. The FAI test results show that LVI can reduce the fatigue life. But such effect is limited for small loading levels. It is worth noticing that even slight impact damage can reduce the static and fatigue performance significantly. To understand the mechanisms behind it, the damage evolution in TAI and FAI tests is analyzed through the CT technique. The results show that even though low energy LVI does not cause fiber fracture, the stress concentrations induced by matrix cracking and delamination still reduce the uniformity of the internal stresses, thus causing fiber fracture in sequence and reducing the mechanical and fatigue performance of 3D woven composites.

This study focuses on the design, behavior and experimental analysis of a novel metamaterial, consisting of an asymmetric auxetic three-dimensional structure (AATS) infused with polyester resin. Utilizing FDM additive printing, samples were created with customizable responses to compressive loads through varied design parameters. The objective is to surpass traditional material blending by enhancing stiffness and energy absorption. Striking a delicate balance, the AATS energy absorption properties are preserved while leveraging the stiffness of the resin. Despite its compact cubic form, not exceeding 27 mm on each side, this metamaterial showcases amplified characteristics, blending the AATS and polyester resin. The results hint at promising applications across military defense, automotive, aerospace sectors, and even potential replacements for articulated human skeletal components.