Composites Part C Open Access最新文献

In this study, to address environmental challenges stemming from plastic wastes, we produced carbon material derived from polyethylene (PE-C) using thermal oxidation and carbonization processes. Prior to thermal oxidation, e-beam irradiation was employed to enhance oxidation reactions which facilitated transformation of linear chains to cyclic ladder structures, resulting in a threefold increase in carbonization yield compared to conventional methods. Our analysis using XRD, Raman spectroscopy, XPS, and SEM revealed that PE-C exhibited a crystal structure similar to commercial CB (C-CB). However, it featured three times more oxygen functional groups on its surface and consisted of individual particles without forming aggregates or agglomerates. We incorporated PE-C into a PA6 polymer matrix to create composite materials with various compositions, systematically comparing their electrical, thermal, and mechanical properties to C-CB/PA6. PE-C outperformed C-CB in terms of mechanical properties (65 MPa vs. 41 MPa) due to its surface oxygen functional groups, uniform dispersion even at high loadings, and a rough surface. Moreover, PE-C exhibited a lower surface area, which reduced interfacial thermal resistance and consequently enhanced thermal conductivity, resulting in a 16 % improvement compared to C-CB at 30 wt%.

Natural fiber reinforced plastics (NFRP) are increasingly used as a sustainable material alternative to glass or carbon fiber reinforced plastics in lightweight solutions. Visible and/or decorative coated components must meet high surface qualities and defects such as fiber print-through due to different expansion behavior of fiber and matrix are not permitted. Various studies investigate the expansion behavior of NFRP under the influence of temperature and humidity on mechanical properties. In contrast, there are no studies that relate these properties to decoratively coated NFRP and the importance for surface quality. The present study aims to fill this gap using a flax fiber reinforced bio-based epoxy resin (FFRP) manufactured by resin transfer molding process (RTM). The surface roughness and the coefficient of thermal expansion (CTE) were determined as a function of the fiber mass fraction. Further, FFRP and carbon fiber reinforced plastics (CFRP) were decoratively coated and subjected to an alternating climate test. The results showed that reducing the fiber mass fraction of an FFRP to 40 % and using a glass-fiber non-woven on the surface, in combination with 50 % fiber mass fraction, were the most promising methods for reducing roughness in the uncoated state. In addition, the FFRP exhibited an increased CTE longitudinally of 11 ppmK⁻¹ and transversely of 105 ppmK⁻¹ to the fiber direction compared to the CFRP (5 and 79 ppmK⁻¹⁾, along with increased roughness of Ra 0.8 compared to 0.6. The effect of fiber print-through was shown for all variants by the stress in the alternating climate test.

Low-velocity impacts represent a critical dynamic condition for engineering structures. Combining two reinforcing fibers in a single matrix, i.e., hybridization, is considered a feasible way to improve composite performance. In this context, this paper presents an experimental work on composites with Kevlar and glass fabrics and a novel thermoset polyurethane matrix. The coupons are manufactured by vacuum infusion technique and low-velocity impact tests are carried out. First, the impact behavior of Kevlar and glass laminates of different thicknesses is assessed, and then impact tests are performed on different configurations of hybrid laminates, both symmetric and non-symmetric. For the non-symmetric specimens, impact tests were conducted on both sides of the stack. Load vs displacement curves are reported along with absorbed energy. To investigate the damage mechanism, the front, back, and cross-section views of the specimens are analyzed, and features related to the stacking sequences are discussed. Thermographic analyses are carried out on the impacted specimens to further analyze damage. The failure mechanisms are different from traditional epoxy composites and a hybridization effect is reported. The results evidence that the hybrid coupons are viable for structural applications, being capable of absorbing high-impact energies, in particular, non-symmetric hybrid laminates outperformed the Kevlar, glass, and symmetric ones, absorbing roughly 15% less energy for the highest energy impact.

The key to effective mechanical reinforcement in polymer nancomposites lies within the stress transfer mechanisms and the distribution of the nanofillers within a polymer matrix. In this work, the micromechanics of Ti₃C₂T_x MXene-reinforced poly(vinyl alcohol) (PVA) nanocomposites have been studied in detail. Ti₃C₂T_x MXene/PVA nanocomposites were prepared by solution blending. The spatial orientation of Ti₃C₂T_x MXene in the nanocomposites was characterized by polarized Raman spectroscopy and the orientation factor was correlated to the effective Young's modulus of the flakes through well-established micromechanical theories. The mechanical properties of the nanocomposites were evaluated by tensile testing. A 27% increase in Young's modulus and a 24% improvement in tensile strength were achieved by addition of only 0.6 wt% Ti₃C₂T_x. Efficient stress transfer from the polymer matrix to Ti₃C₂T_x MXene in bulk nanocomposites has been observed through strain-induced Raman band shifts for the first time. The effective Young's modulus of the MXene nanoplatelets was calculated to be in the order of 300 GPa, in good agreement with the values derived from the application of micromechanical models.

Symmetry requires that the material configuration, geometry, restraints, loads, and material properties are symmetrical. It is generally not recommended to use symmetry for buckling and frequency studies. Symmetry can be used to model a portion of a construction instead of the entire model. Results in unmodeled fragments are derived from modeled fragments. In justified situations, the use of symmetry can reduce the size of the problem and increase the accuracy of the results. The analysis of symmetry of composite plated/shell 2D structures is connected with the description of deformations, failure modes and the scale of considerations (nano-, micro-, meso‑ and macro/global scale). For composites made with the use of filament winding method the cyclic symmetry is usually adopted.

Due to the anisotropy of composite materials, the assumption of symmetry is related to the accuracy of the description of deformation and damage of the structure in relation to the results obtained experimentally. Typically, the analysis of composite structures is associated with the introduction of high values ​​of safety factors. It is necessary to determine how and when it is necessary and possible to introduce material property dispersion values ​​even when using a linear approach in geometric or physical approach. The description options are related to the use of statistical analysis, fuzzy set methods or the introduction of anti-optimization.

Glass fiber-reinforced polymer composites are important structural materials and are widely used in structure engineering. In this study, a new V-notch non-standard tensile specimen is proposed. All the in-plane stiffness coefficients of glass fiber-reinforced polymer composites could be obtained by the virtual fields method with only one uniaxial tensile test. First, the special virtual fields method for inversion of elastic constitutive parameters of orthotropic materials in the uniaxial tensile test was introduced. The optimization of the geometrical design of the specimen was conducted using finite element simulation experiments. Batch modeling calculation was conducted within the designed range of the geometric parameters of the specimen. The generated ideal strain field data were substituted into the virtual fields method to invert and identify the stiffness coefficients. The optimized geometry of the specimen was determined according to the objective function of minimum error. Through a tensile experiment on glass fiber composites, the influence of specimen deformation on the identification results was assessed, and the load level suitable for parameter identification was determined. Based on the results, it can be concluded that the inversion identification accuracy meets the requirements of engineering measurement.

Developing efficient nitrate removal technologies is crucial for ensuring the safety of drinking water, a polypyrrole-grafted activated carbon (PPy-AC) was synthesized via in situ chemical oxidative polymerization to enhance nitrate adsorption from water. It was showed that the PPy-AC composite featured a maximum adsorption capacity of 13.36 mg NO₃⁻-N/g and exhibited high selectivity toward nitrate in the presence of co-existing anions. The PPy-AC composite exhibited a considerable capacity for adsorbing nitrate over a wide pH range of 3.0–9.0. The absorption performances were well-fitted by the Redlich-Peterson isotherm model, and the adsorption kinetics were well-described by the pseudo-second-order equation. Furthermore, the mass and charge balance calculations showed that 8.4% of the nitrogen atoms in the PPy-AC facilitated the adsorption of nitrate. The mechanisms of nitrate removal by the PPy-AC composite were determined through the electrostatic attraction and ion-exchange process, in which the nitrate ions are replaced by doped chloride ions, and the other N⁺ sites in PPy were occupied by nitrate ions. The PPy-AC is a promising material for the nitrate removal from wastewater.

A new approach that utilizes Thermoelastic Stress Analysis (TSA) is proposed to investigate fatigue-induced material degradation in laminated fiber-reinforced polymer composites (FRP). The proposed model accounts for non-adiabatic conditions, the effects of the material temperature on the material properties, and the effects of stiffness material degradation due to damage. Experimental data from the literature is used to validate the part of the model that simulates the heat transfer, which results in a non-adiabatic contribution to the thermoelastic response. Specimens made from E-glass FRP representative of those used in wind turbine blade manufacture are used in the study, which make a challenging proposition for TSA. The evolution of tunneling cracks caused by cyclic loading causes stiffness degradation and changes in the thermoelastic response. The added features of the proposed model are shown to be necessary to interpret the thermoelastic response. The model improves correspondence with experimental data compared to previous TSA methods. Hence a generalized framework is proposed for incorporating the mechanisms that affect the thermoelastic response as materials degrade due to fatigue loading.

The use of adhesive joints in structures subjected to dynamic loads, such as wind turbines and cars, makes it important to study them under those conditions. Numerical models are an integral part of that. Commonly the Finite Element Method (FEM) is used, but meshless methods can be an interesting alternative. These models do not require elements, and as such they can model complex geometries more easily. The current work aims at performing a first study on adhesive joints under impact using a meshless method, the Radial Point Interpolation Method (RPIM). Since the strength prediction of adhesive joints is also an important field and because the commonly used Cohesive Zone Models (CZM) have some limitations, like the use of special cohesive elements, this work also aims to expand the use of the ISSF criterion to impact conditions. The results show that the RPIM can be used in this type of problem without numerical difficulties, and the ISSF gives acceptable strength predictions, with errors between 30.5% and 13.5%.

Adhesive bonding is a joining technique that offers some advantages, when compared to other common joining techniques, like bolting or riveting. One of those advantages is that adhesive joints are generally lighter than the alternatives, which is very important in the search for more efficient modes of transportation since lighter vehicles consume less energy. Given the interest in the use of adhesive joints, it is important to study their behaviour under different conditions. Currently, the static behaviour of adhesive joints is very well documented, with many research works dedicated to it. However, the number of publications on their dynamic behaviour is still scarce, with only a few works dedicated to fatigue, impact and free vibrations. Additionally, the use of meshless methods to study adhesive joints is also currently mostly limited to static analysis, and even in that case it is still very incipient. Therefore, this work aims at extending the use of meshless methods to the dynamic analysis of adhesive joints, to help in the advancement of both fields.

As drone technology grows in popularity, its application to automate aspects of society is increasing at a similar rate, where drones are now being trialled for delivering payloads over short distances. In order to progress the technology, 3D composite printing is being used to develop complicated parts for improved aerodynamic design that can be produced efficiently, where the resultant composite part has high specific strength and rigidity. This article reports 3D printing of high specific strength, high-temperature Polyamide 6 (Onyx), continuous glass-fibre reinforced Onyx, and carbon-fibre reinforced Onyx composites and characterising their mechanical and fracture behaviour. The Onyx + CF composites displayed up to 1243 % and 1344 % improvement in Young's modulus and tensile strength over neat Onyx samples. The flexural strength of Onyx + CF samples was up to 316.6 % higher than the flexural strength of the neat Onyx sample. SEM micrographs showed a strong bond between the hydration products and the carbon fibres, increasing their tensile and flexural strengths by preventing micro-crack propagation through fibre pull-out and breaking. The statistical analysis was conducted to ensure the validity of the results for the population and establish stress-strain relations, along with estimating errors. In addition, the carbon-fibre-reinforced Onyx composite was compared with commercially used alternatives for producing drone components. Finally, a finite element model was developed using a numerical homogenisation approach and validated to predict the tensile and flexural behaviour of Onyx and carbon-fibre reinforced Onyx samples. This study provides a direction for the next generation of drone manufacturers.