Applied Composite Materials最新文献

Glass Fiber Reinforced Polymer (GFRP) is commonly used in outdoor applications that expose it to environmental conditions capable of degrading its properties, notably ultraviolet (UV) radiation. In this study, we subjected GFRP to UV radiation for a duration of up to 180 days in an accelerated aging chamber. The composites underwent mechanical testing through tensile and flexural evaluations, while chemical and physical changes in the composite were assessed using Fourier-Transform Infrared Spectroscopy, Thermogravimetric analysis, and optical microscopy. Tensile tests revealed a noticeable reduction in GFRP strength after just one month of UV exposure, with a decrease of 18.7% observed at 90 days of exposure. In contrast, the behavior of the composite under flexural testing showed an initial improvement in strength after 30 days of UV exposure, with a significant increase of 54.1%. With longer exposure times, flexural strength gradually decreased but remained 18.9% higher than the strength of the unaged composite after 180 days of UV exposure. Other characterizations indicated material degradation, marked by phenomena such as photo-oxidation, composite yellowing, and the appearance of microcracks on the surface. These factors collectively contribute to the reduction in composite strength. Despite the visible degradation, the aged composite may exhibit improvements attributed to post-curing. However, over more extended periods, it may experience a decline in mechanical properties. Consequently, longer degradation times may unveil a behavior pattern distinct from what is observed during shorter periods, contingent upon the specific mechanical load under consideration.

Although development of high char-yielding polymers has reduced the manufacturing costs of carbon/carbon composites associated with multiple densification cycles, manufacturing highly customized complex-shaped carbon/carbon composites can still be expensive due to molds/tooling surfaces used by traditional preform production techniques. In this study, we explored whether extrusion deposition additive manufacturing (EDAM) could be used as a mold-less approach to manufacturing complex-shaped carbon/carbon composites. The thermogravimetric analysis and coupon distortion results of several short carbon fiber-reinforced thermoplastic polymers used for 3D printing were investigated, including polyphenylene sulfide, polyetherimide, poly sulfone, polyether ether ketone, and polyether sulfone. Although polyetherimide had the highest char yield (left(57 wt.%right)), carbon fiber-reinforced polyphenylene sulfide was the best preform for manufacturing complex shapes because of its dimensional stability, with carbonized strains of (-4.18times{10}^{-2}) and (1.82times{10}^{-1}) at 1 (^circ C/min) in the 1- and 3- direction, respectively, after heat treating to (900;^circ C). The distortion results of more complex shapes showed that EDAM can be a practical alternative over more traditional preform production techniques for manufacturing complex-shaped carbon/carbon composites.

The present study focuses on the effect of CNT nanofillers on the interlaminar static and fatigue crack propagation in carbon fiber reinforced composite laminates. Multi-walled carbon nanotubes (MWCNTs) were dispersed over the laminate interface through solvent spraying technique. The mode I fracture toughness and R curve behavior were determined first from DCB specimens. Then, the fatigue tests were performed at different stress ratios for laminates containing different contents of CNTs to determine the delamination growth rate da/dN from fatigue crack growth (FCG) curves. When FCG curves are expressed as a function of G, where G is the energy release rate, the growth curves are dependent on the R-ratio. It was found that the addition of CNTs enhances the delamination resistance in the initial part of FCG curves, i.e. low cyclic region. As the test progresses, the effect gradually diminishes making nanofillers ineffective. It is then shown that the FCG curves can be characterized when crack growth rates are expressed as a function of the crack‐driving force (overline{Delta kappa }) used in the Hartman‐Schijve equation. Therefore, the present paper presents a methodology to account for the stress ratio effect to evaluate the crack growth rate for any given R-ratio and to obtain a valid, upper-bound FCG rate curves in CNT reinforced laminates that exhibit high degree of scatter.

Woven lattice truss sandwich panel (WLTSP) has excellent debonding resistance, but is limited to the weak core shear performance. To relax the limit of mono-layer thickness and improve the shear rigidity, foam-filled double-layered WLTSPs (FDWLTSPs) were designed and manufactured by vacuum infusion process (VIP), hot-pressing technology (HPT) and filling-foam technique. Flatwise compression and edgewise compression experiments were performed to reveal the composite effects of multi-layered and filling-foam techniques on the mechanical performances of WLTSP. The results show that the strength, stiffness, and energy absorption of FDWLTSPs are significantly improved. The flatwise compression strength of FDWLTSPs is 5.03 MPa, increased by 403%. The edgewise compression strengths of FDWLTSPs with warp-warp, weft-warp, and weft-weft core arrangements, are 21.97 MPa, 24.1 MPa, and 25.63 MPa, increased by 310%, 283%, and 165%, respectively. The failure patterns of coupling of core compression and shear in flatwise compression and those of buckling and face fracture in edgewise compression were revealed.

Aluminium alloy is a commonly used material in the superstructure of naval vessels. This alloy is prone to sensitisation when exposed to the marine environment for an extended period, which leads to the formation of stress corrosion cracks. Because welding is unsuitable for repairing sensitised aluminium alloy with cracks, this study used carbon-fibre-reinforced plastic (CFRP) patches for repair. The repair effect of CFRP patches was examined through experiments and numerical simulation to clarify the mechanical properties of cracked aluminium alloy repaired with CFRP patches. The experimental results revealed that the tensile strength of cracked aluminium alloy was increased by 40% after its repair with a CFRP patch, and the obtained tensile strength was higher than the yielding strength of this alloy. With regard to numerical simulation, this study employed the extended finite-element method (XFEM) and traction-separation law to simulate crack propagation in cracked aluminium alloy and the bonding strength at the repair interface. The numerical simulation results were consistent with the experimental results, which confirmed that the established numerical model accurately captures the failure trends and ultimate strength of cracked aluminium alloy repaired with a CFRP patch. Future researchers can use the numerical simulation method established in this study to predict the effectiveness of using CFRP patches in the repair of naval vessel superstructures.

In this article, the tensile failure mechanism and load-bearing capacity of the equal-thickness (ET) and variable-thickness (VT) L-shaped joint structures of CCF300/QY9511 materials in different transition regions were analyzed by numerical simulation and experiments. Based on the ABAQUS finite element simulation software, the improved Hashin criterion and the stiffness reduction method considering damage accumulation were used to write a user-defined subroutine, establishing a progressive damage model for carbon fiber composite materials. Numerical simulations were carried out to investigate structural failure and obtain the damage generation, evolution, and failure process of the L-shaped joint structure with bolt connections. The bearing capacity of the structure under two forms of equal-thickness transition and variable-thickness transition were studied in comparison; and the failure mechanism of the structure was determined by comparing with the experimental results. The study found that there were different failure mechanisms in the two joint structures: when the ET joint was loaded, the damage occurred first around the bolt hole, and then the damage expanded to the arcs until it completely failed; the initial failure of the VT joint occurred at the arcs, but when the load continued to increase to the peak load, the damage occurred near the bolt hole of the L-shaped frame, and the load dropped sharply.

Two different experimental techniques are employed to visualize the impact damage generated by a low-velocity impact on a carbon-fibre reinforced-polymer (CFRP) composite laminate. At the relatively low impact-velocity of 1.69 m.s⁻¹, and a corresponding impact energy of 7.5 J, used in the present work the damage induced in the CFRP panel is barely visible to the naked eye but the techniques of ultrasonic C-scan and X-ray computed tomography (CT) can detect the damage that has occurred. This damage is mostly interlaminar damage, i.e. delaminations, between the plies due to a change in modulus from one ply to the next in the laminate. This interlaminar damage is usually accompanied by intralaminar damage, e.g. matrix cracking, in the ply itself. The type and extent of damage detected from using these two techniques is discussed and the relative merits of these techniques are compared. In general, the CT gave the better resolved picture of damage but the lateral extent of the damage was underestimated relative to C-scan which was more sensitive to very fine delamination cracks. In addition, a numerical approach, based on a finite-element analysis model, is employed to predict the type, location and extent of damage generated by the impact event and the modelling predictions are compared to the experimental results.

Composite structures in transportation industries have gained significant attention due to their unique characteristics, including high energy absorption. Non-destructive testing methods coupled with machine learning techniques offer valuable insights into failure mechanisms by analyzing basic parameters. In this study, damage monitoring technologies for composite tubes experiencing progressive damage were investigated. The challenges associated with quantitative failure monitoring were addressed, and the Genetic K-means algorithm, hierarchical clustering, and artificial neural network (ANN) methods were employed along with other three alternative methods. The impact characteristics and damage mechanisms of composite tubes under axial compressive load were assessed using Acoustic Emission (AE) monitoring and machine learning.Various failure modes such as matrix cracking, delamination, debonding, and fiber breakage were induced by layer bending. An increase in fibers/matrix separation and fiber breakage was observed with altered failure modes, while matrix cracking decreased Signal classification was achieved using hierarchical and K-means genetic clustering methods, providing insights into failure mode frequency ranges and corresponding amplitude ranges. The ANN model, trained with labeled data, demonstrated high accuracy in classifying data and identifying specific failure mechanisms. Comparative analysis revealed that the Random Forest model consistently outperformed the ANN and Support Vector Machine (SVM) models, exhibiting superior predictive accuracy and classification using ACC, MCC and F1-Score metrics. Moreover, our evaluation emphasized the Random Forest model's higher true positive rates and lower false positive rates. Overall, this study contributes to the understanding of model selection, performance assessment in machine learning, and failure detection in composite structures.

In this research, a high-efficiency joining technique of resistance welding is proposed to achieve high-quality joining of carbon fiber/epoxy (CF/Epoxy) composites. The effects of mechanical sanding and dielectric barrier discharge (DBD) plasma surface modification were investigated on joint properties. Through morphology observation, wettability research, and surface chemical element analysis, it was found that both methods effectively improved joint performance. Mechanical sanding increased surface roughness, facilitating mechanical interlocking between composite layers. DBD plasma treatment enhanced surface wettability, promoting better adhesion between the materials. Notably, the failure mode of the welded joint transformed from interface failures to interlayer failures, indicating improved joint integrity and strength. The combined treatment method, using both mechanical sanding and plasma treatment, yielded the highest single lap shear strength (LSS) of 25.78 MPa, which was an impressive 141.2% higher than the untreated sample.

Filament winding is a technique to manufacture tubular composite structures and, therefore, is among the most appealing techniques for fabricating critical structures such as hollow tubes. Despite the recent advances, these structures are prone to a varying degree of porosity that may affect their mechanical performance. Therefore, the accurate detection and quantification of the manufacturing porosity is crucial. Micro-CT is most suitable for performing this activity at various scales. This work employs micro-CT for studying porosity inside an as-manufactured filament-winded composite structure. Void characteristics like volume, orientation, size, and relative volume fraction inside the hoop and helical layers are quantified inside a representative curved panel extracted from a glass fiber-vinyl ester tubular composite structure, which has not been studied in detail previously. It was observed that most voids are present in the matrix region. The voids are elliptical rod-like and spherical, with the latter present in the helical layers, which also host the majority of voids and the highest void volume fractions. The voids are highly aligned along the fiber orientation direction with higher misorientations for helical layers than the hoop layer. Large voids in base layers were created due to gaps formed during the winding process. Hence, the main goal of this study is to measure the voids' characteristics and the volumetric fraction during the stacking of filament wound hoop and helical layers during a generic filament winding pattern. The data can be further exploited as input for modeling filament winded composites in the presence of voids by researchers.