Search

The primary objective of the paper is the numerical and experimental investigation related to the damage recognition effects for CFRP tubes of four dynamic parameters. Four damage identification indexes consisting of natural frequency‐based index, Mode Shape‐based index (MS), Mode Shape Curvature‐based index (MSC), and Modal Flexibility Curvature‐based index (MFC) are established by analyzing the dynamic parameter data obtained before and after damage occurs. The performances of dynamic parameters are thoroughly discussed in the context of numerical simulations and experiment. The results indicate that the effect of natural frequency is not as significant as that of mode shape. MFC has the most notable effectiveness out of the four indexes. The simulation peak index pair is predicted to rise from 0.3 to 0.6 as the damage in the simulation model increases by 25% from 12.5%, indicating that MFC can feedback the damage degree. Moreover, the circumferential curvature index exhibits superior performance compared to the axial curvature index. To enhance the accuracy of the axial curvature index, it is proposed to increase the number of measuring sites along the tube's long direction. Highlights: Damage identification indexes of four dynamic parameters are established.Discuss the identification ability of dynamic parameters by simulation and test.Two numerical models of CFRP tube with delamination damage are established.Impact and modal tests are executed to study the ability of four indexes. [ABSTRACT FROM AUTHOR]

Highlights: The homogeneous hybridization of organic–inorganic-metal elements in 3D aerogel was achieved by an expeditious method. The aerogel tightly integrates excellent thermal insulation (49.6 mW m−1 K−1), ablative resistance, mechanical strength, and superhydrophobic properties. The ablated carbon aerogel combines notable electromagnetic interference shielding properties (31.6 dB) and load-carrying properties (272.8 kN·m kg−1). Vehicles operating in space need to withstand extreme thermal and electromagnetic environments in light of the burgeoning of space science and technology. It is imperatively desired to high insulation materials with lightweight and extensive mechanical properties. Herein, a boron–silica–tantalum ternary hybrid phenolic aerogel (BSiTa-PA) with exceptional thermal stability, extensive mechanical strength, low thermal conductivity (49.6 mW m−1 K−1), and heightened ablative resistance is prepared by an expeditious method. After extremely thermal erosion, the obtained carbon aerogel demonstrates noteworthy electromagnetic interference (EMI) shielding performance with an efficiency of 31.6 dB, accompanied by notable loading property with specific modulus of 272.8 kN·m kg−1. This novel design concept has laid the foundation for the development of insulation materials in more complex extreme environments. [ABSTRACT FROM AUTHOR]

Owing to their excellent physical and chemical properties, the carbon fibre reinforced poly(ether‐ether‐ketone) composites (CF/PEEK) are widely used in aerospace applications such as rockets, missiles, and high‐speed vehicles. However, both carbon fibre (CF) and poly(ether‐ether‐ketone) (PEEK) have inert molecular chain structures, which seriously affect the interfacial properties of CF/PEEK composites. In this study, to improve the properties of CF/PEEK composites, carboxylated PEEK (PEEK‐COOH) with different carboxylation degrees is synthesized as the sizing agent by a "two‐step" method. Then, the activated CF surface is coated by PEEK‐COOH sizing layers with different functionalization degrees to prepare the CF/PEEK composites. The results show that the interfacial properties of CF/PEEK composites are improved after applying the sizing agent. When the carboxylation degree of PEEK‐COOH is 19.61%, the flexural strength, flexural modulus, and interlaminar shear strength (ILSS) of CF/PEEK composites reach 489.34 MPa, 25.387 GPa, and 81.3 MPa, respectively. In addition, the use of PEEK‐COOH sizing agents can form an excellent transition layer between CF and PEEK, creating an efficient stress transfer system and facilitating an even stress distribution between CF and PEEK. Furthermore, the main mechanism of material fracture changes from CF debonding to CF and resin fracture. [ABSTRACT FROM AUTHOR]

The resin matrix and CF fibers itself of CF/PEEK composites exhibit surface inertness, resulting in poor interface bonding between CF and PEEK matrix. This phenomenon seriously affects the mechanical properties of CF/PEEK composites especially the interlaminar shear strength (ILSS). In order to improve the interfacial properties of CF/PEEK composites, a novel sizing agent of CF fibers namely PPS‐NH2 was synthesized, and its influence on the fibers–matrix interface interaction and properties of CF/PEEK composites was investigated by using scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, atomic force microscopy. The results showed that the interface of CF/PEEK composite was improved by coating PPS‐NH2 sizing agent on the surface of CF. When the amination degree of PPS‐NH2 reaches 31.25%, the ILSS, flexural strength and modulus of CF/PEEK Composites reach 73.9 MPa (119%), 671.4 MPa (63%) and 32.8GPa (51%) and, respectively. At the same time, the main failure mechanism of CF/PEEK composites changes from fibers–matrix debonding into interface layer deformation and resin fracture. This method can effectively improve the interface defects between CF/PEEK composites. [ABSTRACT FROM AUTHOR]

As a high‐performance thermoplastic polymer, poly(ether‐ether‐ketone) (PEEK) has excellent thermal stability and mechanical properties; it is widely used in the aerospace field. However, PEEK has high viscosity, high processing temperature and poor fluidity in the molten state. In preparing carbon fibre (CF)/PEEK composites, poor impregnation performance will occur, resulting in high porosity and poor mechanical properties of the CF/PEEK composites. This mini‐review focuses on improving the interface of the CF/PEEK composite by coating the CF surface and introduces the preparation of CF/PEEK composites by coating CF with a resin‐based sizing agent, a mixed sizing agent and nanoparticles. Meanwhile, the properties of CF/PEEK composites prepared by different coating methods are compared. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

To further improve the anti‐ablation property of boron phenolic resin (BPR), high‐temperature resistant reactive trisilanolheptaphenyl POSS (3OH‐POSS) was synthesized to modify BPR. The thermal stability of BPR was significantly improved. The initial decomposition temperature of the prepared 3OH‐POSS modified BPR (POSSBPR) was increased from 226.0 to 390.2°C and the chars at 800 and 1000°C was increased from 71.1 and 66.7% to 75.1 and 73.7%, respectively with 20% 3OH‐POSS addition. The prepared POSSBPR castings obtained linear ablation rate (LAR) and mass ablation rate (MAR) were as low as −0.122 mm/s and 0.0465 g/s. And the LAR and MAR of high silica fiber reinforced composites (HSC/POSSBPR) were 0.123 mm/s and 0.0602 g/s, respectively. Moreover, the mechanism of high‐temperature carbon microcrystalline and ceramic structure transformation, and ablation performance enhancement of POSSBPR were determined by X‐ray diffraction, X‐ray photoelectron spectroscopy, and Raman spectroscopy. Results indicated that the introduction of 3OH‐POSS promotes the formation of ordered graphite structure of BPR and forms high‐temperature species, such as SiC ceramic, on the ablated surface, which subsequently improves the ablation resistance of the material. [ABSTRACT FROM AUTHOR]

In this article, we proposed a new approach to design the winding patterns of filament-wound composite pressure vessel with unequal polar openings with non-geodesics. To ensure the continuity of winding angles between trajectories along the cylinder and the dome, the non-geodesics for cylindrical part were used. The developed winding patterns of the vessels were simulated using the MATLAB software to verify the feasibility of the acquired trajectories. To demonstrate the performance in designing the winding path for big polar ratios, we analyzed vessels with polar pole ratios of 1:2–1:4, respectively. The developed winding patterns have successfully achieved uniform fiber distributions along the mandrel without severe overlap, except for the polar pole regions. To avoid the severe overlap between filament bands, we further studied the relationship among the winding pattern, bandwidth, and the number of tangent points, and derived a suitable bandwidth based on the winding pattern. These simulated results proved the effectiveness of the developed method in design of winding pattern with unequal polar openings. [ABSTRACT FROM AUTHOR]

3,13‐Diglycidyloxypropyloctaphenyl double‐decker silsesquioxane (EP‐DDSQ) was synthesized by process of alkaline hydrolysis condensation of phenyltrimethoxysilane and corner capping reaction of methyldichlorosilane, followed by hydrosilylation with allyl glycidyl ether, and the resultant structure was confirmed by fourier transform infrared spectrometer (FTIR) and nuclear magnetic resonance (NMR), respectively. The thermosetting phenol‐formaldehyde (PF) resin was then modified by EP‐DDSQ, and the reactivity of PF resin with EP‐DDSQ and thermal pyrolysis of modified cured resin were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The surface morphologies of modified resins at high temperature were characterized with field emission scanning electron microscope (FESEM), and chemical structure of modified resins was analyzed through X‐ray photoelectron spectrometer (XPS). The results showed that the appropriate addition of EP‐DDSQ did not affect the curing temperature of the PF resin itself, but could improve the heat resistance of the system. When the amount of EP‐DDSQ added was 10%, the initial degradation temperature of PF resin was increased by 49.31°C, and when the amount of EP‐DDSQ added was 16%, the char yield of which was reached up to 61.39%, compared with that of pure PF resin (TGA1,000°C of 57.62%) at Ar atmosphere. More importantly, the modified resin formed a regular and dense layer of SiC and SiOx ceramic on the surface after ablation in the muffle furnace at 800°C air atmosphere, which is very important for ablative resistant materials. [ABSTRACT FROM AUTHOR]

A new solution method to synthesize NaTiO with titanium powder is presented, and the C/NaTiO nanocomposite with high specific surface area and tunnel structure as the electrode material has excellent electrochemical performance. The single electrode composed of the C/NaTiO nanocomposite based on carbon fiber fabric (CFF) has the highest area capacitance of 1066 mF cm at a current density of 2 mA cm, which is superior to other titanates and Na-ion materials for supercapacitors (SCs). By scan-rate dependence cyclic voltammetry analysis, the capacity value shows both capacitive and faradaic intercalation processes, and the intercalation process contributed 81.7% of the total charge storage at the scan rate of 5 mV s. The flexible symmetric solid-state SCs (C/NaTiO/CFF//C/NaTiO/CFF) based on different C/NaTiO mass were fabricated, and 7 mg SCs show the best supercapacitive characteristics with an area capacitance of 309 mF cm and a specific capacitance of 441 F g, it has a maximum energy density of 22 Wh kg and power density of 1286 W kg. As for practical application, three SCs in series can power 100 green light-emitting diodes (LEDs) to light up for 18 min, which is much longer than our previous work by Wang et al. lighting 100 LEDs for 8 min. Thus, the C/NaTiO nanocomposite has promising potential application in energy storage devices. [ABSTRACT FROM AUTHOR]

The article presents a study that dealt with the influence of oxygen plasma treatment on surface properties of poly(p-phenylene benzobisox-azole) (PBO) fibers and interfacial properties of PBO fiber reinforced poly(phthalazinone ether sulfone ketone). The study used X-ray photoelectron spectroscopy, Atomic force microscopy, and scanning electron microscopy to analyze surface chemical composition, and surface morphologies. Dynamic contact angle analysis enabled characterization of surface energy.

Porous materials have superior electrochemical performance owing to its their structure, which could increase the specific and contact area with the electrode. The spinel Li4Mn5O12 has a three-dimensional tunnel structure for a better diffusion path, which has the advantage of lithium ion insertion and extraction in the framework. However, multi-space spherical materials with single morphologies are rarely studied. In this work, waxberry-like and raspberry-like nanospheres for Li4Mn5O12 have been fabricated by the wet chemistry and solid-state methods for the first time. The diameter of a single waxberry- and raspberry-like nanosphere is about 1 μm and 600 nm, respectively. The specific capacitance of Li4Mn5O12 was 535 mF cm−2 and 147.25 F g−1 at the scan rate of 2 mV s−1, and the energy density was 110.7 Wh kg−1, remaining at 70% after 5000th charge-discharge cycles. Compared with raspberry-like nanosphere Li4Mn5O12, the waxberry-like nanoporous spinel Li4Mn5O12 shows the better electrochemical performance and stability; furthermore, these electrochemical performances have been improved greatly compared to the previous studies. All these results indicate that the waxberry-like nanoporous spinel Li4Mn5O12 could provide a potential application in high performance supercapacitors. [ABSTRACT FROM AUTHOR]