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In this contribution, we propose a new approach to enhance the ablation properties of carbon/carbon (C/C) composites. 2.5D CFMP/C composites were obtained by mesophase pitch-based carbon fiber (CFMP) as the reinforcing carbon fibers, which facilitates the high aerodynamic heat flow near the stagnation to be rapidly guided to the low heat flow region at the rear of the structure. The results show that the surface temperature of 2.5D CFMP/C composites is 100 °C lower than that of 2.5D CFPAN/C composites prepared by traditional PAN-based carbon fiber (CFPAN), and the mass ablation rate and linear ablation rate of 2.5D CFMP/C composites decreased from 3.307 mg/s to 1.412 mg/s and from 3.067 µm/s to 0.501 µm/s, respectively. In addition, the mechanical properties of the 2.5D CFMP/C composites are outstanding, which will lay the foundation for their stability in ablative environments. Our work will bring new blessings for the further development of C/C composites in the aerospace field. [ABSTRACT FROM AUTHOR]

The mechanical properties of graphene reinforced composites are often hampered by challenges related to the dispersion and aggregation of graphene within the matrix. This paper explores the mechanism of cooling rate, process temperature, and process pressure's influence on the agglomeration behavior of graphene and the tensile response of composites from a computer simulation technology, namely molecular dynamics. Our findings reveal that the cooling rate exerts minimal influence on the tensile response of composites. Conversely, processing temperature significantly affects the degree of graphene aggregation, with higher temperatures leading to the formation of larger-sized graphene clusters. In contrast, processing pressure exhibits negligible impact on the degree of graphene aggregation, and increasing pressure effectively mitigates the formation of large-sized graphene clusters. Moreover, we elucidate the intrinsic factors governing the mechanical response to variations in processing parameters. Notably, we observe that the stretching process facilitates the decomposition of large-sized graphene clusters into smaller ones. This research contributes to the advancement of lightweight metal matrix composites by offering insights into optimizing processing parameters. Additionally, it provides crucial theoretical underpinnings for developing high-performance graphene-reinforced composites. [ABSTRACT FROM AUTHOR]

Pores are common defects generated during fabrication, which restrict the application of carbon/carbon (C/C) composites. To quantitatively understand the effects of pores on mechanical strength, this paper proposes a representative volume element model of unidirectional (UD) C/C composites based on the finite element method. The Hashin criterion and exponential degraded rule are used as the failure initiation and evolution of pyrolytic carbon matrices, respectively. Interfacial zones are characterized using the cohesive constitutive. At the same time, periodic boundary conditions are employed to study transverse tensile, compressive, and shear deformations of UD C/C composites. Predicted results are compared with the experimental results, which shows that the proposed model can effectively simulate the transverse mechanical behaviors of UD C/C composites. Based on this model, the effects of microstructural parameters including porosity, pore locations, the distance between two pores, pore clustering, and pore shapes on the mechanical strength are investigated. The results show that porosity markedly reduces the strength as porosity increases. When the porosity increases from 4.59% to 12.5%, the transverse tensile, compressive, and shear strengths decrease by 35.91%, 37.52%, and 30.76%, respectively. Pore locations, the distance between two pores, and pore clustering have little effect on the shear strength of UD C/C composites. For pore shapes, irregular pores more easily lead to stress concentration and matrix failure, which greatly depresses the bearing capacity of UD C/C composites. [ABSTRACT FROM AUTHOR]

Needled carbon/carbon composites contain complex microstructures such as irregular pores, anisotropic pyrolytic carbon, and interphases between fibers and pyrolytic carbon matrices. Additionally, these composites have hierarchical structures including weftless plies, short-cut fiber plies, and needled regions. To predict the effective elastic properties of needled carbon/carbon composites, this paper proposes a novel sequential multiscale method. At the microscale, representative volume element (RVE) models are established based on the microstructures of the weftless ply, short-cut fiber ply, and needled region, respectively. In the microscale RVE model, a modified Voronoi tessellation method is developed to characterize anisotropic pyrolytic carbon matrices. At the macroscale, an RVE model containing hierarchical structures is developed to predict the effective elastic properties of needled carbon/carbon composites. For the data interaction between scales, the homogenization results of microscale models are used as inputs for the macroscale model. By comparing these against the experimental results, the proposed multiscale model is validated. Furthermore, the effect of porosity on the effective elastic properties of needled carbon/carbon composites is investigated based on the multiscale model. The results show that the effective elastic properties of needled carbon/carbon composites decrease with the increase in porosity, but the extent of decrease is different in different directions. [ABSTRACT FROM AUTHOR]

Thermal protective textiles are crucial for safeguarding individuals, particularly firefighters and steelworkers, against extreme heat, and for preventing burn injuries. However, traditional firefighting gear suffers from statically fixed thermal insulation properties, potentially resulting in overheating and discomfort in moderate conditions, and insufficient protection in extreme fire events. Herein, an innovative soft robotic textile is developed for dynamically adaptive thermal management, providing superior personal protection and thermal comfort across a spectrum of environmental temperatures. This unique textile features a thermoplastic polyurethane (TPU)‐sealed actuation system, embedded with a low boiling point fluid for reversible phase transition, resembling an endoskeleton that triggers an expansion within the textile matrix for enhanced air gap and thermal insulation. The thermal resistance improves automatically from 0.23 to 0.48 Km2 W−1 by self‐actuating under intense heat, exceeding conventional textiles by maintaining over 10 °C cooler temperatures. Additionally, the knitted substrate incorporated into the soft actuators can substantially mitigate convective heat transfer, as evidenced by the thermal resistance tests and the temperature mapping derived from numerical simulations. Moreover, it boasts significantly increased moisture permeability. The thermoadaptation and breathability of this durable all‐fabric system signify considerable progress in the development of protective clothing with high comfort for dynamic and extreme temperature conditions. [ABSTRACT FROM AUTHOR]

In short-fiber composites (SFCs), fiber length distribution (FLD) is complicated and has a considerable impact on the mechanical properties of SFCs. This work proposes a fractal FLD in SFCs on the basis of the fractal theory, and develops a multi-step mean-field homogenization (MSMFH) method to accurately and efficiently predict the mechanical properties of SFCs with fractal FLD. In the developed MSMFH method, SFCs are first decomposed into virtual pseudo-grains (PGs) according to fiber orientation distribution (FOD), followed the further division of the PGs into virtual sub-pseudo-grains (SPGs) according to FLD. The Mori–Tanaka or Double-Inclusion model is adopted to homogenize the mechanical properties of each SPG in the first step, and the Voigt model is implemented to homogenize the mechanical properties of all the SPGs and the PGs, respectively, in the sequential steps. Fiber length and orientation averaging algorithms for the developed MSMFH method are detailed. The developed MSMFH method and the proposed fractal FLD are validated to accurately predict the mechanical properties of SFCs by the means of the comparison with the FE method and the available experimental tests. [ABSTRACT FROM AUTHOR]

Graphene exhibits enormous advantages in mid‐infrared (MIR) regulation because of the active control, precise regulation, and large modulation depth. Such graphene films are prepared via chemical vapor deposition (CVD) or reduction, which cannot realize large‐scale production and limit the applications. Graphene films with van der Waals (vdW) structure enable excellent mechanical and electrical performance for flexible electrodes and electronics and might be a candidate for MIR regulation. However, current techniques for preparing vdW graphene films require binder or solution assistance, resulting in chemical residues and performance degradation. Here, a new strategy for preparing large‐area vdW graphene films by simple mechanical adhesion without any additives was proposed. By selecting the carriers and substrates with proper fracture energies, graphene nanosheets can be transferred from one polymer to another with a layer‐by‐layer structure. The obtained graphene films possess desired thickness and comparable electrical conductivity (92.8 ± 4.6 ohm sq–1) with those by chemical vapor deposition. They are of high compactness even for ions to intercalate reversibly, which exhibit excellent electrochemical activity and electro‐optical regulation capability, effectively suppressing 90% thermal radiation. This strategy can be extended to prepare high‐performance vdW graphene films on various polymer substrates and used for sustainable and smart electro‐optical applications. [ABSTRACT FROM AUTHOR]

Interfacial solar vapor generation (ISVG) was first proposed in 2014 and it has gained more and more attention from academia due to its tremendous improvement in evaporation efficiency compared with previous bottom and volumetric heating designs. With significant efforts put into this field, the current evaporation rate of the system can attain 4 kg m−2 h−1 under one sun irradiation. To catch up with the up-to-date development of ISVG systems, we prepare this review article to summarize the recent development in this field. In this review, we first introduce the constituent elements of an ISVG system, namely substrates and photothermal materials. Following this, several fabrication techniques for ISVG systems are highlighted to enable all-in-one ISVG architecture designs. The central parts of this review include the design principles and optimization strategies of ISVG systems, salt rejection and condensation strategies. Finally, various application scenarios, including seawater desalination, sterilization, and water-electricity/water-fuel production, are introduced in detail, followed by conclusions and future perspectives. ISVG is a green and low-cost technique for producing clean water driven by solar energy, which shows great application potential in remote and off-grid regions. With continuous efforts and improvement, it is envisioned that ISVG will become a complementary technique to current water treatment technologies soon. [ABSTRACT FROM AUTHOR]

The classic single-fiber efficiency model based on ordered packing of fiber composites has been widely used to predict filtration efficiency of fibrous filters for 40 years. However, the simplified single-fiber model often overestimates the filtration efficiency as most fibrous composite filters are composed of randomly distributed fibers. The numerical methods have been successfully employed to re-construct the realistic fiber composites, but simulation of the multi-mechanism filtration process in the complex fibrous architecture is computationally expensive and case-based and derivation of a compact versatile model for broad applications remain challenging. In this work, a fractal-based homogenization model is developed to predict the filtration efficiency of the fibrous composites, by considering the spatially randomly distributed fibers and the quasi-random distribution of pore size. A comparison with available experimental results collected from references shows that the proposed model is of high accuracy in predicting the filtration of submicron aerosol particles. The calculated results show that the Kuwabara hydrodynamic factor is sensitive to the pore fractal dimension. The filtration efficiency for different particle diameters can be divided into three stages, which increase as the proportion of fibers warped by the fluid decreases. In addition, the total efficiency decreases with the increasing pore fractal dimension in a nonlinear trend. For the given fractal dimension, the filtration efficiency increases with the increase of pore size ratio, indicating that the more uniform the pore size distribution, the higher the efficiency. [ABSTRACT FROM AUTHOR]

The output power density of a triboelectric nanogenerator can be enhanced by several orders of magnitude by a field‐effect transistor like structure. However, the previously reported strip top electrode is not ideal for optimum generation and stable transfer of charges under practical dynamic conditions. Switched on by an impinged droplet, the bridged closed‐loop electric circuit transfers the accumulated charges by converting the conventional interfacial effect into a bulk effect. Randomly falling droplets cannot always exactly impinge the electrode with the desired spreading contact to achieve a high peak voltage, and a large fraction of low‐voltage direct‐contact and sliding‐contact modes will lead to low output and instability. To address this critical challenge, a topology‐optimized droplet energy harvesting fabric (TO‐DEHF) for stable and efficient output from randomly falling droplets is reported. The optimized fabric electrodes in a hexagonal network feature a stable open‐circuit voltage under moving and rotating patterns, threefold over that with the strip electrodes. The peak power density of the TO‐DEHF (71.8 mW m–2) is 4.8‐fold versus the latter (14.8 mW m–2). Moreover, the all‐fabric TO‐DEHF has high flexibility and breathability, based on which a self‐powered wireless wearable prototype is successfully demonstrated for detection of crucial droplet properties, including temperature, pH, and salinity. [ABSTRACT FROM AUTHOR]

The components of carbon/carbon (C/C) composites have significant influence on the thermal and mechanical properties, so a quantitative characterization of component is necessary to study the microstructure of C/C composites, and further to improve the macroscopic properties of C/C composites. Considering the extinction crosses of the pyrocarbon matrix have significant moving features, the polarized light microscope (PLM) video is used to characterize C/C composites quantitatively because it contains sufficiently dynamic and structure information. Then the optical flow method is introduced to compute the optical flow field between the adjacent frames, and segment the components of C/C composites from PLM image by image processing. Meanwhile the matrix with different textures is re-segmented by the length difference of motion vectors, and then the component fraction of each component and extinction angle of pyrocarbon matrix are calculated directly. Finally, the C/C composites are successfully characterized from three aspects of carbon fiber, pyrocarbon, and pores by a series of image processing operators based on PLM video, and the errors of component fractions are less than 15%. [ABSTRACT FROM AUTHOR]