Composites Science and Technology最新文献

Phase change materials (PCMs) are widely applied in passive thermal management and energy storage fields because of their large latent heat capability near phase transition points. However, molten leakage, inherent rigidity, and low thermal conductivity limit the thermal management applications of PCMs. In this work, a scalable doctor-blading technique was developed to prepare anti-leakage, flexible, and highly thermally conductive PCM composites. Paraffin wax (PW) works as the thermal energy storage unit, polydimethylsiloxane (PDMS) encapsulates the molten PW and imparts the composites with flexibility, and 1-Butyl-3-methylimidazolium Hexafluorophosphate (BMIMPF6)-modified boron nitride nanosheets (BPs) ensure high thermal conductivity. BPs were firstly achieved from bulk boron nitride (BN) powders and BMIMPF6 ionic liquid (IL) by the one-step ball milling process, then high-oriented alignment of BPs in PDMS/PW matrix was obtained by the strong shearing forces along the blade-casting direction. Owing to the high quality of BPs and interconnected structure of BPs network, the composites possessed high in-plane thermal conductivity of 2.87 W·m⁻¹·K⁻¹ at 15 wt% BPs, exhibiting a remarkable enhancement of 1494 % compared with PDMS/PW. The flexible composites showed effective heat dissipation performance by reducing the working temperature of smartphones over 11 °C. Finite element analysis demonstrated that the parallel alignment of BPs network and the thermal energy buffering of PW were crucial for improving the thermal management capability. Furthermore, the PDMS/PW/BP composites exhibited excellent flame-retardant and electrically insulating properties. This work provides a feasible method to prepare high-performance PCM composites, which show great application prospects in the thermal management of electronic devices.

The meta-structural design of flat absorbers demonstrates significant potential for improving microwave attenuation performance. However, the single mechanism of amplitude attenuation through resonance-enhanced effect necessitates considerable material thickness, restricting its application in electromagnetic (EM) defense. Utilizing the synergistic effect of multiple mechanisms is expected to break through the performance limits of microwave stealth metamaterials at the sub-wavelength scale. Herein, absorption-diffusion integration stacked metamaterials (ADISM) were designed using a multi-compound strategy, which comprises bionic porous spherical carbonyl iron powder (SCIP) coatings and stacked vortex metasurfaces (VMs). Such a metamaterial integrates EM scattering modulation with microwave absorption, enabling the creation of a broadband, high-efficiency, low-reflection design, providing an effective absorption bandwidth (EAB) reaching 10.42 GHz (7.58–18 GHz) at a thickness of 2.48 mm. Manipulating the orbital angular momentum (OAM) to effect wavefront transformation, the dissipation of EM wave energy is achieved. The absorption peak frequency modulation and absorption bandwidth broadening are achieved by the intrinsic loss capability of the porous coating, and corresponding mechanisms are demonstrated by simulation models. In short, the synergistic effects of microwave absorption and scattering modulation significantly enhance the return loss capability and facilitate broadband microwave attenuation. This research offers new insights into the multifunctional integration of EM stealth metamaterials.

The emergence of vitrimers breaks through the limitation of traditional carbon fiber reinforced thermoset composites (CFRP) caused by their permanent crosslinking molecular networks. Herein, the dynamic cross-linked network of vitrimer was synthesized from Bisphenol A diglycidyl ether (DGEBA) and glutaric anhydride (GA) under the catalysis of zinc acetylacetonate (Zn(acac)₂), and the corresponding carbon fiber reinforced vitrimer composites (CF/V_x) were prepared via an impregnation and hot pressing process. The dynamic covalent adaptable networks (CANs) of vitrimer endow CF/V_x with stress relaxation and creep characteristics. By adjusting the catalyst content, the dynamic performance of CF/V_0.05 can be optimized to achieve the highest viscous flow activation energy (60 kJ/mol) and the lowest characteristic relaxation time (1.0 × 10⁻³ s). The unique dynamic properties enable CF/V_x with reprocessability at high temperature. Typically, the flexural modulus of CF/V_0.05 decreased from 87 ± 1.81 GPa at room temperature to 4.62 ± 0.28 GPa at 220 °C, which confirms the feasibility of thermoplastic forming of CF/V_0.05 at high temperatures. Based on this, a CF/V_0.05-based cap-shaped component was successfully manufactured through a thermoforming process. Additionally, the CF/V_0.05 composites also exhibit repairability for interlaminar fractures. The optimal CF/V_0.05 can achieve a repair efficiency of 128 % under the hot press conditions of 180 °C, 10 MPa and 1 h. Hence, the reprocessable and repairable CF/V_x composites hold enormous potential in the engineering field.

The structural design strategies of MXene-based nanocomposites have demonstrated critical significance for electromagnetic interference (EMI) shielding applications. Herein, novel asymmetric multilayered cellulose nanofiber/multiwalled carbon nanotube@ferroferric oxide/MXene (CNF/MWCNT@Fe₃O₄/MXene) composite membranes with electrical-magnetic dual-gradient structures were prepared via layered-by-layered self-assembly strategy. Briefly, CNF/MWCNT@Fe₃O₄ layers are designed as the negative gradient absorption layers which provide dielectric/magnetic double loss. Meanwhile, MXene layers serve as the positive gradient reflection layers which generate multiple reflections and conduct loss. Thus, gradient multilayered CNF/MWCNT@Fe₃O₄/MXene composite membranes exhibit a total electromagnetic interference shielding effectiveness (EMI SE_T) of 73.20 dB at the thickness of 180 μm and R-value of 0.99934 in the X-band. Furthermore, the asymmetric gradient multilayer composite membrane reveals a superior EMI shielding performance in comparison with that of homogeneous multilayered composite membranes. When electromagnetic waves (EMWs) pass through the gradient multilayered CNF/MWCNT@Fe₃O₄/MXene composite membrane, the rational asymmetric gradient multilayered structures contribute to a “gradually decreasing absorption-gradually increasing reflection” shielding mechanism. Thereby, the design strategy of asymmetric electrical-magnetic dual-gradient structures is advantageous in enhancing the EMI shielding ability of polymeric composites.

Based on Hashin's fracture plane assumption, a matrix failure criterion for brittle fiber-reinforced composites is proposed. The failure function is expressed as a quadratic polynomial of the stress components on the fracture plane. The unknown coefficients in the failure criterion are only calibrated by the three basic strengths of unidirectional composites, i.e., the transverse tensile strength, transverse compressive strength, and longitudinal shear strength, thus overcoming the limitation of requiring empirical parameters in most previous matrix failure criteria. Especially, under plane stress states (${\sigma }_{22},{\tau }_{21}$), an analytical solution for the fracture angle of unidirectional composites can be provided. The prediction results of the proposed criterion are consistent with a large number of experimental data, confirming its applicability. In addition, the study establishes the relationship among the three transverse basic strengths ($Y_t$, $Y_c$ and $S_{23}$). It can be used to predict $S_{23}$ which is difficult to measure experimentally.

This paper reports the performance of protective structure inspired by elasmoid fish scales, employing a combination of experimental and numerical techniques. The composite scale-tissue structures were fabricated using a 3D printer with a dual-material extruder. Each structure was subjected to low-velocity impact using a drop-weight tower system. Investigation of the progressive failure mechanisms relied on finite element analysis and high-speed photography. Geometrical parameters of fish scales, including scale volume fraction, scale overlapping angle, and radius of curved scales were studied for their influence on impact resistance. Further, using Taguchi's method for the design of experiments, it was determined that enhancing impact resistance was achievable through an increase in scale volume fraction (by 15.1 %) and a larger scale overlapping ratio (by 39.4 %). The outcomes suggest that using a composite scale-tissue structure can contribute to developing more effective protective structures.

Herein, liquid metal microfibers (LMM) were constructed in poly (ε-caprolactone) (PCL) matrix and PCL/carbon nanotubes (CNT) composites via an in-situ microfibrilization of liquid metal (LM) droplets by a layer-by-layer stacking method. The aspect ratios of LMMs in the composites can be easily adjusted by controlling the number layers. The effect of LMM aspect ratios on electromagnetic interference (EMI) shielding effectiveness (SE) and thermal conductivity is discussed. The results show that the EMI SE value and the thermal conductivity increase with increasing aspect ratios of LMMs. In addition, the EMI shielding mechanism of PCL/LMM and PCL/LMM/CNT composites is evaluated comprehensively through the combination of electromagnetic simulation and experimental investigation. The efficiently conductive network can be formed in the composites with LMMs, which enhance EMI SE and thermal conductivity. Furthermore, the electric field distribution on the LMM surface is uneven, which enhances the polarization loss ability to electromagnetic waves.

The modern 5G communication electronics and systems require lightweight and flexible films that have superior electromagnetic interference (EMI) shielding performance as well as high thermal conductivity. This work reports a facile “one-pot” synthesis strategy to create EMI shielding films with a structure inspired by “jujube cake”. The two-dimensional Ti₃C₂T_x MXene nanosheets were combined with one-dimensional bacterial cellulose (BC) to form a mechanically entangled supporting framework resembling the structure of a “sponge cake”, wherein zero-dimensional liquid metal (LM) droplets like “jujubes” were ingeniously introduced. A series of multifunctional Ti₃C₂T_x/LM/BC (TLB) EMI shielding films with highly efficient conductive networks and complete thermal conductivity pathways were prepared through a simple, eco-friendly and highly scalable fabrication process involving vacuum-assisted filtration and hot pressing. Such ultrathin (18 μm) and lightweight (0.63 g cm⁻³) TLB composite film demonstrates an outstanding specific SE (SSE/t) of 21695.8 dB cm² g⁻¹. Meanwhile, it exhibits a remarkable in-plane thermal conductivity of 10.44 W m⁻¹ K⁻¹ and exceptional Joule heat performance from room temperature to 95 °C at 3.0 V in seconds. These attractive properties and scalable fabrication of TLB composite film showcase its potential in the realm of flexible electronics, particularly for applications pertaining to EMI shielding protection, electromagnetic compatibility and thermal management.

Fragmentation of high modulus carbon fibres is relevant to the failure mechanisms of advanced polymer matrix composites in compression. In situ spatially-resolved Raman spectroscopy during the fragmentation of model single fibre composites is used to map local stress distributions during failure events. The characteristic graphitic band (the G band) located around 1580 cm⁻¹ is associated with the in-plane carbon-carbon bonds; this band shifts its position, and can be calibrated, with the local axial stress in the fibre. The analysis maps the evolution of local stresses with increasing overall composite compression strain, identifying a series of critical events, including fibre fracture, interfacial debonding, and the formation of inter-fragment ‘wedges’. Fitting shear lag models provides interfacial shear strength values. Multiple failure maps of two examples of high modulus PAN carbon fibres (M46J and M55J) demonstrate the possibility of local fragment bending due to fragment end contact. A timeline of potential fragmentation events is proposed for carbon fibres undergoing compression.