Chunrui Lu

The fabrication of CF/PEEK composites using two‐dimensional braid premix has garnered significant attention as a promising alternative to traditional prepreg due to its flexibility and conformability. However, the microstructure and properties of the interface between CF and PEEK are crucial in determining the final mechanical properties of the composite and its potential applications. To enhance the interfacial wettability and adhesion of composites, a two‐dimensional braid CF/PEEK premix, consisting of CF as warp yarns and PEEK fibers as weft yarns, was subjected to plasma treatment using argon (Ar) and air in sequence for varying durations. Analytical methods, including SEM, AFM, Boehm titration, contact angle analysis, and microdroplet tests, were employed to compare surface roughness, surface acidic groups, surface energy, wettability, and interfacial properties. SEM and AFM analyses demonstrated that plasma treatment altered the fiber surface morphology and increased roughness with longer treatment times. Boehm titration indicated that the acidic groups on the fibers initially increased and then decreased in treatment duration. Surface energy calculations revealed specific alterations in components, with a notable enhancement in the polarity component. The work of adhesion ( W _a ) between CF and PEEK, treated for different durations, exhibited an identically consistent change with the interfacial shear strength (IFSS). The IFSS improved from 44.87 ± 5.76 MPa to 61.73 ± 3.89 MPa following a 60‐s Ar and 60‐s air treatment, representing a 37.58% increase. This improvement underscores the effectiveness of plasma treatment, suggesting that modifying and controlling the fiber‐matrix interface offers a viable method for enhancing the interfacial properties of CF/PEEK composites.

PEEK and CF/PEEK are two significant materials whose properties are intricately linked to their crystallization behavior. This study employed three analytical techniques—density method, differential scanning calorimetry (DSC), and x‐ray diffraction (XRD)—to explore and quantify the crystallinity of Poly (ether ether ketone) (PEEK) and its composites. Thermogravimetric analysis was used to determine the resin content of the composites, which is essential for the density and DSC methods. The density method, based on Archimedes' principle, calculated both mass and volume crystallinity. DSC assessed crystallinity by analyzing differences in melting enthalpy, while XRD determined crystallinity through diffraction patterns and peak analysis. The results demonstrate that these three techniques can be effectively utilized for calculating the crystallinity of PEEK and its composites. Using the density method, PEEK exhibited a crystallinity of (26.53 ± 1.30)% by mass and (24.57 ± 1.24)% by volume. The prepreg, CF/PEEK, and CF/PEEK‐AA1 composites showed enhanced crystallinity values. Crystallinity calculated by DSC was 29.16% for PEEK, 55.35% for prepreg, 55.48% for CF/PEEK, and 53.50% for CF/PEEK‐AA1. XRD results provided crystallinity values of 46.35% for PEEK, 63.20% for prepreg, 64.80% for CF/PEEK, and 66.57% for CF/PEEK‐AA1, along with detailed information about unit cells and crystal planes. This study contributes to a better understanding of these methods, paving the way for future refinement and integration, thereby improving the precision of crystallinity determination.Highlights: Crystallinity study of PEEK and CF/PEEK composites by density, DSC and XRD methods. Crystallinity calculated by methods in different principles are irrelevant. Crystallinity estimated by density and DSC requires resin content. Information on crystal and crystallinity can be obtained by XRD independently. Crystallinity calculated by XRD is the highest. Results obtained by density and DSC method are close.

Ultra‐high molecular weight polyethylene (UHMWPE) is commonly used with many layers to realize protection and this can greatly benefit from advancements in fabric mechanical properties. This research introduces an innovative approach to crafting a composite felt, leveraging UHMWPE fabric, carbon nanotubes (CNTs), shear thickening fluid (STF), and polyvinyl alcohol (PVA) binder through a spray technique. The method results in a fabric with exceptional tensile strength and anti‐impact characteristics. Observations during the fabrication process reveal profound surface morphology alterations, showcasing an intricate layering of PVA binder, CNTs, and STF that seamlessly encapsulates each component of the STF/CNTs/UHMWPE system. The tensile strength and anti‐impact properties including punch residual velocity and energy absorbed are 564.0 ± 12.4 MPa, 1.537 ± 0.032 m/s and 22.952 ± 1.158 J in 12 ms, increased by 143.3%, 24.3% and 193.3%, respectively, compared to neat UHMWPE. This substantial performance uplift is attributed to multiple factors: the reinforcing friction between fibers/yarns fostered by the PVA binder and the full or partial embedding of CNTs, the additional reinforcing strength imparted by the CNTs matrix, and the dynamic viscosity enhancement of STF under impact forces. Highlights: Anti‐impact felt was prepared by spraying PVA, CNTs, and STF onto UHMWPE. The tensile strength of anti‐impact felt was improved by 143.3%. The energy absorbed and impact depth was raised by 193.3%. The enhanced friction between fibers is caused by PVA and CNTs. The strength of CNTs and increased viscosity of STF under impact are notable.

To enhance the ductility of carbon fiber‐reinforced polymer (CFRP) composites, a variety of nacre‐inspired structures with discontinuities were constructed based on the ratio of overlapping length to CFRP laminate thickness. The damage mechanisms and tensile characteristics of discontinuous laminates were elucidated using finite element analysis and experimental investigation. To anticipate the mechanical behavior of the CFRP laminate, an improved Chang‐Chang failure criteria was devised. Moreover, a model adopts the Benzeggagh‐Kenane criterion on cohesive surfaces for delamination initiation and propagation. The predicted stress–strain values are validated using experimental data under tensile stress. Furthermore, a mathematical model accurately predicted the relationship between the tensile performance of nacre‐inspired laminate and overlapping length. According to the findings, the longer the overlapping length (more than 19.5 mm) is, the lower the pseudo‐ductility. Meanwhile, the shorter the overlapping length (less than 17.5 mm) is, the lower the tensile strength. Furthermore, the laminate exhibits some pseudo‐ductility as well as little decrease in tensile strength when the overlapping length is approximately 18.5 mm.Highlights: A mathematical model for predicting the tensile properties of various nacre‐inspired laminates was established. The relationship between the discontinuous structure and the pseudo‐ductility of the nacre‐inspired laminate was revealed. Compared with other similar structural laminates, the laminate with an overlapping length of 17.5 mm has better overall performance. Proposed an improved Chang‐Chang progressive failure criterion that was utilized to simulate and analyze the mechanical response and damage of the nacre‐inspired laminates under tension.

Shear thickening fluid (STF), carbon nanotubes (CNTs) are both promising in body protection and anti‐impact for the drastic viscosity change of STF and the extremely high tensile strength and elongation of CNTs. The excellent performance of the above two combined with traditional Kevlar fabrics can significantly improve the mechanical properties and reduce the number of layers used for body protection. This work reports a new method to prepare STF/CNTs/Kevlar with excellent tensile properties and anti‐impact performance by spraying method with 1 wt% polyvinyl alcohol (PVA) solution as a binder for better integration between CNTs and Kevlar. Surface morphology changes in the preparation process indicate the combined structure of PVA binder, CNTs, and STF, presenting a uniform macroscopic and nonuniform microscopic surface of STF/CNTs/Kevlar composite. The tensile strength and anti‐impact properties including punch residual velocity and energy absorbed were studied and results for STF/CNTs/Kevlar composite are 669.8 ± 18.1 MPa, 1.602 ± 0.045 m/s, and 21.683 ± 1.182 J in 12 ms, increased by 46.4%, 23.0%, and 240.2%, respectively, compared with neat Kevlar, owing to the improved tight bonding and friction between fabrics yarns caused by PVA adhesive and tangled CNTs, accompanied with the enhanced viscosity of STF under forces.Highlights: Composites were made by spraying PVA, CNTs, and STF onto Kevlar fabrics; The tensile strength of the composite was 46.4% higher than Kevlar; The energy absorbed in 12 ms in anti‐impact tests was improved by 240.2%; Tight bonding and friction between yarns are reasons to improve properties; The raised viscosity of STF under forces is useful for mechanical properties.

Urea formaldehyde (UF) and phenol formaldehyde (PF) foam possess outstanding flame‐retardant properties, excellent insulation, and low thermal conductivity. These properties make them suitable for thermal insulation in buildings. However, the mechanical properties still need to be improved. In this study, orthogonal test was designed to optimize the level components of PF/UF composite foam first, then nano ZnO was added to the PF/UF composite foam to improve its toughness. The effects of nano ZnO on the morphology, apparent density, pulverization rate, thermal conductivity and thermal degradation property, flame retardancy, and mechanical properties of the ZnO/PF/UF nanocomposite foam were studied. The addition of nano ZnO improved the bending and compressive strength and decreased the pulverization rate of the composite foam significantly. The ZnO/PF/UF nanocomposite foam also presented better flame retardant properties than PF/UF composite foam. The largest oxygen index values of ZnO/PF/UF nanocomposite foam could reach 39.31%, while the thermal conductivity and the maximum rate of weight loss temperature were increased to 0.036 W/(m∙K) and 279°C, respectively. Moreover, ZnO/PF/UF nanocomposite foam showed low apparent density property (0.27 g/cm³).

Effective multiwalled carbon nanotube (MWCNT) fiber manufacturing methods have received a substantial amount of attention due to the low cost and excellent properties of MWCNTs. Here, we fabricated hybrid microfibers composed of hyaluronic acid (HA) and multiwalled carbon nanotubes (MWCNTs) by a wet-spinning method. HA acts as a biosurfactant and an ionic crosslinker, which improves the dispersion of MWCNTs and helps MWCNT to assemble into microfibers. The effects of HA concentration, dispersion time, injection speed, and MWCNT concentration on the formation, mechanical behavior, and conductivity of the HA/MWCNT hybrid microfibers were comprehensively investigated through SEM, UV-Vis spectroscopy, tensile testing, and conductivity testing. The obtained HA/MWCNT hybrid microfibers presented excellent tensile properties in regard to Young’s modulus (9.04 ± 1.13 GPa) and tensile strength (130.25 ± 10.78 MPa), and excellent flexibility and stability due to the superior mechanical and electrical properties of MWCNTs. This work presents an effective and easy-to-handle preparation method for high-performance MWCNT hybrid microfibers assembly, and the obtained HA/MWCNT hybrid microfibers have promising applications in the fields of energy storage, sensors, micro devices, intelligent materials, and high-performance fiber-reinforced composites.